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20 pages, 11365 KiB

Open AccessArticle

On the Connection between Atmospheric Moisture Transport and Dry Conditions in Rainfall Climatological Zones of the Niger River Basin

by Rogert Sorí, Raquel Nieto, Anita Drumond, Milica Stojanovic and Luis Gimeno

Water 2019, 11(3), 622; https://doi.org/10.3390/w11030622 - 26 Mar 2019

Cited by 8 | Viewed by 4963

Abstract

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 [...] Read more.

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. Full article

(This article belongs to the Special Issue Selected Papers from the 1st International Electronic Conference on the Hydrological Cycle (ChyCle-2017))

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14 pages, 5266 KiB

Open AccessArticle

Atmospheric Rivers over the Arctic: Lagrangian Characterisation of Their Moisture Sources

by Marta Vázquez, Iago Algarra, Jorge Eiras-Barca, Alexandre M. Ramos, Raquel Nieto and Luis Gimeno

Water 2019, 11(1), 41; https://doi.org/10.3390/w11010041 - 26 Dec 2018

Cited by 9 | Viewed by 5257

Abstract

In recent years, the Arctic has become a subject of special interest due to the drastic effect of climate change over the region. Despite that there are several mechanisms that influence the Arctic region; some recent studies have suggested significant influences of moisture [...] Read more.

In recent years, the Arctic has become a subject of special interest due to the drastic effect of climate change over the region. Despite that there are several mechanisms that influence the Arctic region; some recent studies have suggested significant influences of moisture transport over the observed loss of sea ice. Moisture transport can affect the region in different ways: direct precipitation over the region, radiative effect from the cloud cover and through the release of latent heat. Atmospheric rivers (ARs) represent one of the main events involved in moisture transport from the tropics to the mid-latitudes and despite having been shown especially relevant on the northward advection, their effect over the Arctic has not been deeply investigated. The aim of this work was to establish the groundwork for future studies about the effect of ARs linked to moisture transport over the Arctic region. For this purpose, an automated algorithm was used to identify regions of maximum AR occurrence over the Arctic. This was done by analysing the number of AR detections every month over a band of 10° of latitude centred on 60° N. The Lagrangian model FLEXPART was used to find the areas where the ARs take their moisture to the Arctic. Using this model, the anomalous moisture contribution to these baroclinic structures was analysed taking into account only the dates of AR occurrence. From the results, it appears that the main moisture sources for AR events extend over the North Atlantic and North Pacific oceans; moreover, the local input of moisture over the region of maximum AR occurrence seems to be especially relevant. In general terms, moisture comes from major evaporative areas over the western part of the oceanic regions in the band between 30° and 40° N for most months in the year, showing a continental origin in the summer months. This behaviour agrees with the climatological moisture transport into the Arctic determined in previous studies. However, in special association with AR events, an intensification of local moisture uptake is observed over the area of maximum AR activity and nearby. The study of the origin of this moisture and associated anomalies for Arctic ARs is an important step in the analysis of the effect of these structures on the Arctic environment. Full article

(This article belongs to the Special Issue Selected Papers from the 1st International Electronic Conference on the Hydrological Cycle (ChyCle-2017))

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19 pages, 3739 KiB

Open AccessArticle

Assessing the Use of Satellite-Based Estimates and High-Resolution Precipitation Datasets for the Study of Extreme Precipitation Events over the Iberian Peninsula

by Riccardo Hénin, Margarida L. R. Liberato, Alexandre M. Ramos and Célia M. Gouveia

Water 2018, 10(11), 1688; https://doi.org/10.3390/w10111688 - 19 Nov 2018

Cited by 30 | Viewed by 4278

Abstract

An assessment of daily accumulated precipitation during extreme precipitation events (EPEs) occurring over the period 2000–2008 in the Iberian Peninsula (IP) is presented. Different sources for precipitation data, namely ERA-Interim and ERA5 reanalysis by the European Centre for Medium-Range Weather Forecast (ECMWF) and [...] Read more.

