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.