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  • Open access
  • 31 Reads
Iber as a tool to analyse flooding scenarios

Abstract: Floods are one of the most dangerous extreme events that can affect people and properties. These events have intensified worldwide over the last decades due to climate change. Therefore, the capability to predict and analyse, in a quick and accurate way, the effects of these floods is of crucial importance to avoid or minimize the hazards associated to them. This task can be accomplished by means of numerical tools as Iber. Iber is a 2-D numerical model, developed by GEAMA (Universidade da Coruña) and Flumen (Universitat Politècnica de Catalunya), that uses the finite volume technique to solve the 2-D Shallow Water Equations in order to obtain the water depth and velocity components of the flow under different scenarios. To assess the capabilities of Iber  a series of test cases have been reproduced following the document “Benchmarking the latest generation of 2D hydraulic modelling packages” published by the non-departmental public body Environment Agency of the U.K. Government. The results show that Iber is a suitable tool to reproduce accurately different flooding scenarios. A new implementation of the model has been developed by EPHYSLAB. This implementation takes advantage of the modern hardware capabilities and provides significant speedups over the original code. The new possibilities offered by a faster code will be studied.

  • Open access
  • 15 Reads
Daily precipitation extremes in isolated and mesoscale precipitation for the southeastern United States

This paper investigates the connection of precipitation organization to the frequency distribution of precipitation intensity, including extremes. The organization of precipitating systems, for example isolated thunderstorms and mesoscale convective systems, is an expression of the influence of the large-scale environment on precipitation. A recent climatology of precipitation organization in the southeastern United States (Rickenbach et al., 2015, QJRMS) demonstrated that a simple framework of identifying the scale of precipitation organization from a radar precipitation dataset was able to capture important differences of the seasonal evolution in precipitation organization. The present study will focus on the question of whether the heaviest daily precipitation values are associated with isolated or mesoscale precipitation organization, and whether this association changes seasonally.

The analysis employs a four-year dataset of daily precipitation values across the southeastern United States to examine the association of heavy precipitation extremes with isolated versus mesoscale organization.  Daily precipitation data covering the four-year period 2009-2012 is derived from the National Mosaic and Multi-sensor Quantitative Precipitation Estimation (NMQ) radar-based dataset on a 1 km x 1 km grid that extends 100 km offshore (see Rickenbach et al. 2015 for details). Each pixel is associated with either mesoscale precipitation features (> 100 km in spatial scale) or isolated precipitation features (< 100 km in spatial scale). Preliminary results will be presented at the online conference.

Reference: Rickenbach, T. M., Nieto-Ferreira, R., Zarzar, C. and Nelson, B. (2015), A seasonal and diurnal climatology of precipitation organization in the southeastern United States. Q.J.R. Meteorol. Soc., 141: 1938–1956. doi:10.1002/qj.2500

 

  • Open access
  • 21 Reads
Preservation of the cultural heritage from floods using the numerical code Iber

Abstract: Preserving the cultural heritage of antiquity is one of the most important tasks of the mankind. On this basis, the European Parliament, via the Policy Department Structural and Cohesion Policies, published the study entitled: “Protecting The Cultural Heritage From Natural Disasters”. This study analyses the actions that are being carried out to protect the cultural heritage from floods, earthquakes and other natural phenomena in Europe. In this work the numerical code Iber has been used to design the protection barriers from floods of the Roman Military Camp of “Aquis Querquennis” (69-79 A.C.). This roman camp, inside the Roman Itinerary “Via Nova”, is located in the shore of the “Las Conchas” impoundment in the Northwest of Spain. This camp is subjected to the floods associated to this impoundment of “Las Conchas”. Therefore, and according to the directives of the European Parliament, a series of protecting measures have been analysed using Iber, which is a 2-D numerical code developed by GEAMA (Universidade da Coruña) and Flumen (Universitat Politècnica de Catalunya) that uses the finite volume technique to solve the 2-D Shallow Water Equations.

  • Open access
  • 17 Reads
The role of ocean variability for droughts and wet periods in South America

Interannual precipitation over South America is largely modulated by the large-scale modes of variability in the surrounding oceans. In particular, the El Niño – Southern Oscillation (ENSO) affects South American rainfall generating a dipole pattern of precipitation over the northern and southeastern regions. In this study the role of the oceans for South American rainfall variability is investigated using the National Centre for Atmospheric Research (NCAR) Community Earth System Model (CESM). Multi-century simulations are performed to estimate rainfall mean and variability in South America in a fully coupled climate system and in the absence of ocean variability. Results show that interannual and decadal rainfall variability over South America is primarily associated with sea surface temperature anomalies in the Indo-Pacific region and variations in the extent of the Pacific warm pool. In the absence of ocean variability, droughts tend to last longer, particularly over the northeastern region. Thus, ENSO acts as a restoring mechanism for rainfall deficits and surplus over the continent. Interestingly, ENSO events are not only crucial for modulating rainfall variability, but also for determining mean precipitation over South America.

 

  • Open access
  • 12 Reads
ANALYSIS OF THE VARIABILITY OF WATER LEVELS OF TITICACA LAKE

The purpose of this research was to compare the variability of the Titicaca Lake water level to the Pacific Decadal Oscillation (PDO) between 1914 and 2014 and relate it was compared to El Niño - Southern Oscillation (ENSO) between 1969 and 2014 to evalute the hydrological cycle and perform rainfall forecast. The results show that the Lake Titicaca water level to decrease (increase) in the positive (negative) phase of the PDO. Likewise, the negative phase (positive) of ENSO generates patterns of positive anomalies (negative) of precipitation. Therefore, the positive (negative) phase of PDO, with greater probability of positive phase ENSO events (negative), precipitation anomalies shows negative (positive) which can be associated with the decrease (increase) in Titicaca Lake water level.

