Ximena Vargas - Academia.edu (original) (raw)

Papers by Ximena Vargas

HAL (Le Centre pour la Communication Scientifique Directe), Dec 14, 2015

HAL is a multidisciplinary open access archive for the deposit and dissemination of scientific re... more HAL is a multidisciplinary open access archive for the deposit and dissemination of scientific research documents, whether they are published or not. The documents may come from teaching and research institutions in France or abroad, or from public or private research centers. L'archive ouverte pluridisciplinaire HAL, est destinée au dépôt et à la diffusion de documents scientifiques de niveau recherche, publiés ou non, émanant des établissements d'enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.

HAL (Le Centre pour la Communication Scientifique Directe), Sep 18, 2018

HAL (Le Centre pour la Communication Scientifique Directe), Apr 17, 2016

HAL is a multidisciplinary open access archive for the deposit and dissemination of scientific re... more HAL is a multidisciplinary open access archive for the deposit and dissemination of scientific research documents, whether they are published or not. The documents may come from teaching and research institutions in France or abroad, or from public or private research centers. L'archive ouverte pluridisciplinaire HAL, est destinée au dépôt et à la diffusion de documents scientifiques de niveau recherche, publiés ou non, émanant des établissements d'enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.

Drought is one of the main hydroclimatic hazards worldwide, affecting water availability, ecosyst... more Drought is one of the main hydroclimatic hazards worldwide, affecting water availability, ecosystems and socioeconomic activities. Since 2010, Central Chile (30–38°S) has been experiencing a drought with unprecedented duration and severity (also known as the Central Chile megadrought), producing drastic reductions in river flows, snow cover and reservoir levels. Nevertheless, there is limited understanding of how hydrological processes have been altered and whether such variations will persist during the 21st century. In this study, we characterize the magnitude, frequency, and duration of drought events under historical conditions and future climate scenarios across different hydrological regimes in Central Chile. To this end, we generate daily time series of streamflow, evapotranspiration, soil moisture and other hydrological variables in six case study basins with little human intervention for the period 1981-2100, using the Structure for Unifying Multiple Modeling Alternatives (...

Hydrological Sciences Journal

In Chile, due to very steep mountainous areas near urban zones, it is almost impossible to establ... more In Chile, due to very steep mountainous areas near urban zones, it is almost impossible to establish forecasting hydrological models with enough lead-time to take non-structural measures to mitigate the effects of floods. During construction of a highway inside the Mapocho River, a meteorological model was performed to forecast the magnitude of rainfall and temperature three days in advance, making possible an improvement in the lead-time of predictions. This paper analyses the use of these results in a basin, near Santiago, the country's capital city, which is characterized by having a variable snowfall area depending on prevailing temperature. Two gage stations situated in tributaries, located a certain distance upstream from the highway works, control the streamflow that arrives at the place of work. Meteorological results, for mean area conditions for the watershed in the next 3 days, were distributed in time using empirical daily rainfall distributions and then used as inpu...

Distributed hydrological models are useful tools to explicitly simulate the spatial heterogeneity... more Distributed hydrological models are useful tools to explicitly simulate the spatial heterogeneity of water and energy fluxes and storages. Nevertheless, their parameters are typically calibrated using streamflow-based objective functions that integrate information on the spatial variability of physical processes into a single metric. Additionally, these models contain several soil parameters that can be distributed in space, affecting the spatial representation of hydrological variables. Here, we examine the implications of streamflow-based calibration metric selection and spatial heterogeneity in soil parameters on the realism of model simulations, with emphasis on spatial patterns. To this end, we conduct several calibration experiments in six pilot basins with different hydrological regimes (two snowmelt-driven, two mixed-regime, and two rainfall-driven basins), in central-southern Chile, using the Variable Infiltration Capacity (VIC) model coupled with the mizuRoute routing model. In each experiment we assess, for a given calibration objective function, the effects of distributing individual soil parameters using a spatial regularization strategy based on principal component analysis of physiographic and soil characteristics (elevation, slope, clay content, sand content and bulk density), defining the case of spatially constant soil parameters as the benchmark (i.e, only meteorological forcing data and vegetation attributes are spatially distributed). To evaluate simulated spatial patterns, we use satellite remote sensing data of soil moisture from the ESA-CCI product, and fractional snow-covered area, actual evapotranspiration (ET), and land surface temperature from MODIS products. The results show that similar streamflow performance metrics can be achieved with different combinations of regularized soil parameter and calibration metric; however, the simulated spatial patterns can be considerably different, without clear connections with the hydrological regime. Further, a streamflow-based calibration is insufficient to represent the seasonality of other variables, especially in water-limited catchments, where important shifts (e.g., up to five months) in peak ET can be obtained compared to the reference product.

