Change and attribution of pan evaporation throughout the Qinghai-Tibet Plateau during 1979-2017 using China meteorological forcing dataset

Pan evaporation (E-pan) analysis in the Qinghai-Tibet Plateau (QTP) is important for improving the understanding of the climatic and environmental changes in the QTP and China. However, uneven station coverage, sparse and inconsistent observations hamper the in-depth understanding of the spatiotemporal E-pan patterns throughout the QTP over long time periods. Based on the PenPan model driven by the monthly gridded China meteorological forcing dataset, this study attempted to estimate monthly and annual grid pan evaporation (E-PenPan) for the pan with a depth of 10 cm and a diameter of 20 cm at 0.1 degrees resolution throughout the QTP and its surrounding areas during 1979-2017, then the spatiotemporal variations in E-PenPan as well as the potential causative climatic variables were thoroughly examined. Results showed that the spatiotemporal patterns of E-PenPan were in reasonably good agreement with the observations. The high values of mean annual E-PenPan tended to distribute in the areas with water limitation or strong solar radiation like the southwest QTP. The wide decreases in annual E-PenPan have reversed in the study area in around 1993, with some exceptions such as the continuous increase in the southwest QTP and monotonous decrease in the areas to the west and east of the Qaidam Basin. Comparatively, the trends in annual E-PenPan in the QTP were less than the surrounding areas in the different periods, and overall accelerating annual E-PenPan appeared in the both areas after 1993. With the Budyko curve, it was expected that drought severity would increase in the south of the surrounding areas in future, but the warming and wetting in the other areas would be kept. The wind speed (WS) was the primary contributor to decreasing annual E-PenPan in the study area before 1993. Nevertheless, the most dominant factor for increasing E-PenPan was vapour pressure deficit in the QTP and WS in the surrounding areas during 1994-2017.

Automated summary

Pan evaporation analysis in the Qinghai-Tibet Plateau (QTP) using the PenPan model showed agreement with observations, indicating high evaporation in areas with water limitation or strong solar radiation. A widespread decrease in evaporation around 1993 was observed, with exceptions like the continuous increase in the southwest QTP. After 1993, annual evaporation trends accelerated in both the QTP and surrounding areas, with different factors influencing evaporation before and after 1993.