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

Abstract. Global-scale reservoir construction has significantly enhanced 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 non-aquatic terrestrial evaporation, overlooking the intricate evaporation dynamics within aquatic systems. In this study, we address 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 model 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 water depths and associated 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−1, with a notable upward trend at a rate of 0.117 × 106 m3 d−1 yr−1. Attribution analysis shows that while the combined effects of climate change marginally reduced evaporation rates in this study region, 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 that evaporation losses are comparable to surface water withdrawals in this region, future water management and hydraulic projects must consider such substantial losses. This study fills gaps by quantifying aquatic evaporation across the Loess Plateau and underscores the need for integrated strategies addressing climate change, reservoir expansion, and evaporation.