An assessment of daily accumulated precipitation during extreme precipitation events (EPEs) occurring over the period 2000–2008 in the Iberian Peninsula (IP) is presented. Different sources for precipitation data, namely ERA-Interim and ERA5 reanalysis by the European Centre for Medium-Range Weather Forecast (ECMWF) and Tropical Rainfall Measuring Mission (TRMM) Multisatellite Precipitation Analysis (TMPA), both in near-real-time and post-real-time releases, are compared with the best ground-based high-resolution (0.2° × 0.2°) gridded precipitation dataset available for the IP (IB02). In this study, accuracy metrics are analysed for different quartiles of daily precipitation amounts, and additional insights are provided for a subset of EPEs extracted from an objective ranking of extreme precipitation during the extended winter period (October to March) over the IP. Results show that both reanalysis and multi-satellite datasets overestimate (underestimate) daily precipitation sums for the least (most) extreme events over the IP. In addition, it is shown that the TRMM TMPA precipitation estimates from the near-real-time product may be considered for EPEs assessment over these latitudes. Finally, it is found that the new ERA5 reanalysis accounts for large improvements over ERA-Interim and it also outperforms the satellite-based datasets. Full article

(This article belongs to the Special Issue Selected Papers from the 1st International Electronic Conference on the Hydrological Cycle (ChyCle-2017))

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23 pages, 5086 KiB

Open AccessArticle

The Influence of Climate and Land-Cover Scenarios on Dam Management Strategies in a High Water Pressure Catchment in Northeast Spain

by J. Zabalza-Martínez, S. M. Vicente-Serrano, J. I. López-Moreno, G. Borràs Calvo, R. Savé, D. Pascual, E. Pla, E. Morán-Tejeda, F. Domínguez-Castro and C. L. Tague

Water 2018, 10(11), 1668; https://doi.org/10.3390/w10111668 - 16 Nov 2018

Cited by 14 | Viewed by 4911

Abstract

This paper evaluates the response of streamflow in a Mediterranean medium-scaled basin under land-use and climate change scenarios and its plausible implication on the management of Boadella–Darnius reservoir (NE Spain). Land cover and climate change scenarios supposed over the next several decades were [...] Read more.

This paper evaluates the response of streamflow in a Mediterranean medium-scaled basin under land-use and climate change scenarios and its plausible implication on the management of Boadella–Darnius reservoir (NE Spain). Land cover and climate change scenarios supposed over the next several decades were used to simulate reservoir inflow using the Regional Hydro-Ecologic Simulation System (RHESsys) and to analyze the future impacts on water management (2021–2050). Results reveal a clear decrease in dam inflow (−34%) since the dam was operational from 1971 to 2013. The simulations obtained with RHESsys show a similar decrease (−31%) from 2021 to 2050. Considering the ecological minimum flow outlined by water authorities and the projected decrease in reservoir’s inflows, different water management strategies are needed to mitigate the effects of the expected climate change. Full article

(This article belongs to the Special Issue Selected Papers from the 1st International Electronic Conference on the Hydrological Cycle (ChyCle-2017))

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16 pages, 4521 KiB

Open AccessArticle

Extreme Drought Events over the Amazon Basin: The Perspective from the Reconstruction of South American Hydroclimate

by Beatriz Nunes Garcia, Renata Libonati and Ana M. B. Nunes

Water 2018, 10(11), 1594; https://doi.org/10.3390/w10111594 - 7 Nov 2018

Cited by 21 | Viewed by 5703

Abstract

The Amazon basin has experienced severe drought events for centuries, mainly associated with climate variability connected to tropical North Atlantic and Pacific sea surface temperature anomalous warming. Recently, these events are becoming more frequent, more intense and widespread. Because of the Amazon droughts [...] Read more.

The Amazon basin has experienced severe drought events for centuries, mainly associated with climate variability connected to tropical North Atlantic and Pacific sea surface temperature anomalous warming. Recently, these events are becoming more frequent, more intense and widespread. Because of the Amazon droughts environmental and socioeconomic impacts, there is an increased demand for understanding the characteristics 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. Due to uneven spatial distribution and gaps found in station data in tropical South America, and the need of more refined climate assessment in those regions, satellite-enhanced regional downscaling for applied studies (SRDAS) is used in the reconstruction of South American hydroclimate, with hourly to monthly outputs from January 1998. 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 vertically 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. Full article

(This article belongs to the Special Issue Selected Papers from the 1st International Electronic Conference on the Hydrological Cycle (ChyCle-2017))

