Abstract:

The alternation between drought and flood is more destructive than a single drought or flood disaster. Studying its evolution patterns and prediction methods is of great significance for enhancing disaster prevention and mitigation capabilities. Based on monthly precipitation data from 70 national meteorological stations in Hubei Province from 1960 to 2024, and the fifth-generation reanalysis data from the European Centre for Medium-Range Weather Forecasts, this study analyzes the temporal evolution characteristics of the Long-cycle Drought-Flood Abrupt Alternation Index (LDFAI) in typical years of summer drought-flood alternation (drought-to-flood and flood-to-drought) in Hubei Province, and explores the corresponding atmospheric circulation and water vapor transport anomalies. The results are as follows: 1) From 1960 to 2024, a total of 21 summer drought-flood alternation events occurred in Hubei Province, including 10 drought-to-flood events and 11 flood-to-drought events. The LDFAI showed a weak upward trend at a rate of 0.03 per decade, while its intensity decreased at a rate of 0.07 per decade, but both didn’t pass the significance test. 2) The LDFAI exhibits distinct decadal variation characteristics: the 1960s was a period with frequent drought-flood alternation, a total of 7 events occurrence (4 drought-to-flood and 3 flood-to-drought); in the 1970s, there was frequent flood-to-drought events, reaching 4 times; after the 1980s, the frequency of drought-flood alternation events tended to be balanced. The intensity of LDFAI experienced an abrupt change in 1973, and significantly decreased after 1980. 3) High-incidence areas for drought-to-flood events were concentrated in central and western Hubei, with the southern part of Shennongjia and the northwestern part of Yichang being high-risk regions. High-incidence areas for flood-to-drought events were widespread in central, western, and eastern Hubei, with Enshi being a high-risk region for flood-to-drought events. 4) During the drought period of drought-to-flood years, it was controlled by a southerly Western Pacific Subtropical High (referred to as “the subtropical high”) and mid-to-high latitude zonal circulation in Hubei Province, coupled with subsidence motion and water vapor divergence, leading to less precipitation. During the flood period, a mid-high latitude meridional circulation developed, and the ascending movement and water vapor convergence on the northwest side of the subtropical high increased, leading to more precipitation. The circulation and water vapor anomalies in flood-to-drought years were opposite to these.

Key words: Hubei Province, anomaly, long-cycle, drought-flood alternation index, atmospheric circulation

摘要：

旱涝转折相较于单一旱涝灾害具有更强的破坏性，研究其演变规律与预测方法对提升防灾减灾能力具有重要意义。基于1960—2024年湖北省70个国家级气象观测站点的月降水量资料及欧洲中期天气预报中心第五代再分析数据，分析湖北省夏季旱涝转折（旱转涝、涝转旱）典型年的长周期旱涝转折指数（Long-cycle Drought-Flood Abrupt Alternation Index，LDFAI）时间演变特征，并探讨其对应的大气环流与水汽输送异常。研究表明：1）1960—2024年湖北省共发生21次夏季旱涝转折事件，其中旱转涝10次，涝转旱11次；LDFAI呈微弱上升趋势[0.03 （10 a）^-1]，其强度以0.07（10 a）^-1速率下降，但均未通过显著性检验。2）LDFAI具有明显年代际变化特征：1960年代为旱涝转折多发期，共发生7次（旱转涝4次、涝转旱3次）；1970年代涝转旱频发，达4次；1980年代后旱涝转折事件频率趋于均衡；LDFAI强度在1973年发生突变，1980年后显著下降。3）旱转涝事件高发区集中在湖北中部及西部，神农架南部与宜昌西北部为高风险区；涝转旱事件高发区遍及湖北中部、西部和东部，恩施是涝转旱高风险区。4）旱转涝年旱期西太平洋副热带高压（简称西太副高）偏南，湖北受中高纬纬向环流控制，配合下沉运动与水汽辐散，导致降水偏少；涝期则伴随中高纬经向环流发展，西太副高西北侧上升运动与水汽辐合增强，降水偏多。涝转旱年的环流与水汽异常特征与之相反。

关键词: 湖北省, 异常, 长周期, 旱涝转折指数, 大气环流