A multi-sourced assessment of the spatiotemporal dynamics of soil moisture in the MARINE flash flood model

The MARINE (Model of Anticipation of Runoff and INundations for Extreme events) hydrological model is a distributed model dedicated to flash flood simulation. Recent developments of the MARINE model are explored in this work. On one hand, transfers of water through the subsurface, formerly relying on water height, now take place in a homogeneous soil column based on the soil saturation degree (SSF model). On the other hand, the soil column is divided into two layers, which represent, respectively, the upper soil layer and the deep weathered rocks (SSF–DWF model). The aim of the present work is to assess the accuracy of these new representations for the simulation of soil moisture during flash flood events. An exploration of the various products available in the literature for soil moisture estimation is performed. The efficiency of the models for soil saturation degree simulation is estimated with respect to several products either at the local scale or spatially distributed: (i) the gridded soil moisture product provided by the operational modeling chain SAFRAN-ISBA-MODCOU; (ii) the gridded soil moisture product provided by the LDAS-Monde assimilation chain, which is based on the ISBA-A-gs land surface model and assimilating satellite derived data; (iii) the upper soil water content hourly measurements taken from the SMOSMANIA observation network; and (iv) the Soil Water Index provided by the Copernicus Global Land Service (CGLS), which is derived from Sentinel-1 C-SAR and ASCAT satellite data. The case study is performed over two French Mediterranean catchments impacted by flash flood events over the 2017–2019 period. The local comparison of the MARINE outputs with the SMOSMANIA measurements, as well as the comparison at the basin scale of the MARINE outputs with the gridded LDAS-Monde and CGLS data, lead to the following conclusion: both the dynamics and the amplitudes of the soil saturation degree simulated with the SSF and SSF–DWF models are better correlated with both the SMOSMANIA measurements and the LDAS-Monde data than the outputs of the base model. Finally, the soil saturation degree simulated by the two-layers model for the deep layer is compared to the soil saturation degree provided by the LDAS-Monde product at corresponding depths. In conclusion, the developments presented for the representation of subsurface flow in the MARINE model enhance the soil saturation degree simulation during flash floods with respect to both gridded data and local soil moisture measurements

Temperature measurements - Vallon de Nant - Synthesis report

A field campaign was set up from July 2021 to September 2023 in order to have in-situ temperature measurements, which represent an additional data source for estimating the performance of the temperature products and better describe the local site effects in the valley. A serie of 28 mini-temperature sensors (ibutton loggers) distributed in the basin is installed, in particular at the bottom of the valley. 28 loggers (12 masts + 18 single loggers) were installed in August 2021. The data were recorded in August 2022 and the loggers were finally uninstalled in September 2023. This report synthesizes the method and the main results of the 2-years field campaign

Characterization hydro-climatic systems at the local scale in the Nepalese Himalayas