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18 pages, 6258 KiB

Open AccessArticle

The Role of Moisture Sources and Climatic Teleconnections in Northeastern and South-Central Iran’s Hydro-Climatology

by Mojtaba Heydarizad, Ezzat Raeisi, Rogert Sori, Luis Gimeno and Raquel Nieto

Water 2018, 10(11), 1550; https://doi.org/10.3390/w10111550 - 31 Oct 2018

Cited by 18 | Viewed by 4393

Abstract

Iran faces climate disparities due to extreme topographic anomalies, the Caspian Sea and the Persian Gulf water bodies, influences from diverse air masses and moisture sources, and its considerable area. FLEXPART model has been utilized to determine the main marine and continental moisture [...] Read more.

Iran faces climate disparities due to extreme topographic anomalies, the Caspian Sea and the Persian Gulf water bodies, influences from diverse air masses and moisture sources, and its considerable area. FLEXPART model has been utilized to determine the main marine and continental moisture sources for south-central (Shiraz box) and northeastern (Mashhad box) parts of Iran. The marine moisture sources directly influenced extreme drought and wet conditions in Shiraz and Mashhad boxes during the wet period, while no correlation was observed during the dry period. In addition to local components, extreme drought and wet conditions have also been influenced by the climatic teleconnections. Extreme drought conditions mainly occurred during the La Niña phase, while wet conditions mainly occurred during the El Niño phase. Scrutinizing the effect of marine moisture sources on the hydrology of water resources demonstrated that the moisture contribution from the Arabian Sea directly influenced the discharges of Chenar-rahdar (in the Shiraz box) and Kardeh (in the Mashhad box) rivers during the wet period. However, the Red Sea inversely correlated with the discharges of both rivers during the dry period. Hydrogeologists, hydrologists, and meteorologists can utilize the outputs of this survey to develop climatology and hydrology models in the future. Full article

(This article belongs to the Special Issue Selected Papers from the 1st International Electronic Conference on the Hydrological Cycle (ChyCle-2017))

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23 pages, 7755 KiB

Open AccessArticle

An Accelerated Tool for Flood Modelling Based on Iber

by Orlando García-Feal, José González-Cao, Moncho Gómez-Gesteira, Luis Cea, José Manuel Domínguez and Arno Formella

Water 2018, 10(10), 1459; https://doi.org/10.3390/w10101459 - 16 Oct 2018

Cited by 84 | Viewed by 6971

Abstract

This paper presents Iber+, a new parallel code based on the numerical model Iber for two-dimensional (2D) flood inundation modelling. The new implementation, which is coded in C++ and takes advantage of the parallelization functionalities both on CPUs (central processing units) and GPUs [...] Read more.

This paper presents Iber+, a new parallel code based on the numerical model Iber for two-dimensional (2D) flood inundation modelling. The new implementation, which is coded in C++ and takes advantage of the parallelization functionalities both on CPUs (central processing units) and GPUs (graphics processing units), was validated using different benchmark cases and compared, in terms of numerical output and computational efficiency, with other well-known hydraulic software packages. Depending on the complexity of the specific test case, the new parallel implementation can achieve speedups up to two orders of magnitude when compared with the standard version. The speedup is especially remarkable for the GPU parallelization that uses Nvidia CUDA (compute unified device architecture). The efficiency is as good as the one provided by some of the most popular hydraulic models. We also present the application of Iber+ to model an extreme flash flood that took place in the Spanish Pyrenees in October 2012. The new implementation was used to simulate 24 h of real time in roughly eight minutes of computing time, while the standard version needed more than 15 h. This huge improvement in computational efficiency opens up the possibility of using the code for real-time forecasting of flood events in early-warning systems, in order to help decision making under hazardous events that need a fast intervention to deploy countermeasures. Full article

(This article belongs to the Special Issue Selected Papers from the 1st International Electronic Conference on the Hydrological Cycle (ChyCle-2017))

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13 pages, 4331 KiB

Open AccessArticle

Using Water Temperature, Electrical Conductivity, and pH to Characterize Surface–Groundwater Relations in a Shallow Ponds System (Doñana National Park, SW Spain)

by Miguel Rodríguez-Rodríguez, Ana Fernández-Ayuso, Masaki Hayashi and Francisco Moral-Martos

Water 2018, 10(10), 1406; https://doi.org/10.3390/w10101406 - 10 Oct 2018

Cited by 16 | Viewed by 6634

Abstract

The physical limnology of a shallow pond system was characterized using field measurements of water temperature, pH, and electrical conductivity (EC). We determined the spatial variability in surface and groundwater temperature, pH, and EC along the pond’s shore and along the several pond-shore [...] Read more.

