Dynamical versus statistical downscaling for the generation of regional climate change scenarios at a Western Mediterranean basin: the Júcar River District

Current climate change (CC) predictions for the Western Mediterranean show a significant increase in temperature, and a decrease in precipitations, with great variability depending on general circulation models (GCM) and downscaling approaches. This paper analyses how dynamic downscaling improves statistically based CC scenarios. The study area was the Júcar River Basin (JB), with results from ECHAM5 GCM, and a close time frame of 2010–2040 appropriated for decision-making. The dynamic downscaling was performed with the regional climate model (RCM) RegCM3. It was applied to a coarse grid over the Iberian Peninsula, and then to a finer grid over the JB. The RCM was customized to reproduce Western Mediterranean climatic conditions using the convective precipitation scheme of Grell; the non-convective scheme was customized by changing the default RH_min and C_ptt parameters to reproduce precipitations originated by larger-scale atmospheric circulations. The RCM results, compared to current official Spanish Agency of Meteorology (AEMET) scenarios–statistically based–reproduce much better historical data (used to verify scenarios generation). They foresee a 21.0% precipitation decrease for 2010–2040, compared to previous ECHAM4 predictions with statistical downscaling (−6.64%). The most significant reductions are in February, September and October. Average estimated temperature increase is 0.75 °C, with high increments in July (+3.05 °C) and August (+1.89 °C).