This Special Issue (SI) aims to investigate the relationships between hydrological and ecological processes and how these interactions can contribute to the optimization of water resources in arid and semi-arid areas. This SI collected 10 original contributions on sustainable land management and the optimization of water resources in fragile environments that are at elevated risk due to climate change. The topics mainly concern transpiration, evapotranspiration, groundwater recharge, deep percolation, and related issues. The collection of manuscripts presented in this SI represents a contribution of knowledge in ecohydrology.