Influences of removing linear and nonlinear trends from climatic variables on temporal variations of annual reference crop evapotranspiration in Xinjiang, China.
Reference crop evapotranspiration (ETo) is a key parameter in field irrigation scheduling, drought assessment and climate change research. ETouses key prescribed (or fixed or reference) land surface parameters for crops. The linear and nonlinear trends in different climatic variables (CVs) affect ETochange. This research aims to reveal how EToresponds after the related CVs were linearly and nonlinearly detrended over 1961-2013 in Xinjiang, China. The ETo-related CVs included minimum (Tmin), average (Tave), and maximum air temperatures (Tmax), wind speed at 2m (U2), relative humidity (RH) and sunshine hour (n). ETowas calculated using the Penman-Monteith equation. A total of 29 EToscenarios, including the original scenario, 14 scenarios in Group I (ETowas recalculated after removing linear trends from single or more CVs) and 14 scenarios in Group II (ETowas recalculated after removing nonlinear trends from the CVs), were generated. The influence of U2was stronger than influences of the other CVs on ETofor both Groups I and II either in northern, southern or the entirety of Xinjiang. The weak influences of increased Tmin, Taveand Tmaxon increasing ETowere masked by the strong effects of decreased U2&n and increased RH on decreasing ETo. The effects of the trends in CVs, especially U2, on changing ETowere clearly shown. Without the general decreases of U2, ETowould have increased in the past 53years. Due to the non-monotone variations of the CVs and ETo, the results of nonlinearly detrending CVs on changing EToin Group II should be more plausible than the results of linearly detrending CVs in Group I. The decreasing EToled to a general relief in drought, which was indicated by the recalculated aridity index. Therefore, there would be a slightly lower risk of water utilization in Xinjiang, China.
College of Water Resources and Architecture Engineering, Northwest Agriculture and Forestry University, Yangling, Shaanxi 712100, China. Electronic address: liyikitty@126.com.
Yi
Y
Li
College of Water Resources and Architecture Engineering, Northwest Agriculture and Forestry University, Yangling, Shaanxi 712100, China.
Ning
N
Yao
Department of Soil and Physical Sciences, Faculty of Agriculture and Life Science, Lincoln University, Lincoln, Canterbury 7647, New Zealand.
Henry Wai
HW
Chau
Climatic scenario; Detrended climatic variable; Reference crop evapotranspiration; Temporal variation; Xinjiang