Increased surface water evaporation loss induced by reservoir development on the Loess Plateau

Abstract. Global-scale reservoir construction has significantly enhanced local water supply for local production and livelihoods, yet the evaporation losses from these surface water bodies remain poorly understood, particularly in the context of climate change. The majority of existing studies have predominantly focused on terrestrial evaporation, overlooking the intricate evaporation dynamics within these aquatic systems. This study addresses this gap by investigating water body evaporation in the Loess Plateau of China, a region characterized by extensive reservoir development over the past decades. By employing a modified Penman equation and utilizing long-term remote sensing water body data to calculate water depths while accounting for the thermal storage capacity of water bodies, we estimated water evaporation rates and total evaporation volumes for the period 2000–2018. Validation against pan evaporation observations demonstrates the efficacy of our improved approach in capturing the evaporation patterns of diverse water bodies in the Loess Plateau. Results reveal a subtle decreasing trend in evaporation rates across the region. However, the total evaporation volume amounts to a substantial 4.16×10⁶ m³/d, with a notable upward trend at a rate of 0.117×10⁶ m³/d/yr. Attribution analysis shows that while the combined effects of climate change marginally reduced evaporation rates, the expansion of water bodies has counteracted this trend, resulting in a significant increase in total evaporation losses. Particularly, the development of small- and medium-sized reservoirs and check dams is the primary driver of increased evaporation losses on the Loess Plateau. Given comparable evaporation losses to surface water withdrawals in this region, future water management and hydraulic projects must consider such substantial losses. This study fills gaps in evaporation dynamics and underscores the need for integrated strategies addressing climate change, reservoir expansion, and evaporation.