Simulation of urbanization effect on East China regional climate using a WRF/SSIB/URBAN model

With the rapid development of urbanization, urbanization has been an unignorable factor on regional climate change, and the feedbacks of urban land-use change to earth system process have become more important. In this study, the effects of large scale urbanization on regional climate change over the east of China during East Asian Summer Monsoon were explored using the WRF-ARW.3.7/SSIB/URBAN model. This SSIB/URBAN scheme aimed to properly simulate the radiation budget in the urban canopy. Two experiments were designed for the study: one is without urban scheme and the other is with the urban scheme. There are three major urbanization areas in China that are assigned in the model: North China, Yangtze River Delta, and Pearl River Delta. NCEP2 reanalysis data was used as the initial and lateral boundary conditions. The simulation begins from May 1 to September 1 including 2007-2013. The outputs of June, July and August (JJA) were selected for the analysis. The main results show that: (1) urbanization has significant effects on precipitation, surface temperature, surface energy and water budget. Precipitation decreases over North China and Pearl River Delta, and increases over Yangtze River Delta. (2) Surface Temperature increases over all of the three urban areas, indicating the heat island effect. (3) Albedo decreases and net shortwave radiation increases due to the trapping of shortwave radiation inside the urban canyon. (4) The urban areas produce significant lower evaporation and higher sensible heat flux. The affected surface energy and water budget cause the change of the upper atmospheric circulation, leading to the precipitation increase over Yangtze River Delta. (5) Compared with observations, the simulation of precipitation and surface temperature with urban scheme show some improvements compared with those without urban scheme.