Simulation and Future Projections of Reference Evapotranspiration in Egypt

With the intensification of climate change, there is an increasing need to assess its potential impacts on hydrology and water resource systems. The reference evapotranspiration (ET_o) plays a crucial role as an indicator for calculating the hydrological cycle and understanding these effects. The main objective of this study was to analyse the projected changes in simulated ET_o over Egypt until the end of the 21st century. This analysis was conducted using the global climate models (GCMs) of the latest phase of the Coupled Model Intercomparison Project (CMIP6) framework, which incorporates the shared socioeconomic pathways (SSPs)—SSP1-2.6, SSP2-4.5, SSP3-7.0 and SSP5-8.5. The Penman–Monteith equation was applied to calculate ET_o utilising data from four CMIP6 GCMs for the historical (1970–2014) and two future periods, the near future (2020–2059) and far future (2060–2100). The results revealed an overall increase in ET_o for all scenarios and periods. The highest increase in annual ET_o was observed under SSP5-8.5, reaching 14.2% during the far future, while the lowest projected increase was 4.36% for SSP1-2.6 in the near future. In addition, the projected ET_o demonstrated the greatest increase during winter, while the lowest increase was in summer. Geographically, the increases will be more in the southwest and the least in the southeast for all scenarios and future periods. These findings emphasise the potential consequences that Egypt, a global water stress hotspot, could face if ET_o rises due to escalating temperatures. It underscores the importance of addressing these challenges to ensure the sustainability of water resources in the face of climate change.