Hydrological models are powerful tools, that allows users to create a simplified representation o... more Hydrological models are powerful tools, that allows users to create a simplified representation of real-world system and that serve to understand the hydrological processes in a basin, and predict their future behavior, including, for example, the effects of climate change. However, these models are subject to multiple sources of uncertainty, including structural uncertainty, related to the hydrological processes simulated and to the spatial discretization applied (lumped, semi-distributed or distributed models). The effects of this modelling decision could be particularly relevant when the objective is to simulate more than one hydrological process.The objective of this work is to determine if the use of different model structures (lumped or semi-distributed), and the selection of process to be simulated allows reducing the uncertainty of the estimation of more than one hydrological process. Using Raven, a robust and flexible hydrological modelling framework, that supports a wide variety of modelling options, and sits atop a robust and extendible software architecture, eight model structures have been constructed to simulate the River Colorado en Junta con Palos Basin. This basin located in the central zone of Chile (Lat.-35.25, Lon. 71), has a snow-pluvial regime and an average annual rainfall of 1796 mm for the period 1979-2020. Additionally, this basin covers an area of 879 km2, with a wide elevation range, from 643 m.a.s.l. to 4074 m.a.s.l.The results have shown some differences at modelling daily streamflow (KGE from 0.68 to 0.72 in the lumped models, and from 0.68 to 0.8 in semi-distributed models). Furthermore, other important changes have been visualized related to the characterization of snow cover and soil moisture in the first layer of soil. The simulated series have been compared to satellite data (products MODIS10A2 for snow cover and NASA-USDA Enhanced SMAP Global Soil Moisture Data for superficial soil moisture).In the case of the snow cover, the annual duration of snow cover was evaluated, obtaining Pearson's coefficient values between 0.4 and 0.56 for lumped models, while these values reach 0.65 in the case of semi-distributed models. Regarding soil moisture, the changes were more significant when changing the structure of the model (selection and parameterizations of the processes), rather than its spatial discretization, with a range of KGE values from 0.34 to values close to 0.7, strongly influenced by the methods used to evaluate evapotranspiration and infiltration, as well as by the characteristics of the soil.Overall, this work demonstrates the potential of a flexible hydrologic modeling framework to assess and reduce the structural uncertainty of hydrologic models, taking advantage of the potential of these tools.

EGU General Assembly Conference Abstracts, May 1, 2014

Snow plays a key role in the hydrologic cycle over mountainous areas of Central Chile. Its princi... more Snow plays a key role in the hydrologic cycle over mountainous areas of Central Chile. Its principal function is to store a large amount of water during winter season and release it in spring creating a time gap between precipitation and streamflow. Surface observations of snow like snow pillows or snow depths measurements are unable to capture fully the spatial and temporal variability of snow. Moreover, in this area is easy to find volcanoes and mountains over 6000 masl, but registers are found generally under 3000 masl. Nevertheless, additional information about snow can be obtained from hydrological models that are forced with surface meteorological variables (precipitation, air temperature, wind, etc.) and represent the effects of topography, soil and vegetation on snow processes, but these forcing registers are equally poor across this area. In this work, a combined in situ measurement and MODIS land surface temperature images were related to create daily maximum and minimum air temperature maps for two catchments of Central Chile located in Los Andes mountains, Colorado antes Junta Olivares and Olivares antes Junta Colorado, without any meteorological records available. To overcome the lack of this information we used the results of WRF (Weather Research and Forecasting) for wind and a vicinity gauge for precipitation. The aim of this work was to validate the dynamics of snow cover comparing MODIS snow cover images with hydrological model results once streamflow calibration was performed. In this case, a gridded or "checkerboard type" model was required to compare both results. The chosen model was the Variable Infiltration Capacity (VIC) because it grids spatially the results and recently was released the "Data Set Global VIC Input Parameters at 0.5-Degree Resolution" reducing calibration effort time. However, VIC model has been used to assess water availability on continental and global scales using mainly 0.125 to 2 degree resolutions, a very low resolution for Chilean Andes, so we reduced the scale to 0.03 degree to observe snow cover elevation gradient effects. In this manner, is possible to observe the dynamics of snow cover since year 2000 until today (availability of MODIS images). Results for streamflow calibration using Nash Sutcliffe efficiency were 0.64 and 0.70 during 2002/2012 period. Respect to snow cover, we obtained 84% and 82% of similitude between images and model's results in both basins, Colorado and Olivares respectively.

