| Urbanization has an important impact on weather and climate.In this paper,using reanalysis data,through weather diagnosis and mesoscale numerical model WRF coupling SLUCM methods,we conducted research and analysis of the warm-sector heavy rainfall in Southern China on June 23,2012 and May 8,2014,respectively,and obtained the following conclusions: More successful simulations of the warm-sector heavy rainfall cases in Southern China,May 8,2014 and June 23,2012.The urban canopy and parameter allocation schemes that are suitable for localization are derived;1)To explore the impact of anthropogenic heat(AH)on warm-sector heavy rainfall in Southern China,The numerical simulation was carried out the warm rainstorm in the Pearl River Delta(PRD)for May 8,2014,using the WRF-SLUCM model and considering the appropriate AH release.Analysis of the simulation results with or without the AH effect shows that precipitation is sensitive to the impact of AH,and the AH effect reduces the total urban precipitation by about 10%.The possible mechanisms are: thermal field and flow field redistribution caused by the increase of AH,making the local convergence shift to the border area of PRD to enhance the convection and precipitation of urban and rural borders;the more homogeneous urban thermal environment in PRD urban areas reduces thermal contrast and weakens convergence,thereby reducing precipitation in urban areas.2)Since the warm-sector heavy rainfall in Southern China is sensitive to the impact of AH,in order to explore the relative contribution of urbanization(Urban)effects(incorporating the city's underlying surface and urban canopy schemes),through comparative assessment,it was found that heavy rainfall responds to changes in single AH,single urban element,comprehensive AH and Urban element,but the latter is not a simple linear superposition of the former two.Through comparative analysis,it was found that the Urban effect increased the total precipitation in the PRD urban area by 10.2%.In the course of the response to the Urban effect in the increase of precipitation,the regional difference was significant,especially the increase effect of the downwind to the urban area was particularly significant,with an increase of 12.6%.Urban and AH effects have oppositely distributed effects on precipitation.Compared with the Urban effect,AH caused a 7.8% reduction in urban precipitation.It can be seen that the Urban effect contributes more to the change in precipitation in urban areas.However,in terms of precipitation distribution modalities,correlation analysis shows that AH contributes more to the effect of the Urban effect on precipitation distribution modes.By comparative analysis of the Urban and AH effects on the changes of meteorological elements in the near-surface and boundary layers of the city,and the synergistic changes with precipitation changes,it was found that the height of the planetary boundary layer,the near-surface moisture and temperature are the dominant factors that determines Urban's contribution to the modal distribution of the warm-sector heavy rainfall in Southern China.And the effect of AH effect on precipitation is mainly related to near-surface temperature and humidity and ground surface pressure.Through the analysis of the temperature and moisture stratification and stability of the three experimental programs,it was found that the precipitation intensity of the urban area was greatly affected by the convective instability of the lower atmosphere.After considering the Urban effect and then increasing the AH effect,due to the increase of surface heat flux in cities and the decrease of water vapor in the city's underlying surface,the vertical profile of the moist static energy,which reflects the comprehensive effect of temperature and humidity,showed a trend of increasing first and then decreasing with the increase of urban factors in the low boundary layer.Convective instability led to change,and the final triggering of precipitation in urban areas also showed an evolution of first increase and then decrease.3)Taking into account the prevailing wind direction and the effects of upstream and downstream urbanization,it was found that the increase in precipitation was mainly concentrated in the adjoining urban-rural boundary in the upwind direction.The distribution of PBLH caused by near-surface temperature difference(T2)and its upward transmission effect forms a large urbanization gradient at the interface between urban and rural areas.This boundary effect leads to mass accumulation and local convergence,leading to an increase in precipitation at the urban-rural interface at the windward,a decrease in precipitation in urban areas.The above studies not only help to understand the mechanism of the occurrence and development of warm-sector heavy rainfall in Southern China,but also improve the reference for improving simulation and forecasting. |
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