毛乌素沙地参考作物蒸散量变化特征与成因分析

Spatio-temporal distribution characteristics of reference crop evapotranspiration in the Mu Us desert

根据毛乌素沙地典型站点近60年(1955—2014年)逐日气象数据,利用Penman-Monteith公式计算毛乌素沙地各气象站点参考作物蒸散量(reference crop evapotranspiration,ET_0)及研究区域内整体ET_0。Mann-Kendall趋势检验法和Arc GIS的协同克里格插值法用于分析ET_0时空变化特征,同时,利用敏感性分析方法对ET_0的变化成因进行分析。结果表明:(1)近60年毛乌素沙地ET_0多年平均值为1048.81mm,年际变化呈现缓慢上升趋势。年内变化夏季最高,冬季最低。区域内ET_0空间分布整体呈现自西向东递减趋势。(2)ET_0年变化对风速的敏感程度最大,日照时数和气温次之,相对湿度最小。春、秋两季ET_0变化对日照时数最为敏感;夏、冬两季ET_0变化对相对湿度最为敏感。空间分布上,毛乌素沙地东南部地区为气温敏感系数高值区,西北部地区为相对湿度和日照时数敏感系数高值区,南部为风速敏感系数高值区。(3)通过计算气象因子对ET_0变化的贡献量得出,气温是影响毛乌素沙地ET_0年变化的主导因子。夏季ET_0变化的主导因子是风速;春、秋、冬三季主导因子是气温。空间分布上,毛乌素沙地西南部地区ET_0变化的主导因子为风速,东部地区主导因子为气温。

Reference crop evapotranspiration （ETo ） is often used to evaluate the capacity of atmospheric evaporation in the terrestrial hydrology cycle. Simulations with climate models and atmospheric general circulation models have shown that changes in meteorological factors affect ETo. The Mu Us desert is located in the arid and semi-arid region of northwest China, which experiences severe water shortages. To better understand the ETo spatio-temporal distribution characteristics in the Mu Us desert, the Penman-Monteith equation recommended by the FAO in 1998 was used to calculate ETo at typical meteorological stations, as well as the overall Mu Us desert ETo, based on 60 years of daily meteorological data （ 1955- 2014）. A Mann-Kendall trend test was used to determine the ETo spatio-temporal distribution characteristics. Furthermore, a Co-Kriging interpolation was used to draw ETo maps, which presented a clear spatial distribution of ET0 in the Mu Us desert. In addition, a sensitivity analysis was used to analyze the causes of ETo change. Annual average ETo was 1048.81 mm for the past 60 years. There was a slight increasing trend in the inter-annual variation. The trend of annual ETo showed a single peak curve, with the highest value in June （5.77 mm/d）, and the lowest value was in January （0.54 mm/d）. The average summer ETo was 5.23 mm/d, and average winter ETo was 0.70 mm/d. Spatially, ETo decreased gradually from west to east, ranging from 1058.53 to 1103.85 mm in the west, and from 1014.05 to 1043.44 mm in the east. The sensitivity analysis indicated that ETo was positively related to wind speed, air temperature, and solar duration, but negatively related to relative humidity. Furthermore, ETo was most sensitive to changes in wind speed, then solar duration, air temperature, and relative humidity, respectively. Seasonally, ETo was more sensitive to solar duration in spring and autumn, but more sensitive to relative humidity in summer and winter. Wind speed was the dominant controlling factor on ETo in summer, but in spring, autumn and winter, it was air temperature. Overall, air temperature was the dominant controlling factor on annual ETo in Mu Us desert. Spatially, ETo was more sensitive to temperature in the southeast region of the Mu Us desert, to relative humidity and solar duration in the northwest region, and to wind speed in the south. The spatial distribution of ETo＇s dominant controlling factor was different from its sensitive coefficient. Wind speed was the dominant controlling factor on ET0 distribution in southwest of Mu Us desert, and air temperature in east. The meteorological factors here were considered dominant in controlling the spatio-temporal variations of the Mu Us desert ETo. However, advection variation caused by wind speed, temperature and relative humidity, inter-annual variation of the atmospheric circulation, surface uniformity, and human activities, also influence ETo in China＇ s arid and semi-arid region. Therefore, the results presented here only reflect the meteorological variables that were included in the analyses. More comprehensive hydrological studies are therefore required in the future.