Catalogue of the drought episodes in the IPCC reference regions from 1980 to 2015, available online, with an analysis of the moisture transport during the most severe meteorological drought episodes Droughts are complex and may be triggered by different mechanisms, such as atmospheric circulation, moisture transport, and thermodynamic processes. Significant research has been completed to characterise precipitation in the IPCC reference regions (RRs) but a systematic analysis of atmospheric transport linked to drought episodes is still missing. This article describes a catalogue in which the drought episodes over the RRs are identified during 1980-2015, and the role of the moisture transport anomalies from the respective major climatological moisture sources during the most severe meteorological drought episode registered for each RR is analysed. For each of the 27 RRs defined in the 5th IPCC Assessment Report, drought episodes were identified at 1-, 6-, and 12-month time scales through the Standardized Precipitation Evapotranspiration Index (SPEI). SPEI values were computed using time series of the monthly precipitation and Atmospheric Evaporative Demand (AED) averaged over each RR. The approach, which was applied to both identify the major climatological moisture sources and sinks for each RR and to investigate anomalies in moisture transport during the episode, is based on the Lagrangian model FLEXPART, integrated with the ERA-Interim data. For each RR, the following components were analysed: a) moisture uptake over sources; b) moisture supply from the sources into the RR; and c) moisture supply from the RR into its sink. Although performed for just one case, this analysis illustrates how the moisture transport may impact the RR during extreme conditions. The results are organized in a webpage available to the scientific community and stakeholders.
On the Connection between Atmospheric Moisture Transport and Dry Conditions in Rainfall Climatological Zones of the Nige...Published: 26 March 2019 by MDPI in Water
The hydroclimatology of the Niger River basin, located in West Africa, is very complex. It has been widely studied because of its importance to the socioeconomic activities of the countries that share its natural resources. In this study, to better understand the causes and mechanisms that modulate the rainfall over the Niger River basin, we identified the most relevant moisture sources for precipitation within the basin. The Lagrangian model FLEXPART was utilised to track backward trajectories of air parcels initially losing humidity over climatological rainfall zones of the basin. Along 10-day backward trajectories, we computed the budget of the difference between evaporation and precipitation (E − P) from 1000 to 0.1 hPa, permitting the identification of those regions where moisture uptake ((E − P) > 0) prevail. The study was conducted for the period 1980–2017. Monthly maps of ((E − P) > 0 were developed to illustrate the regions from where moisture is transported, contributing to precipitation in the Niger River basin. The spatial variability of the sources matches the precipitation variability over the basin restricted to surrounding areas of the Niger River basin during months with low average precipitation and widely spreading over the continent and the Atlantic Ocean in months with high average precipitation. During climatological dry months (e.g., December, January and February) the continental sources of West and Northeast Africa and the climatological rainfall zones themselves provide most of the moisture for precipitation. However, during the rainy season, the moisture supplies from oceanic sources increase, becoming greater than the contribution from land-based sources during August (the rainiest month). Dry conditions were identified for each climatological rainfall zone using the Standardised Precipitation Index. Similar to many previous studies, we found that the 1980s were highlighted by dry conditions. Local recycling and particularly moisture uptake from the tropical South Atlantic Ocean seem to be highly related to dry and wet conditions in the basin. A reduction on the moisture uptake from surrounding continental sources and the tropical South Atlantic Ocean is almost persistent during extremely dry conditions. Ascending movements are restricted to the lower troposphere during extremely dry conditions and oscillate latitudinally as well as precipitation.
Contribution of Moisture from Mediterranean Sea to Extreme Precipitation Events over Danube River BasinPublished: 04 September 2018 by MDPI in Water
In the most recent decades, central Europe and the Danube River Basin area have been affected by an increase in the frequency and intensity of extreme daily rainfall, which has resulted in the more frequent occurrence of significant flood events. This study characterised the link between moisture from the Mediterranean Sea and extreme precipitation events, with varying lengths that were recorded over the Danube River basin between 1981 and 2015, and ranked the events with respect to the different time scales. The contribution of the Mediterranean Sea to the detected extreme precipitation events was then estimated using the Lagrangian FLEXPART dispersion model. Experiments were modelled in its forward mode, and particles leaving the Mediterranean Sea were tracked for a period of time determined with respect to the length of the extreme event. The top 100 extreme events in the ranking with durations of 1, 3, 5, 7, and 10 days were analysed, and it was revealed that most of these events occurred in the winter. For extreme precipitation, positive anomalies of moisture support from the Mediterranean were found to be in the order of 80% or more, but this support reached 100% in summer and spring. The results show that extreme precipitation events with longer durations are more influenced by the extreme Mediterranean anomalous moisture supply than those with shorter lengths. However, it is during shorter events when the Mediterranean Sea contributes higher amounts of moisture compared with its climatological mean values; for longer events, this contribution decreases progressively (but still doubles the climatological moisture contribution from the Mediterranean Sea). Finally, this analysis provides evidence that the optimum time period for accumulated moisture to be modelled by the Lagrangian model is that for which the extreme event is estimated. In future studies, this fine characterisation could assist in modelling moisture contributions from sources in relation to individual extreme events.
Variations in Moisture Supply from the Mediterranean Sea during Meteorological Drought Episodes over Central EuropePublished: 19 July 2018 by MDPI in Atmosphere
The climate in Central Europe (CEU) during the 20th century is characterized by an overall temperature increase. Severe and prolonged drought events began occurring towards the end and these have continued into the 21st century. This study aims to analyze variations in the moisture supply from the Mediterranean Sea (MDS) during meteorological drought episodes occurring over the CEU region over the last three decades. A total of 51 meteorological drought episodes (22 with summer onsets, and 29 with winter) are identified over the CEU during the period 1980–2015 through the one-month Standardized Precipitation Evapotranspiration Index (SPEI-1), and their respective indicators, including duration, severity, intensity, and peak values, are then computed. Lagrangian forward-in-time analysis reveals that negative anomalies of moisture coming from the MDS prevail in all episodes except seven. Linear regression analysis between variations in the MDS anomalies and indicators of the drought episodes shows a significant linear relationship between severity, duration, peak values (winter), and MDS anomalies, which implies that drought episodes last longer and are more severe with an increase in the negative anomaly of moisture supply from the MDS. Nevertheless, no linear relationship is found between the intensity and peak values (annual, summer) of drought episodes and anomalies in the moisture contribution from the MDS.
We analyzed changes in surface relative humidity (RH) at the global scale from 1979 to 2014 using both observations and the ERA-Interim dataset. We compared the variability and trends in RH with those of land evapotranspiration and ocean evaporation in moisture source areas across a range of selected regions worldwide. The sources of moisture for each particular region were identified by integrating different observational data and model outputs into a Lagrangian approach. The aim was to account for the possible role of changes in air temperature over land, in comparison to sea surface temperature (SST), but also the role of land evapotranspiration and the ocean evaporation on RH variability. The results demonstrate that the patterns of the observed trends in RH at the global scale cannot be linked to a particular individual physical mechanism. Our results also stress that the different hypotheses that may explain the decrease in RH under a global warming scenario could act together to explain recent RH trends. Albeit with uncertainty in establishing a direct causality between RH trends and the different empirical moisture sources, we found that the observed decrease in RH in some regions can be linked to lower water supply from land evapotranspiration. In contrast, the empirical relationships also suggest that RH trends in other target regions are mainly explained by the dynamic and thermodynamic mechanisms related to the moisture supply from the oceanic source regions. Overall, while this work gives insights into the connections between RH trends and oceanic and continental processes at the global scale, further investigation is still desired to assess the contribution of both dynamic and thermodynamic factors to the evolution of RH over continental regions.
