Influence of Direct-Downscaling and One-Way Nesting on Daily Mean Air Temperature of Egypt Using the RegCM4

Daily mean air temperature (TMP) is an important indicator for a climate change study and it reflects the daily changes of maximum minimum temperature. Downscaling General Circulation Model (GCM) to regional scale ensure accurate simulation TMP. To address this issue, comparison was conducted between Direct (DIR) one-way nesting (NEST) using Regional Climate (RegCM4) in period 1997-2017 over Egypt. The ERA-Interim reanalysis 1.5 degrees (EIN15) used as atmospheric forcing downscale RegCM4 Egypt, while fifth generation ECMWF evaluate concerning Total Cloud Cover (CLT), surface short longwave radiation fluxes (RSDS RLDS), ground (TS), sensible heat flux (HFSS) Results showed that there no difference DIR NEST regarding CLT RSDS; overestimated RLDS more than particularly summer autumn seasons with ERA5. Furthermore, TS all particular seasons. This noted overestimation propagated HFSS explaining high warm bias simulated TMP; which higher DIR. Such findings suggest only affected by uncertainty associated EIN15. Additionally, amplified because EIN15 first mother domain then from nested one. Despite observed biases, shows promising results NEST. Therefore, can be recommended future studies