Advancing hydrological modeling for understanding drought dynamics in the Ebro river basin. The role of Land Surface Models in coupled natural-human systems

Les sequeres són un fenomen complex i multidimensional descrit en termes senzills com a períodes sostinguts de dèficit hídric en comparació amb les condicions normals. Encara que de caràcter global, les seves conseqüències més greus s'observen a regions àrides o semiàrides, com la península Ibèrica. No obstant això, aquests extrems hidrològics no es deuen únicament a processos naturals. Les activitats humanes, com la construcció de preses, les extraccions d'aigües subterrànies i les pràctiques de regadiu, han alterat significativament el flux natural de l'aigua, cosa que ha fet que l'era actual s'anomeni Antropocè. Això posa en relleu la importància crítica de la gestió dels recursos hídrics a regions que ja s'enfronten a una disponibilitat d'aigua variable i limitada. En conseqüència, hi ha una creixent necessitat de metodologies que representin amb precisió la resposta hidrològica de les conques en sistemes naturals-humans acoblats, especialment durant els períodes de baix cabal, per gestionar eficaçment els recursos hídrics. La modelització és una eina adequada utilitzada en la gestió de l’aigua per afrontar els reptes de gestionar uns recursos hídrics escassos i mitigar els impactes del canvi climàtic en el cicle de l’aigua. En aquesta investigació s'apliquen diversos enfocaments per millorar les simulacions hidrològiques emprant la plataforma hidrometeorològica SASER (SAFRAN-SURFEX-Eaudyssée-Rapid), de base física i distribuïda espacialment. Aquests enfocaments tenen per objecte millorar la representació dels processos hidrològics, en particular per als cabals baixos, i incorporar-hi consideracions relatives a la gestió humana de l'aigua. Aquest document presenta dos treballs interrelacionats. En primer lloc, s'han introduït millores al model SASER per augmentar-ne el rendiment. En segon lloc, s'ha implementat un model de preses, forçat tant per les observacions com pel model SASER, per estudiar els impactes de les preses a les sequeres. Aquest treball s'ha dut a terme en una zona que abasta el domini pirinenc, incloent-hi la conca de l'Ebre, les conques que flueixen cap al Golf de Biscaia, les conques catalanes, algunes llenguadocianes, i les conques de l'Adur-Garona, però aquestes metodologies poden aplicar-se a qualsevol regió. Per obtenir resultats precisos i fiables dels models de superfície terrestre (Land Surface Model, LSM) és essencial disposar de dades de forçament d’entrada adequades amb una resolució espacial i temporal apropiada. A aquest efecte, s'ha introduït un nou mètode de correcció lineal del forçament de les precipitacions que aprofita les dades dels models climàtics regionals (MCR). En utilitzar una finestra de correcció setmanal, el mètode capta millor la variabilitat temporal i els patrons de precipitació, cosa que resulta en una representació més realista dels esdeveniments de precipitació en termes estadístics. L'impacte en l'escorriment simulat s'ajusta a les expectatives, mentre que els canvis en el drenatge i l'evapotranspiració estan influïts per diversos factors, com ara el règim climàtic i la resposta en climes humits. A més, el model SASER per defecte presentava un biaix negatiu als cabals baixos, cosa que resulta problemàtica en els estudis sobre la sequera. La causa dels cabals baixos és la manca d'un esquema d'aigües subterrànies al model SASER. La inclusió d'un esquema conceptual d'embassaments per regular el drenatge va millorar la simulació dels cabals, com demostren els valors positius a les mètriques de rendiment. L'aplicació de l'esquema d'embassaments va ser senzilla i va millorar eficaçment la representació dels cabals baixos sense comprometre els cabals alts. A més, es va aplicar un enfocament de regionalització que va permetre la integració de l'embassament conceptual com a mòdul extern a SURFEX. Aquest enfocament va facilitar l'establiment de relacions entre els paràmetres i les variables climàtiques i fisiogràfiques mitjançant un algorisme genètic, fet que va permetre tenir en compte la variabilitat dins de la conca a tota la zona d'estudi. Tot i que l'embassament no té una base física, vincula amb èxit els nous paràmetres amb variables físiques, aconseguint un equilibri favorable entre la modelització distribuïda i la representació física. A més, l'enfocament de regionalització amplia l'aplicabilitat de l'embassament més enllà dels sistemes naturals, i abasta tant les conques naturals com les influenciades per l'home. Per incorporar la gestió humana de l’aigua a l’estudi, es va triar la zona regada pel Canal d’Aragó i Catalunya com a cas d’estudi per aplicar un mòdul prototip de presa. Aquest ha estat utilitzat en combinació amb el nou esquema de reg de SURFEX, que permet estimar les demandes reals. Aquest enfocament combina un model d’explotació d’embassaments i l’esquema de reg de SURFEX, capturant amb precisió la dinàmica de la sequera. El nou mòdul simula eficaçment l'emmagatzematge i els fluxos de sortida i demostra una bona concordança amb les dades de referència. A més, el nou esquema de reg de SURFEX capta la variabilitat interanual de la demanda d'aigua, cosa que dona lloc a una representació millorada del sistema, permetent anar més enllà de les habituals taules de demanda "climatològiques" emprades en aquest tipus d'estudis. L'estudi revela que les influències humanes agreugen la sequera hidrològica, però alleugen l'agronòmica. Les característiques de la sequera hidrològica s'allarguen i el moment dels pics de sequera hidrològica es desplaça sota la influència humana. El regadiu influeix tant en la sequera hidrològica com en l'agronòmica, cosa que subratlla la necessitat de tenir en compte aquests factors en les estratègies de gestió de la sequera. Aquests resultats milloren la nostra comprensió de les complexes interaccions entre les activitats humanes, els recursos hídrics i la dinàmica de la sequera. En conclusió, aquesta investigació avança significativament la representació dels processos hidrològics en un model basat en LSM en una regió semiàrida sensible a les sequeres mitjançant la incorporació de diversos enfocaments i el desenvolupament d'un mòdul per integrar el factor humà. Les millores aconseguides en la representació de les precipitacions i en la modelització hidrològica aporten valuosos coneixements sobre la complexa dinàmica de la resposta hidrològica i la sequera, abastant tant les influències naturals com les antropogèniques. Aquest treball és un primer