| In recent years,land use/cover types have changed rapidly in the Sichuan Basin,formed a double star city cluster with Chengdu and Chongqing as the center,it is of great significance to study the effect of this change on meteorology and even climate.This paper uses the land use/cover type data of the Sichuan Basin,site observation data from meteorological stations,ERA-Interim and NCEP reanalysis data as research data.Analyze the change of land use/cover type in the Sichuan Basin and its impact on the temperature of the basin and its typical cities,then,the WRF model coupled with the urban canopy scheme and underlying surface data at different periods were used for sensitivity tests,the effects of urbanization in Chengdu on the local summer and winter climate and the influence of meteorological conditions on the spread of winter pollution are studied.The main conclusions are drawn as follows:(1)The types of land use/cover are mainly green vegetation in the marginal areas of the Sichuan Basin,and within the basin are agricultural and natural vegetation mosaics and farmland.The major change in land use/cover types from 1981 to 1990was the large-scale increase in drylands in the Sichuan Basin.From 1990 to 2000,a large number of drylands became paddy fields and mosaics of agricultural and natural vegetation in the basin.From 2000 to 2010,the area of paddy fields decreased,and the areas of evergreen broad-leaved forest and deciduous broad-leaved forest increased in the basin,the urban areas of Chengdu and Chongqing continued to expand,but Chengdu's expansion rate and area were larger than those of Chongqing.From 1980 to2017,changes in land use/cover types in the Sichuan Basin caused the temperature rise in most regions,and the temperature rise became stronger,the temperature trends in Chengdu and Chongqing are roughly the same as those in the basin,and Chengdu's urbanization is stronger than Chongqing.(2)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 height of boundary layer increases by about 150 m,in winter,the surface temperature increases by about 0.6?in the urban area,and the height of boundary layer increases by about 25 m.The diurnal temperature range both in summer and winter decreases.In summer and winter in Chengdu area,the relative humidity of 2m decreases and the sensible heat flux increases and the latent heat flux decreases due to the influence of urbanization,but the degree of change in summer is stronger than in winter.(3)In summer and winter,wind speed decreases by about 0.1m·s-1?0.6 m·s-1in urban area due to increase of 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.In summer,due to urbanization,the average daily precipitation and daytime precipitation increase in the urban upwind direction and downwind direction,nighttime precipitation increases in downwind direction areas in urban,but it has no significant effect on urban upwind areas.(4)During the period of heavy pollution and non-pollution,the urbanization of Chengdu significantly increased the temperature of 2m,and the temperature range is consistent,urbanization has also caused warming areas over urban areas,with warming periods concentrated in the afternoon and inversion periods,but,during the pollution-free period,the temperature rise area is larger and the intensity is stronger than during the heavy pollution period.Urbanization also reduces the relative humidity of 2m,and the reduction range is the same,the relative humidity reduction in urban areas during non-polluting periods is lower than during heavy pollution periods.(5)The urbanization of Chengdu will increase the daily average boundary layer height of the urban area,reduce the daily average wind speed,and have a significant negative correlation with AQI changes.During heavy pollution and non-pollution periods,urbanization reduces wind speed in urban areas and downwind areas,but the reduction values and ranges are different,during the period of heavy pollution,the area of reduced wind speed was concentrated in the leeward side of the city and its downwind area,wind speed did not decrease significantly in the windward area,during the pollution-free period,urbanization reduces the wind speed of the entire urban area and its downwind area,and the wind speed reduction value is greater than that during the heavy pollution period.Urbanization also increased the vertical velocity over the urban expansion area,but the range and height of the vertical velocity increase during the pollution-free period were greater than during the heavy pollution period,urbanization also makes the height of the boundary layer of the urban area increase less during periods of heavy pollution than during periods of no pollution. |
PDF Full Text Request