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

One of the greatest challenges facing environmental science is to better understand the impacts of predicted future changes in the terrestrial hydrological cycle. It has been recognized that human activities play a key role and must therefore be considered in future climate simulations. The representation of anthropization in land surface schemes within global earth system models is at a relatively nascent stage and must be improved for more accurate future projections of water resources. The understanding of the impact of anthropogenic processes has been hampered by the lack of consistent and extensive observations. Here, we present the Land surface Interactions with the Atmosphere over the Iberian Semi-arid Environment (LIAISE) project field campaign which brought together ground-based (surface energy budget estimated at 7 sites, 269 radio soundings made at 2 sites and multiple remote sensing instruments for profiling the lower atmosphere), airborne measurements (3 airplanes and numerous drones measuring surface and atmospheric properties) and satellite data (to derive estimates of irrigation timing, soil moisture, evapotranspiration and surface temperature) to improve our understanding of key natural and anthropogenic land processes and boundary layer feedbacks. The study area is in the Ebro basin of northeastern Spain in a hot, dry Mediterranean climate, with a sharp demarcation between a vast intensively irrigated region and a much drier rainfed zone to the east. Analysis of the observations reveal strong surface heterogeneities of evapotranspiration within the irrigated zone (differences upwards of approximately 7 mm day-1 between fields), linked to the crop type, vegetation phenology and soil moisture, all of which were modulated by irrigation. The significant surface flux differences between the irrigated and rainfed zones were found to result in strongly contrasting atmospheric boundary layer properties (between 2 supersites​ separated by 14 km) extending upwards through the lowest several km of the atmosphere.