  • Open access
  • 26 Reads
Drought and wet episodes in Amazonia: the role of atmospheric moisture transport

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 (E-P). This permitted to identify those regions from where air masses gain humidity (E-P>0) 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 (E-P) 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.

  • Open access
  • 16 Reads
The Mediterranean moisture supply in the genesis of climatological and extreme monthly continental precipitation

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.

  • Open access
  • 13 Reads
Impacts of Atmospheric Rivers in extreme precipitation on the European Macaronesian islands

Extreme precipitation events in Europe during the winter half of the year have major socio-economic impacts associated with floods, landslides, extensive property damage and life losses. In recent years, a number of works have shed new light on the role played by Atmospheric Rivers (ARs) in the occurrence of extreme precipitation events in Europe as was the case in major historical floods in Duero (Pereira et al., 2016) and Tagus (Trigo et al., 2015) rivers in Iberia. The flash flood event that occurred on the Madeira Island on the 20 February 2010 with a deal toll of near 50 was due to an AR (Couto et al., 2012).

However, regarding the European Macaronesia islands (Azores, Madeira, and Canary) no comprehensive study has been made concerning the relationship between ARs and extreme precipitation. To do so, we have analysed recorded daily precipitation from different locations in the different European Macaronesia islands and computed the percentiles into 10% bins.

Regarding the ARs database we have used the method of Guan and Waliser et al., (2015) applied to 4 different reanalysis datasets (ERA-Interim; CFSR; MERRA2 and NCEP/NCAR). The use of multiple reanalyses is necessary to ensure more robust results since the Atlantic islands are relatively small and therefore changes in the resolution of the reanalysis datasets could influence the results.

It is shown that the ARs influence over extreme precipitation (above the 90th percentile) is higher in the Azores islands when compared with the Madeira or the Canary Islands. In the Azores, for the most extreme precipitation days, the presence of ARs is particularly high between 60% and 70% of the days) while for Madeira the importance of the ARs is reduced to 50-60% of the most extreme precipitation days. For the Canary Islands, the occurrence of ARs on extreme precipitation is usually below 50% of the days.

Acknowledgements: This work was supported by the project FORLAND – Hydrogeomorphologic risk in Portugal: driving forces and application for land use planning (PTDC/ATPGEO/1660/2014) funded by Fundação para a Ciência e a Tecnologia, Portugal (FCT). A. M. Ramos was also supported by a FCT postdoctoral grant (FCT/DFRH/ SFRH/BPD/84328/2012).

  • Open access
  • 23 Reads
CLLJ and WHWP heat content as a constrain to North American Monsoon activation moisture supply

With a well defined long term basis analysis of moisture supply to the North American Monsoon (NAM) domain based upon FLEXPART Lagrangian trajectories, the role of the Caribbean Sea and the Gulf of Mexico as the primary moisture source for the monsoon onset is analyzed. Regardless the NAM area requires the input from other sources, it is the eastern source which provides the required supply to activate the land moisture processes. Here we study how the warm SSTs of the WHWP enclosed region increase the moisture content, modulate the depth of the boundary layer and to which extent the CLLJ is able to advect the moist air towards the eastern Sierra Madre region. The analysis focuses on how different these processes are for warm and cold ENSO events and the relevance of this variability mode as a control of the meridional rainfall distribution across tropical north America under ENSO forcing. For this analysis, a different approach for the WHWP characterization is implemented as a new volume heat content definition is used for the WHWP instead of the traditional area defined index.

  • Open access
  • 39 Reads
Analysis of Amazon Humidity Transport to South East of Brazil During the Southern Summer (DJF)

The moisture transport from the Amazon to the Southeast (SE) of Brazil is an important atmospheric mechanism that contributes to the high precipitation rates during the austral summer (DJF) in this region, or more specifically, in the Sao Paulo state (27 and 20oS and longitude between 315 and 305oW). This transport originates from the entrance of moisture from the North Atlantic Ocean, moving to inside of the Amazon (10oS and 3oN, and longitude between 290o and 310oW), where it is supplied by rivers and aerial lakes, resulting of rain forest evapotranspiration. After this supply, the moisture flow is diverted to larger latitudes (South and Southeast) due to the Andes mountain range. Another important system that also assists precipitation in the SE region during the summer period is the frontal systems that are supplied by the transport of this moisture and, when they remain stationary, form a large band of cloudiness with NW / SE orientation, called the South Atlantic Convergence Zone (SACZ), which supplies, along with the frontal systems (on average 5 passes during the summer (DJF)) the SE region. This integrated vertical moisture transport (from the surface up to 500hPa) was studied for the years that occurred El Niño Southern Oscillation (ENSO) events and in neutral years. The results show an intensification of this flow in years of ENSO. In neutral years, thereabout 45.1 kg / kg enter the Amazon territory and thereabout 27.5 kg / kg of this moisture exits, and in the region of São Paulo it receives an average amount of 8.9 kg / kg and loses 7kg / kg. When the ENSO phenomenon occurs, the flow pattern increases significantly in the two regions: the input (54.8 kg / kg) and the outflow (47.4 kg / kg) in Amazon are larger, with São Paulo receiving 42, 2 kg / kg and loses 11.8 kg / kg of all moisture received. In years of ENSO, there is an intensification of the jet stream in the central part of Brazil, blocking the passage of frontal systems. The reduction of precipitation in this period in the SE region by the SACZ is compensated by the greater humidity transport from the Amazon, and therefore, not changing in the precipitation pattern.

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