Trends in precipitation extremes and long-term memory of runoff records in Zhejiang, East China

Extreme weather events have a huge impact on human beings and therefore it is of vital importance to investigate trends in relevant climatological and hydrological variables. In this study, precipitation and streamflow trends in Zhejiang Province in east China are analysed. Trends in annual and extreme precipitation for 18 meteorological stations (data periods 42 to 58 years) are studied using the Mann-Kendall test. Trends in the plum season (May–July) and typhoon season (August–October) are analysed separately as well. The scaling properties of streamflow for three hydrological stations (data periods 47 to 57 years) are determined using the detrended fluctuation analysis (DFA) method. Results show a positive trend in annual precipitation in the east and a negative one in the west. The major part of Zhejiang shows a positive trend in extreme precipitation, being more significant for 95% non-exceedence values than for 99% non-exceedence values. Precipitation intensity exhibits an upward trend in most areas and in both plum and typhoon seasons, especially in the coastal areas. The results of the DFA method show that longterm memory properties exist for one year in all three rivers. This time scale can be explained since the main source of the streamflow variation comes from climatic variability and the fact that annual streamflow cycles did not change.