WIT Transactions on Ecology and the Environment, Apr 3, 2003

In Chile, due to very steep mountainous areas near urban zones, it is almost impossible to establ... more In Chile, due to very steep mountainous areas near urban zones, it is almost impossible to establish forecasting hydrological models with enough lead-time to take non-structural measures to mitigate the effects of floods. During construction of a highway inside the Mapocho River, a meteorological model was performed to forecast the magnitude of rainfall and temperature three days in advance, making possible an improvement in the lead-time of predictions. This paper analyses the use of these results in a basin, near Santiago, the country's capital city, which is characterized by having a variable snowfall area depending on prevailing temperature. Two gage stations situated in tributaries, located a certain distance upstream from the highway works, control the streamflow that arrives at the place of work. Meteorological results, for mean area conditions for the watershed in the next 3 days, were distributed in time using empirical daily rainfall distributions and then used as inputs for a neural network hydrological model, previously calibrated with observed rainfall and runoff data in each station. Comparisons with a transfer function hydrological model are made. For each event, with both forecasting methods, results are extrapolated to downstream, where highway construction is performed, and conclusions related to false alerts or no alert, and effective alert warnings for

HAL (Le Centre pour la Communication Scientifique Directe), 2018

EGU General Assembly Conference Abstracts, Apr 1, 2019

HAL (Le Centre pour la Communication Scientifique Directe), Sep 18, 2018

Hydrological Sciences Journal-journal Des Sciences Hydrologiques, Jun 29, 2023

Zenodo (CERN European Organization for Nuclear Research), Apr 17, 2023

EGU General Assembly Conference Abstracts, May 1, 2010

Water Resources Research, Apr 1, 2014

The Andes Cordillera remains a sparsely monitored and studied snow hydrology environment in compa... more The Andes Cordillera remains a sparsely monitored and studied snow hydrology environment in comparison to similar mountain ranges in the Northern Hemisphere. In order to uncover some of the key processes driving snow water equivalent (SWE) spatial variability, we present and analyze a distributed SWE dataset, sampled at the end of accumulation season 2011. Three representative catchments across the region were monitored, obtaining measurements in an elevation range spanning 2000 to 3900 m asl and from 32.4° to 34.0°S in latitude. Climatic conditions during this season corresponded to a moderate La Niña phenomenon, which is generally correlated with lower-than normal accumulation. Collected measurements can be described at the regional and watershed extents by altitudinal gradients that imply an increase by a factor of two in snow depth between 2200 and 3000 m asl, though with significant variability at the upper sites. In these upper sites, we found north-facing, wind-sheltered slopes showing 25% less average SWE values than southfacing, wind-exposed ones. This suggests that under these conditions, solar radiation dominated wind transport effects in controlling end-of-winter variability. Nevertheless, we found clusters of snow depth measurements above 3000 m asl that can be explained by wind exposure differences. This is the first documented snow depth dataset of this spatial extent for this region, and it is framed within an ongoing research effort aimed at improving understanding and modeling of snow hydrology in the extratropical Andes Cordillera.