pas cap a la integració de les influències humanes, com el regadiu i l'explotació d'embassaments, a la plataforma SASER, fet que obre noves possibilitats per estudiar la dinàmica de la sequera i desenvolupar estratègies millorades d'avaluació i gestió de la sequera en sistemes naturals-humans acoblats.Las sequías son un fenómeno complejo y multidimensional descrito en términos sencillos como periodos sostenidos de déficit hídrico en comparación con las condiciones normales. Aunque de carácter global, sus consecuencias más graves se observan en regiones áridas o semiáridas, como la Península Ibérica. Sin embargo, estos extremos hidrológicos no se deben únicamente a procesos naturales. Las actividades humanas, como la construcción de presas, las extracciones de aguas subterráneas y las prácticas de regadío, han alterado significativamente el flujo natural del agua, lo que ha llevado a la era actual a denominarse Antropoceno. Esto pone de relieve la importancia crítica de la gestión de los recursos hídricos en regiones que ya se enfrentan a una disponibilidad de agua variable y limitada. En consecuencia, existe una creciente necesidad de metodologías que representen con precisión la respuesta hidrológica de las cuencas en sistemas naturales-humanos acoplados, especialmente durante los periodos de caudales bajos, para gestionar eficazmente los recursos hídricos. La modelización es una herramienta adecuada utilizada en la gestión del agua para afrontar los retos de gestionar unos recursos hídricos escasos y mitigar los impactos del cambio climático en el ciclo del agua. En esta investigación se aplican varios enfoques para mejorar las simulaciones hidrológicas utilizando la plataforma hidrometeorológica SASER (SAFRAN-SURFEX-Eaudyssée-Rapid), de base física y distribuida espacialmente. Estos enfoques tienen por objeto mejorar la representación de los procesos hidrológicos, en particular para los caudales bajos, e incorporar consideraciones relativas a la gestión humana del agua. Este documento presenta dos trabajos interrelacionados. En primer lugar, se han introducido mejoras en el modelo SASER para mejorar su comportamiento. En segundo lugar, se ha implementado un modelo de presas, forzado tanto por las observaciones como por el modelo SASER, para estudiar los impactos de las presas en las sequías. Este trabajo se ha llevado a cabo en una zona que abarca el dominio pirenaico, incluyendo la cuenca del Ebro, las cuencas que fluyen hacia el Golfo de Vizcaya, las cuencas catalanas y algunas languedocianas, y las cuencas Adour-Garonne, pero estas metodologías pueden aplicarse en cualquier lugar. Para obtener resultados precisos y fiables de los modelos de superficie terrestre (LSM, en inglés) es esencial disponer de datos de forzamiento de entrada adecuados con una resolución espacial y temporal apropiada. Con este fin, se ha introducido un nuevo método de corrección lineal del forzamiento de las precipitaciones que aprovecha los datos de los modelos climáticos regionales (RCM). Al utilizar una ventana de corrección semanal, el método capta mejor la variabilidad temporal y los patrones de precipitación, lo que resulta en una representación más realista de los eventos de precipitación en términos estadísticos. El impacto en la escorrentía simulada se ajusta a las expectativas, mientras que los cambios en el drenaje y la evapotranspiración están influidos por diversos factores, entre ellos el régimen climático y la respuesta en climas húmedos. Además, el modelo SASER por defecto presentaba un sesgo negativo en los caudales bajos, lo que resulta problemático en los estudios sobre la sequía. La causa de este sesgo en los caudales bajos es la falta de un esquema de aguas subterráneas en el modelo SASER. La inclusión de un esquema conceptual de embalses para regular el drenaje mejoró la simulación de los caudales, como demuestran los valores positivos en las métricas de rendimiento. La aplicación del esquema de embalses fue sencilla y mejoró eficazmente la representación de los caudales bajos sin comprometer los caudales altos. Además, se aplicó un enfoque de regionalización que permitió la integración del embalse conceptual como módulo externo en SURFEX. Este enfoque facilitó el establecimiento de relaciones entre los parámetros y las variables climáticas y fisiográficas mediante un algoritmo genético, lo que permitió tener en cuenta la variabilidad dentro de la cuenca en toda la zona de estudio. Aunque el embalse carece de una base física, vincula con éxito los nuevos parámetros con variables físicas, logrando un equilibrio favorable entre la modelización distribuida y la representación física. Además, el enfoque de regionalización amplía la aplicabilidad del embalse más allá de los sistemas naturales, abarcando tanto las cuencas naturales como las influenciadas por el hombre. Para incorporar la gestión humana del agua en el estudio, se eligió la zona regada por el Canal de Aragón y Cataluña como caso de estudio para aplicar un módulo prototipo de presa. Éste se ha utilizado en combinación con el nuevo esquema de riego SURFEX, que permite estimar las demandas reales. Este enfoque combina un modelo de explotación de embalses y el esquema de riego SURFEX, capturando con precisión la dinámica de la sequía. El nuevo módulo simula eficazmente el almacenamiento y los flujos de salida, demostrando una buena concordancia con los datos de referencia. Además, el nuevo esquema de riego de SURFEX capta la variabilidad interanual de la demanda de agua, lo que da lugar a una representación mejorada del sistema, permitiéndonos ir más allá de las habituales tablas "climatológicas" de demanda utilizadas en este tipo de estudios. El estudio revela que las influencias humanas agravan la sequía hidrológica, pero alivian la agronómica. Las características de la sequía hidrológica se alargan y el momento de los picos de sequía hidrológica cambian bajo la influencia humana. El regadío influye tanto en la sequía hidrológica como en la agronómica, lo que subraya la necesidad de tener en cuenta estos factores en las estrategias de gestión de la sequía. Estos resultados mejoran nuestra comprensión de las complejas interacciones entre las actividades humanas, los recursos hídricos y la dinámica de la sequía. En conclusión, esta investigación avanza significativamente la representación de los procesos hidrológicos en un modelo basado en LSM en una región semiárida, sensible a las sequías, mediante la incorporación de varios enfoques y el desarrollo de un módulo para integrar el factor humano. Las mejoras logradas en la representación