Analysis of historical drought and flood characteristics of Hengshui during the period 1649-2018: a typical city in North China

The objective of this study was to reconstruct the long-term drought and flood time series to analyze their changing characteristics in Hengshui City of North China. Disaster records of the city for 550 years (1649–2018) were collected from different sources and sorted to reconstruct the sequences of droughts and floods. Advanced statistical methods for climate data analysis, including the Mann-Kendall test, Sen's slope estimator, Morlet wavelet analysis, mutation point tests, and Rescaled range analysis, were used to analyze the historical changes and predict the direction of possible future changes in droughts and floods. The results showed an increased frequency of droughts and a decreased frequency of floods in Hengshui City, making drought occurrence significantly higher than flood occurrence in the twentieth century. The solar activity cycle of 11-year and its multiple showed the association with 10–15 years and 25 years cycles of droughts and floods, respectively. The mutation points in drought and flood sequences during 1559–1568 and 1909–1918 showed insignificant downward (upward) and upward (downward) trends, respectively, in the drought (flood) subsequence before and after the mutation point. The rescaled range analysis revealed an insignificant decreasing trend in droughts and the continuation of the present decreasing trend in floods in the forthcoming years