Towards a Better Understanding of the Hydrological Cycle Using Altimetry

Earth System Models (ESMs) are the main tools used for both evaluating risks and improving long term prediction. However, there is a very large degree of uncertainty related to the impact of climate change on the global water cycle based on such models (IPCC, 2014). Therefore, there is a need for improved understanding and modeling of the global hydrological cycle. Currently, no model system exists which is able to produce reliable global estimates of river discharge and lake water storage, mostly due to a lack of data with sufficient spatial and temporal coverage. The SWOT mission will provide global measurements of water surface elevation at unprecedented spatial resolutions, from which a discharge product will be derived. Such data will help to improve the input parameters and the physics of the hydrological and hydrodynamic parameterizations in ESMs at the global scale. This is currently a very active area of research as there is a need for better understanding potential impact of climate change on world’s water resources. In addition, the development of methodologies to correct the model (river and lakes storage) prognostic variable trajectories (for hindcast or analysis) to improve estimates of water fluxes and storage at the global scale need to be conducted.

The current work is based on two complementary axis, which will benefit from SWOT altimetry data when available. The first one focuses on rivers and the assimilation of synthetic discharge estimates from existing altimetry data. The Ensemble Kalman Filter is used to correct discharge and water storage over the Amazon from a coupled land surface model and river routing model. The second axis aimed at developing a lake and reservoir mass water budget model to estimate lakes water storage and their variations at the global scale and hence have a better representation of the water cycle. Lakes volume calculation based on geometric consideration will be presented and evaluated against in situ measurements. Results of this method and comparison with other approaches for some individual lakes will be presented.