The physical limnology of a shallow pond system was characterized using field measurements of water temperature, pH, and electrical conductivity (EC). We determined the spatial variability in surface and groundwater temperature, pH, and EC along the pond’s shore and along the several pond-shore transects, analyzed the water column temperature gradient and estimated the groundwater discharge rate using a heat transfer model. The fieldwork was conducted in Santa Olalla and Dulce ponds located in Doñana National Park in southwestern Spain during different stages from 2016 to 2018. The results of this study have improved the understanding of the thermal structure and the surface–subsurface heat exchange in the ponds and highlighted the importance of groundwater discharge in the pond water balance. It also showed the heterogeneous nature of groundwater discharge through the bottom sediments of the Santa Olalla pond. These results are consistent with previous studies and strengthen the existing hydrological and limnological knowledge of these ponds located in the protected area which is receiving a great deal of public attention. Full article

(This article belongs to the Special Issue Selected Papers from the 1st International Electronic Conference on the Hydrological Cycle (ChyCle-2017))

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11 pages, 3685 KiB

Open AccessArticle

A Hydroclimatological Analysis of Precipitation in the Ganges–Brahmaputra–Meghna River Basin

by Scott Curtis, Thomas Crawford, Munshi Rahman, Bimal Paul, M. Giashuddin Miah, M. Rafiqul Islam and Mohin Patel

Water 2018, 10(10), 1359; https://doi.org/10.3390/w10101359 - 29 Sep 2018

Cited by 7 | Viewed by 4662

Abstract

Understanding seasonal precipitation input into river basins is important for linking large-scale climate drivers with societal water resources and the occurrence of hydrologic hazards such as floods and riverbank erosion. Using satellite data at 0.25-degree resolution, spatial patterns of monsoon (June-July-August-September) precipitation variability [...] Read more.

Understanding seasonal precipitation input into river basins is important for linking large-scale climate drivers with societal water resources and the occurrence of hydrologic hazards such as floods and riverbank erosion. Using satellite data at 0.25-degree resolution, spatial patterns of monsoon (June-July-August-September) precipitation variability between 1983 and 2015 within the Ganges–Brahmaputra–Meghna (GBM) river basin are analyzed with Principal Component (PC) analysis and the first three modes (PC1, PC2 and PC3) are related to global atmospheric-oceanic fields. PC1 explains 88.7% of the variance in monsoonal precipitation and resembles climatology with the center of action over Bangladesh. The eigenvector coefficients show a downward trend consistent with studies reporting a recent decline in monsoon rainfall, but little interannual variability. PC2 explains 2.9% of the variance and shows rainfall maxima to the far western and eastern portions of the basin. PC2 has an apparent decadal cycle and surface and upper-air atmospheric height fields suggest the pattern could be forced by tropical South Atlantic heating and a Rossby wave train stemming from the North Atlantic, consistent with previous studies. Finally, PC3 explains 1.5% of the variance and has high spatial variability. The distribution of precipitation is somewhat zonal, with highest values at the southern border and at the Himalayan ridge. There is strong interannual variability associated with PC3, related to the El Nino/Southern Oscillation (ENSO). Next, we perform a hydroclimatological downscaling, as precipitation attributed to the three PCs was averaged over the Pfafstetter level-04 sub-basins obtained from the World Wildlife Fund (Gland, Switzerland). While PC1 was the principal contributor of rainfall for all sub-basins, PC2 contributed the most to rainfall in the western Ganges sub-basin (4524) and PC3 contributed the most to the rainfall in the northern Brahmaputra (4529). Monsoon rainfall within these two sub-basins were the only ones to show a significant relationship (negative) with ENSO, whereas four of the eight sub-basins had a significant relationship (positive) with sea surface temperature (SST) anomalies in the tropical South Atlantic. This work demonstrates a geographic dependence on climate teleconnections in the GBM that deserves further study. Full article