The Atmospheric Branch of the Hydrological Cycle over the Negro and Madeira River Basins in the Amazon RegionPublished: 05 June 2018 by MDPI in Water
The Amazon region, in South America, contains the largest rainforest and biodiversity in the world, and plays an important role in the regional and global hydrological cycle. In the present study, we identified the main sources of moisture of two subbasins of the Amazon River Basin, the Negro and Madeira River Basins respectively. The source-sink relationships of atmospheric moisture are investigated. The analysis is performed for the period from 1980–2016. The results confirm two main oceanic moisture sources for both basins, i.e., oceanic regions in the Tropical North and South Atlantic oceans. On the continents are, the Negro River Basin itself, and nearby regions to the northeast. For the Madeira River Basin, the most important continental sources are itself, and surrounding regions of the South American continent. Forward-trajectory analysis of air masses over the source regions is used to compute the moisture contribution to precipitation over basins. Oceanic (continental) sources play the most important role in the Negro River Basin (Madeira River Basin). The moisture contribution from the Tropical North Atlantic region modulates the onset and demise of the rainy season in the Negro River Basin; while the moisture contribution from the rest of the Amazon River Basin, the Madeira Basin itself, and Tropical South America leads to the onset of the rainy season in the Madeira River Basin. These regions also played the most important role in decreasing the moisture supply during most severe dry episodes in both basins. During ‘’El Niño’’, generally occurs a reduction (increase) of the moisture contribution to the Negro River Basin (Madeira River Basin; mainly from April to August) from almost all the sources, causing a decrease in the precipitation. Generally, the contrary occurs during ‘’La Niña’’.
A Lagrangian analysis of the moisture budget over the Fertile Crescent during two intense drought episodesPublished: 01 May 2018 by Elsevier BV in Journal of Hydrology
The Fertile Crescent (FC) region comprises the east coast of the Mediterranean Sea and the northern part of the Arabian Peninsula. The FC suffered two severe drought episodes separated by a 7-year period, in 1998 – 2000 and 2007 – 2009, which are considered the most severe episodes to hit the region in the last 50 years. A Lagrangian model (FLEXPART) and ERA-Interim data (with a 1°x1° lat-long resolution) were used to identify for the first time the climatological sources of moisture for the FC and their characteristics. Variability and the source-receptor relationships, concerning their contribution to the precipitation, and the implications regarding the transport of moisture changes over the FC, during the wet season (October-May) from 1980 – 2014 were analysed. The main climatological moisture sources during this period were determined to be the FC itself, the eastern Mediterranean Sea, the Red Sea, the Persian Gulf, the Arabian Sea, the Caspian and Black Seas, and the central and western parts of the Mediterranean Sea. The analysis showed higher anomalous conditions in the moisture transport from some moisture sources during the two outstanding drought episodes. The key feature of the wet seasons during these episodes was a deficit in the moisture losses over the studied area related to the FC itself, the Red and Arabian Seas sources, followed and to a lesser extent by the eastern Mediterranean Sea over the northern part of the FC region. Nevertheless, the moisture supply deficit from the sources was much greater during the 2007 – 2009 drought event. The SPEI index at large scales (24 months) showed that the 2007 – 2009 episode was part of longer-term drought conditions that had been developing over the previous months, reinforcing the drought severity given recycling processes attributed to the FC. During the two extreme drought episodes, the mountainous terrain over the northern and eastern FC suffered the highest precipitation deficits, and these areas are, precisely, the most influenced by two of the major moisture sources, namely, the FC and eastern Mediterranean Sea. The decreased moisture contribution from these main sources led to more intense droughts over the region. As a result, both regions should be considered as hotspots to signal severe or extreme droughts in the region.
The Mediterranean Moisture Contribution to Climatological and Extreme Monthly Continental PrecipitationPublished: 21 April 2018 by MDPI in Water
Moisture transport from its sources to surrounding continents is one of the most relevant topics in hydrology, and its role in extreme events is crucial for understanding several processes such as intense precipitation and flooding. In this study, we considered the Mediterranean Sea as the main water source and estimated its contribution to the monthly climatological and extreme precipitation events over the surrounding continental areas. To assess the effect of the Mediterranean Sea on precipitation, we used the Multi-Source Weighted-Ensemble Precipitation (MSWEP) database to characterize precipitation. The Lagrangian dispersion model known as FLEXPART was used to estimate the moisture contribution of this source. This contribution was estimated by tracking particles that leave the Mediterranean basin monthly and then calculating water loss (E − P < 0) over the continental region, which was modelled by FLEXPART. The analysis was conducted using data from 1980 to 2015 with a spatial resolution of 0.25°. The results showed that, in general, the spatial pattern of the Mediterranean source’s contribution to precipitation, unlike climatology, is similar during extreme precipitation years in the regions under study. However, while the Mediterranean Sea is usually not an important source of climatological precipitation for some European regions, it is a significant source during extreme precipitation years.
In the last few decades, many studies have identified an increasing number of natural hazards associated with extreme precipitation and drought events in Europe. During the 20th century, the climate in Central Europe and the Mediterranean region was characterised by an overall temperature increase, and the beginning of the 21st century has been marked by severe and prolonged drought events. The aim of this study is to analyse variations in the moisture supply during the 2003 drought episode that affected large portions of Europe. In order to better characterise the evolution of the episodes across the continent, separate analyses were performed for two spatial domains: Central Europe and the Mediterranean region. These regions were defined according to the 5th Intergovernmental Panel on Climate Change Assessment Report. For both regions, this drought episode was most severe from 1980 to 2015, according to the one-month Standardised Precipitation Evapotranspiration Index (SPEI-1) analysis, which was conducted using monthly precipitation and potential evapotranspiration data from the Climate Research Unit. Analyses of precipitation, potential evapotranspiration, pressure velocity at 500 hPa, and vertically integrated moisture flux were conducted to characterise the anomalous patterns over the regions during the event. A Lagrangian approach was then applied in order to investigate possible continental-scale changes in the moisture supply over the Central European and Mediterranean regions during 2003. This approach is based on the FLEXible PARTicle (FLEXPART) dispersion model, integrated with data from the European Centre for Medium-Range Weather Forecasts (ECMWF): the ECMWF Re-Analysis ERA-Interim. The results indicate that anomalous subsidence, increased evapotranspiration, and reduced precipitation predominated over both regions during the episode. The most intense reduction in the moisture supply over Central Europe was registered for the Mediterranean Sea (MDS) and the Central European region, while for the Mediterranean region, most intense reduction in the moisture supply was observed in the MDS and—in minor-scale—Gibraltar regions.
