Climatic factors influencing changing pan evaporation across China from 1961 to 2001

► E pan over China showed a −3.1 mm/a 2 (−1.8% per decade) change from 1961 to 2001. ► We proposed the PenPan-20 model for evaporation from the Chinese micro-pan. ► We quantified the attribution of changing E pan based on the PenPan-20 model. ► Main causes of changing E pan were declining wind speed in most parts of China. ► Main causes of changing E pan were reducing solar radiation in southwest China. Pan evaporation ( E pan) is an indicator of atmospheric evaporative demand, and downward trends have been reported in many regions over the past several decades. It is important to understand why E pan has changed and determine what the main causes are. This study analyzed daily climate data from 54 meteorological stations across China measured from 1961 to 2001. Climatic factors included E pan measured with the standard Chinese 20 cm diameter pan, global solar radiation ( R s), air temperature ( T a), relative humidity (RH), and wind speed ( U). We modified the PenPan model for pan evaporation from the Class A pan, to estimate Chinese micro-pan evaporation E pan and quantify the contributions of climatic factors ( R s, net longwave radiation R nl, T a, U, and vapor pressure deficit D) to E pan using partial derivatives. For China as a whole, the arithmetic average of E pan from these 54 stations showed a significant decline of −3.1 mm a −2 (−1.8% per decade). The observed change in R s was −4.5 W m −2 decade −1 (−2.6% per decade); the mean T a increased by 0.27 °C per decade; U decreased by −0.10 m s −1 decade −1 (−6% per decade); and D increased by 0.012 kPa per decade (2% per decade). For China as a whole, the dominant factors influencing changing E pan were R s and U; the causes of E pan were very varied: regionally, the main causes for change were in most parts of China, it was the change in U, in southwest China it was the change in R s.