(This article belongs to the Special Issue Selected Papers from the 1st International Electronic Conference on the Hydrological Cycle (ChyCle-2017))

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15 pages, 1495 KiB

Open AccessFeature PaperArticle

Contribution of Moisture from Mediterranean Sea to Extreme Precipitation Events over Danube River Basin

by Danica Ciric, Raquel Nieto, Alexandre M. Ramos, Anita Drumond and Luis Gimeno

Water 2018, 10(9), 1182; https://doi.org/10.3390/w10091182 - 4 Sep 2018

Cited by 8 | Viewed by 4929

Abstract

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 [...] Read more.

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. Full article

(This article belongs to the Special Issue Selected Papers from the 1st International Electronic Conference on the Hydrological Cycle (ChyCle-2017))

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19 pages, 4618 KiB

Open AccessArticle

New Insights on Land Surface-Atmosphere Feedbacks over Tropical South America at Interannual Timescales

by Juan Mauricio Bedoya-Soto, Germán Poveda and David Sauchyn

Water 2018, 10(8), 1095; https://doi.org/10.3390/w10081095 - 17 Aug 2018

Cited by 13 | Viewed by 4812

Abstract

We present a simplified overview of land-atmosphere feedbacks at interannual timescales over tropical South America as structural sets of linkages among surface air temperature (T), specific humidity at 925 hPa (q₉₂₅), volumetric soil water content (Θ), precipitation (P), and evaporation (E), [...] Read more.

We present a simplified overview of land-atmosphere feedbacks at interannual timescales over tropical South America as structural sets of linkages among surface air temperature (T), specific humidity at 925 hPa (q₉₂₅), volumetric soil water content (Θ), precipitation (P), and evaporation (E), at monthly scale during 1979–2010. Applying a Maximum Covariance Analysis (MCA), we identify the modes of greatest interannual covariability in the datasets. Time series extracted from the MCAs were used to quantify linear and non-linear metrics at up to six-month lags to establish connections among variables. All sets of metrics were summarized as graphs (Graph Theory) grouped according to their highest ENSO-degree association. The core of ENSO-activated interactions is located in the Amazon River basin and in the Magdalena-Cauca River basin in Colombia. Within the identified multivariate structure, Θ enhances the interannual connectivity since it often exhibits two-way feedbacks with the whole set of variables. That is, Θ is a key variable in defining the spatiotemporal patterns of P and E at interannual time-scales. For both the simultaneous and lagged analysis, T activates non-linear associations with q₉₂₅ and Θ. Under the ENSO influence, T is a key variable to diagnose the dynamics of interannual feedbacks of the lower troposphere and soil interfaces over tropical South America. ENSO increases the interannual connectivity and memory of the feedback mechanisms. Full article

(This article belongs to the Special Issue Selected Papers from the 1st International Electronic Conference on the Hydrological Cycle (ChyCle-2017))

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15 pages, 3113 KiB

Open AccessArticle

Adaptation Strategies of the Hydrosocial Cycles in the Mediterranean Region

by Ana Arahuetes, María Hernández and Antonio M. Rico

Water 2018, 10(6), 790; https://doi.org/10.3390/w10060790 - 15 Jun 2018

Cited by 15 | Viewed by 4708

Abstract

The Spanish Mediterranean region has been affected by several factors over the years (climatic conditions of aridity, high water demands, rapid and intense urban and population growth, climate change), that have generated a negative water balance whereby water resources are unable to meet [...] Read more.

The Spanish Mediterranean region has been affected by several factors over the years (climatic conditions of aridity, high water demands, rapid and intense urban and population growth, climate change), that have generated a negative water balance whereby water resources are unable to meet the demand. Diversifying supply sources by resorting to new resources has been a necessity that has stimulated the expansion and integration of non-conventional water sources (desalination and reuse of reclaimed water) and sustainable solutions. The aim of this paper is to evaluate the adaptation strategies that have been developed in Alicante, Benidorm and Torrevieja in order to adjust their hydrosocial cycles to development and future scenarios. The theoretical analysis developed in this paper is corroborated by the study of the hydrosocial cycle evolution of three cities in the southeast of Spain, and the adaptive measures that the different stakeholders involved in the cycle have developed in each of them. The input and output of the systems are accounted for with information provided by the management companies in each of the phases (urban consumption; treated, reused and desalinated volumes), which highlight how the diversification of resources and the incorporation of non-conventional resources have been essential for adaptation. Full article