The atmospheric branch of the hydrological cycle over the Indus, Ganges, and Brahmaputra river basinsPublished: 15 December 2017 by Copernicus GmbH in Hydrology and Earth System Sciences
The atmospheric branch of the hydrological cycle over the Indus, Ganges, and Brahmaputra river basins (IRB, GRB, and BRB respectively) in the South Asian region was investigated. The 3-dimensional model FLEXPART v9.0 was utilized. An important advantage of this model is that it permits the computation of the freshwater budget on air parcel trajectories both backward and forward in time from 0.1 to 1000hPa in the atmospheric vertical column. The analysis was conducted for the westerly precipitation regime (WPR) (November–April) and the monsoonal precipitation regime (MPR) (May–October) in the period from 1981 to 2015. The main terrestrial and oceanic climatological moisture sources for the IRB, GRB, and BRB and their contribution to precipitation over the basins were identified. For the three basins, the most important moisture sources for precipitation are (i) in the continental regions, the land masses to the west of the basins (in this case called western Asia), the Indian region (IR), and the basin itself, and (ii) from the ocean, the utmost sources being the Indian Ocean (IO) and the Bay of Bengal (BB), and it is remarkable that despite the amount of moisture reaching the Indus and Ganges basins from land sources, the moisture supply from the IO seems to be first associated with the rapid increase or decrease in precipitation over the sources in the MPR. The technique of the composites was used to analyse how the moisture uptake values spatially vary from the sources (the budget of evaporation minus precipitation (E − P) was computed in a backward experiment from the basins) but during the pre-onset and pre-demise dates of the monsoonal rainfall over each basin; this confirmed that over the last days of the monsoon at the basins, the moisture uptake areas decrease in the IO. The Indian region, the Indian Ocean, the Bay of Bengal, and the basins themselves are the main sources of moisture responsible for negative (positive) anomalies of moisture contribution to the basins during composites of driest (wettest) WPR and MPR.
<strong>Drought and </strong><strong>wet episodes in Amazonia: the role of atmospheric moisture transport</strong>Published: 06 November 2017 by MDPI AG in Proceedings of First International Electronic Conference on the Hydrological Cycle
<p>The Amazon River basin (ARB) in Sud-America contains the world largest rainforest and biodiversity and plays an important role in the regional and global hydrological cycle. It consist of several sub-basins as the Negro River basin (NRB) in the north and the Madeira River basin (MRB) to the south, both considered of utmost importance in the Amazonia for the Amazon River. The precipitation annual cycle in both basins experiences an opposite annual cycle and as a consequence their contributions to the Amazon River are lagged in time. Here we utilized the Standardized Precipitation Index (SPEI) to identify drought and wet conditions in the NRB and MRB along the period 1980-2016. This index has the advantages over other index because considers the effect of the Atmospheric Evaporation Demand (AED) on drought severity. Besides, the Lagrangian dispersion model FLEXPART v9.0 was used to track backward in time air masses residing over the basins and to calculate along the trajectories the budget of (<em>E-P</em>). This permitted to identify those regions from where air masses gain humidity (<em>E-P>0</em>) before arriving at the basins, what we consider as moisture sources. FLEXPART has been successfully utilized for the same goal in several studies. This allowed investigating the hydrological budget of <em>(E-P)</em> over the NRB and MRB as well as their role as sources of moisture for surrounded continental regions. This study examines the variability of moisture uptake by the basins from these sources during drought and wet episodes in the basins. We consider this a new approach to be a useful method for understanding the causes and variability of drought and wet events in other regions worldwide.</p>
<span>The Mediterranean moisture supply in the genesis of climatological and extreme monthly continental precipitation</...Published: 06 November 2017 by MDPI AG in Proceedings of First International Electronic Conference on the Hydrological Cycle
<p>The moisture transport from its sources to the continents is one of the most relevant topics in the hydrology, and its role in extremes events is crucial to understand several processes in the Earth, as intense precipitations and/or flooding. Using the global precipitation (P) dataset from the Multi-Source Weighted-Ensemble Precipitation (MSWEP) from 1980 to 2015 with a 3-hourly temporal and 0.25° spatial resolution, a monthly precipitation climatology were done over the area of the Mediterranean Sea, checking grid by grid which year exhibits the maximum precipitation. As is well known, the Mediterranean Basin is a clear source of moisture for the surrounding areas. To link this source of moisture with the precipitation, in this work we have made use of the Lagrangian dispersion model FLEXPART to track, in its forward mode, those particles that monthly leave the Mediterranean Basin and we have calculated the loss of moisture (E-P<0) modelled by FLEXPART (P-FLEX) over the continental region. The aim of this study is to calculate the monthly climatological percentage of the Mediterranean contribution grid by grid, and the changes of this contribution for extreme monthly precipitation checking the importance of this sea source of moisture during the maximum peak of precipitation.</p>
<strong>A lagrangian analysis of the moisture transport during the 2003 drought episode over the Mediterranean region </...Published: 05 November 2017 by MDPI AG in Proceedings of First International Electronic Conference on the Hydrological Cycle
<p>In the last decades many studies have pointed out an increasing number of natural hazards associated with extremes in precipitation and drought conditions. Generally, dry and hot conditions across the Europe impact on the Mediterranean region. The Mediterranean is located at the border between the tropical climate zone and the mid latitude climate belt. Due to its large extension and diverse topography, it shows large climatic differences that make its climate scientifically interesting. </p> <p>The aim of this study is to analyze the moisture transport during the 2003 drought episode observed over the surroundings of the Mediterranean. The region was defined according to the 5th Intergovernmental Panel on Climate Change (IPCC) Assessment Report. The episode was identified using Standardized Precipitation Evapotranspiration Index (SPEI), calculated using monthly CRU (TS3.24.01) precipitation and potential evapotranspiration (PET). One of the crucial advantages of the SPEI over the other widely used drought indexes is its multi-scalar characteristics, which enable identification of different drought types. Therefore, the monthly SPEI-1, SPEI-3, SPEI-6, SPEI-12 and SPEI-24 indexes were used to identify the episodes on different time scales. This episode was the most severe during the period 1980-2015 according to the SPEI-1 analysis. Analyses of precipitation, potential evapotranspiration, omega at 500hPa, and vertically integrated moisture flux have been conducted to characterize the anomalous patterns over the region during the event. A Lagrangian approach was then applied in order to investigate possible changes in the moisture transport from and toward the Mediterranean region during the episode. This approach is based on the FLEXPART model integrated with the ERA-Interim data set.</p>
Moisture Transport Anomalies over the Danube River Basin during Two Drought Events: A Lagrangian AnalysisPublished: 03 October 2017 by MDPI in Atmosphere
In this paper, we provide a Lagrangian analysis of the anomalies in the moisture transport during two important drought events (1989/1990 and 2003) configured over the Danube River Basin (DRB) region. Firstly, we identified the drought episodes that occurred over the DRB in the period of 1980–2014 through the Standardized Precipitation Evapotranspiration Index (SPEI). SPEI was calculated using monthly Climatic Research Unit (CRU) Time-Series (TS) Version 3.23 precipitation and potential evapotranspiration (PET) datasets with a spatial resolution of 0.5 degrees. The monthly SPEI-1 index was applied to identify the drought episodes and their respective indicators, including duration, severity, and intensity. Two significant drought events were selected: 1989/1990 (presenting dry conditions during October 1989–March 1990) and 2003 (presenting dry conditions during April 2003–September 2003). These events were associated with the two most severe SPEI-1 episodes identified over the DRB during 1980–2014. Then, an analysis of anomalies in the moisture transport was conducted in order to verify possible changes in the moisture supply from the climatological sources for the DRB during these episodes. The moisture transport analysis was performed through a Lagrangian approach, which uses the outputs of the FLEXiblePARTicle dispersion model FLEXPART integrated with one of the reanalysis produced by the European Centre for Medium-Range Weather Forecasts (ECMWF): the ECMWF Re-Analysis (ERA)-Interim dataset. The DRB receives moisture from seven different moisture source regions: the North Atlantic Ocean (NATL), North Africa (NAF), the Mediterranean Sea (MED), the Black Sea (BS), the Caspian Sea (CS), the DRB, and Central and Eastern Europe (Rest of Land (RestL)). The analysis of drought events shows that the precipitation and moisture supply from the selected sources weakened mainly during both drought events. Anomalous subsidence and an increased PET also prevailed over the DRB during these SPEI-1 episodes. RestL and MED registered the most intensive reduction in the moisture supply over the DRB during both periods.