La partie centrale de la chaîne himalayenne présente d’importantes hétérogénéités, en particulier en termes de topographie et de climatologie. La caractérisation des processus hydro-climatiques dans cette région est limitée par le manque de descriptif des milieux. La variabilité locale est alors difficilement représentée par les modélisations mises en œuvre à une échelle régionale.L’approche proposée dans ce travail est de caractériser les systèmes hydro-climatiques à l’échelle locale pour réduire les incertitudes liées à l’hétérogénéité du milieu. L’intégration de données localement précises est testée pour la modélisation de bassins versants peu instrumentés et fortement hétérogènes.Deux sous-bassins du bassin de la Dudh Koshi (Népal) sont utilisés comme échantillons représentatifs des milieux de haute et moyenne montagne, hors contribution glaciaire. Le schéma de surface ISBA est appliqué à la simulation des réponses hydrologiques des types de surface décrits à partir d’observations de terrain. Des mesures de propriétés physiques des sols sont intégrées pour préciser la paramétrisation des surfaces dans le modèle. Les données climatiques nécessaires sont interpolées à partir des observations in situ disponibles. Une approche non déterministe est appliquée pour quantifier les incertitudes liées à l’influence de la topographie sur les précipitations, ainsi que leur propagation aux variables simulées. Enfin, les incertitudes liées à la structure des modèles sont évaluées à l’échelle locale à travers la comparaison des paramétrisations et des résultats de simulation obtenus d'une part avec le schéma de surface ISBA, couplé à un module de routage à réservoir et d'autre part avec le modèle hydrologique J2000.The central part of the Hindukush-Himalaya region presents tremendous heterogeneity, in particular in terms of topography and climatology. The representation of hydro-climatic processes for Himalayan catchments is limited due to a lack of knowledge regarding their hydrological behavior. Local variability is thus difficult to characterize based on modeling studies done at a regional scale. The proposed approach is to characterize hydro-climatic systems at the local scale to reduce uncertainties associated with environmental heterogeneity.The integration of locally reliable data is tested to model sparsely instrumented, highly heterogeneous catchments. Two sub-catchments of the Dudh Koshi River basin (Nepal) are used as representative samples of high and mid-mountain environments, with no glacier contribution. The ISBA surface scheme is applied to simulate hydrological responses of the surfaces that are described based on in-situ observations. Measurements of physical properties of soils are integrated to precise surface parametrization in the model. Necessary climatic data is interpolated based on available in-situ measurements. A non deterministic approach is applied to quantify uncertainties associated with the effect of topography on precipitation and their propagation through the modeling chain. Finally, uncertainties associated with model structure are estimated at the local scale by comparing simulation methods and results obtained on the one hand with the ISBA model, coupled with a reservoir routing module, and on the other hand, with the J2000 hydrological model

Caractérisation des systèmes hydro-climatiques à l'échelle locale dans l'Himalaya népalais

The central part of the Hindukush-Himalaya region presents tremendous heterogeneity, in particular in terms of topography and climatology. The representation of hydro-climatic processes for Himalayan catchments is limited due to a lack of knowledge regarding their hydrological behavior. Local variability is thus difficult to characterize based on modeling studies done at a regional scale. The proposed approach is to characterize hydro-climatic systems at the local scale to reduce uncertainties associated with environmental heterogeneity.The integration of locally reliable data is tested to model sparsely instrumented, highly heterogeneous catchments. Two sub-catchments of the Dudh Koshi River basin (Nepal) are used as representative samples of high and mid-mountain environments, with no glacier contribution. The ISBA surface scheme is applied to simulate hydrological responses of the surfaces that are described based on in-situ observations. Measurements of physical properties of soils are integrated to precise surface parametrization in the model. Necessary climatic data is interpolated based on available in-situ measurements. A non deterministic approach is applied to quantify uncertainties associated with the effect of topography on precipitation and their propagation through the modeling chain. Finally, uncertainties associated with model structure are estimated at the local scale by comparing simulation methods and results obtained on the one hand with the ISBA model, coupled with a reservoir routing module, and on the other hand, with the J2000 hydrological model.La partie centrale de la chaîne himalayenne présente d’importantes hétérogénéités, en particulier en termes de topographie et de climatologie. La caractérisation des processus hydro-climatiques dans cette région est limitée par le manque de descriptif des milieux. La variabilité locale est alors difficilement représentée par les modélisations mises en œuvre à une échelle régionale.L’approche proposée dans ce travail est de caractériser les systèmes hydro-climatiques à l’échelle locale pour réduire les incertitudes liées à l’hétérogénéité du milieu. L’intégration de données localement précises est testée pour la modélisation de bassins versants peu instrumentés et fortement hétérogènes.Deux sous-bassins du bassin de la Dudh Koshi (Népal) sont utilisés comme échantillons représentatifs des milieux de haute et moyenne montagne, hors contribution glaciaire. Le schéma de surface ISBA est appliqué à la simulation des réponses hydrologiques des types de surface décrits à partir d’observations de terrain. Des mesures de propriétés physiques des sols sont intégrées pour préciser la paramétrisation des surfaces dans le modèle. Les données climatiques nécessaires sont interpolées à partir des observations in situ disponibles. Une approche non déterministe est appliquée pour quantifier les incertitudes liées à l’influence de la topographie sur les précipitations, ainsi que leur propagation aux variables simulées. Enfin, les incertitudes liées à la structure des modèles sont évaluées à l’échelle locale à travers la comparaison des paramétrisations et des résultats de simulation obtenus d'une part avec le schéma de surface ISBA, couplé à un module de routage à réservoir et d'autre part avec le modèle hydrologique J2000

