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  • Open access
  • 60 Reads
The influence of climate and land-cover scenarios on dam management strategies in a high water pressure catchment in North-east Spain

The water management of Boadella-Darnius reservoir (NE Spain) has been analysed for the period 1971-2013 to understand the different strategies applied in the past. Streamflow has been projected under climate conditions included in the Third Report on Climate Change in Catalonia (TCCC) and under land-use change scenarios. We have simulated Darnius-Boadella reservoir inflow (2021-2050) using the Regional Hydro-Ecologic Simulation System (RHESsys) with two objectives: (i) to analyse the impact of climate and land-use changes on the water resources of the basin and (ii) to analyse the different plausible strategies of water management at mid-term period (2021-2050). Results reveal a clear negative trend in dam inflow (-34.7%) since it was built in 1971. The simulations obtained with RHESsys show a similar trend at mid-term (2021-2050) with -31.1% under climate and land-use change conditions. Considering the ecological minimum flow outlined by Catalan Water Agency (ACA) and the possible dam inflow decrease, different water management strategies are needed to mitigate the effects of the expected climate change.

  • Open access
  • 123 Reads
Evaluating extreme precipitation events on the Iberian Peninsula using TRMM satellite data

An assessment of extreme precipitation events (EPEs) is performed using the high-resolution (0.2°) gridded daily precipitation database available for the IP, the accumulated precipitation from ERA-Interim reanalysis by EMCWF at 6-hour intervals, and the Tropical Rainfall Measuring Mission (TRMM) Multisatellite Precipitation Analysis (TMPA) dataset, based on multisatellite estimates of precipitation and gauges measurements, for the common period since 1998. This study presents an analysis and validation of the extreme precipitation characteristics over IP, using both satellite and ground observations. Results show that there is a good general agreement between total precipitation analysis from observational gridded and TRMM datasets, both temporal and spatially, although TRMM TMPA results are underestimated when compared to observations and ERA Interim data.

  • Open access
  • 55 Reads
The late spring Caribbean rain-belt: climatology and dynamics

This study examines the dynamics of late spring rainfall (the Early Rainy Season, ERS) in the Caribbean region, in hopes of identifying mechanistic-based predictors for low-frequency climate modulations of the system. The subtropical Caribbean rain-belt develops in May as seasonal warming proceeds. By July, the rain-belt retreats north apparently following the westerlies and their vigorous synoptic disturbances. Daily climatology data suggest a physical definition of the Caribbean ERS as mid-May to mid-late June. Based on an examination of daily loops for several seasons, we hypothesize that rainfall occurs quasi-randomly throughout tongues of air with sufficiently high (above 45–50 mm) precipitable water (PW). These moist airmasses are brought north from the deep tropics by low-level southerlies, and typically bent over into SW-NE bands by latitudinal shear of the westerlies. The low-level flow that transports PW tongues is partly induced by upper-level synoptic disturbances in the westerlies, but also involves the gentle persistent flow around a geographically anchored Panama Low. While forced ascent is sometimes active ahead of these upper-level troughs, convective and mesoscale processes can produce rain wherever PW is sufficient. In summary, we hypothesize that rainfall hinges largely on the Lagrangian statistics of moist air tongues. Comparison is drawn between the Caribbean rain-belt and its East Asian counterpart (Meiyu-Baiu), and other mechanisms and diagnostics from that literature are discussed. Statistical prediction exercises, based on mechanistically chosen predictors, could both test hypotheses and aid local agricultural interests in the region.

  • Open access
  • 217 Reads
Transient-mean flow interactions over the northern tropical Americas

The Mid Summer Drought (MSD) over the Mesoamerican region constitutes a unique feature of its precipitation seasonal cycle. The MSD is a relative minimum in convective activity during July and August that coincides with an intensification of the Caribbean Low Level Jet (CLLJ) (mean flow at 925 hPa). There is not a unique theory on what maintains the CLLJ is, but the effect of the mean meridional convergence of easterly momentum related to tropical extratropical interactions over the Caribbean Sea, appars to play an important role. The barotropicaly unstable nature of the CLLJ shows that when this mean circulation is intense the amplification of high frequency transients (eg, easterly waves) is inhibited. Empirical observational evidence shows that as the CLLJ intensifies above a certain magnitude, transient activity decreases. Such transient activity is related to easterly waves, a key element in producing precipitation over the tropical Americas. Therefore, the CLLJ acts as a modulator of tropical convection in relation to the MSD, as the period of relatively minor tropical convection coincides with a decrease in high frequency Perturbation Kinetic Energy (PKE). Its role in the modulation of convective activity over the tropical Americas on interannual and even on interdecadal time scales makes it one of the key elements to understand climate variability over the tropical Americas.