de las precipitaciones y en la modelización hidrológica aportan valiosos conocimientos sobre la compleja dinámica de la respuesta hidrológica y la sequía, abarcando tanto las influencias naturales como las antropogénicas. Este trabajo es un primer paso hacia la integración de las influencias humanas, como el regadío y la explotación de embalses, en la plataforma SASER, lo que abre nuevas posibilidades para estudiar la dinámica de la sequía y desarrollar estrategias mejoradas de evaluación y gestión de la sequía en sistemas naturales-humanos acoplados.Droughts are a complex and multidimensional phenomenon described in simple terms as sustained periods of water deficit compared to normal conditions. While global in nature, their most severe consequences are observed in arid or semi-arid regions, such as the Iberian Peninsula. However, these hydrological extremes are not solely driven by natural processes. Human activities, including dam construction, groundwater abstractions, and irrigation practices, have significantly altered the natural water flow, leading to the current era being labeled the Anthropocene. This highlights the critical importance of water resources management in regions already facing variable and limited water availability. Consequently, there is a growing need for methodologies that accurately represent the hydrological response of basins in coupled natural-human systems, especially during low flow periods, to effectively manage water resources. Modeling is an adequate tool used in water management to address the challenges of managing scarce water resources and mitigating the impacts of climate change on the water cycle. In this research, various approaches are applied to improve hydrological simulations using the physically based and spatially distributed hydrometeorological platform SASER (SAFRAN-SURFEX-Eaudyssée-Rapid). These approaches aim to enhance the representation of hydrological processes, particularly for low flows, and incorporate human water management considerations. This document presents two interrelated works. First, improvements have been implemented in the SASER model in order to improve its performance. Second, a dam model has been implemented, which is forced by both observations and the SASER model to study the impacts of dams in droughts. This work has been implemented in an area encompassing the Pyrenean domain, including the Ebro basin, basins flowing to the Bay of Biscay, the Catalan and some Languedocian basins, and the Adour-Garonne basins, but these methodologies can be applied anywhere. Adequate input-forcing data with appropriate spatial and temporal resolution are essential for obtaining accurate and reliable results from Land Surface Models (LSMs). To this end, a novel linear correction method in precipitation forcing that leverages regional climate model (RCM) data was introduced. By utilizing a weekly correction window, the method better captures the temporal variability and patterns in precipitation, resulting in a more realistic portrayal of precipitation events in statistical terms. The impact on simulated runoff aligns with expectations, while changes in drainage and evapotranspiration are influenced by various factors, including climate regime and response in wet climates. Additionally, the default SASER model exhibited a negative bias in low flows, which is problematic in drought studies. The cause of this bias in the low flows is the lack of a groundwater scheme in the SASER model. The inclusion of a conceptual reservoir scheme to regulate drainage improved streamflow simulation, as evidenced by positive values in performance metrics. The implementation of the reservoir scheme was straightforward and effectively enhanced the representation of low flows without compromising high flows. Moreover, a regionalization approach was implemented, allowing the integration of the conceptual reservoir as an external module in SURFEX. This approach facilitated the establishment of parameter relationships with climate and physiographic variables using a genetic algorithm, enabling the consideration of within-catchment variability across the study area. While the reservoir lacks a physical basis, it successfully links the new parameters with physical variables, striking a favorable balance between distributed modeling and physical representation. Furthermore, the regionalization approach extends the applicability of the reservoir beyond natural systems, encompassing both natural and human-influenced basins. To incorporate human water management in the study, the area irrigated by the Canal de Aragón y Cataluña was chosen as a case study to apply a prototype dam module. This has been used in combination with the new SURFEX irrigation scheme, which allows us to estimate actual demands. This approach combines a reservoir operation model and the SURFEX irrigation scheme, accurately capturing drought dynamics. The new module effectively simulates storage and outflows, demonstrating good agreement with reference data. Furthermore, SURFEX's new irrigation scheme captures interannual water demand variability, leading to an improved representation of the system, allowing us to go further than the usual “climatological” demand tables used in such studies. The study reveals that human influences exacerbate hydrological drought but alleviate agronomical drought. Hydrological drought characteristics lengthen, and the timing of peak hydrological drought events shifts under human influences. Irrigation impacts both hydrological and agronomical droughts, emphasizing the need to consider these factors in drought management strategies. These findings enhance our understanding of the complex interactions between human activities, water resources, and drought dynamics. In conclusion, this research significantly advances the representation of hydrological processes in a LSM-based model in a semi-arid region, sensitive to droughts, through the incorporation of various approaches and the development of a module to integrate the human factor. The improvements achieved in precipitation representation and hydrological modeling provide valuable insights into the complex dynamics of hydrological response and drought, encompassing both natural and anthropogenic influences. This work is a first step towards the integration of human influences, such as irrigation and reservoir operation, into the SASER platform, opening up new possibilities for studying drought dynamics and developing improved strategies for drought assessment and management in coupled natural-human systems

