Towards a French lysimetric network: ONE WATER project

Groundwater recharge is a complex and local process which is governed by many factors. Understanding and following recharge require long term and local observations, in particular during extreme events, that are projected to be more intense due to climate change. Only lysimeters can give access directly to the recharge over long periods. In this study, 24 lysimeters from three different sites in north-eastern France  (Homécourt-GISFI, Osne le Val-OPE Andra, Fagnières-INRAE) are used to study intense events, such as intense precipitation. The lysimeters in the 3 different sites have different dimensions, setup, soil and vegetation, which give complementary results. At Fagnières  the data achieved over 50 years present a significant decrease of the recharge, but no significant trend of the intense precipitation event nor in the associated drainage they generate. Indeed, only 10% of intense precipitation events generate drainage, in particular if the soil is uncovered and if the intense events occur in winter. These results are in line with soil water content/storage measurements of GISFI/OPE sites.  These lysimeters are also used to assess the groundwater recharge of the land model surface ISBA, by using different soil water retention/hydraulic curves and many pedotransfer functions.  These results reinforce the need to maintain and develop a network of lysimeters in France, to get continuous observation across the territory of groundwater recharge, but also to study other components such as the water transpired by the plant or the pollution of water. This is one of the aims of the new ONEWATER project. This network should help us to improve our understanding of the processes that can occur in the vadose zone of the soil, and to enhance seasonal forecasts from some numerical models. The main steps of this project are i) to identify and share lysimeters already available in France; ii) to create new lysimeters across the national territory to ensure spatial heterogeneity; iii) to definited an appropriated and homogeneous development method. The development of this network will largely be coordinated with CEREEP's ecotron (www.cereep.ens.psl.eu/) and the GISFI research consortium dedicated to the knowledge and the development on remediation technologies for degraded and polluted lands (www.gisfi.univ-lorraine.fr).