近60年来中国北方半干旱区界线与范围时空变化特征研究
Study on Spatial and Temporal Variation of the Boundary and Area of the Semi-arid Region in Northern China over the past 60 Years

中国北方半干旱区是湿润区与干旱区的过渡区,与我国农牧交错带以及受夏季风北边缘带摆动影响的夏季风影响过渡区大部分地区分布大体一致。该区域水资源缺乏,降水年际变率较大,是典型的生态环境脆弱带及生态过渡区,对气候变化极为敏感。因此,在全球变暖背景下开展对中国北方半干旱区界线与范围变化研究、夏季降水时空变化特征及成因研究有助于更好的了解半干旱区气候变化规律,具有重要的科学意义。本文利用1960-2016年气象站点资料、环流特征指数资料、NCEP/NCAR再分析资料以及其他基础地理信息资料,分析了中国北方半干旱区范围变化规律及其盛夏(7、8月)降水量时空变化特征,并探讨了典型降水量时空分布型与大气环流及水汽输送的关系。主要结论如下:(1)1960-2016年中国北方干旱界线和半干旱界线的多年加权平均位置分别为(98°59′46″E,37°10′5″N)和(108°26′31″E,38°57′25″N)。57年来干旱界线整体在经向和纬向分别有向西和向北移动的趋势;而半干旱界线整体在经向和纬向上分别存在向西和向南移动的趋势。(2)干旱界线和半干旱界线在各区域变化情况较为复杂,其异常年份也各有不同,在河套平原地区干旱界线变化幅度相对较小,干旱界线河西走廊内陆河地区在20世纪90年代有变湿的趋势,2000-2009年以来变干趋势明显。半干旱界线在黄河流域西部地区有变干的趋势,在黄河流域中部、东部地区以及海河流域地区最明显的特征是20世纪90年代是该区域干旱化最明显的时段,。而半干旱界线在辽河流域地区变化最为激烈,20世纪80年代湿润现象明显,90年代有明显变干趋势。值得注意的是,干旱界线和半干旱界线各区域在最近的十几年干旱化现象都有所缓和,有着逐渐变湿的迹象。(3)干旱、半干旱界线整体在经向和纬向移动存在不同的变化周期,其中干旱界线整体在经向和纬向移动上分别呈现出8年和11年的主周期,半干旱界线整体在经向和纬向移动上分别存在4年和12年的主周期。(4)1960-2016年中国北方半干旱区面积变化十分激烈,是干湿变化的敏感区,57年来我国半干旱区面积有微小的减小趋势,呈现出阶段性特征:1960-1969年半干旱区面积呈增加趋势,1970-1989年呈减少趋势,1990-1999年呈明显增加趋势,2000年以后又呈减少趋势,其中2000-2009年是近57年来半干旱区面积最大也就是干旱化最严重的时段。(5)1960-2016年中国北方半干旱区7月和8月降水量主要存在“区域一致型”和“区内反向型”两种主导时空变化模态。“区域一致型”表示半干旱区整体在7月和8月降水量呈现一致偏多或一致偏少的同位相降水分布特征,该模态下近57年来7、8月降水量均呈减少趋势,但8月减少趋势更明显;“区内反向型”表示中国北方半干旱区东部与西部降水量分布型呈现出相反的变化趋势,该模态下7、8月降水量年际变率较小但年代际变化明显。(6)“区域一致型”模态下,中国北方半干旱区7、8月降水量变化的大气环流配置存在不同。欧亚遥相关以及中纬度西风气流是影响7月降水量变化的重要因素;而西太平洋异常高压是影响半干旱区8月降水量变化的主要原因。在“区内反向型”模态下,当在东亚沿岸形成一个南高北低的气压高度场配置时,北方半干旱区在反气旋性环流的影响下,易形成北方半干旱区西部降水量偏多而东部降水量偏少的格局。

