Analysis of Evapotranspiration in Arid and Semi-Arid Soils in Libya and Its Impact on Agricultural Water Resource Management

Abstract

Evapotranspiration is a central component of the hydrological cycle and a key indicator of atmospheric water demand, crop water requirements, and irrigation scheduling. Its importance is particularly high in Libya, where arid and semi-arid conditions dominate, precipitation is limited and irregular, solar radiation and temperature are high, and irrigated agriculture depends heavily on groundwater. This integrative review analyzes the concepts and controls of evapotranspiration in Libya, evaluates its spatial and temporal variability, compares the main estimation tools, and discusses implications for irrigation management under climate change.

The study synthesizes evidence from FAO-56, NASA POWER-based national mapping, GIS and Omu-ET applications, an Ajdabiya case study for 1991–2021, FAO WaPOR products, and climate-scenario analysis for the Sofuljeen region. Annual reference evapotranspiration ranges from approximately 1,680 mm yr−1 in northern Libya to 3,529 mm yr−1 in the far south. In Ajdabiya, annual potential evapotranspiration reached 2,390.2 mm, with a monthly maximum of 284.9 mm in June and a minimum of 96.6 mm in January. Future projections for Sofuljeen indicate that mean ETo may increase from 6.78 mm day−1 at the baseline to 7.68 mm day−1 under SSP2-4.5 and 8.37 mm day−1 under SSP5-8.5 by 2100, corresponding to increases of 13.27% and 23.45%, respectively.

The paper concludes that operational evapotranspiration assessment in Libya should integrate ground observations, satellite products, FAO Penman–Monteith calculations, CROPWAT, Omu-ET, WaPOR, and locally calibrated crop coefficients. Priority actions include expanding agrometeorological networks, updating national ETo maps, applying precision irrigation, reducing soil evaporation, improving irrigation scheduling, and adopting drought- and heat-tolerant crop varieties.