Changing patterns of extreme water levels in urbanizing plain river network region of Taihu Basin, China: characteristics and causes

Abstract. Water level is an indicating factor in flood control in the plain river network region of Taihu Basin (PRNRTB). It is mainly influenced by climate change and human activity. In this study, the annual and seasonal variations of extreme water level from 1960 to 2012 were analyzed based on daily water level of eight stations in the PRNRTB. The modified Mann-Kendall test and sequential cluster analysis are used to detect trends and points of abrupt change. The results indicated that the extreme water level shows a significant increase at a regional scale. The increases in extreme high water level (EHWL) and extreme low water level (ELWL) were 0.007 and 0.01 m per year, respectively. Detected points of abrupt change was around 1988 for the region and most stations, which correspond to the period of intensive human activities in this region. The changes in average annual EHWL and ELWL between 1989 and 2012 are, respectively, 7.8 and 12.7 % higher than that between 1960 and 1988. Meanwhile, contributions of precipitation and human activity were also assessed in three individual periods (1989–2012, 1989–2000, and 2000–2012). Between 1989 and 2012, the contribution from human activity increased from 20.5 to 70.3 % for EHWL, while human activity was always the main driver responsible for the increase in ELWL in that period. In addition, a thorough discussion is included about the potential driving force on the extreme water level in the PRNRTB. Human activities are suggested to have played more and more important roles in the extreme water level changes since the late 1980s. The results of the study would provide support in water resources management and floods control in urban development.