The Impact of Biases in Precipitation and Evapotranspiration on Aridification Assessment over the Mediterranean Region

Aridification is one of the growing concerns in the Mediterranean region. The estimation of water availability (precipitation minus evaporation; P-E), has been widely used to assess aridification. However, the values of P and E are always associated with biases due to different methodological and observational approaches. In this study, we investigate the impact of estimation biases in assessing aridification in the Mediterranean region. To this end, we use multiple precipitation datasets (EM-Earth, GPM-IMERG, and MSWEP) and methodologies for evapotranspiration estimation. We then compare them with satellite (GRACE), reanalysis (ERA5), and hydrological simulation (mHm, Terraclimate) data products. This evaluation shows the variability in the estimated water availability corresponding to its observational counterpart and how the biases in precipitation and evaporation propagate to the value of P-E. Assessing the variance of water availability derived from different estimation methodologies and observational datasets increases our insight into assessing the aridification in the Mediterranean region.