  • Open access
  • 90 Reads
Spatial and temporal variability of droughts in Estonia (1951-2015)

Droughts have been poorly studied in Estonia despite of the important water deficit that occurred in recent times e.g. 2002 and 2006. We have studied the influence of atmospheric indices on the spatial and temporal variability of droughts in Estonia. We have analyzed 57 monthly precipitation series and 7 atmospheric indices (NAO, EA, EATL/WRUS, SCAND, P/EU, AO and WI) during the period 1951-2015. Estonia has been regionalized in three homogeneous regions according to drought variability, i.e. western, southeastern and northern. Standardized precipitation index at timescale of 1, 3, 6, and 12 months have been computed for each region. From 1951 to 1977 dry conditions prevail. On the other hand, from 1978 to 2015 wet conditions prevail interrupted by some intense but short droughts. The main influence of atmospheric indices on drought variability is recorded with SCAND for spring and autumn (negative correlations) and with WI for winter and summer (positive correlations).

  • Open access
  • 62 Reads
Moisture transport related to the ENSO effects in the Mexican precipitation

In the past, several works addressed the impact of El Niño-Southern Oscillation (ENSO) on Mexican precipitation by using relative scarce observations of the National Weather Service of Mexico or reanalysis data. In this work, we reassessed the ENSO signal in Mexican rainfall by using four precipitation databases (CHIRPS, GPCC, GPCP and CMAP) over a 34-yr period (1981-2014) and three different ENSO indices. Results obtained with different datasets are consistent among them and with previous studies, showing strong positive precipitation anomalies along the winter over the northern Mexico for El Niño events. In contrast, during the summer, negative rainfall anomalies can be found over most of central and southern Mexico, being stronger in August. During La Niña years, the anomalies show approximately the opposite pattern to those observed during El Niño.

A Lagrangian approach is used to track the evaporation minus precipitation (E-P) along trajectories followed by the atmospheric particles that will take precipitable water to the areas with a precipitation amount modulated by ENSO phases. Then, composites of the obtained (E-P) fields are examined for the strong phases of El Niño and La Niña. Finally, the synoptic conditions associated with ENSO-related anomalous atmospheric water vapor fluxes are studied for a better understanding of the origin of the ENSO impact on the Mexican precipitation.

  • Open access
  • 93 Reads
Extreme drought events over Amazon basin: the perspective from regional reconstruction of South American hydroclimate

In less than two decades large areas of the Amazon Basin have experienced severe droughts, namely during 1998, 2005, 2010 and 2015. Due to their several social, economic and environmental impacts there is an increased demand in understanding the behavior of such extreme events in the region. In that regard, regional models instead of the general circulation models provide a promising strategy to generate more detailed climate information of extreme events, seeking better representation of physical processes. In such context, the Satellite-enhanced Regional Downscaling for Applied Studies (SRDAS) product has been used in the analysis of South American hydroclimate, with hourly to monthly outputs from January 1998 to near present. Accordingly, this research focuses on the analyses of recent extreme drought events in the years of 2005 and 2010 in the Amazon Basin, using the SRDAS monthly means of near-surface temperature and relative humidity, precipitation and four-level integrated soil moisture fields. Results from this analysis corroborate spatial and temporal patterns found in previous studies on extreme drought events in the region, displaying the distinctive features of the 2005 and 2010 drought events.

  • Open access
  • 46 Reads
Contribution of tropical cyclones to seasonal precipitation over the tropical Americas

Tropical cyclones (TCs) are an important element of the climate dynamics in the tropical Americas. They produce intense precipitation during a few days of the rainy season. The contribution of tropical cyclone precipitation to seasonal accumulated rainfall may be as large as fifty per cent, particularly in the arid and semi-arid regions of northern Mexico. A positive trend in the number of tropical cyclones over the eastern Pacific, has resulted in more of these systems approaching the Baja peninsula and a positive trend in annual precipitation. However, the contribution of TCs to regional accumulated may be positive or negative depending on the trajectory followed by the system. If the TC is not close enough to the coastal region, it may induce atmospheric moisture divergence over land, reducing the chances of tropical convective activity and rainfall. Years of large but “distant to continent” TC activity result in negative anomalies in precipitation for some regions of the tropical Americas. Seasonal regional climate predictions or regional climate change scenarios provide information on TC activity but not on preferred trajectories. By means of TC cluster analysis, the preferred trajectories of TCs around the tropical Americas are explored in relation to quasi-stationary circulations at the steering level. Some ideas on how to estimate preferred TCs trajectories for a season are given.

  • Open access
  • 67 Reads
Diurnal cycle of convection in the Peruvian Highlands

This manuscript examines from the diurnal convection cycle (DCC) to the interdecadal variability in the region of the Peruvian Altiplano (RPA). Currently, estimating precipitation using satellites is an alternative which can be used to study the spatio-temporal evolution of precipitation systems. Herein CPC data Morphing technique - CMORPH (Joyce et al, 2004) was used between 2002 and 2014 to analyze the DCC in RPA. The CMOPRH data were compared with rainfall data series measured by rain gauges of meteorological stations in the RPA. The results indicate that the DCC shows high variability in the Titicaca Basin and is associated with patterns of lake breeze (day), land breeze (night) and mountain - valley circulation. The CDC starts at 1800 LT (local time) in the northern region of Lake Titicaca, lasting between 2 h and 6 h, and most of 20:00 LT. The DCC over the dry surface of Titicaca Basin starts early at around 12:00 LT, lasting 4 h to 7 h, and maximum at 18:00 HL.