Comparative experimental observations and hydrological response in representative basins of Eastern China

To explore the mechanism of changes in the hydrologic cycle under the changing environment in eastern coastal areas of China,based on intensive observations from the hydrological station network and construction of experimental watersheds,we analyzed the distribution and responses of hydrological elements in areas of different land use and urbanization levels. The research results are as follows:① The spatial distribution of extreme rainfall exhibits differences,reaching 50 mm,and is mainly affected by the micro-topography and wind direction of the basin. ② For the runoff response for two basins with different urbanization levels,the flood response time,water level increase,and water level increase per unit rainfall of the highly urbanized basin are higher than those of the low urbanization basin,which is mainly affected by the size of the watershed and degree of urbanization. ③ Forest land plays a critical role in water conservation,and the decreasing process of soil moisture under forest land is slow,whereas the process in urban and cultivated land is faster;the average soil moisture lag times in 10 cm,20 cm,and 40 cm soil layers are 0-0.25 h,0.25-0.75 h,and 0.5-0.75 h,respectively,while the soil moisture response times for deep soil layers (60 cm and 80 cm) are more complex because of the influence of preferential flow. ④ The peak groundwater occurrence time has a hysteresis relationship with rainfall,and the lag time is 6.5-12 h.