Drought Propagation under Combined Influences of Reservoir Regulation and Irrigation over a Mediterranean Catchment

Drought is a natural phenomenon that is controlled by different factors such as natural climate and catchment controls, and in many worldwide regions, it is now driven by human activities (i.e., reservoirs, irrigation, groundwater abstractions). Reservoirs initially ensure water availability and help cope with drought, especially in semi-arid regions; however, this human modification of the environment may lead to both positive and negative effects on the hydrological cycle, which need to be understood. This involves a better understanding of hydrological processes and incorporating human interactions within coupled human–natural systems to improve drought management. We focused on a strongly irrigated area located in the northeast of the Iberian Peninsula, the northern part of the Canal of Aragon and Catalonia district supplied by the Barasona reservoir. We implemented a simple water management model to simulate the reservoir operation (human-influenced scenario) and examined the contribution of human activities, associated with irrigation, on the water budget and drought propagation. For this purpose, we used simulations performed by the hydrometeorological model SASER (SAFRAN-SURFEX-EauDyssée-RAPID), which provided a natural scenario (without human influence) to contrast with the human-influenced scenario. The model performance was evaluated through the Kling Gupta Efficiency (KGE) metric. The first results demonstrated satisfactory performance to simulate reservoir storage and outflows against observed data, with KGE values of 0.4 and 0.82, respectively. Then we explored the linkages between agricultural drought, associated with evapotranspiration, and hydrological drought. We applied standardized indices to identify different kinds of drought, compared them, and assessed changes induced by human activities. Human modifications modulate the hydrological response of the catchment, and alter the intensity of hydrological drought, while human activities reduce the intensity of agricultural droughts