Authorea (Authorea), Jun 25, 2021

The assessment of climate change impacts on water resources and flood risk is typically underpinn... more The assessment of climate change impacts on water resources and flood risk is typically underpinned by hydrological models calibrated and selected based on observed streamflow records. Yet, changes in climate are rarely accounted for when selecting hydrological models, which compromises their ability to robustly represent future changes in catchment hydrology. In this paper, we test a simple framework for selecting an ensemble of calibrated hydrological model structures in catchments where

HAL (Le Centre pour la Communication Scientifique Directe), Dec 14, 2015

HAL is a multidisciplinary open access archive for the deposit and dissemination of scientific re... more HAL is a multidisciplinary open access archive for the deposit and dissemination of scientific research documents, whether they are published or not. The documents may come from teaching and research institutions in France or abroad, or from public or private research centers. L'archive ouverte pluridisciplinaire HAL, est destinée au dépôt et à la diffusion de documents scientifiques de niveau recherche, publiés ou non, émanant des établissements d'enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.

HAL (Le Centre pour la Communication Scientifique Directe), Sep 18, 2018

HAL (Le Centre pour la Communication Scientifique Directe), Apr 17, 2016

HAL is a multidisciplinary open access archive for the deposit and dissemination of scientific re... more HAL is a multidisciplinary open access archive for the deposit and dissemination of scientific research documents, whether they are published or not. The documents may come from teaching and research institutions in France or abroad, or from public or private research centers. L'archive ouverte pluridisciplinaire HAL, est destinée au dépôt et à la diffusion de documents scientifiques de niveau recherche, publiés ou non, émanant des établissements d'enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.

Drought is one of the main hydroclimatic hazards worldwide, affecting water availability, ecosyst... more Drought is one of the main hydroclimatic hazards worldwide, affecting water availability, ecosystems and socioeconomic activities. Since 2010, Central Chile (30–38°S) has been experiencing a drought with unprecedented duration and severity (also known as the Central Chile megadrought), producing drastic reductions in river flows, snow cover and reservoir levels. Nevertheless, there is limited understanding of how hydrological processes have been altered and whether such variations will persist during the 21st century. In this study, we characterize the magnitude, frequency, and duration of drought events under historical conditions and future climate scenarios across different hydrological regimes in Central Chile. To this end, we generate daily time series of streamflow, evapotranspiration, soil moisture and other hydrological variables in six case study basins with little human intervention for the period 1981-2100, using the Structure for Unifying Multiple Modeling Alternatives (...

Hydrological Sciences Journal

In Chile, due to very steep mountainous areas near urban zones, it is almost impossible to establ... more In Chile, due to very steep mountainous areas near urban zones, it is almost impossible to establish forecasting hydrological models with enough lead-time to take non-structural measures to mitigate the effects of floods. During construction of a highway inside the Mapocho River, a meteorological model was performed to forecast the magnitude of rainfall and temperature three days in advance, making possible an improvement in the lead-time of predictions. This paper analyses the use of these results in a basin, near Santiago, the country's capital city, which is characterized by having a variable snowfall area depending on prevailing temperature. Two gage stations situated in tributaries, located a certain distance upstream from the highway works, control the streamflow that arrives at the place of work. Meteorological results, for mean area conditions for the watershed in the next 3 days, were distributed in time using empirical daily rainfall distributions and then used as inpu...

Distributed hydrological models are useful tools to explicitly simulate the spatial heterogeneity... more Distributed hydrological models are useful tools to explicitly simulate the spatial heterogeneity of water and energy fluxes and storages. Nevertheless, their parameters are typically calibrated using streamflow-based objective functions that integrate information on the spatial variability of physical processes into a single metric. Additionally, these models contain several soil parameters that can be distributed in space, affecting the spatial representation of hydrological variables. Here, we examine the implications of streamflow-based calibration metric selection and spatial heterogeneity in soil parameters on the realism of model simulations, with emphasis on spatial patterns. To this end, we conduct several calibration experiments in six pilot basins with different hydrological regimes (two snowmelt-driven, two mixed-regime, and two rainfall-driven basins), in central-southern Chile, using the Variable Infiltration Capacity (VIC) model coupled with the mizuRoute routing model. In each experiment we assess, for a given calibration objective function, the effects of distributing individual soil parameters using a spatial regularization strategy based on principal component analysis of physiographic and soil characteristics (elevation, slope, clay content, sand content and bulk density), defining the case of spatially constant soil parameters as the benchmark (i.e, only meteorological forcing data and vegetation attributes are spatially distributed). To evaluate simulated spatial patterns, we use satellite remote sensing data of soil moisture from the ESA-CCI product, and fractional snow-covered area, actual evapotranspiration (ET), and land surface temperature from MODIS products. The results show that similar streamflow performance metrics can be achieved with different combinations of regularized soil parameter and calibration metric; however, the simulated spatial patterns can be considerably different, without clear connections with the hydrological regime. Further, a streamflow-based calibration is insufficient to represent the seasonality of other variables, especially in water-limited catchments, where important shifts (e.g., up to five months) in peak ET can be obtained compared to the reference product.