Soil Sampling results at Vallon de Nant : Soil moisture measurements, granulometry and infiltrometry

<p>This technical report presents the methods applied for soil sampling, granulometry analysis and infiltrometry tests for soil study in Vallon de Nant. Continuous soil moisture measurements are also presented. This report is a notice related to uploaded soil data (particule size distribution and soil moisture time series).</p&gt

Influence de la dynamique du manteau neigeux et des stocks en sub-surface sur la disponibilité en eau de surface en Himalaya

International audienc

ibutton temperature measurements - Vallon de Nant

A field campaign was set up from July 2021 to September 2023 in order to have in-situ temperature measurements, which represent an additional data source for estimating the performance of the temperature products and better describe the local site effects in the valley. A series of 28 mini-temperature sensors (ibutton loggers) distributed in the basin is installed, in particular at the bottom of the valley. 28 loggers (12 masts + 18 single loggers) were installed in August 2021. The data were recorded in August 2022 and the loggers were finally uninstalled in September 2023. The sensors are installed on a mast, under a plastic shelter at 2 m from the ground. The measurement time step is 2 hours

Application du modèle hydro-nival HDSM sur deux petits bassins versants himalayens (Népal)

International audienc

Influence of snow pack and soil water dynamics on river flows in un-glaciarized Himalayan catchments.

International audienceIn the Central Himalayas, it is generally accepted that 80 % of the annual precipitation occurs during the monsoonmonths (June – September). However, surveys with local populations show that surface water is availablethroughout the year. The main question then is to identify the origin of these surface flows. One hypothesisproposes that they are provided by glacial melt during the dry season. However, on the one hand, this historically“permanent” supply is also observed in catchments with little or no glacial contribution, and on the other hand,annual volumes cannot be totally explained by the glacial mass balances currently monitored.Therefore, a better understanding of the hydrological processes is needed for quantifying the influence ofthe inter-seasonal surface (snow) and sub-surface storage on surface flows outside of the monsoon season. Onesolution consists in the application of modelling tools. However, simulations for Himalayan catchments are limiteddue to a lack of knowledge regarding their hydrological behaviour. The main source of uncertainty in poorlymonitored environments is the scarcity of observations, which can be used for model calibration and evaluation.In this study, physically-based modelling with the ISBA Soil-Vegetation-Atmosphere transfer scheme is appliedto small catchments whose physical characteristics are well studied, therefore this approach could constitute aninteresting way for understanding hydrological systems.For that purpose, two small slope catchments selected in the Dudh Koshi River basin (Eastern Nepal),which represent high and mid-mountain environments, are studied in order to evaluate the spatial variability ofthe studied processes. They are equipped with 6 stations for air temperature and precipitation observations. Adistributed approach allows a better representation of the spatial variation of hydro-climatic processes. Moreover,the descriptions of surfaces currently available at global scales are enhanced, based on field observations andpoints of measurements of soil properties. A reduced number of internal parameters of the model can then becalibrated through a multi-objective optimization step. Both hourly measured flows and remote sensing data forsnow cover can be used as criteria for validation. In this presentation, we estimate from modelling results thecontribution of snow melt and sub surface flows to the river discharges during the seasons with low precipitation

Critical discussion on the "observed" water balances of five sub-basins in the Everest region

International audienceThe hydrometeorological components of five Dudh Koshi River sub-basins on the Nepalese side of the Mount Everest have been monitored during four hydrological years (2013-2017), with altitudes ranging from 2000 m to Everest top, areas between 4.65 and 1207 km², and proportions of glaciated areas between nil and 45%. This data set is completed with glacier mass balance observations. The analysis of the observed data and the resulting water balances show large uncertainties of different types: aleatory, epistemic or semantic, following the classification proposed by Beven (2016). The discussion is illustrated using results from two modeling approaches, physical (ISBA, Noilhan and Planton, 1996) and conceptual (J2000, Krause, 2001), as well as large scale glacier mass balances obtained by the way of a recent remote sensing processing method