FIG. 7. The same as Fig. 4, but for light rain days.
To further quantify the contribution of climate change and urbanization
to the precipitation, Table 2 shows the changes of the relative
contributions in the two stages in the five UAs of the LP. Spatially,
the urbanization tends to exert
negative impacts on the extreme precipitation indices in the basin areas
(such as Taiyuan and Xi’an) except for Luoyang in the southeastern LP,
while positive urbanization effects are mainly found in the UAs located
in the north and the west of the LP (including Hohhot and Xining). It is
also found that the effect and contribution of urbanization are not only
dependent on the study period, but also strongly correlated to the trend
of th extreme precipitation index.
In the first stage, the effect and
contribution of urbanization on
the urban precipitation are relatively weak, and the climate change is
the dominant factor. In the second stage, the effect and contribution of
urbanization have increased dramatically in most UAs, while the
contribution of climate change is much weaker than that in the first
stage. Among these extreme precipitation indices, the
R10mm and the R95p in Luoyang and the
R10mm in Hohhot demonstrate little differences of urban
effect between the two stages, indicating that the urbanization does not
always have a strong effect on all the extreme precipitation indices. In
addition, the urbanization tends to augment the trends of precipitation
caused by the climate change in all the five UAs. (For example, the
urban areas of Taiyuan and Xi’an have become drier and Hohhot and Xining
become wetter than their surrounding rural areas. The wetting trend in
northwestern LP and the drying trend in southeastern LP were only
attributed to the climate change in the previous researches. The results
in this study demonstrate that the urbanization also plays an important
role in the extreme precipitation change in the recent two decades.
TABLE
1. Mean trend of presummer precipitation from 1979 to 2018.