The Danube River Basin is the second longest catchment basin in Europe and exhibits intense climatological diversity. In recent decades, the frequency and intensity of daily precipitation extremes have suffered from an increment in many parts of the world, including Central and Eastern Europe. Wet spells are defined by the number of consecutive rainy days with different thresholds. The identification of wet spells and their trends in the rainfall time is very important for many sectors, such as agriculture, ecology, hydrology and water resources. Wet spells can lead to extreme events and cause floods and other disasters. In this study, we will attempt to characterise global precipitation in the context of wet spells and associated precipitation depth of wet spells in the Danube River Basin area using daily precipitation data, as well as analysing different approaches to identifying wet spells. The ten most intense wet spells were detected, and the most intense, which occurred on 23 September 1996, was studied in depth in terms of precipitation and associated anomalies, the synoptic situation and the anomalous transport of moisture using a Lagrangian approach. The existence of a marked west-east dipole in the field of sea level pressure between the Atlantic Ocean and the eastern Mediterranean leads to the anomalous moisture transport from the Northern Atlantic Ocean to the Mediterranean Sea, where a higher available amount of moisture existed, and subsequently penetrated within the low positioned over the Danube River Basin. In addition, an Atmospheric River was also responsible for the wet conditions in the Danube River Basin. The combination of all these factors was responsible for the extreme precipitation linked with the wet spell.
The Lagrangian model FLEXPART is used to identify the moisture sources of the Congo River basin (CRB) and investigate their role in the hydrological cycle. This model allows us to track atmospheric parcels while calculating changes in the specific humidity through the budget of evaporation minus precipitation. This method permits the annual-scale identification of five continental and four oceanic principal regions that provide moisture to the CRB from both hemispheres over the course of the year. The most important is the CRB, which provides more than 50% of the total atmospheric moisture contribution to precipitation over itself. Additionally, both the land that extends to the east of the CRB and the eastern equatorial South Atlantic Ocean are very important sources, while the Red Sea source is merely important in the (E − P) budget over the CRB despite its high evaporation rate. The moisture-sink patterns over the CRB in air masses that were tracked forward in time from all the sources follow the latitudinal rainfall migration and are mostly highly correlated with the pattern of the precipitation rate, ensuring a link between them. In wet (dry) years, the contribution of moisture to precipitation from the CRB over itself increases (decreases). Despite the enhanced evaporative conditions over the basin during dry years, the vertically integrated moisture flux (VIMF) divergence inhibits precipitation and suggests the transport of moisture from the CRB to remote regions.
The atmospheric branch of the hydrological cycle over the Indus, Ganges and Brahmaputra River basinsPublished: 24 July 2017 by Copernicus GmbH in Hydrology and Earth System Sciences Discussions
The atmospheric branch of the hydrological cycle over the Indus, Ganges, and Brahmaputra river basins in the South Asian region was investigated. The 3-dimensional model FLEXPART v9.0 was utilized. An important advantage of this model is that it permits the computation of the freshwater budget on air parcels both backward and forward in time trajectories from 0.1 and 1000 hPa in the atmospheric vertical column. The analysis was conducted for the Westerly Precipitation Regime (WPR) (November–April) and the Monsoonal Precipitation Regime (MPR) (May–October) in the period from 1981–2015. The main terrestrial and oceanic climatological moisture sources for the IRB, GRB and BRB and their contribution to precipitation over the basins were identified. For the three basins, the most important moisture sources for precipitation are (i) on the continental regions, the land masses to the west of the basins (in this case called West Asia), the Indian region (IR) and the basin itself, and (ii) from the ocean, the utmost sources are the Indian Ocean (IO) and the Bay of Bengal (BB), and it is remarkable that despite the amount of moisture reaching the IRB and GRB from land sources, the moisture supply from the IO seems to be first associated with the rapid increase/decrease in precipitation over the sources in the MPR. The technique of the composites was used to analyse how the moisture uptake spatially vary from the sources (the budget of evaporation minus precipitation (E − P) was computed in a backward experiment from the basins) but during the preonset and predemise dates of the monsoonal rainfall over each basin; this confirmed that over the last days of the monsoon at the basins, the moisture uptake areas decrease in the IO. The Indian region, the Indian Ocean and the basins itself are the main sources of moisture responsible for negative (positive) anomalies of moisture contribution to the basins during composites of driest (wettest) WPR and MPR.
<p>In West Africa, is located the Niger River Basin (NRB). Dry and wet conditions were investigated in this basin during the rainy (May-October) and dry (November-April) seasons, from 1980 to 2014. To do this was, calculated the Standardized Precipitation-Evapotranspiration Index (SPEI) at the time scale of 6-months for the whole NRB. The Lagrangian model FLEXPART v9.0 has been used to compute over the main semi-annual climatological moisture sources of the NRB, the budget of evaporation minus precipitation <em>(E-P)</em> over 10-day backward trajectories from the NRB itself. Positive (negative) <em>(E-P)</em> values indicate moisture uptake (loss). This permit evaluating the role of continental and oceanic sources of moisture separately for composites of extremely and severely dry and wet conditions in the basin. The results show for the dry season the negative trend of the April-SPEI6 values and the <em>(E-P)>0</em> values obtained over the tropical east-north Atlantic Ocean (NAtl), the western Sahel and the Mediterranean region. Over these sources, the anomalies of <em>(E-P)</em> for driest and wettest composites indicate their direct response. On the contrary, for the rainy season, the October-SPEI6 values trend is positive, as well it occurs for the moisture uptake over the South Sahel (SSah) and the NRB itself. The anomalies of the <em>(E-P)</em> values for driest and wettest rainy seasons composites suggest a direct relationship with those obtained mainly over SSah, SAtl and the NRB itself.</p>
We analyzed changes in surface relative humidity (RH) at the global scale from 1979 to 2014 using both observations and ERA-Interim dataset. We compared the variability and trends of RH with those of land evapotranspiration and ocean evaporation in moisture source areas across a range of selected regions worldwide. The sources of moisture for each particular region were identified by integrating different observational data and model outputs into a lagrangian approach. The aim was to account for the possible role of changes in air temperature over land, in comparison to sea surface temperature (SST), on RH variability. Results demonstrate a strong agreement between the interannual variability of RH and the interannual variability of precipitation and land evapotranspiration in regions with continentally-originated humidity. In contrast, albeit with the dominant positive trend of air temperature/SST ratio in the majority of the analyzed regions, the interannual variability of RH in the target regions did not show any significant correlation with this ratio over the source regions. Also, we did not find any significant association between the interannual variability of oceanic evaporation in the oceanic humidity source regions and RH in the target regions. Our findings stress the need for further investigation of the role of both dynamic and radiative factors in the evolution of RH over continental regions at different spatial scales.
