Comparing surface-soil moisture from the SMOS mission and the ORCHIDEE land-surface model over the Iberian Peninsula

The aim of this study is to compare the surface soil moisture (SSM) retrieved from ESA's Soil Moisture and Ocean Salinity mission (SMOS) with the output of the ORCHIDEE (ORganising Carbon and Hydrology In Dynamic EcosystEm) land surface model forced with two distinct atmospheric data sets for the period 2010 to 2012. The comparison methodology is first established over the REMEDHUS (Red de Estaciones de MEDición de la Humedad def Suelo) soil moisture measurement network, a 30 by 40. km catchment located in the central part of the Duero basin, then extended to the whole Iberian Peninsula (IP). The temporal correlation between the in-situ, remotely sensed and modelled SSM are satisfactory (r. >. 0.8). The correlation between remotely sensed and modelled SSM also holds when computed over the IP. Still, by using spectral analysis techniques, important disagreements in the effective inertia of the corresponding moisture reservoir are found. This is reflected in the spatial correlation over the IP between SMOS and ORCHIDEE SSM estimates, which is poor (¿. ~. 0.3). A single value decomposition (SVD) analysis of rainfall and SSM shows that the co-varying patterns of these variables are in reasonable agreement between both products. Moreover the first three SVD soil moisture patterns explain over 80% of the SSM variance simulated by the model while the explained fraction is only 52% of the remotely sensed values. These results suggest that the rainfall-driven soil moisture variability may not account for the poor spatial correlation between SMOS and ORCHIDEE products.Peer ReviewedPostprint (published version

Analyse et modélisation de l'humidité des sols et des processus d'évaporation, implications pour le réchauffemet climatique

This thesis deals with the study of evaporation and soil moisture, t wo main parameters of the hydrological cycle, and thus the climate system. First, potential evaporation (ET P ) is analysed. It is an important input to hydrological and agronomic models, key to describe the interactions between the surface e and the atmosphere, and the basis of most of the estimations of actual evapora tion. Physically-based and empirical methods to estimate ET P are evaluated, at a global scale, under current climate conditions and in a changing climate. The former methods correspond to those implemented in land surface models (LSM) and the Food and Agriculture Organization (F AO) reference evapotranspiration equation. The assumptions made in FAO's method underest imate ET P if compared to LSM methods. They also result in a lower sensitive ty of ET P to climate change. In addition, empirical equations are not able to reproduce the impact of climate change on ET P if compared to that from LSM methods. Soil moisture is the second aim of this thesis. It is treated t hrough the analysis of brightness temperatures (TB). These are a measure of the radiation emitted by the surface , and thus an optimum parameter to use in remote sensing techniques for soi l moisture retrieval. Measured TB from the Soil Moisture and Ocean Salinity (SMOS) mission are compared, over the Iberian Peninsula, to two sets of TB modelled estimates from two LSM. There is a good agreement in the temporal evolution between them. However, discrepancy es are found regarding the spatial structures, which become more evident during fall and winter and are mainly explained by differences in the annual cycle of measured and modelled TB.Cette thèse étudie l'évaporation et l'humidité du sol, deux paramètres clefs du cycle hydrologique et du système climatique.L'évaporation potentielle (ETP) est un paramètre clef pour les modèles hydrologiques et agronomiques qui décrit les interactions entre la surface et l'atmosphère. Il constitue la base des estimations de l'évaporation réelle. Nous avons évalué, à l'échelle globale et pour le climat actuel ainsi que pour les changements attendus, des estimations de l'ETP basées sur des principes physiques ainsi que des approches empiriques. La méthode d'estimation du flux potentiel conseillée par la Food and Agriculture Organization (FAO) montre une sous évaluation par rapport au schéma de surface, ce qui a pu être relié à certaines hypothèses faites. Ceci implique aussi une sensibilité plus faible au changement climatique de la formulation proposée par la FAO. Nous avons aussi constaté que les méthodes empiriques ne représentent pas correctement l'impact du changement climatique sur l'ETP.L'humidité du sol est analysée du point de vue de la température de brillance en Bande-L (TB). Cette mesure du rayonnement émis par la surface dans une bande spectrale sensible à l'eau dans les premiers centimètres du sol, constitue une des pistes pour l'estimation de l'humidité de surface depuis l'espace. Des mesures de TB ont été comparées, au dessus de la Péninsule Ibérique, à des données simulées par deux schémas de surface. Un bon accord a été trouvé entre les observations et les simulations sur l'évolution temporelle des signaux. Par contre, les structures spatiales peuvent être très différentes au cours de l'automne et l'hiver à cause de cycles annuels très contrastés

Potential evaporation estimation through an unstressed surface energy balance and its sensitivity to climate change

