成都地区城市化对气候影响的模拟研究

Simulation Study of Urbanization Impact on Climate in Chengdu

为了研究成都地区城市化对当地气候的影响,利用不同时期的下垫面土地利用类型数据和耦合单层城市冠层模型(UCM)的WRF(Weather Research and Forecasting)模式对成都夏季和冬季城市化效应进行了模拟研究,得到以下主要结论:1)成都地区城市化使夏季城区上空出现增温区域。城区地表气温升高约2.8℃,边界层高度升高约150 m,冬季地表气温平均升高约0.6℃,边界层高度升高约25 m。夏冬两季气温日较差均减小。2)受城市化影响,成都地区夏季和冬季2 m相对湿度减小,感热通量增加,潜热通量减小,且夏季变化程度强于冬季。3)城市化使地表的粗糙度增加,进而使夏季和冬季风速在城区减小,减小约0.1~0.6 m s^-1,但夏季风速减小区域较冬季更大。城市化还使城市上空低层散度减小,辐合作用增强,垂直速度增大,夏季水汽往高层输送明显。4)夏季,城市化作用使日平均和白天时段降水量在城区的迎风区和下风区均增加,夜间降水量在下风区域增加,对迎风区域影响不明显。

To study the impact of urbanization on the local climate in Chengdu,the urbanization effects during summer and winter over Chengdu are simulated by using data about the underlying surface land use type of different periods and the WRF(Weather Research and Forecasting)model,coupled with a single-layer urban canopy model(UCM).The main conclusions are drawn as follows.First,in summer,the urbanization of Chengdu causes a temperature-increasing area over the urban area.The surface temperature increases by about 2.8℃in the urban area,and the boundary layer height increases by about 150 m.In winter,the surface temperature increases by about 0.6℃in the urban area,and the boundary layer height by about 25 m.In addition,the diurnal temperature range in both summer and winter decreases.Second,during summer and winter,the 2-m relative humidity decreases,while the sensible heat flux increases and the latent heat flux decreases due to the impact of urbanization,but the degree of change in summer is stronger than in winter.Third,during both seasons,the wind speed decreases by around 0.1–0.6 m s^-1 in the urban area due to an increase in surface roughness,but the area where the wind speed decreases in summer is larger than in winter.Due to urbanization,in the lower atmosphere over the city,divergence decreases,convergence and vertical velocity increases,while water vapor is transported significantly from the lower layer to the upper layer in summer.Finally,during summer,because of urbanization,the average daily precipitation and daytime precipitation both increase in the urban upwind and downwind directions.On the other hand,nighttime precipitation increases in urban downwind areas,but it has no significant effect on urban upwind areas.