Analysis The Effect Of Urbanization On The Yangtze River Delta With High Resolution Simulation

The effect of urbanization on local weather and regional climate is paid to more and more attention. As one of the world's six major urban agglomerations, the Yangtze River Delta has the unique characteristics of monsoon climate and highly urbanization developed; to study the effect of urbanization is of great scientific and practical significance. In this paper, the regional climate model WRF (v3.1.1) is used to analysis the summer storms, extreme rainfall year as well as simulate climatology regional climate characteristics, and to analysis the application of the simulation of summer rainfall and temperature in the Yangtze River Delta by regional climate model, and the effect of urbanization on heavy rainfall and regional climate change.Firstly, using the numerical model WRF (v3.1.1), with the Japan Meteorological Agency 20km data, GMS-5 satellite image, NCEP 1°×1°FNL data and automatic weather station observation data to simulate the heavy rainfall event occuring in Shanghai on 25 August 2008, and designed three numerical experiments of different land surface characteristics to analysis the impact of urbanization on this heavy rainfall main character. The results indicate that the WRF model can represent the main distribution of rainfall, storm rainfall center and the time serials of heavy rainfall well; with the effect of urbanization, precipitation over the central area and in the windward region of Shanghai increased, but reduced over the leeward area of the city; the low level wind in urban areas was blocked by the dynamic effect of land surface roughness changes due to urbanization, which enhanced vertical motion and increased water vapor in the windward region and it may be the main reason of the enhancement of rainfall in the windward area of city.Subsequently, the regional climate model was used to simulate the extreme precipitation year with high resolution, the results show that the model could more reasonably represent the main distribution of the summer precipitation in Huaihe River Basin in 2003, the simulated monthly mean precipitation in summer and heavy rainfall center and the rainfall intensity are very close to observation; WRF model also reasonably simulate the time serials characteristics of many heavy precipitation events in the ChangJiang HuaiHe Meiyu period, the simulated and observed time series of regional average daily precipitation have high correlation coefficient; at the same time, the model better simulated the probability of three different categories precipitation, the storm rainfall is most close to observation; In addition, the model reasonably simulate many storm rainfall events during the Huaihe River rainy period, the occurrence time and region of heavy rainfall and the rain belt moved southward and shifted northward, are very close to the observation; At last, the model also simulated very well the two mesoscale heavy precipitation events on 30 June to 1 July 2003 and 6 July to 7 July 2003, the simulated storm rainfall intensity and development process are very close to GMS-5 satellite image.Regional climate model simulated reasonably the hot weather in 2003, and the high temperature bias between the south and north region of the Yangtze River caused by the cooling effect of many heavy rainfall events, the simulated spatial distribution of minimum and maximum temperature and there maxima center are close to the station observations, the minimum temperature is closer to observations. The simulated time serials of daily maximum and minimum temperature are closer to the station observation than precipitation, and both have a higher correlation coefficient.Finally, the simulation period was extended to the summer of 2001 to 2007 to explore the applicability of high resolution simulation to the climatology regional climate characteristics. The results show that the model could simulate the main distribution of climatology summer precipitation in the Yangtze River Delta, the simulated climatology summer monthly mean precipitation and the center of heavy rainfall and precipitation intensity, are all close to observation; the model reasonably simulated the spatial distribution of probability of three different categories precipitation, the simulated moderate and heavy rainfall are closer to the reality; the model also represent well the timely evolution characteristics of several heavy rainfall events during the MeiYu period in three sub-regions, the simulated and observed time series of regional average daily precipitation has higher correlation coefficient; regional climate model also reproduced reasonably the climatology summer daily mean precipitation and annual precipitation anomalies in three sub-regions, both very close to station observations.The model also well simulated the spatial distribution of every monthly average temperature and the significant cooling trend in temperature caused by persistent precipitation in Huaihe River Basin; model reasonably simulated the time serials of regional average daily temperature in all three sub-areas, with a higher correlation coefficient between the simulated and observed regional average daily temperature than precipitation; the simulated annual change of temperature and interannual anomalies in three sub-regions are very close to observations, and particularly well simulated the lower temperature in Huaihe River in 2003 caused by many heavy rainfall events, as well as the abnormal high temperature trends caused by the high temperature weather in Zhejiang in 2003.Urbanization significantly enhanced precipitation in the central area Yangtze River urban region for both heavy rainfall events in 2003, enhanced the vertical circulation and increased the rainwater mixing ratio in the windward region. Urbanization decreased the climatology daily and daytime mean precipitation in the Yangtze River urban areas, but increased the nighttime mean precipitation; The urbanization significantly increased the daily, daytime and nighttime mean temperature, and the urban heat island effect was stronger during the nighttime, the climatology temperature daily change also indicated that the urban heat island intensity enhanced at night; urbanization also enhanced the daily maximum and minimum temperatures, but decreased the diurnal range, the minimum temperature also increased more significantly. Urbanization caused land surface changes in land use, significantly decreased the latent heat flux, but enhanced the sensible heat flux and the planetary boundary layer during the daytime.