Hydrological models are powerful tools, that allows users to create a simplified representation o... more Hydrological models are powerful tools, that allows users to create a simplified representation of real-world system and that serve to understand the hydrological processes in a basin, and predict their future behavior, including, for example, the effects of climate change. However, these models are subject to multiple sources of uncertainty, including structural uncertainty, related to the hydrological processes simulated and to the spatial discretization applied (lumped, semi-distributed or distributed models). The effects of this modelling decision could be particularly relevant when the objective is to simulate more than one hydrological process.The objective of this work is to determine if the use of different model structures (lumped or semi-distributed), and the selection of process to be simulated allows reducing the uncertainty of the estimation of more than one hydrological process. Using Raven, a robust and flexible hydrological modelling framework, that supports a wide variety of modelling options, and sits atop a robust and extendible software architecture, eight model structures have been constructed to simulate the River Colorado en Junta con Palos Basin. This basin located in the central zone of Chile (Lat.-35.25, Lon. 71), has a snow-pluvial regime and an average annual rainfall of 1796 mm for the period 1979-2020. Additionally, this basin covers an area of 879 km2, with a wide elevation range, from 643 m.a.s.l. to 4074 m.a.s.l.The results have shown some differences at modelling daily streamflow (KGE from 0.68 to 0.72 in the lumped models, and from 0.68 to 0.8 in semi-distributed models). Furthermore, other important changes have been visualized related to the characterization of snow cover and soil moisture in the first layer of soil. The simulated series have been compared to satellite data (products MODIS10A2 for snow cover and NASA-USDA Enhanced SMAP Global Soil Moisture Data for superficial soil moisture).In the case of the snow cover, the annual duration of snow cover was evaluated, obtaining Pearson's coefficient values between 0.4 and 0.56 for lumped models, while these values reach 0.65 in the case of semi-distributed models. Regarding soil moisture, the changes were more significant when changing the structure of the model (selection and parameterizations of the processes), rather than its spatial discretization, with a range of KGE values from 0.34 to values close to 0.7, strongly influenced by the methods used to evaluate evapotranspiration and infiltration, as well as by the characteristics of the soil.Overall, this work demonstrates the potential of a flexible hydrologic modeling framework to assess and reduce the structural uncertainty of hydrologic models, taking advantage of the potential of these tools.

EGU General Assembly Conference Abstracts, May 1, 2014

Snow plays a key role in the hydrologic cycle over mountainous areas of Central Chile. Its princi... more Snow plays a key role in the hydrologic cycle over mountainous areas of Central Chile. Its principal function is to store a large amount of water during winter season and release it in spring creating a time gap between precipitation and streamflow. Surface observations of snow like snow pillows or snow depths measurements are unable to capture fully the spatial and temporal variability of snow. Moreover, in this area is easy to find volcanoes and mountains over 6000 masl, but registers are found generally under 3000 masl. Nevertheless, additional information about snow can be obtained from hydrological models that are forced with surface meteorological variables (precipitation, air temperature, wind, etc.) and represent the effects of topography, soil and vegetation on snow processes, but these forcing registers are equally poor across this area. In this work, a combined in situ measurement and MODIS land surface temperature images were related to create daily maximum and minimum air temperature maps for two catchments of Central Chile located in Los Andes mountains, Colorado antes Junta Olivares and Olivares antes Junta Colorado, without any meteorological records available. To overcome the lack of this information we used the results of WRF (Weather Research and Forecasting) for wind and a vicinity gauge for precipitation. The aim of this work was to validate the dynamics of snow cover comparing MODIS snow cover images with hydrological model results once streamflow calibration was performed. In this case, a gridded or "checkerboard type" model was required to compare both results. The chosen model was the Variable Infiltration Capacity (VIC) because it grids spatially the results and recently was released the "Data Set Global VIC Input Parameters at 0.5-Degree Resolution" reducing calibration effort time. However, VIC model has been used to assess water availability on continental and global scales using mainly 0.125 to 2 degree resolutions, a very low resolution for Chilean Andes, so we reduced the scale to 0.03 degree to observe snow cover elevation gradient effects. In this manner, is possible to observe the dynamics of snow cover since year 2000 until today (availability of MODIS images). Results for streamflow calibration using Nash Sutcliffe efficiency were 0.64 and 0.70 during 2002/2012 period. Respect to snow cover, we obtained 84% and 82% of similitude between images and model's results in both basins, Colorado and Olivares respectively.

