Study on Characteristics of Abrupt Alternation Events between Drought and Flood in Northern China

Abrupt alternation events between drought and flood (AAEDF) are classified as a special category in extreme climate events, it consists of drought-flood abrupt alternation events (DFAAE) and flood-drought abrupt alternation events (FDAAE). These events could lead to severe socio-economic losses and have significant impacts on ecological environment. A number of valuable progresses have been made on AAEDF and these studies focused on the southern part of China. However, little attention has been paid to northern China whose ecological environment is quite vulnerable. The purpose of this study is to reveal spatial-temporal variation characteristics of AAEDF with focus on northern part of China. An index in daily time scale is conducted for monitoring AAEDF by using precipitation data from 329 in situ stations spanning from January 1961–December 2015. The results show that the index has great ability to detect AAEDF in northern China. Furthermore, frequency and intensity for both DFAAE and FDAAE are significantly high in southern and northeastern Qinghai, southern Shaanxi, northern Hebei, southeastern Jilin and Liaoning and most of Heilongjiang province. DFAAE are mostly occurred in June and July, followed by autumn and spring. In winter, the frequency of DFAAE is minimal and this is partly because of scarce precipitation in cold season over northern China. By contrast, FDAAE are mostly appeared in April to June, followed by winter and spring. In autumn, the frequency of FDAAE is minimal. Note that the maximum and minimum frequency of FDAAE both occurred one month ahead of that of DFAAE. In recent 55 years, the frequency of DFAAE has decreased at a rate of -1.43 per decade, while that of FDAAE has increased at a rate of 1.21 per decade. Frequency of DFAAE and FDAAE present similar inter-decadal variation, which indicating increasing trends since 1980s. The innovation of this analysis includes the concept and the monitoring index of AAEDF. In addition, the results would be helpful for improving the technical level on monitoring, predicting and warning of abrupt alternation events.