乌拉特草原2018年上半年干旱监测与成因浅析

Monitoring and Cause Analysis of Drought on Urat Grassland in the First Half of 2018

干旱是自然界一种复杂的异常现象,基于气象因素对干旱分析研究具有重要意义。选取1971-2018年降水量和气温资料、2018年3-6月气候概况,结合欧亚大陆大气环流演变,分析研究气象因素对干旱的影响;采用土壤测墒、无人机航拍等方式,在乌拉特草原选取了具有典型代表的22个区域,对土壤深度10、20、30、40 cm进行土壤相对湿度的测定;利用高分卫星,对乌拉特草原6月中旬植被长势情况进行遥感监测,并与去年同期以及近3年同期植被长势进行比较分析,研究干旱等级空间分布及旱灾发生程度。结果表明:(1)2018年春季,东亚大槽偏弱、亚洲纬向环流异常偏强,位于阴山北麓的乌拉特草原3-5月份500 hPa在高压脊控制下,降水异常偏少,气温异常偏高、日照时间长,风沙天气多,地表水分蒸发量大,加剧地表土层水分散失,导致牧草迟迟不能返青。(2)2018年春夏之交,副热带高压依然偏南且呈纬向型分布,阻碍了偏南、东南、西南水汽向北输送,致使乌拉特草原直到6月中旬没有出现透雨,土壤水分没有得到有效补给和保持,土壤保墒差,干土层厚,导致乌拉特草原干旱的发生发展,出现严重旱灾。

Drought is a complex abnormal phenomena in nature,which is of great significance to drought analysis and research based on meteorological factors.Based on the precipitation and temperature data selected from 1971 to 2018 and the climate survey from March to June in 2018,the effect of meteorological factors on drought was analysed combined with the evolution of atmospheric circulation in Eurasia.By methods of soil moisture measurement and UAV aerial photography,22 typical regions were selected in Urat grassland,where the soil relative humidity were measured at the depth of 10,20,30 and 40 cm.In order to study the spatial distribution of drought grade and the occurrence degree of drought,the vegetation growth of Urat grassland in mid June was monitored by remote sensing with high resolution satellite,and compared with that of the corresponding period of last year and of the recent three year.The results show that:(1)In the spring of 2018,the East Asian Trough was weak and the Asian zonal circulation was abnormally strong.From March to May,Urat grassland,at the northern foot of Yinshan Mountain,whose 500 hPa was under the control of high pressure ridge,has abnormally less precipitation,abnormally high temperature,long sunshine time,windy sand weather,large surface water evaporation,and severe surface soil moisture loss,leading to the delay of grass returning to green.(2)At the turn of spring and summer in 2018,the subtropical high was still southward and distributed in a latitudinal pattern,which hindered the water vapor of South,Southeast and Southwest to transport to the North.As a result,there was no soaking rain in Urat grassland until the mid June.Soil moisture was not effectively replenished and maintained;soil moisture conservation ability was poor,and dry soil layer was thick,which led to the occurrence and development of drought in Urat grassland,resulting in severe drought.