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ABSTRACT:Observed pan evaporation data from 588 stations covering the entire territory of China are analysed using the modified Mann-Kendall trend test method. Fuzzy C-Means clustering is conducted for regionalization. Sensitivity analysis is performed to identify the principal influencing factors. Results indicate that: (1) the entire country can be categorized into three parts, i.e. A: southern, central and southwestern China; B: northwestern China and C: strip zone extending from northeastern to southwestern China; (2) significant decreasing pan evaporation can be identified in southern, central, southwestern, eastern and northwestern China. Stations with significant increasing pan evaporation seem to be scattered sporadically across China. Besides, the strip zone extending in the NE-SW direction is dominated by significant and also nonsignificant increasing trends of pan evaporation and (3) sensitivity analysis indicates that relative humidity is the principal influencing factor for pan evaporation, especially in northwestern, northern and northeastern China. Generally, in northwestern, northern and northeastern China, relative humidity has an adverse relation with pan evaporation, implying pan evaporation paradox and also intensifying hydrological cycle in these regions. In southeastern China, particularly the middle and lower Yangtze River basin and the Pearl River basin, relations between pan evaporation and relative humidity are relatively complex, showing that other factors in addition to relative humidity can have impacts on pan evaporation changes, such as cloud coverage, temperature and aerosol concentration. Local features of aerodynamic and radiative drivers of the hydrological cycle and their regional responses to climate changes, and also different features of ground surface may play considerable roles in pan evaporation changes.

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