Drought episodes in the climatological sinks of the Mediterranean moisture source: The role of moisture transportPublished: 01 April 2017 by Elsevier BV in Global and Planetary Change
The Lagrangian model FLEXPART was used to identify the moisture sources of the Congo River Basin (CRB) and investigate their role in the hydrological cycle. This model allows us to track atmospheric parcels while calculating changes in the specific humidity through the budget of evaporation-minus-precipitation. The method permitted the identification at an annual scale of five continental and four oceanic regions that provide moisture to the CRB from both hemispheres over the course of the year. The most important is the CRB itself, providing more than 50% of the total atmospheric moisture income to the basin. Apart from this, both the land extension to the east of the CRB together with the ocean located in the eastern equatorial South Atlantic Ocean are also very important sources, while the Red Sea source is merely important in the budget of (E − P) over the CRB, despite its high evaporation rate. The moisture sink patterns over the CRB in air masses tracked forwards from all the sources follow a latitudinal rainfall migration and are mostly highly correlated with the pattern of precipitation rate, ensuring a link between them. The analysis of the wet and dry periods in the CRB confirms the key role of the basin in modulating the fresh water balance within the basin itself.
The Niger River basin (NRB) is located in the important climatic region of the African Sahel. In this study we use the Lagrangian tridimensional model FLEXPART v9.0 to identify and characterise the moisture sources for the NRB. This method allows the integration of the budget of evaporation minus precipitation over 10-day backward trajectories, thereby identifying the origins of the air masses residing over the NRB. The analysis was performed for the 35-year period from 1980 to 2014, which allowed us to identify the main semi-annual climatological moisture sources of the NRB, for November–April (NDJFMA) (dry season) and May–October (MJJASO) (wet season), and to quantify the respective moisture uptakes. Throughout the year, the NRB main moisture sources are located on the tropical eastern North Atlantic Ocean near Africa, the tropical eastern South Atlantic Ocean in the Gulf of Guinea, in the regions surrounding the Sahel and in the Mediterranean Sea. The extents of these sources vary between dry and wet seasons. In NDJFMA two regions appear in the east of the basin, which then join up, forming a larger source to the northeast of the basin in MJJASO, when three other less important moisture sources can be seen in central-equatorial Africa, the tropical western Indian Ocean and the Persian Gulf. In NDJFMA the majority of the moisture uptake comes from the NRB itself but then, later in MJJASO, when the precipitation increases over the basin the greatest uptake of moisture occurs over the tropical eastern South Atlantic Ocean, northeast Africa and the NRB, which suggests that these are the effective sources of precipitation in the basin in overall terms. The seasonal moisture uptake quantification over the moisture sources of the NRB, reveals that largest fraction of moisture income to the basin from outside its boundaries. Despite providing moisture to the NRB the source located in the tropical eastern North Atlantic Ocean does not contribute that much to precipitation in the basin. A daily (ten-day) backward analysis shows the importance of the moisture uptake within the NRB and from near moisture sources during the first few (backward) days, while the Atlantic Ocean sources and the Mediterranean became more important during the last five (backward) days of the analysis.
The Arctic system has experienced in recent times an extreme reduction in the extent of its sea ice. The years 2007 and 2012 in particular showed maxima in the loss of sea ice. It has been suggested that such a rapid decrease has important implications for climate not only over the system itself but also globally. Understanding the causes of this sea ice loss is key to analysing how future changes related to climate change can affect the Arctic system. For this purpose, we applied the Lagrangian FLEXible PARTicle dispersion (FLEXPART) model to study the anomalous transport of moisture for 2006/2007 and 2011/2012 in order to assess the implications for the sea ice. We used the model results to analyse the variation in the sources of moisture for the system (backward analysis), as well as how the moisture supply from these sources differs (forward analysis) during these years. The results indicate an anomalous transport of moisture for both years. However, the pattern differs between events, and the anomalous moisture supply varies both in intensity and spatial distribution for all sources.
In this study, we investigate the sources of moisture (and moisture for precipitation) over the Danube River Basin (DRB) by means of a Lagrangian approach using the FLEXPART V9.0 particle dispersion model together with ERA-Interim reanalysis data to track changes in atmospheric moisture over 10-day trajectories. This approach computes the budget of evaporation-minus-precipitation by calculating changes in specific humidity along forward and backward trajectories. We considered a time period of 34 years, from 1980 to 2014, which allowed for the identification of climatological sources and moisture transport towards the basin. Results show that the DRB mainly receives moisture from seven different oceanic, maritime, and terrestrial moisture source regions: North Atlantic Ocean, North Africa, the Mediterranean Sea, Black Sea, Caspian Sea, the Danube River Basin, and Central and Eastern Europe. The contribution of these sources varies by season. During winter (October–March) the main moisture source for the DRB is the Mediterranean Sea, while during summer (April–September) the dominant source of moisture is the DRB itself. Moisture from each source has a different contribution to precipitation in the DRB. Among the sources studied, results show that the moisture from the Mediterranean Sea provides the greatest contribution to precipitation in the basin in both seasons, extending to the whole basin for the winter, but being more confined to the western side during the summer. Moisture from the Caspian and Black Seas contributes to precipitation rather less.
Moisture transport into the Arctic: Source-receptor relationships and the roles of atmospheric circulation and evaporati...Published: 27 November 2016 by Wiley in Journal of Geophysical Research: Atmospheres
Hydrological processes play a key role in the Arctic, as well as being an important part of the response of this region to climate change. The origin of the moisture arriving (and then precipitating) in the Arctic is a crucial question in our understanding of the Arctic hydrological cycle. In an attempt to answer this, the present study uses the Lagrangian diagnosis model FLEXPART to localize the main sources of moisture for the Arctic region, to analyze their variability and their contribution to precipitation, and to consider the implications of any changes in the transport of moisture from particular sources within the system. From this analysis, four major moisture sources appear as the most important moisture supplies into the system: the subtropical and southern extratropical Pacific and Atlantic oceans, North America, and Siberia. Oceanic sources play an important role throughout the year, whereas continental ones only take effect in summer. The sink areas associated with each source have been shown to be moderately influenced by changes in atmospheric circulation, mainly associated with the East Atlantic (EA) pattern for the Atlantic source and related to West Pacific (WP) and Pacific/North American (PNA) teleconnection patterns for the Pacific one. On the other hand, the variability over the sinks does not seem to be significantly related to changes in evaporation at an interannual scale.
