[目的]揭示黄土高原典型区域百年尺度干旱演化特征,与地貌类型耦合阐明气象干旱的时空变化规律,进而为北洛河流域综合治理提供科技支撑.[方法]基于1915-2020年北洛河流域1 km分辨率的平均气温及降水数据,计算了年际标准化降水蒸散指数(SPED,并结合Theil-Sen Median趋势分析、Mann-Kendall检验、小波分析、反距离权重插值(IDW)等方法,分析了流域内100余年不同地貌类型区的气象干旱时空演变特征.[结果](1)北洛河流域降水量及平均气温的空间分布差异较大,总体呈现东南向西北递减的特点;降水量多呈条带状分布,平均气温沿河道自上而下梯度增加,上游区(丘陵沟壑区)降水量相对较少,下游区(阶地平原区)平均气温相对偏高;(2)1915-2020年北洛河流域SPEI-12震荡明显,干旱事件交替出现且弱减,下降速率为-0.04/10 a,1942年,1990年和2010年为旱势转折年,并以1990年最为明显;周期变化大致可从1960年分为两个时期,之前以10 a,17 a为主,其后为3 a,7 a,30 a左右,10 a和30 a周期在不同时期干旱变化中起主导作用;(3)SPEI-12的不显著下降趋势具有全域性且由东北向西南有增大趋势,表明北洛河流域总体呈弱旱化发展;(4)不同年代干旱事件发生频率差异较大,1990s重旱和特旱发生频率最高;2000s不同类型干旱事件发生的总频率最大,其中上游区(丘陵沟壑区)和下游区(阶地平原区)可达70%,而中游区(土石山林区和高原沟壑区)约为60%;(5)不同类型干旱空间分布存在异质性,轻旱发生频率有自南向北逐渐降低的趋势,中旱发生频率与之相反.总体来看,北洛河流域上游区(丘陵沟壑区)易发生中旱,下游区(阶地平原区)更易发生轻旱,重旱高发区在流域内零散分布,特旱的发生概率仅为1.69%~2.10%.[结论]全球变暖引发的旱化趋势在黄土高原地区的影响客观存在,北洛河流域不同地貌类型区气象干旱发生的高频类型略有差别,未来应提升中下游地区的抗旱减灾能力.
[Objective]The aims of this study are to reveal the century-scale drought evolution characteristics in typical areas of the Loess Plateau,couple with landform types to clarify the spatiotemporal variation of meteorological drought,and provide scientific and technological support for the comprehensive management of the Beiluo River Basin.[Methods]The annual standardized precipitation evapotranspiration index(SPEI)was calculated by using average temperature and precipitation data with a resolution of 1 km in the Beiluo River Basin from 1915 to 2020,and the spatiotemporal variations of meteorological drought in various land-form types were examined by using the Theil-Sen Median trend analysis,Mann-Kendall test,wavelet analy-sis,and inverse distance weighted interpolation(IDW).[Results](1)The Beiluo River Basin's spatial distri-bution of temperature and precipitation was quite diverse,showing a general decreasing trend from southeast to northwest along with a top-to-bottom gradient distribution of temperature along the channel.The temper-ature was relatively high in the downstream area(terrace plain area)while there was comparatively little precipitation in the upstream area(the hilly-gully area).(2)Throughout the study period,the SPEI-12 of this basin changed dramatically,suggesting that drought occurrences appeared in cycles.Overall drought occurrences displayed the decreasing tendency in terms of quantity,with a decline rate of-0.04/decade.Among them,the trend turned in 1942,1990,and 2010,with 1990 marking the biggest turning point.Drought cycle variations could be loosely separated into two periods:the period prior to 1960,when the primary cycles were the 10 years and 17 years,and the period following 1960,when the dominant cycles were the 3 years,7 years,and 30 years.The 10-year and 30-year cycles predominated the basin drought fluc-tuations across the whole time span.(3)The reduction in SPEI-12 was increasing from the northeast to the southwest,indicating that the Beiluo River Basin was often experiencing weak drought.This decline was global,but not statistically significant.(4)In the time domain,the frequency of drought events varied sub-stantially.The 2000 s could be seen the highest frequency of all types of drought events,with the upstream(hilly-gully area)and the downstream(terrace plain area)both reaching 70%and the midstream(rocky-mountain area and table-gully area)at about 60%.The 1990 s could be seen the highest frequency of severe and extreme drought.(5)Different types of droughts distributed differently.While the frequency of moderate droughts slowly rose from the south to the north,the frequency of mild droughts gradually reduced from the south to the north.In general,moderate droughts were more likely to occur in the upper parts of the Beiluo River Basin(the hills-gully area),whereas mild droughts were more likely to occur in the downstream sections(the terrace plain area).The probability of experiencing an acute drought was just 1.69 to 2.10%in the majority of the basin's high-incidence zones,which dispersed throughout the basin.[Conclusion]Drought trends caused by global warming have an objective impact on the Loess Plateau region.The high-frequency types of meteorological droughts in different geomorphic types of the Beiluo River Basin are slightly different.In the future,drought resistance and disaster reduction capabilities in the middle and lower reaches should be improved.