The semiarid region of Northern China is a transitional zone between humid and arid regions,which distribution is roughly the same as that of the agriculture-animal husbandry ecotone and the transition zone affected by the oscillation of the northern margin of the summer monsoon.Due to the shortage of water resources and the large interannual variability of precipitation in this region,it is a typical eco-environment fragile zone and ecological transition zone,and it is very sensitive to climate change.Therefore,it is of great scientific significance to study the spatial and temporal variation characteristics of summer precipitation and its causes in the semi-arid region of northern China under the background of global warming,which is helpful to better understand the climate change law in the semiarid region.Based on the meteorological station data,circulation characteristic index data,NCEP/NCAR reanalysis data and other basic geographic information data from 1960 to 2016,this paper analyzed the variation law of the semi-arid area in northern China and the spatial-temporal variation of precipitation in midsummer(July and August),and the relationships between the typical spatial-temporal precipitation pattern and atmospheric circulation/water vapor transport has also been discussed.The main conclusions were as follows:(1)From 1960 to 2016,the multi-year weighted average positions of the arid and s emi-arid boundary lines in northern China were(98°59′46′′E,37°10′5′′N)and(108°26′31″E,38°57′25″N).During the past 57 years,the arid boundary has a tendency to move westward in the longitude,and a tendency to move northward in the latitude;The semi-arid boundary has a tendency to move westward in the longitude,and a tendency to move southward in the latitude.(2)The changes of arid and semi-arid boundaries in different regions were complex,and the anomalous years were also different.The variation range of drought boundary was relatively small in Hetao plain area.In the inland river area of Hexi Corridor there was a trend of becoming wet in the 1990 s and the trend of drying has been obvious from 2000 to 2009.The semi-arid boundary tends to dry in the western part of the Yellow River Basin,and the most obvious characteristic in the central and eastern parts of the Yellow River Basin,the Haihe River Basin was that the 1990 s is the most obvious period of drought in theses areas.The semi-arid boundary changes fiercely in Liaohe River basin,and the phenomenon of wetting was obvious in the 1980 s.and it tends to dry obviously from 1990 s.However,it is worth noting that the arid and semi-arid regions in the last ten years have alleviated their phenomena of drought,there were signs of gradually becoming wet.(3)The arid and semi-arid boundaries generally have different cycles of change in the meridional and latitudinal movements,the primary periods of the arid boundary in the meridional and zonal shift were 8a and 12 a respectively in general,while that of the semiarid boundary in the meridional and zonal shift were 4a and 12 a.(4)The area change of semi-arid area in northern China from 1960 to 2016 was very intense,and it was a sensitive area for dry-wet change.In the past 57 years,the area change of semiarid area in China has a slight decreasing trend,and its area change shows a stage characteristic: the area of semi-arid areas showed an increasing trend from 1960 to 1969,a decreasing trend from1970 to1989,an obvious increasing trend from 1990 to 1999,and a decreasing trend after 2000.Among them,the period from 2000 to 2009 was the period of the largest semi-arid area and the most severe drought in the past 57 years.(5)There were two dominant spatial modes of July and August precipitation in semiarid region of Northern China from 1960 to 2016,which can be summarized as the "regional inphase type" and the "subregional out-of-phase type".The "regional in-phase type" showed that the precipitation in July and August of semi-arid area is uniformly large or less in the same phase.In this mode,the precipitation in July and August has shown a decreasing trend in recent 57 years,but the decreasing trend in August is more obvious.The "subregional outof-phase type" indicates that the distribution of precipitation in the east and the west of the semi-arid area of Northern China has shown an opposite trend,and the interannual variability of precipitation in July and August of the model is relatively small,but the interdecadal variability is obvious.(6)Under the "regional in-phase type" mode,there were differences in the atmospheric circulation configuration of precipitation changes in July and August in the semi-arid regions of northern China.The Eurasian teleconnection and the mid-latitudes westerlies were closely correlated with the precipitation variations in July,while the WPSH was the main factor affecting the interannual variations of precipitation in the semiarid region August.Under the "subregional out-of-phase type" mode,when a south-high-north-low barometric height field was formed along the coast of East Asia,the anticyclonic circulation controls the semiarid northern China,it was easy to form a distribution pattern with more precipitation in the western part of the northern semi-arid region and relatively lower precipitation in the eastern part.

半干旱区; 界线; 降水; 盛夏; 水汽输送; 大气环流;

Semiarid region; Boundary; Precipitation; Midsummer; Water vapor transport; Atmospheric circulation;

王宁练;

P426.616

181815843K