2.3.2. Estimation of urbanization and climate change
contribution
In this study, we evaluate the contribution of climate change and
urbanization based on the “trajectory” method (Feng, H. et al. 2014,
Feng and Huihui 2016). At local scales, climate change and urbanization
jointly influence the precipitation trends at some certain grids. Their
potential contributions at a certain UA can be calculated as follows.
UE = Ru-Rr , (1)
UC =Ssub ×(Ru -Rr)/Ru×100% , (2)
CC = (Rr/Ru)×100% , (3)
where Ru and
Rr are the precipitation trends in urban and rural
areas, respectively. The urbanization effect (UE) is defined as the
trend difference between the urban and the rural series in Eq. 1.
Ssub is the proportion of urban grids to total grids. If
the rural and the urban grids have the same number in the contribution
analysis at regional scale, the parameter Ssub can still
be remained for the sake of equation generality. The relative
urbanization contribution (UC) in percentage is defined as the fraction
of the overall trends of the extreme precipitation events attributed to
the UE in Eq. 2. The relative climate change contribution (CC) is
defined as the ratio of the precipitation trend in the rural areas to
that in the urban areas in Eq. 3 (Gu, Zhang et al. 2019).
2.3.4. Extreme
precipitation index
We adopt the precipitation data from April 1 to July 1 in this study,
excluding the persistent heavy precipitation caused by summer monsoon.
Four extreme precipitation indices are selected to represent the
intensity of presummer precipitation over the LP based on the gridded
data in the CMFD. The four indices include the maximum daily
precipitation (Rmax), the very wet day precipitation
(R95p) which is the total precipitation when daily
precipitation > 95th percentile mean
daily precipitation, the extremely heavy precipitation
(R>10mm) which is the total precipitation
when daily precipitation >10 mm and the number of light
rain days (R<10mm) which is the count of days
with daily precipitation < 10 mm during the presummer season.