4. Conclusion and discussion
The variation patterns of the extreme precipitation and the contributions of climate change and urbanization in the UAs over the LP from 1979 to 2018 are analyzed in this study. The results reveal that the precipitation intensity during the presummer season has decreased in the southeastern LP and increased in the northwestern LP, and the variation trends are much more significant in the urban areas than in the rural areas. Specifically, the urbanization can aggravate the decreasing trends of extreme precipitation in Taiyuan and Xi’an UAs while enhance the increasing trends in Luoyang, Hohhot and Xining UAs. The number of light rain days is very sensitive to the urbanization, which decreases in almost all the cities. Although Xining UA has a lower level of urbanization compared to the other UAs over the LP, the urbanization effect is also detected in the wetting trend.
The results also display that the climate change is the dominant factor for the urban precipitation trends, but the urbanization exhibits different influences in different periods. In the first twenty years, the urbanization contribution in the urban precipitation is relatively weak, and the climate change is the primary factor. In the last twenty years, the urbanization contribution increases dramatically, while the contribution of climate change is much weaker than that in the first stage. The urbanization tends to exert negative impacts on the extreme precipitation indices in Xi’an and Taiyuan UAs and positive effects in Luoyang, Hohhot and Xining UAs. In addition, the stronger intensification of extreme precipitation in the urban areas may be closely connected with the faster increase of surface temperature and aerosol particles. To further examine the physical processes of the urbanization effect on the extreme events in the UAs over different geographical locations and under different climate backgrounds across the LP, the dynamic experiments based on the Weather Research and Forecasting model will be performed in our forthcoming studies.
The climate environment of the UAs over the LP is very sensitive and fragile. Due to the considerable trends of extreme precipitation caused by the climate change and amplified by the urbanization, urban disasters, such as urban water shortage and urban waterlogging, are expected to be further strengthened. Scientific urbanization planning and construction should attract attention to alleviate the urbanization consequences, particularly in large cities.
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