In order to study the effect of urbanization and lakes on the urban heat island (UHI) effect of cities in Yunnan midland in summer, the weather research forecasting model (WRF) numerical model is used. The downwind urban heat island is found in these cities in the summer night. The expansion of city will expand the scope of the downwind urban heat island, but the intensity of the heat island would not be enhanced significantly. The presence of the city will change the surface roughness, resulting in the reduction of wind speed near the surface. In the daytime, lakes and the city influence surface wind speed by changing the local thermal difference. The existence of city increases the thermal difference between city and lake, which enhances both the lake-land breeze and the surface wind speed. The presence of city will reduce the supply of low-level moisture, but the impact of urban expansion on moisture is relatively small. In the early morning, the wet island exists in the city (humidity in city is slightly larger than the surrounding area), due to the convergence filled near surface. At other moments, the dry island exists in the city (humidity in city is smaller than the surrounding area), and has the downwind effect as well.

A rainstorm process over west of Kunming city during the night of May 24, 2012 is numerically simulated to study the effect of urbanization on the precipitation by using the weather research forecasting model (WRF) numerical model with single-layer urban canopy model. It is found that the precipitation process is well simulated by comparing the spatial distribution of precipitation between the satellite observation and simulated result. The presence of the city changes the latent heat and low level vertical motion over urban area significantly, resulting in slight reduction of the precipitation intensity in the precipitation center and enhancement of the downwind precipitation. The area where precipitation increases coincides with the area where water vapor flux convergence at 750 hPa increases. The reduction of precipitation in center may be due to restraint of the moisture supply in the lower atmosphere by urban underlying. While the increase of precipitation over downwind area may result from the relatively strong vertical motion which transports more water into upper atmosphere. If the urbanization continues expansion from its current level, not only the vertical motion and atmospheric instability but also the limiting of the moisture supply in the lower atmosphere will be enhanced. The combination of these two effects will enlarge the uncertainty of precipitation over downwind area.

To understand the climate change in Dianzhong region, Yunnan Province, the near-surface observations from 1963 to 2013 in four cities (i.e. Kunming, Chuxiong, Yuxi, and Qujing) were analyzed. Significant warming trend was found in the past 51 years in all the four cites. Comparing the warming trend in different seasons, it was found that the warming rate was fastest in winter. The warming phenomenon was most significant in Kunming, which might be relevant to the urbanization there in the past decades. The annual precipitation presented a slightly decreasing trend. The precipitation increased in the dry seasons (spring and winter), while decreased in the wet seasons (summer and autumn). In the four cities, the decrease of precipitation was most significant in Kunming, while it was slight in Chuxiong. In addition, the decrease of relative humidity was found, and the different between the seasons is not huge. The correlations between different meteorological variables can also be found through the wavelet analysis. It was found that the 36-year cycle of temperature was relevant to that of relative humidity, and the 16?32 years cycle of relative humidity was also related to that of precipitation in Dianzhong region.