<p>The Niger River basin (NRB) is located on the important climatic region of the African Sahel. In this work we use the Lagrangian tridimensional model FLEXPART v9.0, to identify and characterize the moisture sources for the NRB. The method allowed integrating the evaporation minus precipitation budget through 10 days backward trajectories and thus, identifying the origin of air masses residing over the NRB. The analysis was performed for 35 years from 1980 to 2014. There were identified the main seasonal climatological moisture sources of the NRB and quantify their contribution to the total moisture influx. At first day backward in time the NRB appears as the main moisture source, contributing less and less humidity to the particles during last days, suggesting the importance of local moisture supply to recycling process. Through the 10 days backward, the pattern of (E – P) shows the spatial expansion of sources and sinks regions. Across the year, the moisture supply to the NRB mainly comes from itself and the tropical-east south Atlantic Ocean, but are also important the rest of the sources located on the tropical-east north Atlantic Ocean near Africa, the Sahel surrounded regions, the Mediterranean Sea, the east Africa, the north-east Africa and less important small regions on central-equatorial Africa and the <br /> tropical-west Indian Ocean.<span></span></p>
<span>Tracking the Origin of Moisture (and Moisture for Precipitation) over the Danube River Basin through a Lagrangian ...Published: 15 July 2016 by MDPI AG in Proceedings of The 1st International Electronic Conference on Atmospheric Sciences
<p>In this study we investigate the sources of moisture (and moisture for precipitation) over the Danube River Basin (DRB) through a Lagrangian approach which uses the FLEXPART V9.0 Lagrangian particle dispersion model together with ERA-Interim reanalysis data to track changes in atmospheric moisture along 10-day trajectories. This approach computes the budget of evaporation minus precipitation by calculating changes in specific humidity along forward and backward trajectories. We considered a temporal period of 34 years, from 1980 to 2014 which allowed identifying climatological sources and moisture transport towards the basin at interannual scale. Results showed that the DRB receives moisture mainly from seven different oceanic, maritime and terrestrial moisture source regions: North Atlantic Ocean, North Africa, Mediterranean Sea, Black Sea, Caspian Sea, Danube River Basin and Central and Eastern Europe. The contribution of these sources differs with the season. During the Wet season (October–March) the main moisture source for the DRB is the Mediterranean Sea, while during the Dry season (April–September) the dominant source of moisture in the DRB itself. Moisture coming from each source has a different contribution for the precipitation in the DRB. Between the studied sources results show that the moisture coming from the Mediterranean Sea provides the highest values for precipitation in the basin during both seasons, extending to the whereas the whole basin for the Wet season and more confined to the western side during the Dry one. Moisture coming from the Caspian Sea and the Black Sea was that less contribute to precipitation.</p>
<p>Recently, the Arctic system has been suffering an extreme reduction in its sea ice extension. 2007 and 2012 represent those years showing the maximum sea ice loss. This rapid decrease has been suggested to have important implications on climate not only over the system itself but also globally. Understanding the causes of this sea ice loss is key to analyzing how future changes related to climate change can affect the Arctic system and the global system. For this purpose, we have applied the Lagrangian model FLEXPART to study the anomalous transport of moisture for these years and to analyze the implications on the sea ice it may produce. Throughout this model, we will analyze the variation in the sources of moisture for the system (backward analysis), and how the moisture supply from these sources is affected (forward analysis). From the results an anomalous transport of moisture have been proved to occur for both years. However, the pattern is different for each event, being the anomalous moisture supply different in both intensity and spatial distribution from every source.</p>
A Lagrangian approach was used to identify the moisture sources for 14 ice-core sites located worldwide for the period of 1980–2012. The sites were classified into three domains: Arctic, Central (Andes, Alps, and Kilimanjaro), and Antarctic. The approach was used to compute budgets of evaporation minus precipitation by calculating changes in the specific humidity along 10-day backward trajectories. The results indicate that the oceanic regions around the subtropical high-pressure centres provide most of moisture, and their contribution varies throughout the year following the annual cycles of the centres. For the Arctic Domain, the sources lie in the subtropical North Atlantic and Pacific. The subtropical South Atlantic, Indian, and Pacific oceans provide moisture for the Antarctic Domain. The sources for South America are the Atlantic and South Pacific, for Europe the sources are in the Mediterranean and the North Atlantic, and for Asia the sources are the Indian Ocean and the Arabian Sea.
The present work proposes a Lagrangian diagnostic scheme to investigate the anomalous moisture transport before, during, and after the occurrence of drought episodes. The Lagrangian approach proposed here uses the model FLEXPART integrated with the ERA-Interim data set and it has been successfully applied in previous studies concerning the climatological characterization of the sources and sinks of moisture in several regions around the world. The drought episodes will be identified and characterized through the SPEI index. The anomalies of the moisture sources for the area affected will be analyzed, as well as the impact of the droughts on the moisture transport from the area affected towards its climatological sinks (previous studies suggest that some heat wave episodes can be associated with anomalies in moisture transport). In other words, the methodology proposes to investigate the role of the area affected as a receptor/source of moisture during the drought episodes. As an example of applicability of the methodology, the severe drought episode over central U.S. in 2012 is analyzed. An analysis of the 2012 anomalies suggests that there was some reduction in the contribution from the local and continental climatological moisture sources for the central U.S. mainly from June to October. The period from July to October 2012 was also characterized by the reduction of the moisture transport from the drought area towards its climatological sinks located over northeastern North America. A better understanding not only of the transport of humidity, but also of the relationship between sources/sinks of moisture and of possible impacts generated by variations in the sources is crucial for a more accurate weather forecast, helping to minimize the consequences of the natural hazards.
Anomalous patterns of SST and moisture sources in the South Atlantic Ocean associated with dry events in southeastern Br...Published: 21 March 2016 by Wiley in International Journal of Climatology
This paper examines the distributions of anomalies of sea surface temperature (SST) and of the moisture sources in the South Atlantic Ocean during extreme dry events in southeastern Brazil in the austral autumn, winter and spring for the period 1982–2009. The extreme dry events were identified based on a combination in which consecutive dry days and variable percentiles were considered in five homogeneous regions in terms of precipitation in southeastern Brazil, as defined through cluster analysis. Composites of anomalies of SST and moisture sources for the dry events selected for the different homogeneous regions show specific characteristics for each region, but some similarities were apparent for the southern and northern parts of southeast Brazil. During spring in all regions, and during autumn and winter in the southern regions, a tripole pattern of SST anomalies was found (negative, positive and negative), together with an anomalous anticyclonic circulation in the Atlantic Ocean transporting moisture to southern Brazil associated with positive SST anomalies. A decrease in the climatological moisture sources in the south of Brazil then ensues, and dry conditions prevail in the regions of interest. In winter and autumn in the northern regions, the same tripole pattern of SST anomalies was also found, but shifted northwards. An anomalous cyclone is associated with the negative SST anomalies, and the climatological moisture sources to the northeast of Brazil reduce their contribution to the region of interest, where negative precipitation anomalies are registered. It seems that the events selected show the results of reductions both in terms of the availability of moisture and in atmospheric instability.
