甘肃河东地区气象干旱时空变化及干旱危险性分析

Temporal and Spatial Variations of Meteorological Drought and Drought Risk Analysis in Hedong Area of Gansu Province

基于标准化降水蒸散指数(SPEI),利用甘肃河东地区1988-2017年60个气象站月值气候数据,通过线性倾向估计、Mann-Kendall突变检测、小波功率谱、Hurst指数等方法对河东地区干旱事件发生次数、干旱烈度和持续时间3种干旱指标的时空变化、突变、变化周期和趋势延续性进行分析,并对气象干旱危险性进行评估。结果表明:年际变化上,1988-2017年河东地区干旱事件发生次数、干旱烈度和持续时间均呈显著增加趋势(P<0.05),变化倾向率分别为0.31次·10a^(-1)、0.61级·10a^(-1)和0.48个月·10a^(-1),陇中高原为增加趋势最显著的分区。空间上,干旱事件发生次数、干旱烈度和持续时间呈显著增加的站点占站点总数的比例分别为18.0%、31.1%和26.2%,区域内仅存在少数变化率为负值的站点,但这些站点变化趋势均不显著(P>0.05)。Hovmoller图显示,干旱事件发生次数、干旱烈度和持续时间在时空上具有集聚性,反映河东地区相邻近站点具有类似的干旱时空特征。Hurst指数显示,在未来河东地区的干旱事件发生次数、干旱烈度和持续时间仍会主要呈现增加趋势,但强持续性(Hurst值接近1)的区域范围较小。研究区干旱指标突变年份为1994年,突变后干旱事件发生次数、干旱烈度和持续时间分别增加0.76次、2.29级、1.70个月,体现出近年来干旱化的态势。小波功率谱显示河东地区干旱指标震荡周期均在6a内,反映干旱具有短期波动特征。30a内研究区总体干旱危险性较大的区域为陇中高原,但研究区每10a的干旱危险性分布存在显著差异,1988-1997年河东地区面临的干旱危险性最大,2008-2017年干旱危险性较小。

Meteorological drought in rain-fed agricultural areas has always been the focus of attention,especially for the area at the junction of monsoon and arid areas with less precipitation.Understanding the characteristics of meteorological drought is particularly important for agricultural production.Based on the monthly climate data of 60 meteorological stations from 1988 to 2017 in Hedong,Gansu,linear tendency estimation,Mann-Kendall abrupt change detection,wavelet power spectrum and hurst index were used to analyze the spatio temporal changes,abrupt change,periods of change and the continuity of trends of the three drought indicators:occurrence times,intensity and duration of drought events in Hedong area.The risk of meteorological drought in different time periods in Hedong area was shown by the drought risk index.The results showed that,firstly,as for the interannual change,the occurrence times,intensity and duration of drought events in Hedong area increased significantly(P<0.05)from 1988 to 2017,and the change tendency rates were 0.31 times·10 y-1,0.61 level·10 y-1 and 0.48 months·10 y-1 respectively.Among all the geographic zones,increasing trend in Longzhong plateau was the most significant.Secondly,in space,the proportions of stations with significant increase in the occurrence times,intensity and duration of droughts events among the total stations were 18.0%,31.1%and 26.2%respectively.There were only a few stations with decreasing trend in Hedong area,but the change trend of these stations was not significant(P>0.05).Thirdly,the Hovmoller chart showed that the occurrence times,intensity and duration of drought events were clustered in years and space,reflecting that the adjacent stations in Hedong area had similar spatial and temporal characteristics of drought.The Hurst index showed that in the future,the occurrence times,intensity and duration of drought events in most area of Hedong will still maintain an increasing trend,but there was only a small area with strong persistence(hurst values close to 1).What’s more,the drought indicator abrupt change appeared in 1994,the occurrence times,intensity,and duration of drought events after the abrupt change increase by 0.76 times,2.29 level,1.70 months,which also reflected the trend of drought in recent years.The oscillation period of drought index in Hedong area was within 6 years,reflecting that drought has a short-term fluctuation.Furthermore,the area with the highest risk of drought among all study areas within 30 years was Longzhong plateau.However,there was a significant difference in the distribution of drought risk in study areas in every 10 years.From 1988 to 1997,Hedong area faced the greatest drought risk,while from 2008 to 2017,the drought risk was relatively small.