(This article belongs to the Special Issue Selected Papers from the 1st International Electronic Conference on the Hydrological Cycle (ChyCle-2017))

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29 pages, 8388 KiB

Open AccessArticle

The Atmospheric Branch of the Hydrological Cycle over the Negro and Madeira River Basins in the Amazon Region

by Rogert Sorí, José A. Marengo, Raquel Nieto, Anita Drumond and Luis Gimeno

Water 2018, 10(6), 738; https://doi.org/10.3390/w10060738 - 5 Jun 2018

Cited by 25 | Viewed by 7691

Abstract

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 [...] Read more.

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’’. Full article

(This article belongs to the Special Issue Selected Papers from the 1st International Electronic Conference on the Hydrological Cycle (ChyCle-2017))

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19 pages, 4557 KiB

Open AccessFeature PaperArticle

The Mediterranean Moisture Contribution to Climatological and Extreme Monthly Continental Precipitation

by Danica Ciric, Raquel Nieto, Lucia Losada, Anita Drumond and Luis Gimeno

Water 2018, 10(4), 519; https://doi.org/10.3390/w10040519 - 21 Apr 2018

Cited by 24 | Viewed by 7724

Abstract

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 [...] Read more.

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. Full article

(This article belongs to the Special Issue Selected Papers from the 1st International Electronic Conference on the Hydrological Cycle (ChyCle-2017))

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19 pages, 30292 KiB

Open AccessFeature PaperArticle

Anomalies in Moisture Supply during the 2003 Drought Event in Europe: A Lagrangian Analysis

by Milica Stojanovic, Anita Drumond, Raquel Nieto and Luis Gimeno

Water 2018, 10(4), 467; https://doi.org/10.3390/w10040467 - 12 Apr 2018

Cited by 20 | Viewed by 5299

Abstract

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 [...] Read more.

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. Full article

(This article belongs to the Special Issue Selected Papers from the 1st International Electronic Conference on the Hydrological Cycle (ChyCle-2017))

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20 pages, 31663 KiB

Open AccessArticle

Meteorological Driving Mechanisms and Human Impacts of the February 1979 Extreme Hydro-Geomorphological Event in Western Iberia

by Luís Rebelo, Alexandre M. Ramos, Susana Pereira and Ricardo M. Trigo

Water 2018, 10(4), 454; https://doi.org/10.3390/w10040454 - 10 Apr 2018

Cited by 8 | Viewed by 3985

Abstract

The large number of floods and landslides that occurred on 5–16 February 1979 in Portugal was a major hydro-geomorphologic extreme event according to the DISASTER database in terms of number of displaced people. The February 1979 event is the top ranked episode in [...] Read more.

The large number of floods and landslides that occurred on 5–16 February 1979 in Portugal was a major hydro-geomorphologic extreme event according to the DISASTER database in terms of number of displaced people. The February 1979 event is the top ranked episode in terms of the total number of evacuated people (4244), displaced people (14,322) and also on the number of days of event duration (12 days) for the period 1865–2015. In this event, 62 damaging floods and five damaging landslides causing eight fatalities were recorded in Portugal. This event was driven by an unusually intense atmospheric forcing mechanism acting at different time scales. Despite the intense magnitude and the widespread impact on the population, this event has not been studied in detail. In this study, we show that the precipitation period of February 1979 had produced several multi-day accumulated precipitation events over the Portuguese continental territory, ranking among the top 10 events observed between 1950–2008. Additionally, most of the precipitation from this event occured in days in which atmospheric circulation was dominated by “wet” circulation weather types (CWTs), namely, cyclonic (C), west (W) or southwest (SW) types. Full article

(This article belongs to the Special Issue Selected Papers from the 1st International Electronic Conference on the Hydrological Cycle (ChyCle-2017))

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16 pages, 4598 KiB

Open AccessArticle

Return Level Estimation of Extreme Rainfall over the Iberian Peninsula: Comparison of Methods

by Francisco Javier Acero, Sylvie Parey, José Agustín García and Didier Dacunha-Castelle

Water 2018, 10(2), 179; https://doi.org/10.3390/w10020179 - 9 Feb 2018

Cited by 14 | Viewed by 3546

Abstract

Different ways to estimate future return levels (RLs) for extreme rainfall, based on extreme value theory (EVT), are described and applied to the Iberian Peninsula (IP). The study was done for an ensemble of high quality rainfall time series observed in the IP [...] Read more.