Analysis of the past and future water resources of the Pyrenees by means of a land-surface simulation

International audienceThe Pyrenees are the Water Towers of several key river basins in France, Andorra and Spain, being the Adour-Garonne and the Ebro the largest ones. The water of these basins is used by agricultural and industrial economic sectors which have a significant socioeconomic impact. Furthermore, the water of these rivers also sustains ecosystems which have an intrinsic value and provide ecosystem services to society. For this reason, an assessment of the past and future evolution of the water resources of the Pyrenees is necessary. Until now, these assessments have often been done at the basin or at the national level, but never the water resources of the Pyrenees were assessed as a whole. This is the main aim of the PIRAGUA project, within which we develop our research. In order to simulate the continental water cycle of the Pyrenees we have used the SASER (SAFRAN-SURFEX-Eaudysse-RAPID) modeling chain. SAFRAN is a meteorological analysis system, that allows us to create a gridded dataset of all the variables needed by the SURFEX land-surface model. SURFEX outflows (runoff and drainage) are used by Eaudysse and RAPID to calculate streamflow.Until now there were two separate implementation of SAFRAN in France (8 km resolution) and Spain (5 km resolution). For this project we have taken the climatic zone level SAFRAN data of both countries and interpolated it to a new common grid at a resolution of 2.5 km. The dataset covers a domain that includes the Adour-Garonne, the Ebro and all other Pyrenean river basins, its time period is 1979/80-2014/15 (which will be extended to 2016/17). The RAPID river routing scheme has been implemented in the simulation domain using HydroSheds to describe the river network. In order to simulate the future evolution of the continental water cycle we use the Pyrenean climate scenarios developed within the CLIMPY project. These include precipitation and maximum and minimum temperature. SURFEX needs other variables too, such as wind speed, relative humidity and radiation. We solve this problem using an analog based approach similar to Clemins et al (2019). The simulated streamflow is compared to observed streamflow of natural basins. The results show that 18 (out of 38) non influenced stations present a KGE of daily streamflow larger than 0.5. For monthly streamflow, KGE is larger than 0.5 on 22 stations (out of 38). The next steps of our research are to quantify the improvement due to the increased resolution (comparing to a lower resolution simulation), calculate trends of relevant variables at the sub-bassin scale and compared them to the observed ones in the past, and analyze future trends of these variables. Finally, we will assess the impacts of these changes on water resources. This research is funded by the EFA210/16-PIRAGUA project, within the INTERREG V-A Espana-Francia-Andorra POCTEFA2014-2020 program

