基于干旱指数的宁夏干旱时空变化特征及其Morlet小波分析

Temporal and spatial variations of the drought in Ningxia based on aridity index and Morlet wavelet analysis

基于宁夏9个气象站点1961—2012年逐日气温、降水、风速、日照时数和相对湿度数据,应用Penman-Monteith模型、Arc GIS反距离加权插值、突变检验和Morlet小波等方法,分析其参考作物蒸散量、降水量和干旱指数(AI)时空变化及其影响因素。结果表明:近52年来,宁夏潜在蒸散量(ET0)和降水量在波动中呈降低趋势,倾向率为分别-8.64 mm·10 a-1和-10.04 mm·10 a-1,AI指数则在波动中略呈增加趋势,倾向率为0.01 10 a-1,表明宁夏气候有变干的趋势;从年内分布看,ET0和降水量呈单峰型分布,峰值分别为8月的118.12 mm和7月的66.82 mm,而AI指数呈谷状分布,以8月最小,为0.42;AI指数空间差异明显,呈自南向北递增趋势,表明气候自南向北依次变干;宁夏ET0、降水量和AI指数均在1970年末期、1980年早期和1980年中期发生突变,均存在21 a中尺度的优势周期,并与太阳黑子活动22 a的海尔(磁)准周期基本一致,短周期为3、5、7 a,可能受大气环流和厄尔尼诺等影响。

Based on the climate data of daily temperature, precipitation, wind speed, sunshine hours as well as relative humidity at nine meteorological stations in Ningxia during 1961-2012, evapotranspiration （ETo） was estimated by the Penman-Monteith model. Additionally, inverse distance weighting was applied to investigate the temporal-spatlal variations of ETo, precipitation and aridity index. The abrupt change and the period in ETo, precipitation and aridity index were characterized using a time series analysis conducted with moving t-test and Morlet wavelet. The results showed that in recent 52 years, the ETo and precipitation presented a decreasing trend on the whole with rates of-8.64 mm · 10 a-1 and -10.04 mm · 10 a-1, respectively; aridity index displayed a slightly increasing trend （0.01 10 a-1）, suggesting a drier climate trend in Ningxia. Moreover, both the ETo and precipitation exhibited a unimodal type of distribution with peaks ap- pearing in August （66.82 mm） and July （ 118.12 mm）, respectively, and aridity index showed a valley-like type with minimum （0.42） in August. For spatial distribution of the aridity index, it presented an increasing trend from south to north, suggesting that climate got drier from south to north. Abrupt changes of ETo, precipitation and aridity index primarily happened in the late 1970s, early and mid-term 1980s, and the large time scales of these abrupt changes were same （21 a） and in agreement with the period （22 a） of sunspot activity. Besides, their fluctuations in the short periods of 3, 5 and 7 years were correlated to atmospheric circumfluence and E1 Nino events to some extent.