Decreasing relative humidity dominates a reversal of decreasing pan evaporation in mainland China after 1989.

• Distinct seasonal and geographical variations of E pan trends are observed in China. • Declining wind speed plays a dominant role in the decreasing of E pan before 1989. • Decreasing relative humidity predominates the reversal of E pan trend after 1989. • Flash drought would likely occur over the subtropical monsoon zone. Pan evaporation (E pan) reflects the evaporation potential of surface water and is a key indicator of atmospheric evaporative demand. Previous studies have found a substantial decrease in E pan across China, dominated by declining wind speed and solar radiation before the late 2000 s. However, how E pan responds to the recovery of wind speed and solar radiation since the late 2000 s remains unclear. Here, we investigate the spatial and temporal patterns of E pan and analyze its controlling factors, based on the daily meteorological observations during 1965–2018 at 2,018 stations over China. We find that the annual E pan in the northwest and south of China is higher than that in the northeast and central parts of China. The national mean E pan decreases significantly during 1965–1989 at a rate of −6.57 mm yr−2, then reverses at a rate of 4.58 mm yr−2. Distinct seasonal discrepancies and geographical heterogeneities in E pan trends are observed. Declining wind speed mainly contributes to the decrease in E pan before 1989, while relative humidity is shown as the dominant factor that drives the growth of E pan after the turning point. The recovery of wind speed still has significant impact on E pan variation in parts of China, while E pan is only mainly affected by solar radiation in parts of central China in autumn. Our findings highlight the importance of understanding E pan variations and driving factors, and call for precautions and adaptation actions to combat and prevent flash droughts over China, especially in the south of China. [ABSTRACT FROM AUTHOR]