On the Sensitivity of Potential Evapotranspiration in Egypt to Different Dynamical Downscaling Options and Boundary Layer Schemes Using a High-Resolution Regional Climate Model

Abstract

Accurate information on potential evapotranspiration (PET) is mandatory for arid regions (such as Egypt) to assess crop water requirements. Such precision is limited by the dynamical downscaling options and the physical settings used in regional climate models (like the RegCM4). To address these issues, four simulations were run as part of the current study. The first two simulations take direct (DIR) and one-way nesting (NEST) into account, while the other two use two boundary layer techniques (HOLTSLAG; HOLT) and (the University of Washington; UW). All simulations were driven via an ERA-Interim reanalysis of 1.5 degrees. The simulated PET was evaluated for the high-resolution reanalysis gridded derived product of ERA5-Land (hereafter ERA5). The findings revealed no discernible difference between DIR and NEST regarding global incident solar radiation (RSDS). Also, NEST had a higher mean air temperature (TMP) than DIR. Additionally, UW had a lower TMP than HOLT, but switching between HOLT and UW did not significantly impact the simulated RSDS. Concerning PET, it is neither affected by DIR and NEST nor HOLT and UW. Such results suggest that the RSDS is the main driver in controlling PET variability, followed by TMP. Therefore, by using the DIR downscaling option and UW boundary layer scheme throughout the period of 1990–2020, as recommended by the World Meteorological Organization, the RegCM4 can be used to develop a regional PET map of Egypt.

Keywords

• DIR
• NEST
• HOLT
• regional climate model
• PET