In this work we use a Lagrangian model (FLEXPART) to investigate the contribution of moisture from the Atlantic Warm Pool (AWP) to the atmospheric hydrological budget during the period from 1982 to 1999, and to identify which regions are affected by the moisture transport from this source. FLEXPART computes budgets of evaporation minus precipitation by calculating changes in the specific humidity along 10-day forward trajectories. A monthly analysis was made for May-October, the typical development period of the AWP. Climatologically, the moisture transported from the AWP to North and Central America increases from June onwards. Humidity is also transported towards western Europe from July to October, probably favoured by the positioning of the North Atlantic Subtropical High and its associated flows. The largest moisture sinks associated with transport from the AWP were found from August to October, when the warm pool can extend to the north-western coast of Africa. The technique of composites was used to analyse how the interannual variability of moisture contribution from the AWP depends on changes in the pool’s areal extension, and on the El Niño Southern Oscillation (ENSO). The results indicate that during episodes when the AWP is at its maximum extent, its moisture contribution increased to the Caribbean, to the region of the Inter-tropical Convergence Zone (ITCZ), and to the North Atlantic. By contrast, less moisture was transported to southeastern North America during July and August, or to central North America during September and October. The differences in moisture sink regions for extreme ENSO episodes suggest that there are favoured sinks in the Caribbean and in the ITCZ region during La Niña events.
The role of the Amazon Basin moisture in the atmospheric branch of the hydrological cycle: a Lagrangian analysisPublished: 11 July 2014 by Copernicus GmbH in Hydrology and Earth System Sciences
We used a Lagrangian model (FLEXPART) together with the 1979–2012 ERA-Interim reanalysis data to investigate the role of the moisture in the Amazon Basin in the regional hydrological budget over the course of the year. FLEXPART computes budgets of evaporation minus precipitation by calculating changes in the specific humidity along forward and backward trajectories. The tropical Atlantic is the most important remote moisture source for the Amazon Basin. The tropical North Atlantic (NA) mainly contributed during the austral summer, while the contribution of the tropical South Atlantic (SA) prevailed for the remainder of the year. At the same time, the moisture contribution from the Amazon Basin itself is mainly for moisture supplying the southeastern South America. The 33-year temporal domain allowed the investigation of some aspects of the interannual variability of the moisture transport over the basin, such as the role of the El Niño Southern Oscillation (ENSO) and the Atlantic Meridional Mode (AMM) on the hydrological budget. During the peak of the Amazonian rainy season (from February to May, FMAM) the AMM is associated more with the interannual variations in the contribution from the tropical Atlantic sources, while the transport from the basin towards the subtropics responds more to the ENSO variability. The moisture contribution prevailed from the SA (NA) region in the years dominated by El Niño/positive AMM (La Niña/negative AMM) conditions. The transport from the Amazon towards the subtropics increased (reduced) during El Niño (La Niña) years.
Leaving aside the contribution made by recycling, it is the main oceanic moisture sources that are responsible for most of the precipitation that falls on the continents. The transport of moisture from these sources can be affected by large-scale variability according to the hemispheric annular modes. The influence of the two dominant modes of extratropical winter climate: the Northern and the Southern Annular Modes (NAM and SAM) are herein investigated to assess how they affect the transport of moisture from the major oceanic moisture sources. A Lagrangian model was used, together with ERA-Interim reanalysis data (1979–2012), and differences between the composites of the six strongest higher and lower events observed for both phases of the two modes for the period were analyzed. The method is able to reproduce the general pattern of known variations for both annular patterns. Lower values of the NAM Index are associated with the displacement of the storm track toward tropical latitudes. Thus, moisture transport is enhanced from the Northern Pacific toward the northeastern basin and from the Northern Atlantic and Mediterranean toward southern Europe. On the other hand, during higher values of NAM, moisture transport is favored from the Northern Pacific toward eastern Asia, and moisture transport is enhanced from the Northern Atlantic toward the Caribbean Sea. In the Southern Hemisphere, during higher values of SAM more moisture is transported from the Atlantic and Indian oceanic sources southwards and eastwards than during the opposite phase. In this SAM phase it is also noted by an enhancement of moisture transport from the Coral Sea and Southern Pacific sources toward the Indian Ocean/West Pacific Warm Pool. Southeastern South America received more moisture from the Pacific and Atlantic sources during years with a lower SAM, episodes which also favored the influx of moisture from the Southern Atlantic toward Africa, causing monsoon conditions to occur.
This technical note describes a catalog of moisture sources for two sets of continental climatic regions: one based on regions with similar late 20th century mean climate and similar projected late 21st century precipitation changes, and the other widely used in IPCC assessment reports. By illustrating with one region by classification, the European one was selected and we identify and characterize all the major sources of moisture, and analyze their interannual variability and the role of the three dominant modes of global climate variability, including the El Niño‐Southern Oscillation (ENSO) and the Northern and Southern Annular Modes (NAM, SAM). We also estimate the influence of those oceanic regions that will see the greatest increases in evaporation rate in future years.
Estimating the Temporal Domain when the Discount of the Net Evaporation Term Affects the Resulting Net Precipitation Pat...Published: 03 June 2014 by Public Library of Science (PLoS) in PLOS ONE
The Lagrangian FLEXPART model has been used during the last decade to detect moisture sources that affect the climate in different regions of the world. While most of these studies provided a climatological perspective on the atmospheric branch of the hydrological cycle in terms of precipitation, none assessed the minimum temporal domain for which the climatological approach is valid. The methodology identifies the contribution of humidity to the moisture budget in a region by computing the changes in specific humidity along backward (or forward) trajectories of air masses over a period of ten days beforehand (afterwards), thereby allowing the calculation of monthly, seasonal and annual averages. The current study calculates as an example the climatological seasonal mean and variance of the net precipitation for regions in which precipitation exceeds evaporation (E-P0) can be discounted after when the integration of E-P is done without affecting the general net precipitation patterns when it is discounted in a monthly or longer time scale.
The role of the ENSO cycle in the modulation of moisture transport from major oceanic moisture sourcesPublished: 06 February 2014 by Wiley in Water Resources Research
The influence that the evolution of the ENSO cycle has on the moisture transport from the major oceanic moisture sources is investigated using a sophisticated Lagrangian approach informed by ERA‐interim data, together with composites of ENSO phases. When maintaining the sources of moisture defined for the climatological period 1980–2012, the variations in the moisture sinks associated with each of these evaporative sources throughout the ENSO cycle reproduce the known patterns of variations of the large‐scale atmospheric and precipitation systems over this cycle. Such variations include those observed in rainfall over the equatorial Pacific, in the major Summer monsoon systems, and in subtropical rainfall. When the areas of the sources were redefined according to the phase of ENSO, most of them remained stationary over the period of interest, nevertheless four of them showed notable differences in terms of their extents, namely the South Pacific and the Coral Sea (Pacific Ocean); the Mexican Caribbean (Atlantic), and the Arabian Sea (Indian).
