<p><span data-ccp-charstyle-defn="{">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 </span><span>E</span><span> 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 (</span><span>mHm</span><span>, </span><span>Terraclimate</span><span>) 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.</span></p>

<p><span xml:lang="EN-US" data-contrast="auto"><span>The Mediterranean has been characterized as a region of enhanced climatic variability. Transitions between dry and wet conditions have repeatedly occurred over the last millennium in various spatial and temporal scales. However, the frequency of these shifts is poorly assessed due to the low amount of paleoclimatic reconstructions and the substantial heterogeneity of the Mediterranean. Here, we examine how often Mediterranean regions have transitioned between different hydroclimatic regimes over the last millennium. For this purpose, we use the Paleo Hydrodynamics Data Assimilation (PHYDA) simulation results to </span><span>i</span><span>dentify</span> <span>transitional changes based on Köppen-Geiger climate types. Our results </span><span>i</span><span>ndicate</span> <span>which regions are more likely to experience transitions between hydroclimatic regimes and their duration distribution. We also examine how the intensity of the shifts have fluctuated during the study period and quantify the uncertainties involved. Our findings contribute to a better understanding of the past hydroclimatic variability, which is crucial for further </span><span>d</span><span>etermining</span> <span>the current state and future aridification in the Mediterranean region. </span></span><span> </span></p>