East-west differentiation on spatiotemporal variations of pan evaporation along the lower Jinsha River

Abstract

[Objective] The lower reaches of the Jinsha River, situated in the transitional zone of Southwest China′s natural geographical boundary, serve as a significant hydropower base. Understanding the spatiotemporal variations in pan evaporation in this region is crucial. It lays the groundwork for analyzing the patterns of hydrological and climatic changes within the area. Furthermore, it provides essential support for the estimation and analysis of evaporative losses in cascade reservoirs. [Methods] Using observed and estimated data of D20 pan from 19 stations along the lower reaches of the Jinsha River from 1980 to 2022, a comparative analysis of the spatiotemporal differences in pan evaporation between the western and eastern parts of the study area is conducted and the driving factors are explored. [Results] The results indicate that the 13 stations located west of 103.5°E have higher pan evaporation(annual average of 1 997.4 mm) compared to the 6 stations in the eastern part(annual average of 1 101.4 mm). At the western stations, pan evaporation in spring(March-May) exceeds that in summer(June-August), with the peak occurring mainly in May. In contrast, at the eastern stations, summer pan evaporation is higher than in spring, with peaks occurring in July or August and a noticeable trough in June. The average pan evaporation at the western stations shows a non-monotonic change with 2000 being the turning point(first decreasing and then increasing), while the eastern stations exhibit a weak increasing trend in both periods. [Conclusion] The spatiotemporal variations of pan evaporation in the lower reaches of the Jinsha River shows a significant east-west differentiation, with 103.5°E as the boundary, impacted by of the Indian Monsoon and the East Asian Monsoon. In the context of evaporation studies in southwestern China, it is essential to account for the east-west disparity in the spatiotemporal patterns of pan evaporation and to explore the underlying driving mechanisms.

Keywords

pan evaporation / Jinsha River / general circle / spatiotemporal variation / climate change / water resources / hydrological cycle / monsoon