Different ways to estimate future return levels (RLs) for extreme rainfall, based on extreme value theory (EVT), are described and applied to the Iberian Peninsula (IP). The study was done for an ensemble of high quality rainfall time series observed in the IP during the period 1961–2010. Two approaches, peaks-over-threshold (POT) and block maxima (BM) with the generalized extreme value (GEV) distribution, were compared in order to identify which is the more appropriate for the estimation of RLs. For the first approach, which identifies trends in the parameters of the asymptotic distributions of extremes, both all-days and rainy-days-only datasets were considered because a major fraction of values of daily rainfall over the IP is zero. For the second approach, rainy-days-only data were considered showing how the mean, variance and number of rainy days evolve. The 20-year RLs expected for 2020 were estimated using these methods for three seasons: autumn, spring and winter. The GEV is less reliable than the POT because fixed blocks lead to the selection of non-extreme values. Future RLs obtained with the POT are greater than those estimated with the GEV, mainly because some gauges show significant positive trends for the number of rainy days. Autumn, rather than winter, is currently the season with the heaviest rainfall for some regions. Full article

(This article belongs to the Special Issue Selected Papers from the 1st International Electronic Conference on the Hydrological Cycle (ChyCle-2017))

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12 pages, 1998 KiB

Open AccessArticle

Land Use Change over the Amazon Forest and Its Impact on the Local Climate

by Marta Llopart, Michelle Simões Reboita, Erika Coppola, Filippo Giorgi, Rosmeri Porfírio Da Rocha and Diego Oliveira De Souza

Water 2018, 10(2), 149; https://doi.org/10.3390/w10020149 - 3 Feb 2018

Cited by 50 | Viewed by 11354

Abstract

One of the most important anthropogenic influences on climate is land use change (LUC). In particular, the Amazon (AMZ) basin is a highly vulnerable area to climate change due to substantial modifications of the hydroclimatology of the region expected as a result of [...] Read more.

One of the most important anthropogenic influences on climate is land use change (LUC). In particular, the Amazon (AMZ) basin is a highly vulnerable area to climate change due to substantial modifications of the hydroclimatology of the region expected as a result of LUC. However, both the magnitude of these changes and the physical process underlying this scenario are still uncertain. This work aims to analyze the simulated Amazon deforestation and its impacts on local mean climate. We used the Common Land Model (CLM) version 4.5 coupled with the Regional Climate Model (RegCM4) over the Coordinated Regional Climate Downscaling Experiment (CORDEX) South America domain. We performed one simulation with the RegCM4 default land cover map (CTRL) and one simulation under a scenario of deforestation (LUC), i.e., replacing broadleaf evergreen trees with C₃ grass over the Amazon basin. Both simulations were driven by ERA Interim reanalysis from 1979 to 2009. The climate change signal due to AMZ deforestation was evaluated by comparing the climatology of CTRL with LUC. Concerning the temperature, the deforested areas are about 2 °C warmer compared to the CTRL experiment, which contributes to decrease the surface pressure. Higher air temperature is associated with a decrease of the latent heat flux and an increase of the sensible heat flux over the deforested areas. AMZ deforestation induces a dipole pattern response in the precipitation over the region: a reduction over the west (about 7.9%) and an increase over the east (about 8.3%). Analyzing the water balance in the atmospheric column over the AMZ basin, the results show that under the deforestation scenario the land surface processes play an important role and drive the precipitation in the western AMZ; on the other hand, on the east side, the large scale circulation drives the precipitation change signal. Dipole patterns over scenarios of deforestation in the Amazon was also found by other authors, but the precipitation decrease on the west side was never fully explained. Using budget equations, this work highlights the physical processes that control the climate in the Amazon basin under a deforestation scenario. Full article

(This article belongs to the Special Issue Selected Papers from the 1st International Electronic Conference on the Hydrological Cycle (ChyCle-2017))

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