Assessment of water use efficiency in arid ecosystems of the coastal land of Egypt using MODIS dataset

In drylands, the limited availability of reliable measurements makes it more difficult to understand how climatic and biogeochemical factors shape ecosystem processes across spatial gradients compared to mesic or humid regions. Water use efficiency (WUE) is a key physiological indicator for assessing interactions between carbon and water cycles in any ecosystem. Yet, in dryland ecosystems with sparse vegetation where evaporation represents a large fraction of total evapotranspiration (ET), the response of WUE to land use changes needs more investigation. To address this gap, the present study examines the spatial and temporal patterns of WUE in coastal dryland ecosystems of Egypt to better understand how land use practices affect water dynamics. Using an integrated approach that combines remote sensing products, WUE trends were assessed across representative sites. The results show high spatial variation in the WUE pattern over the 25-year period, with absolute values ranging from below 1.0 × 10^-3 g C mm^-1 in sparsely vegetated zones up to 2.9 × 10^-3 g C mm^-1 in reclaimed lands. The highest values of WUE are for the vegetated areas of croplands and reed vegetation, where the biomass reflects the growth of developed vegetation. The natural land covers are subjected to various changes due to human activities and expansion in the reclaimed agricultural areas where the urbanization activities increase ET and reduce WUE. These insights can contribute to a better understanding of dryland ecosystem functioning and can inform sustainable water and land management strategies in arid regions facing increasing water scarcity.