巴丹吉林沙漠周边地区降水量的时空变化特征

Spatial and Temporal Variation of Precipitation over Areas Surrounding the Badan Jaran Desert

分析了巴丹吉林沙漠周边17个常规气象测站1951—2005年的逐月降水量及沙尘暴频次和东亚夏季风指数。(1)沙漠周边地区降水量的空间分布明显受地形影响:紧靠沙漠的区域地势低、干旱,各季降水量都小;沙漠外围较远处(特别是受祁连山影响的西南边)地势高、湿润,各季降水量都大;地形增高会使降水量增多1个量级以上,但对其季节配额无明显影响。夏季降水量配额最大,平均高达61.6%。(2)依据各站降水量年际变化间的相关系数及测站间的地域关系和地貌相似程度,可将该区域划为4个分区:一为地势较低、紧挨沙漠、极为干旱的沙漠西北缘区,二为气候较湿、受祁连山影响的沙漠西南缘区(或称祁连山影响区),三为位于巴丹吉林沙漠和腾格里沙漠之间的民勤区,四为远离沙漠、但与其周边地区地貌相似的沙漠东侧区。(3)1951—2005年的各个年代,4个分区各季降水量由大到小的顺序均为:祁连山影响区、沙漠东侧区、民勤区和沙漠西北缘区,与其平均海拔由高到低的顺序一致;就各季降水量及其配额的年代际演变位相而言,祁连山影响区可以代表整个区域。(4)1971—2005年各分区年降水量呈增大趋势,春季降水量增加尤为显著(增幅约为0.41mm·a-1),夏季降水量有减小趋势;随海拔增高,春季及年降水量增幅加大,夏季降水量减幅减小;祁连山影响区对全区年降水量增大的贡献最大。(5)各季及年降水量与东亚夏季风的强弱间均呈复相关;其中冬、夏季及年降水量与夏季风间的负相关随海拔升高而加大,说明夏季风对沙漠以南高海拔处的降水影响更为显著。(6)各季沙尘暴与降水量间以负相关为主,各分区冬、春季降水量偏多时,其冬、春季及夏季沙尘暴的发生频次一般偏少。

Based upon analyses on the monthly precipitation,sandstorm frequency and East-Asian Summer Monsoon Index series during 1951-2005 from17 meteorological stations surrounding the Badan Jaran Desert,the following facts have been disclosed.(1)The spatial pattern of precipitation over the study area is apparently affected by the topography,resulting in the drier climate over the lower-altitude regions,lying more closely to the desert,with less precipitation in each season,and a wetter climate over the higher-altitude regions farther to the desert,especially over the areas southwest to the desert affected by the Qilian Mountain,with a larger seasonal precipitation.The precipitation can be raised by one or more orders due to elevation in altitude,but with little influence on its seasonality.The summer precipitation contribution to the annual total reaches the maximum by about 61.6% on average.(2)According to correlation between one station and another in the inter-annual precipitation variation,the regional relation and the similarity in landforms,the study area can be divided into four sub-regions,including(a)the northwestern boundary region(NWD),closest to the desert,with a lower altitude and extremely dry climate,(b)the southwestern nearby region,with a more satisfying soil moisture due to more direct influence of the Qilian Mountain(QM),(c)the Minqin region(MQ),located near and between Badan Jaran Desert and Tengger Desert,and(d)the region east to the desert(ED),away from the desert,but with very similar landforms with other regions.(3)During each decade,each seasonal precipitation varied from one sub-region to another,with the sequence always being QM,ED,MQ and NWD from the large to small,in good agreement with their average altitudes.QM agreed very well with the whole study area in the inter-decadal variation phases of each seasonal precipitation and its contribution to the annual total.(4)During 1971-2005,the annual precipitation over each sub-region had generally increased,especially owing to the spring precipitation with its rise rate having reached+0.41 mm·a-1,even with the summer precipitation having a little dropped.Besides,with the altitude getting higher,the spring and annual precipitations had risen by a larger rate,but the summer precipitation seemed to have reduced more gently;and QM had the greatest contribution to the whole study area in the rise rate of the annual total precipitation.(5)Each seasonal precipitation over the study area had increased with the East-Asian summer monsoon weakening.Besides,the elevated terrain seems to make the correlation coefficient between the East-Asian Summer Monsoon Index and the winter,summer or annual precipitation more negative,with the absolute coefficient getting larger,inferring that the East-Asian summer monsoon will more significantly affect higher-altitude areas such as the sub-region of QM.(6)Each seasonal precipitation mostly has a negative correlation to the sandstorm frequency,especially in that the increased winter and spring precipitations always corresponded very well with the dropped dust storm frequencies in the same,or the next season over each sub-region.