Improvement of low flows simulation in the SASER hydrological modeling chain

The physically-based, spatially-distributed hydrometeorological model SASER, which is based on the SURFEX LSM, is used to model the hydrological cycle in several domains in Spain and southern France. In this study, the modeled streamflows are validated in a domain centered on the Pyrenees mountain range and which includes all the surrounding river basins, including the Ebro and the Adour-Garonne, with a spatial resolution of 2.5 km. Low flows were found to be poorly simulated by the model. We present an improvement of the SASER modeling chain, which introduces a conceptual reservoir, to enhance the representation of the slow component (drainage) in the hydrological response. The reservoir introduces two new empirical parameters. First, the parameters of the conceptual reservoir model were determined on a catchment-by-catchment basis, calibrating against daily observed data from 53 hydrological stations representing near-natural conditions (local calibration). The results show, on the median value, an improvement (ΔKGE of 0.11) with respect to the reference simulation. Furthermore, the relative bias of two low-flow indices were calculated and reported a clear improvement. Secondly, a regionalization approach was used, which links physiographic information with reservoir parameters through linear equations. A genetic algorithm was used to optimize the equation coefficients through the median daily KGE. Cross-validation was used to test the regionalization approach. The median KGE improved from 0.60 (default simulation) to 0.67 (ΔKGE = 0.07) after regionalization and execution of the routing scheme, and 79 % of independent catchments showed improvement. The model with regionalized parameters had a performance, in KGE terms, very close to that of the model with locally calibrated parameters. The key benefit if the regionalization is that allow us to determine the new empirical parameter of the conceptual reservoir in basins where calibration is not possible (ungauged or human-influenced basins)

Drainage assessment of irrigation districts: on the precision and accuracy of four parsimonious models

International audienceAbstract. In semi-arid irrigated environments, the agricultural drainage is at the heart of three agro-environmental issues: it is an indicator of water productivity, it is the main control to prevent soil salinization and waterlogging problems, and it is related to the health of downstream ecosystems. Crop water balance models combined with subsurface models can be used to estimate the drainage quantities and dynamics at various spatial scales. However, the precision (capacity of a model to fit the observed drainage using site-specific calibration) and accuracy (capacity of a model to approximate observed drainage using default input parameters) of such models have not yet been assessed in irrigated areas. To fill the gap, this study evaluates four parsimonious drainage models based on the combination of two surface models (RU and SAMIR) and two subsurface models (Reservoir and SIDRA) with varying complexity levels: RU-Reservoir, RU-SIDRA, SAMIR-Reservoir, and SAMIR-SIDRA. All models were applied over two sub-basins of the Algerri-Balaguer irrigation district, northeastern Spain, that are equipped with surface and subsurface drains driving the drained water to general outlets where the discharge is continuously monitored. Results show that RU-Reservoir is the most precise (average KGE (Q0.5) of 0.87), followed by SAMIR-Reservoir (average KGE (Q0.5) of 0.79). However, SAMIR-Reservoir is the most accurate model for providing rough drainage estimates using the default input parameters provided in the literature

Drainage assessment of irrigation districts: on the precision and accuracy of four parsimonious models

International audienceAbstract. In semi-arid irrigated environments, agricultural drainage is at the heart of three agro-environmental issues: it is an indicator of water productivity, it is the main control to prevent soil salinization and waterlogging problems, and it is related to the health of downstream ecosystems. Crop water balance models combined with subsurface models can estimate drainage quantities and dynamics at various spatial scales. However, such models' precision (capacity of a model to fit the observed drainage using site-specific calibration) and accuracy (capacity of a model to approximate observed drainage using default input parameters) have not yet been assessed in irrigated areas. To fill the gap, this study evaluates four parsimonious drainage models based on the combination of two surface models (RU and SAMIR) and two subsurface models (Reservoir and SIDRA) with varying complexity levels: RU-Reservoir, RU-SIDRA, SAMIR-Reservoir, and SAMIR-SIDRA. All models were applied over two sub-basins of the Algerri–Balaguer irrigation district, northeastern Spain, equipped with surface and subsurface drains driving the drained water to general outlets where the discharge is continuously monitored. Results show that RU-Reservoir is the most precise (average KGE (Q0.5) of 0.87), followed by SAMIR-Reservoir (average KGE (Q0.5) of 0.79). However, SAMIR-Reservoir is the most accurate model for providing rough drainage estimates using the default input parameters provided in the literature