WIT Transactions on Ecology and the Environment, Apr 3, 2003

In Chile, due to very steep mountainous areas near urban zones, it is almost impossible to establ... more In Chile, due to very steep mountainous areas near urban zones, it is almost impossible to establish forecasting hydrological models with enough lead-time to take non-structural measures to mitigate the effects of floods. During construction of a highway inside the Mapocho River, a meteorological model was performed to forecast the magnitude of rainfall and temperature three days in advance, making possible an improvement in the lead-time of predictions. This paper analyses the use of these results in a basin, near Santiago, the country's capital city, which is characterized by having a variable snowfall area depending on prevailing temperature. Two gage stations situated in tributaries, located a certain distance upstream from the highway works, control the streamflow that arrives at the place of work. Meteorological results, for mean area conditions for the watershed in the next 3 days, were distributed in time using empirical daily rainfall distributions and then used as inputs for a neural network hydrological model, previously calibrated with observed rainfall and runoff data in each station. Comparisons with a transfer function hydrological model are made. For each event, with both forecasting methods, results are extrapolated to downstream, where highway construction is performed, and conclusions related to false alerts or no alert, and effective alert warnings for

HAL (Le Centre pour la Communication Scientifique Directe), 2018

EGU General Assembly Conference Abstracts, Apr 1, 2019

HAL (Le Centre pour la Communication Scientifique Directe), Sep 18, 2018

Hydrological Sciences Journal-journal Des Sciences Hydrologiques, Jun 29, 2023

Zenodo (CERN European Organization for Nuclear Research), Apr 17, 2023

EGU General Assembly Conference Abstracts, May 1, 2010

Water Resources Research, Apr 1, 2014

The Andes Cordillera remains a sparsely monitored and studied snow hydrology environment in compa... more The Andes Cordillera remains a sparsely monitored and studied snow hydrology environment in comparison to similar mountain ranges in the Northern Hemisphere. In order to uncover some of the key processes driving snow water equivalent (SWE) spatial variability, we present and analyze a distributed SWE dataset, sampled at the end of accumulation season 2011. Three representative catchments across the region were monitored, obtaining measurements in an elevation range spanning 2000 to 3900 m asl and from 32.4° to 34.0°S in latitude. Climatic conditions during this season corresponded to a moderate La Niña phenomenon, which is generally correlated with lower-than normal accumulation. Collected measurements can be described at the regional and watershed extents by altitudinal gradients that imply an increase by a factor of two in snow depth between 2200 and 3000 m asl, though with significant variability at the upper sites. In these upper sites, we found north-facing, wind-sheltered slopes showing 25% less average SWE values than southfacing, wind-exposed ones. This suggests that under these conditions, solar radiation dominated wind transport effects in controlling end-of-winter variability. Nevertheless, we found clusters of snow depth measurements above 3000 m asl that can be explained by wind exposure differences. This is the first documented snow depth dataset of this spatial extent for this region, and it is framed within an ongoing research effort aimed at improving understanding and modeling of snow hydrology in the extratropical Andes Cordillera.

Authorea (Authorea), Jun 25, 2021

The assessment of climate change impacts on water resources and flood risk is typically underpinn... more The assessment of climate change impacts on water resources and flood risk is typically underpinned by hydrological models calibrated and selected based on observed streamflow records. Yet, changes in climate are rarely accounted for when selecting hydrological models, which compromises their ability to robustly represent future changes in catchment hydrology. In this paper, we test a simple framework for selecting an ensemble of calibrated hydrological model structures in catchments where