黄淮海平原气象干旱的演化特征与时空规律

干旱事件广泛地影响着作物的生长和发育，黄淮海平原是中国主要的粮食产区之一，全面了解该地区干旱变化特征对保障中国粮食安全至关重要。该研究基于标准化降水指数（standardized precipitation index，SPI）、标准化降水蒸散指数（standardized precipitation evapotranspiration index，SPEI）、自校正帕默尔干旱指数（self-calibrating palmer drought index，scPDSI）、干燥度指数（aridity index，AI）4种干旱指数，对黄淮海平原干旱强度、干旱频率、干旱面积占比、干旱持续时间进行对比分析。结果表明，4种干旱指数均指示出1970—2020年黄淮海平原干旱强度逐渐减弱，干旱面积占比先增加后减少、再增加再减少、再增加的波动变化趋势，且在空间上均呈现出平原中部变湿、东西部变干的趋势。但不同指数在表征干旱空间特征上还存在一定的空间分异。对于干旱频率，SPI和AI指数显示出北部地区干旱频率高达60%，而南部地区低于20%；SPEI和scPDSI指数则显示出的南北差异较小，分别介于25%～40%和30%～50%。对于干旱持续时间，SPI指数监测的南北差异最为明显，而SPEI和scPDSI指数监测的区域差异较小。SPI和SPEI两种干旱指数监测的干旱持续时间较短，scPDSI指数监测的干旱持续时间较长。综合来看，北部区域干旱强度更为严重，且干旱发生频率高、持续时间长，而南部地区则相反。研究可为制定应对干旱的农业政策提供科学的参考依据。

Evolutionary characteristics and spatiotemporal trend of meteorological drought in the Huang-Huai-hai Plain

Droughts have posed large threats to crop growth and economic development in the crucial grain-producing region, such as the North China Plain (Huang-Huai-Hai Plain). It is crucial to fully understand the drought characteristics for national food security. Previous studies have relied primarily on the single drought index rather than the multiple drought indices. The single drought index makes it relatively difficult to provide comprehensive and consistent information, compared with the multiple drought indices. However, drought monitoring often varies significantly, because the multiple factors are considered by different drought indices. In this study, four drought indices were utilized to evaluate the spatiotemporal variation of drought in the Huang-Huai-Hai Plain from 1970 to 2020. These indices included the standardized precipitation index (SPI), standardized precipitation evapotranspiration index (SPEI), self-calibrating Palmer drought severity index (scPDSI), and aridity index (AI). Drought events were fully examined from four aspects: intensity, area ratio, frequency, and duration of drought. Data resources were obtained from 564 meteorological stations in the National Meteorological Information Center, including the average, minimum, and maximum temperature, precipitation, wind speed, relative humidity, and sunshine hours. The effective soil water content was collected from the Chinese soil dataset using the World Soil Database provided by the National Tibetan Plateau Research Center. The research results indicate that the better consistency of four drought indices was achieved to characterize the drought intensity and area. The overall drought intensity shared a decreasing trend from 1970 to 2020. The downward trend was ranked in the order of the SPI<SPEI<AI<scPDSI; with a notable decline since the 1980s. In spatial distribution, the four drought indexes showed that the drought intensity increased the most in the eastern and western regions, whereas, the central region showed a gradually moistening trend. The drought area ratio exhibited an increasing trend from 1970 to 1980, followed by a decreasing trend from 1980 to 1990, an increasing trend from 1990 to 2000, a decreasing trend from 2000 to 2010, and an increasing trend from 2010 to 2020. Most drought areas accounted for 10% to 60% of the total area. Among them, scPDSI and AI detected the larger drought areas with significant fluctuations. SPEI was close to the average of monitored drought areas, with the proportions ranging from 20% to 60%. In contrast, the SPI recorded the smallest proportion of drought areas with the less variation, approximately ranging from 20% to 40%. Spatial heterogeneity was found in the different types of drought indices, according to the drought frequency and duration. The SPI and AI detected the drought more frequently in the northern regions than in the southern. Specifically, the highest drought frequency was located in Hebei Province (more than 60%), whereas the drought frequency was lower (less than 20%) in the southern Jiangsu and Anhui Province. However, there was little difference between SPEI and scPDSI monitoring, where the drought frequency was concentrated at approximately 25%-40% and 30%-50%. There was no significant spatial distribution in the SPEI and scPDSI on drought duration. The longer drought durations of the SPI were found in the northern region, compared with the southern. In addition, there was a relatively consistent duration of drought that was monitored by SPI and SPEI, usually between 2 and 7 months, while the duration of drought indicated by scPDSI was between 10 and 20 months. Overall, the droughts were more severe, frequent, and longer-lasting in the northern regions, whereas, the opposite was observed in the southern. This finding can also provide an objective evaluation and valuable insight into drought characteristics in the North China Plain.