Estimating the impact of urbanization on non-stationary models of extreme precipitation events in the Yangtze River Delta metropolitan region

Rapid urbanization has significantly increased the proportion of impervious surfaces in Yangtze River Delta urban agglomeration (YRDUA), hence quantifying its impact on extreme precipitation events is essential for waterlogging control and urban planning. The spatiotemporal evolution patterns of extreme precipitation indices (EPIs) based on a non-stationary Generalized Extreme Value (GEV) model are analyzed in urban, suburban, and rural stations. Additionally, the degree of change of the recurrence levels are calculated to evaluate the effect of the urbanization process on EPIs in these stations. The results indicated that (1) Except for CWD, other EPIs show an increasing trend and EPIs with significantly increasing trend distributed in the downwind direction of the YRD. The percentages of significantly positive trends in EPIs, accounted for more than 85%, are mainly in the urban and suburban stations. (2) The optimal non-stationary GEV model with urbanization factor is predominately distributed in the highly urbanized areas. Urbanization factor has a significant impact on short-term, high-intensity precipitation and PRCPTOT in urban areas. (3) While the proportion of urban impervious areas in the urban area increased from 0.11 in 1985 to 0.63 in 2016, the effect of urbanization on EPIs changes from negative to positive and R95p, R25, R50, PRCPTOT in urban are much higher than those in rural after 2000. Urbanization significantly affects the recurrence levels of Rx5day in the rural, urban, and suburban stations, which increased by 27%, 29%, and 29%, respectively. The degree of change in the recurrence level in the suburban and urban areas is greater than that in the rural areas.