Impact Of Urbanization Of The Eastern China On Extreme Temperature And Regional Climate Change

In this paper, the homogeneity-adjusted daily maximum temperature (Tmax) and daily minimum temperature (Tmin) at312stations in the eastern China for summers (June, July, Augest) and winters (December, January, February) of1979-2008are used to investigate the impact of urbanization of the eastern China on extreme temperature with a spatial filtering method (moving spatial anomaly)to each extreme temperature index at first. Then we use the Weather Research and Forecasting (WRF) model coupled with a single-layer urban canopy model (UCM) to simulate the urbanization effects of the Yangtze River Delta (YRD) in summer and winter from2001to2007with high resolution by designing two experiments (Urban and NoUrban). The simulation results are used to investigate the urbanization effects of the YRD on extreme temperature by comparing the two experiments of each extreme temperature index. The urbanization effects of the YRD on regional climate under summer different wind directions will be analyzed by comparing the two experiments of temperature, pressure and water vapor mixing ratio under different wind directions at last.The observation results show that among the Beijing-Tianjin-Hebei (BTH) city group, the YRD city group and the Pearl River Delta (PRD) city grop in the eastern China, there is a remarkable warming of summer Tmax in the YRD city group and winter Tmin in the BTH city group. The diurnal temperature range (DTR) exhibits increase in summer over the YRD city group, but decrease in winter over the BTH city group. The urbanization can induce a significant increase for summer hot days (HD) in the the YRD city group and the PRD city group and summer muggy days (MD) in the the YRD city group, but a significant decrease for winter ice days (ID) in the BTH city group and winter frost days (FD) in the BTH city group. Meanwhile, a remarkable increase of summer heat wave (HW) in the YRD city group and the PRD city group is resulted from urbanization, and the increase of summer HW is mainly reflected in the increase of severe HW.The simulation results show that the WRF model can well reproduce the summer and winter2m temperature and precipitation over the YRD. The simulated spatial distribution and the intensity of the summer and winter2m temperature and precipitation over a period of7years (2001-2007) agree well with the observation. The regional heat island caused by urbanization is formed as the center of the YRD city group in summer. Compared with Tmin, the warming area of Tmax increases, but the warming intensity decreases. The urban heat island (UHI) effects of winter is much weaker than summer’s. The urbanization can induce different increases for summer HD and MD in most areas of the YRD, especially for SH area, but it has little impact for winter ID and FD. Different increases for summer HW in most areas of the YRD is also resulted from urbanization, especially for SH area, and the increase of summer HW is mainly reflected in the increase of severe HW too.The simulation results also show that the regional heat island caused by urbanization is formed as the center of the YRD city group, and spreads to leeward in summer. Compared with calm wind, the heat island of the leeward of the YRD city group is stronger under the wind condition. Meanwhile, the warming intensity caused by urbanization is weakening in SH and HZW areas under the wind condition, but stronger in NZY area. The UHI induces local ascending motion. The obvious upward flows exist over the UHI areas, and downward flows over the leeward, forming the heat island circulation. The low pressure area caused by UHI is centralized over the YRD city group, and spreads to leeward. Under the wind condition, the heat island of the leeward of the YRD city group strengthens, and the surface pressure decreases remarkably. Further analyses show that a significant decrease of water vapor over the YRD city group and its surrounding is resulted from urbanization. Compared with calm wind, the water vapor of the leeward decreases greater under the wind condition. Becasuse of a large ascending velocity over the center of the dry island, the water vapor transported from near-surface to high altitude increases with the effect of the strong thermal turbulence, causing that the water vapor mixing ratio increases at low-level but decreases at high-level.