Linking woody plants, climate, and evapotranspiration in a temperate savanna

Abstract

Evapotranspiration is the dominant pathway by which water returns from land surfaces and vegetation to the atmosphere in many semiarid and subhumid regions. In this study, we integrated satellite-based estimates of evapotranspiration with climate, runoff, and woody-vegetation data to evaluate how changes in precipitation, air temperature, and canopy cover jointly influence water loss in a temperate savanna that spans both semiarid and subhumid climates. Our validation at the subbasin scale showed that modeled evapotranspiration agreed moderately well with water-balance estimates (coefficient of determination ≈ 0.65, bias −7 mm per water year, and root mean square error 103 mm per water year). Across the region, annual evapotranspiration totals generally reached about 90 % of precipitation, indicating an ecosystem strongly driven by atmospheric water demand. In dry years, water loss occasionally exceeded rainfall, highlighting a heightened sensitivity to soil moisture shortages and extreme heat. Areas with high woody-canopy cover consistently exhibited higher evapotranspiration and lower net water surplus. Notably, where canopy cover exceeded 80 % in the driest portions of the study area, the soil water surplus turned negative over multiple years. These findings underscore the potential for expanding woody cover to limit groundwater recharge and reduce overall water availability, especially under warming and more variable precipitation regimes. Future work could explore fine-scale, long-term impacts of woody plant density and targeted management strategies that optimize trade-offs among vegetation growth, ecosystem health, and water resources.