Spatiotemporal heterogeneity of evapotranspiration controlling factors and their trends in Pakistan

Effective climate change mitigation planning in the water and agriculture sectors necessitates a thorough understanding of trends in potential evapotranspiration (ETp) and its driving factors. This study quantitatively assessed the impact of varying meteorological conditions on ETp across Pakistan. We deciphered the dynamics of recent ETp shifts by analyzing trends in meteorological variables using Princeton Global Meteorological Forcing data (daily maximum and minimum temperatures, wind speed, solar radiation, and relative humidity) at 0.25° resolution. Sobol's sensitivity analysis quantified the influence of each climatic variable on ETp. Nonparametric statistical tests identified trends in ETp and its influencing factors. Our findings reveal wind speed as the most critical element controlling ETp across all seasons in Pakistan, followed by solar radiation and temperature. Daily ETp exhibited increasing trends in the north, west, and east, ranging from 0.05 to 0.4 mm/decade. This rise in ETp can be primarily attributed to increasing temperatures, while other parameters like wind speed and solar radiation remained relatively constant. These results suggest that continued global warming-driven ETp increases may pose significant challenges for Pakistan's water supply and agricultural irrigation systems.