Variation of reference evapotranspiration and its contributing climatic factors in the Poyang Lake catchment, China

Abstract

By using linear regression (parametric), Mann-Kendall (nonparametric) and attribution analysis methods, this study systematically analysed the changing properties of reference evapotranspiration (ETr) calculated using the Penman-Monteith method over the Poyang Lake catchment during 1960-2008 and investigated the contribution of major climatic variables to ETr changes and their temporal evolution. Generally, a significant decreasing trend of annual ETr is found in the catchment. The decrease of annual ETr in the Poyang Lake basin is mostly affected by the decline of summer ETr. Over the study period, climatic variables, i.e. sunshine duration (SD), relative humidity (RH), wind speed (WS) and vapour pressure all showed decreasing trends, whereas mean daily temperature (DT) increased significantly. Multivariate regression analysis indicated that SD is the most sensitive climatic variable to the variability of ETr on annual basis, followed by RH, WS and DT, whereas the effect of vapour pressure is obscure. Although recent warming trend and decrease of relative humidity over the catchment could have increased ETr, the combined effect of shortened SD and reduced WS negated the effect and caused significant decrease of ETr. Our investigation reveals that the relative contributions of climatic variables to ETr are temporally unstable and vary considerably with large fluctuation. In consideration of the changes of climatic variables over time, further analysis indicated that changes of mean annual ETr in 1970-2008 were primarily affected by SD followed by WS, RH and DT with reference to 1960s. However, WS became the predominant factor during the period 2000-2008 compared with reference period 1960s, and followed by SD.