关键词: 极端干湿, 湿润指数, 潜在蒸散, ENSO, 北方地区

Abstract: Global warming has caused non-uniform changes in precipitation intensity and distribution. Therefore, drought and flood events may increase accordingly in Northern China. Based on the daily data of 424 meteorological stations in northern China from 1960 to 2016, ET₀ was calculated by using the Penman-Monteith method to examine the changes of extreme drought and wet events in the study region. We calculated the surface humid indexes based on ET₀ and precipitation, and used the Mann-Kendall (MK) trend test to analyze the frequencies of extreme drought and wet events by standardized surface humid indexes. All spatial distribution maps were plotted using the linear regression interpolation method embedded in the ArcGIS 10.1 software. This paper analyzed the spatio-temporal variations and multiple scale evolvement of extreme drought and wet events in northern China from 1960 to 2016, and explored the influence of El Niño Southern Oscillation (ENSO) on the extreme drought and wet events threshold using the correlation analysis method. The tendency rates of extreme drought and wet frequency were about -0.10 per decade and 0.13 per decade, respectively. In terms of spatial trends, the frequency of overall trend of extreme drought and wet events decreased and increased significantly from 1960 to 2016, respectively. The area where the number of extreme drought events decreased corresponded to the area where that of extreme wet events increased, including Tibetan Plateau, Northwest China, and Northeast China. The frequency of extreme drought decreased significantly in Northwest China, while that of extreme wet events increased significantly in central Tibetan Plateau, northern Xinjiang, and north of Northeast China. The annual occurrence frequency of extreme drought events was greater than that of extreme wet events. In different sub-regions, the frequency of extreme drought decreased, while that of extreme wet events increased. In different decades, the frequency of extreme drought events was higher in North China, while that of extreme wet events was higher in Northeast China and Tibetan Plateau. On month scales, summer witnessed higher probability of occurrence of extreme wet events, and the probability of occurrence of extreme drought in each month was far greater than that of extreme wet events. The probability of extreme drought was greater than that of extreme wet events in sub-regions, with the probability of extreme drought being the highest in North China and that of extreme wet events being the highest in the Tibetan Plateau. The relationship between the ENSO and the humidity index arrived with a delay. The wet events occurred frequently following El Niño, the drought events happened generally following La Nina. SSTA and the humidity index of next year had a significant positive correlation on annual and summer time scales. The SSTA had an important effect on drought and wet conditions in most parts of Northern China. Finally, this paper can benefit drought/flood characterization from the perspective of the overall dimensions of Northern China, and help decision making in risk-based drought/flood management in the context of global warming.

Key words: extreme drought/wet event, ENSO, ET₀, surface humid indexes, Northern China