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Développement d'une modélisation hydrologique incluant la représentation des aquifères : évaluation sur la France et à l'échelle globale

Abstract : Continental hydrological processes play an important role in the global climate system. They influence exchanges of water and energy between land surface and atmosphere. Recently, several studies emphasized the need to account for groundwater in the land surface models used in climate models. The main objective of this thesis is to develop and evaluate a global hydrological modeling including groundwater in the ISBA-TRIP continental hydrological system of the CNRM. In this thesis, a simple groundwater scheme is introduced into the global TRIP river routing model. This original scheme is first test without coupling with the ISBA land surface model over France at high and low resolutions. Resultats are compared to a dense network of in-situ observations and to the fine-tuned SIM hydrometeorological model. In addition, the simu- lated Terrestrial Water Storage (TWS) variations are compared to the TWS estimates from the GRACE satellite mission. Results show that the groundwater scheme allows TRIP to better capture the spatio-temporal variability of the observations. Summer base flows are particularly improved over the main rivers of France. Decreasing the horizontal resolution has a limited impact on the simulated discharges, while it slightly degrades the simulation of water table variations. A similar methodology is used to evaluate the simple groundwater scheme implemented in TRIP at global scale using a 0.5° model resolution. The simulated river discharges are eval- uated against a large dataset of gauging stations compiled from the GRDC institution and other sources. The simulated TWS are compared to the GRACE estimates. Results show that groundwater improves the simulated river discharges for about 70 % of the gauging sta- tions and deteriorates them for 15 %. The simulated TWS are also in better agreement with the GRACE estimates. These results are mainly explained by the lag introduced by the low- frequency variations of groundwater. This lag tends to shift and smooth the simulated river discharges and TWS. A sensitivity study on the global precipitation forcing used in ISBA shows that the groundwater scheme is not influenced by the uncertainties in precipitation data. The last step of development consists in introducing the coupling between the TRIP ground- water scheme and ISBA in order to take into account the capillary rises from the water table to the soil. This coupling require to use the multi-layer version of ISBA. The evaluation of this more physically version of ISBA over France and at global scale shows changes in the surface water budget and significant improvements of the simulated river discharges. It also highlights a lack of dynamic in the soil scheme, which leads to the underestimation of the simulated annual mean discharges, and higher sensitivity to the resolution. The main effect of capillary rises is to increase evapotranspiration during dry periods. Uncertainties remain in the fully coupled ISBA-TRIP system. Some hypothesis in the cou- pling parameterization are questionable and will need to be investigate. Moreover, the ground- water scheme questions parts of the parameterizations introduced in TRIP. Despite these un- certainties, the positive impacts found on the simulated hydrological variables suggest that the groundwater scheme is robust and suitable for global hydrological and climate appications, which is confirmed by the first global applications of the fully coupled ISBA-TRIP system, even though some aspects need to be improved. The ultimate objective will be to introduce the ISBA-TRIP system with aquifers into the CNRM global climate model in order to assess the relevance of groundwater processes for the simulation of both recent and future climates.
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Jean-Pierre Vergnes. Développement d'une modélisation hydrologique incluant la représentation des aquifères : évaluation sur la France et à l'échelle globale. Hydrologie. Institut National Polytechnique de Toulouse - INPT, 2012. Français. ⟨NNT : ⟩. ⟨tel-00989151⟩

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