Abstract:

Against the backdrop of global warming and intensifying human activities, extreme drought and flood events have shown a trend of increasing frequency and intensity. However, research on sub-seasonal drought-flood abrupt alternation events remains relatively limited. In light of this, this study utilizes daily precipitation data from 20 national meteorological observation stations in Ningxia from 1961 to 2023 and employs the multi-threshold run theory to propose a method for sub-seasonal drought-flood abrupt alternation events, which is subsequently validated. Based on this method, drought-flood abrupt alternation events in Ningxia from April to October during 1961-2023 are statistically analyzed, with a focus on examining the spatiotemporal evolution characteristics in terms of event frequency, transition timing, and intensity. The results indicate that the proposed identification method performs well in detecting both drought and flood events and effectively captures the transition process from drought to flood. Since the 1990s, the frequency of drought-flood abrupt alternation events in Ningxia has increased significantly, reaching its peak in the 2010s. The occurrence time of turning points, ranked from most to least frequent, are the sixth pentad of July, the third pentad of July, the fourth pentad of October, the first pentad of July, and the fifth pentad of September. The spatial distribution of event frequency is uneven, showing a clear regional pattern of increase from south to north. Severe drought-flood abrupt alternation events mainly occurred in the 1970s and the 2000s and were largely concentrated in the northern Yellow River irrigation area. Although this region has the lowest annual precipitation, both light and moderate drought-flood abrupt alternation events show an increasing trend.

Key words: Ningxia, sub-seasonal, drought events, flood events, identification of drought-flood abrupt alternation

摘要：

在全球变暖和人类活动加剧背景下，极端旱涝事件呈增多增强趋势，但针对次季节旱涝急转事件的研究仍较为缺乏。鉴于此，利用宁夏20个国家气象观测站1961—2023年逐日降水资料，采用多门槛游程理论，提出了一种识别次季节旱涝急转事件的方法，并对其进行检验。基于该方法，统计宁夏1961—2023年4—10月旱涝急转事件，分析事件发生频次、急转点出现时间、强度等时空演变特征。结果表明：该方法能有效识别干旱与洪涝事件，并能较好地捕捉旱转涝的过程特征；宁夏旱涝急转事件发生频次自1990年代之后显著增多，并在2010年代达到峰值；急转点出现时间主要集中在7月第六候、7月第三候、10月第四候、7月第一候和9月第五候；旱涝急转事件空间分布不均，呈现南少北多的格局；重度旱涝急转事件多发生于1970年代和2000年代，且主要集中在北部引黄灌区，该区域虽年降水量最少，但轻度和中度的旱涝急转事件均呈增多趋势。

关键词: 宁夏, 次季节, 干旱事件, 洪涝事件, 旱涝急转识别