Streamflow droughts aggravated by human activities despite management

Human activities both aggravate and alleviate streamflow drought. Here we show that aggravation is dominant in contrasting cases around the world analysed with a consistent methodology. Our 28 cases included different combinations of human-water interactions. We found that water abstraction aggravated all drought characteristics, with increases of 20%-305% in total time in drought found across the case studies, and increases in total deficit of up to almost 3000%. Water transfers reduced drought time and deficit by up to 97%. In cases with both abstraction and water transfers into the catchment or augmenting streamflow from groundwater, the water inputs could not compensate for the aggravation of droughts due to abstraction and only shift the effects in space or time. Reservoir releases for downstream water use alleviated droughts in the dry season, but also led to deficits in the wet season by changing flow seasonality. This led to minor changes in average drought duration (-26 to +38%) and moderate changes in average drought deficit (-86 to +369%). Land use showed a smaller impact on streamflow drought, also with both increases and decreases observed (-48 to +98%). Sewage return flows and pipe leakage possibly counteracted the effects of increased imperviousness in urban areas; however, untangling the effects of land use change on streamflow drought is challenging. This synthesis of diverse global cases highlights the complexity of the human influence on streamflow drought and the added value of empirical comparative studies. Results indicate both intended and unintended consequences of water management and infrastructure on downstream society and ecosystems

Streamflow droughts aggravated by human activities despite management

Human activities both aggravate and alleviate streamflow drought. Here we show that aggravation is dominant in contrasting cases around the world analysed with a consistent methodology. Our 28 cases included different combinations of human-water interactions. We found that water abstraction aggravated all drought characteristics, with increases of 20%-305% in total time in drought found across the case studies, and increases in total deficit of up to almost 3000%. Water transfers reduced drought time and deficit by up to 97%. In cases with both abstraction and water transfers into the catchment or augmenting streamflow from groundwater, the water inputs could not compensate for the aggravation of droughts due to abstraction and only shift the effects in space or time. Reservoir releases for downstream water use alleviated droughts in the dry season, but also led to deficits in the wet season by changing flow seasonality. This led to minor changes in average drought duration (-26 to +38%) and moderate changes in average drought deficit (-86 to +369%). Land use showed a smaller impact on streamflow drought, also with both increases and decreases observed (-48 to +98%). Sewage return flows and pipe leakage possibly counteracted the effects of increased imperviousness in urban areas; however, untangling the effects of land use change on streamflow drought is challenging. This synthesis of diverse global cases highlights the complexity of the human influence on streamflow drought and the added value of empirical comparative studies. Results indicate both intended and unintended consequences of water management and infrastructure on downstream society and ecosystems

Streamflow droughts aggravated by human activities despite management

Human activities both aggravate and alleviate streamflow drought. Here we show that aggravation is dominant in contrasting cases around the world analysed with a consistent methodology. Our 28 cases included different combinations of human-water interactions. We found that water abstraction aggravated all drought characteristics, with increases of 20%-305% in total time in drought found across the case studies, and increases in total deficit of up to almost 3000%. Water transfers reduced drought time and deficit by up to 97%. In cases with both abstraction and water transfers into the catchment or augmenting streamflow from groundwater, the water inputs could not compensate for the aggravation of droughts due to abstraction and only shift the effects in space or time. Reservoir releases for downstream water use alleviated droughts in the dry season, but also led to deficits in the wet season by changing flow seasonality. This led to minor changes in average drought duration (-26 to +38%) and moderate changes in average drought deficit (-86 to +369%). Land use showed a smaller impact on streamflow drought, also with both increases and decreases observed (-48 to +98%). Sewage return flows and pipe leakage possibly counteracted the effects of increased imperviousness in urban areas; however, untangling the effects of land use change on streamflow drought is challenging. This synthesis of diverse global cases highlights the complexity of the human influence on streamflow drought and the added value of empirical comparative studies. Results indicate both intended and unintended consequences of water management and infrastructure on downstream society and ecosystems