基于SPEI指数的华北冬麦区干旱时空分布特征分析

气候变化的背景下,华北地区干旱化趋势不断加剧。利用华北冬麦区45个气象站1961—2010逐月温度与降水数据,选取标准化降水蒸散指数SPEI(Standardized Precipitation Evapotranspiration Index)作为区域干旱指数进行华北冬麦区近50年干旱时空特征分析。研究表明:(1)近50年来华北地区平均温度明显上升,研究区整体呈现干旱化加剧趋势。华北地区平均SPEI指数对于典型干旱年份的表征准确,与历史资料相符合。(2)华北不同区域之间增温率不同,导致干旱化趋势存在差异。通过对典型站点的分析,发现增温率越大的区域干旱化趋势越严重。(3)不同等级干旱发生的站次比能够较好地反映不同年型干旱的发生特点。对SPEI指数矩阵的EOF分析结果显示出华北地区典型的干旱时空分布特征,第一模态呈现全区旱涝变化一致型的分布形式,高值区包括山东西部、河南北部、河北南部地区,表明这些地区对干旱的反应最为敏感。时间系数序列未显示出明显的变化趋势;第二模态呈现南北相反的分布型,河北及山东的大部分地区空间系数均为正值,而河南大部分地区为负值。时间系数序列整体呈下降趋势,表明研究区北部干旱化趋势加剧,南部干旱化有所缓解;第三模态呈现东西相反的分布形式,这种分布特征的变化趋势不明显。

Analysis of the spatial and temporal characteristics of drought in the North China plain based on standardized precipitation evapotranspiration index

The North China Plain is one of the most severely drought affected areas in China, with global warming intensifying aridification in this alluvial plain. Drought may be attributed to multiple factors, among which precipitation and temperature are the most important. It is widely recognized that the Standardized Precipitation Evapotranspiration Index (SPEI) is advantageous for both spatial-and temporal-scale characteristic assessments; thus, it is a better index for evaluating the evolution of drought in the North China Plain due to climate change than other drought indices, such as the Palmer Drought Severity Index (PDSI), Standardized Precipitation Index (SPI), and Z index. In this study, monthly mean precipitation and temperature data from 45 meteorological stations in the North China Plain were used to calculate the SPEI index and investigate the spatial and temporal characteristics of drought in the North China Plain from 1961 to 2010. The analysis produced the following results. First, during the last 5 decades, a significant increase in temperature and a slight decrease in precipitation occurred in the North China Plain, resulting in a general aridification trend throughout the region. The drought time series in the North China Plain may be characterized from the analysis based on the SPEI index, and was consistent with existing publications.Second, a noticeable warming tendency with a mean warming rate that exceeds the national average level occurred in North China. Diverse aridification tendencies characterized the North China Plain because of variable warming rates. An analysis of typical stations showed that the more noticeable the warming, the deeper the intensity of aridification. Third, the drought feature may be well formulated using the ratio of weather stations with different drought intensities. Empirical orthogonal function (EOF) analysis was conducted based on a 12-month-scale SPEI index of the 45 meteorological stations from 1962 to 2010, and the top three eigenvectors were selected to explore the spatial and temporal distribution of drought occurrence in the North China Plain according to their spatial and temporal coefficients. The first mode shows consistency in the entire region, and it is the most important spatial distribution indicator of drought in the North China Plain. High values emerged in the middle of the region, including the western part of Shandong and the northern and southern parts of Henan, demonstrating that these areas are more sensitive to drought. There was no clear tendency in the time coefficient of the first mode. The second mode shows contrasts between the southern and northern parts of the North China Plain, which are consistent with the distribution of warming rate. The time coefficients show that drought in the northern part of the plain has been aggravated, whereas drought in the southern part has been alleviated, which may be due to differences in the warming rates throughout the research region. Warming rates in the northern part of the North China Plain are higher, so the aridification tendency is far more severe than that in the southern part of the North China Plain. The third mode contrasts the tendency between the eastern and western parts of the North China Plain, showing no significant tendency in the time coefficient.