Basin Scale Atmospheric Moisture Recycling Should be Accounted for in Land-Use Change Studies

Land use change (LUC) affects the water balance, i.e. the partitioning of precipitation into runoff, evaporation and groundwater storage. Given the fact that widespread changes in land use have taken place over the 20th century and are projected for the 21st century, modelling efforts take place to assess the magnitude of the local and river-basin-wide water balance effects of LUC. These modelling efforts typically take place in an uncoupled way: hydrological models are forced with the same atmospheric forcing data and the effects of LUC are calculated in the hydrological model. However, some of the additional evaporated moisture due to LUC may return as precipitation within the same river basin, questioning the validity of the forcing precipitation set. Here, we use a Lagrangian atmospheric moisture tracking model to assess river basin (evaporation) moisture recycling rates to determine what fraction of the evaporation recycles within the same river basin through the atmosphere. We combine this with ISIMIP evaporation estimates over the 20th and 21st century to determine additional basin-wide moisture recycling due to LUC. We find that for some basins the moisture recycling is as high as 70%, with a change in evaporation due to LUC of 20%, making the additional recycled moisture due to LUC non-negligible. We will present results of this analysis for the 26 major global river basins