新疆参考作物蒸散发趋势转折与大尺度气候变率的关系

Relationships between reference crop evapotranspiration trend transitions and large-scale climate variability in Xinjiang of Western China

参考作物蒸散发(reference crop evapotranspiration,ET_(0))能够全面反映一个地区的蒸散发能力,在农业高效节水灌溉等领域得到了广泛应用。近年来大多数研究通常将ET_(0)与局地气象因子的变化进行敏感性分析,忽略了大尺度气候变率对ET_(0)的遥相关影响。该研究基于新疆地区84个气象站点的逐日气象资料和气候变率指数,采用多元线性回归和Cramer’s突变检验等方法,探究了厄尔尼诺南方涛动(El Nino-Southern Oscillation,ENSO)、印度洋偶极子(Indian Ocean Dipole,IOD)、太平洋年代际振荡(Pacific Decadal Oscillation,PDO)和北大西洋多年代际振荡(Atlantic Multidecadal Oscillation,AMO)等大尺度气候变率与新疆地区ET_(0)趋势转折的关系。结果表明:1960—2020年ET_(0)总体呈下降趋势,平均递减率为0.75 mm/a;1998年为ET_(0)的突变点,ET_(0)在1960—1997年呈明显减小趋势,平均递减率为2.50 mm/a,在1998—2020年转为明显上升趋势,平均递增速率为3.18 mm/a。PDO是影响ET_(0)趋势转折的主要气候变率,两者回归系数为−0.34,PDO在1998年由正位相转为负位相,导致风速由下降趋势转为上升趋势,同时AMO由负位相转为正位相增强了风速的趋势转折,进而导致了新疆地区ET_(0)在1998年的趋势转变(ENSO和IOD对风速的影响相对较弱)。海表面温度(sea surface temperature,SST)和ET_(0)的空间回归结果表现为PDO负位相,进一步验证了PDO对新疆地区ET_(0)趋势转折的影响。研究揭示了大尺度气候变率在年代际尺度ET_(0)变化特征和趋势转折中的主导作用,可为蒸散发理论研究提供新思路。

Reference crop evapotranspiration(ET_(0))can fully represent the evapotranspiration capacity in areas,such as efficient water-saving irrigation in agriculture.Most studies have typically conducted sensitivity analyses of changing ET_(0) in the local meteorological factors,without considering the remotely correlated effects of large-scale climate variability on ET_(0).Large-scale climate variability generated by the ocean is a significant driver of global and regional climate change,indicating the non-negligible impact on the evolution pattern of ET_(0).However,it is still lacking in the influence of large-scale climate variability on ET_(0),leading to the inaccurate attribution of ET_(0) changes.Therefore,this study aims to explore the relationships between the large-scale climate variability of El Niño Southern Oscillation(ENSO),Indian Ocean Dipole(IOD),Pacific Decadal Oscillation(PDO),and Atlantic Multidecadal Oscillation(AMO)with the ET_(0) variability characteristics in Xinjiang region.The daily meteorological data and climate variability indices were collected from 84 meteorological stations using multiple linear regression and Cramer's mutation test.The results indicate that the ET_(0) showed a decreasing trend from 1960 to 2020,with an average decreasing rate of 0.75 mm/a;the year 1998 was the mutation of the ET_(0),and the ET_(0) showed an obvious decreasing trend from 1960 to 1997,with an average decreasing rate of 2.50 mm/a,and then turned to an outstandingly increasing trend from 1998 to 2020,with an average increasing rate of 3.18 mm/a.The multivariate linear correlation results show that the ET_(0) was negatively correlated with the RH with a regression coefficients of−0.46,and positively correlated with the U,T,and Rn with regression coefficients of 0.95,0.36,and 0.20,where the changes of ET_(0) were mainly dominated by the changes of U.On the seasonal scale,the interannual variation trend of ET_(0) in the four seasons was more consistent with the annual cumulative ET_(0) variation trend,which decreased at the rate of 0.01,0.54,0.23,and 0.01 mm/a in spring,summer,autumn,and winter,respectively,whereas,the trend change in the spring,summer,and autumn seasons occurred in the mid-1990s,respectively.PDO was the main variable affecting the trend shift of ET_(0),where the regression coefficients between the two was-0.34.There was also a significant negative correlation of U with PDO and AMO,with regression coefficients of−0.31 and−0.34,respectively.The PDO was shifted from a positive to a negative phase in 1998,resulting in the wind speed shifting from a downward to an upward trend,which in turn led to the trend shift of ET_(0) in the Xinjiang region in 1998.The shift of AMO from a negative to a positive phase strengthened the trend change of wind speed,while the effects of ENSO and IOD on wind speed were relatively weak.The negative phase of PDO was achieved in the spatial regression of sea surface temperature(SST)with ET_(0),which further verified the influence of PDO on the trend shift of ET_(0) in the Xinjiang region of western China.