基于相对湿润度指数的西南地区季节性干旱时空分布特征

西南地区是中国重要农业生产区,季节性干旱是该区域最主要的农业气象灾害,研究季节性干旱时空分布特征对西南地区防旱减灾具有重要意义。该文收集西南地区4个省(市)共97个代表气象站50a(1959年-2008年)的逐日降水量、气温、日照时数、相对湿度、风速、水汽压等气象资料,选用国家标准中相对湿润度指数(M)作为干旱指标,以年、季为时间尺度,研究西南地区干旱频率和强度的空间分布特征,并分析近50a干旱强度和发生范围的年际变化规律。结果表明:西南地区年尺度干旱频率呈西部高,东部低的带状分布,高发区位于川西高原、川西南山地、云南西北部和中北部的山地、高原及河谷地带,发生频率在3年2遇以上;年干旱强度以中旱以上为主。不同季节干旱频率差异大:冬旱发生频率最高,春旱次之,秋旱较低,夏旱最低;干旱强度方面,冬旱强度最大,春旱次之,秋旱较小,夏旱最小;总体而言,干旱发生频率高的地方干旱强度也大。从年际变化看,西南地区总体上略有变湿的趋势,年干旱强度明显减弱,其中春旱、秋旱有减轻趋势,夏旱和冬旱有所增强;但近10a,年干旱强度增大明显,夏旱、秋旱、冬旱也明显上升,这与西南地区近几年干旱频繁发生相吻合。

Temporal and spatial distribution of seasonal drought in Southwest of China based on relative moisture index

Southwest of China is an important agricultural area, and seasonal drought is the most common agro-meteorological disaster in this region. Therefore, the study of temporal and spatial distribution of seasonal drought in Southwest of China is important for drought resistance and disaster reduction. In this study, daily precipitation, temperature, sunshine hours, relative humidity, wind speed and vapor pressure of 97 meteorological stations in four provinces (city) in the recent 50 years (from 1959 to 2008) were collected and used to calculate the relative moisture index (M). The spatial distribution of drought frequency and intensity in Southwest of China was analyzed at annual and seasonal time scale, and the annual variation of drought intensity and distribution in the recent 50 years were addressed. The results showed that, drought frequency at annual time scale was higher in the west, and lower in the east, exhibiting pronounced zonation patterns in Southwest of China. The areas with high incidence of drought mainly located at the western Sichuan plateau, the mountainous area in Southwestern Sichuan, and the regions of mountains, plateau and river valley in the northwest and north center of Yunnan. In these areas, drought occurred over twice in every three years, and drought intensities were mainly moderate or severe. The variation of drought frequency was significant between seasons. Drought happened most frequently in winter, followed by spring, autumn and summer. Winter drought was the most severe among the four seasons, followed by spring drought, autumn drought and summer drought. In general, the areas with high drought frequency normally had high drought intensity. In the aspect of annual variation, Southwest of China was getting wetter in recent years. Annual drought intensity was smaller, and drought was less severe in spring and autumn, but more severe in summer and winter over the past 50 years. In the last 10 years, annual drought intensity was obviously higher, and drought was more severe in summer, autumn and winter. This was consistent with the fact of high drought occurrence in Southwest of China over the past few years.