Seasonal precipitation changes in the wet season and their influence on flood/drought hazards in the Yangtze River Basin, China

The present study examines the spatial and temporal trends of precipitation, flood/drought, runoff, high and low river flow during flood season (May–October) for the Yangtze River Basin. Analyses are based on daily meteorological data for 137 stations from 1960 to 2004, daily hydrological data for two discharge-measuring stations at the Yangtze River and monthly hydrological data for one station for the same reference period. Flood/drought examination was done for the western, middle, and lower Yangtze River Basin. Significant precipitation changes can be detected for June and July during 1960–2004. The strongest precipitation increase was detected in the lower Yangtze region. A statistically significant negative trend can be found in September over the Yangtze River Basin, especially at the middle region. Changes of the precipitation extremes from May to October are of direct importance to the occurrences of high and low river flow. The main increase of flooding events can be detected for July in the lower Yangtze region, together with significant upward trends both for the monthly runoff and for the high river water stage. Drought frequency increased in the middle Yangtze River Basin in May, September and October, where downward trends for the monthly runoff and low river flow especially in May. During these months, flood and drought hazards in the Yangtze River Basin have been aggravated.