 In this study, seasonal and interannual variability of the main atmospheric moisture sources over eight regions in the Mediterranean basin were investigated along a 21 year period. The Lagrangian dispersion model FLEXPART, developed by Stohl and James [2004, 2005], was applied to identify the contribution of humidity to the moisture budget of each region. This methodology is used to compute budgets of evaporation minus precipitation (E − P) by calculating changes in the specific humidity along backward trajectories, for the preceding 10 day periods. The results show clear seasonal differences in the moisture sources between wet and dry seasons. The Western Mediterranean Sea is the dominant moisture source for almost all the regions in the Mediterranean basin during the wet season, while the local net evaporation dominates during the dry season. The highest interannual variability is found in contributions to the Iberian Peninsula, Italy, and the Eastern Mediterranean. It is seen that the role of teleconnections is more limited than for the precipitation recorded in the region.
 In this study, we address two key issues in the hydrological cycle that have remained elusive: 1) to what extent can we expect climate change to affect the transport of moisture? and, in particular, 2) how will the changes in the sources’ intensity (that is, more evaporation) affect the distribution of continental precipitation? This was achieved using a multimodel ensemble that allowed delimiting those oceanic areas where climate change will likely lead to an increase in evaporation (E) minus precipitation (P). Finally, a sophisticated Lagrangian model was used to identify which continental regions will be affected by changes in precipitation (E − P < 0) originating in each oceanic moisture source. We find that in boreal winter, wide sectors of Europe, Asia, Middle East, South America, and southern Africa are affected, but North America emerges as the most affected continental region. In austral winter, the largest changes are confined to northern and Central America.
In view of the threat of global climate change, the proper understanding of the intensity of the hydrological cycle and of its development over time is one of the most important challenges of the century, at least in the area of the geosciences. The hydrological cycle can essentially be summarized to be the evaporation of moisture in one location, offset by precipitation elsewhere.
 The most important sources of atmospheric moisture at the global scale are herein identified, both oceanic and terrestrial, and a characterization is made of how continental regions are influenced by water from different moisture source regions. The methods used to establish source‐sink relationships of atmospheric water vapor are reviewed, and the advantages and caveats associated with each technique are discussed. The methods described include analytical and box models, numerical water vapor tracers, and physical water vapor tracers (isotopes). In particular, consideration is given to the wide range of recently developed Lagrangian techniques suitable both for evaluating the origin of water that falls during extreme precipitation events and for establishing climatologies of moisture source‐sink relationships. As far as oceanic sources are concerned, the important role of the subtropical northern Atlantic Ocean provides moisture for precipitation to the largest continental area, extending from Mexico to parts of Eurasia, and even to the South American continent during the Northern Hemisphere winter. In contrast, the influence of the southern Indian Ocean and North Pacific Ocean sources extends only over smaller continental areas. The South Pacific and the Indian Ocean represent the principal source of moisture for both Australia and Indonesia. Some landmasses only receive moisture from the evaporation that occurs in the same hemisphere (e.g., northern Europe and eastern North America), while others receive moisture from both hemispheres with large seasonal variations (e.g., northern South America). The monsoonal regimes in India, tropical Africa, and North America are provided with moisture from a large number of regions, highlighting the complexities of the global patterns of precipitation. Some very important contributions are also seen from relatively small areas of ocean, such as the Mediterranean Basin (important for Europe and North Africa) and the Red Sea, which provides water for a large area between the Gulf of Guinea and Indochina (summer) and between the African Great Lakes and Asia (winter). The geographical regions of Eurasia, North and South America, and Africa, and also the internationally important basins of the Mississippi, Amazon, Congo, and Yangtze Rivers, are also considered, as is the importance of terrestrial sources in monsoonal regimes. The role of atmospheric rivers, and particularly their relationship with extreme events, is discussed. Droughts can be caused by the reduced supply of water vapor from oceanic moisture source regions. Some of the implications of climate change for the hydrological cycle are also reviewed, including changes in water vapor concentrations, precipitation, soil moisture, and aridity. It is important to achieve a combined diagnosis of moisture sources using all available information, including stable water isotope measurements. A summary is given of the major research questions that remain unanswered, including (1) the lack of a full understanding of how moisture sources influence precipitation isotopes; (2) the stationarity of moisture sources over long periods; (3) the way in which possible changes in intensity (where evaporation exceeds precipitation to a greater of lesser degree), and the locations of the sources, (could) affect the distribution of continental precipitation in a changing climate; and (4) the role played by the main modes of climate variability, such as the North Atlantic Oscillation or the El Niño–Southern Oscillation, in the variability of the moisture source regions, as well as a full evaluation of the moisture transported by low‐level jets and atmospheric rivers.
Ocean ocean/oceanic Evaporation ocean/oceanic evaporation and Precipitation ocean/oceanic precipitationPublished: 01 January 2012 by Springer Nature in Encyclopedia of Sustainability Science and Technology
In view of the threat of global climate change, the proper understanding of the intensity of the hydrological cycle and of its development over time is one of the most important challenges of the century, at least in the area of the geosciences. The hydrological cycle can essentially be summarized to be the evaporation of moisture in one location, offset by precipitation elsewhere. The rate of evaporation exceeds the rate of precipitation over the oceans, which are therefore a net source of moisture; this moisture is then transported to the landmasses, which are a net sink for moisture, where precipitation exceeds evapotranspiration. In consequence, surface runoff enters rivers and other watercourses, which discharge into the ocean, thereby completing the cycle. Taken as a whole, the hydrolo
Sources of moisture for China and their variations during drier and wetter conditions in 2000−2004: a Lagrangian approa...Published: 22 December 2011 by Inter-Research Science Center in Climate Research
Characterization of the atmospheric component of the winter hydrological cycle in the Galicia/North Portugal Euro-region...Published: 30 August 2011 by Inter-Research Science Center in Climate Research
Effects of warming processes on droughts and water resources in the NW Iberian Peninsula (1930−2006)Published: 30 August 2011 by Inter-Research Science Center in Climate Research
A Lagrangian analysis of the variation in moisture sources related to drier and wetter conditions in regions around the ...Published: 23 August 2011 by Copernicus GmbH in Natural Hazards and Earth System Sciences
 Globally, the hydrological cycle is characterized by the evaporation of about 500,000 cubic kilometers of water per year, of which 86% is from the oceans and 14% is from the continents [Quante and Matthias, 2006]. Most of the water that evaporates from the oceans (90%) is precipitated back into them, while the remaining 10% is transported to the continents, where the water precipitates. About two thirds of this precipitation is recycled over the continents, and only one third runs off directly into the oceans. Because societies rely on secure water resources, it is important to understand the processes that govern the atmospheric transport of moisture [Trenberth et al., 2003] and how they are related to precipitation over land. Research on these processes is also related to studies on the energetic coupling of the land‐atmosphere system, as well as to paleoclimatology; studies on the latter aim to extract information on past states of the climate system from records such as those of ice cores and stalagmites.