Potential evaporation (ETP) is a basic input for many hydrological and agronomic models, as well as a key variable in most actual evaporation estimations. It has been approached through several diffusive and energy balance methods, out of which the Penman-Monteith equation is recommended as the standard one. In order to deal with the diffusive approach, ETP must be estimated at a sub-diurnal frequency, as currently done in land surface models (LSMs). This study presents an improved method, developed in the ORCHIDEE LSM, which consists of estimating ETP through an unstressed surface-energy balance (USEB method). The results confirm the quality of the estimation which is currently implemented in the model (Milly, 1992). The ETP underlying the reference evaporation proposed by the Food and Agriculture Organization, FAO, (computed at a daily time step) has also been analysed and compared. First, a comparison for a reference period under current climate conditions shows that USEB and FAO's ETP estimations differ, especially in arid areas. However, they produce similar values when the FAO's assumption of neutral stability conditions is relaxed, by replacing FAO's aerodynamic resistance by that of the model's. Furthermore, if the vapour pressure deficit (VPD) estimated for the FAO's equation, is substituted by ORCHIDEE's VPD or its humidity gradient, the agreement between the daily mean estimates of ETP is further improved. In a second step, ETP's sensitivity to climate change is assessed by comparing trends in these formulations for the 21st century. It is found that the USEB method shows a higher sensitivity than the FAO's. Both VPD and the model's humidity gradient, as well as the aerodynamic resistance have been identified as key parameters in governing ETP trends. Finally, the sensitivity study is extended to two empirical approximations based on net radiation and mass transfer (Priestley-Taylor and Rohwer, respectively). The sensitivity of these ETP estimates is compared to the one provided by USEB to test if simplified equations are able to reproduce the impact of climate change on ETP

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

Comparing surface-soil moisture from the SMOS mission and the ORCHIDEE land-surface model over the Iberian Peninsula

The aim of this study is to compare the surface soil moisture (SSM) retrieved from ESA's Soil Moisture and Ocean Salinity mission (SMOS) with the output of the ORCHIDEE (ORganising Carbon and Hydrology In Dynamic EcosystEm) land surface model forced with two distinct atmospheric data sets for the period 2010 to 2012. The comparison methodology is first established over the REMEDHUS (Red de Estaciones de MEDición de la Humedad def Suelo) soil moisture measurement network, a 30 by 40. km catchment located in the central part of the Duero basin, then extended to the whole Iberian Peninsula (IP). The temporal correlation between the in-situ, remotely sensed and modelled SSM are satisfactory (r. >. 0.8). The correlation between remotely sensed and modelled SSM also holds when computed over the IP. Still, by using spectral analysis techniques, important disagreements in the effective inertia of the corresponding moisture reservoir are found. This is reflected in the spatial correlation over the IP between SMOS and ORCHIDEE SSM estimates, which is poor (¿. ~. 0.3). A single value decomposition (SVD) analysis of rainfall and SSM shows that the co-varying patterns of these variables are in reasonable agreement between both products. Moreover the first three SVD soil moisture patterns explain over 80% of the SSM variance simulated by the model while the explained fraction is only 52% of the remotely sensed values. These results suggest that the rainfall-driven soil moisture variability may not account for the poor spatial correlation between SMOS and ORCHIDEE products.Peer Reviewe

Streamflow trends of the Pyrenees using observations and multi-model approach (1980-2013)

18 Pags.- 12 Figs.- 3 Tabls. © 2023 The Authors. Published by Elsevier B. V. This is an open access article under the CCBY-NC-ND license.Study region The Pyrenees. Study focus The Pyrenees is sensitive to changes in climate (both natural and of anthropic origin) and changes in land use and cover (LULC). These changes can influence the water resources. The historical evolution (1980–2013) of the stream flows are studied using observed time series from non-influenced gauging stations and two models (SASER and SWAT). Their comparison helps to detect and analyze changes in flow rates and their trends (trends are computed using the Sen's slope estimator, the significance of which was evaluated using the Mann-Kendall test). Furthermore, it also allows to explore the question of attribution (these models do not simulate LULC change). New hydrological insights for the region A complex and diverse domain such as the Pyrenees gives large differences between modelled trends revealing a large uncertainty that has been observed thanks to the use of two models. For the study period, mostly there are no significant trends. When trends are present in the observations and are also simulated, they are attributed to the effects of climate (natural variability and human induced climate change). When the significant trends observed are not simulated by the models, they are mainly attributed to changes in LULC. In general, models have difficulties detecting observed trends, leading to their attribution to changes in LULCs rather than climate, but there are some notable exceptions.This work was supported by the project EFA210/16/PIRAGUA co-founded by the European Regional Development Fund (ERDF) through the Interreg V Spain-France-Andorre Programme (POCTEFA 2014-2020) of the European Union.Peer reviewe