Land Surface Interactions with the Atmosphere over the Iberian Semi-Arid Environment (LIAISE)

It has been recognized by international organizations, such as the WCRP, that human activities are playing a key role in modifying the continental water cycle, and therefore must be better accounted for in climate projections. As highlighted by the WCRP Grand Challenge on "Water for the Food Baskets of the World," this issue is critical in bread basket regions where water resources are already limited, such as the Mediterranean basin. Such regions are known to be hot spots for biases in climate model variables, in particular land surface temperature and components of the surface energy balance. To a large degree, this stems from highly heterogeneous land cover in terms of both natural and anthropized surfaces . However, the current representation of anthropization in land surface models (LSMs) and therefore within global climate models is in a relatively nascent stage and urgently needs attention if we are to make accurate future projections of water resources and modifications to the global water cycle. Here, we propose a new international project to address these issues. The study domain for LIAISE is the Ebro basin in northeastern Spain, where surface heterogeneity has grown due landscape changes mainly owing to the human imprint resulting from increases in dramatically enlarged irrigated areas. An intensive field campaign is planned from April through October, 2020, which will consist in extensive measurements of surface properties, monitoring of the atmospheric boundary layer and the flux exchanges at the interface. The LIAISE project, which contributes to the HYdrological cycle in the Mediterranean Experiment (HyMeX), will bring together ground-based and airborne measurements with modeling studies to improve our understanding of key natural and anthropogenic land processes and the subsequent feed-backs with the Mediterranean atmospheric boundary layer (ABL) and basin-scale hydrological cycle. The resulting database will form the basis for a number of international modeling experiments that will cut across many areas of interest to GEWEX, such as the impacts of human influence on land surface fluxes, land/atmosphere interactions (natural and anthropogenic) and the impact of humans on the terrestrial water cycle. Here we present the scientific objectives of the project and an overview of the field campaign.