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Publication Date
14 May 2024

Urban feedbacks to deep convection

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Analyses of observations of cloud height, precipitation rates, and RADAR reflectivity indicate that, over Dallas Fort Worth (DFW), downwind urban enhancement of precipitation is only manifest for low & moderate-intensity rainfall rate events. WRF simulations for heavy rainfall events indicate the magnitude/sign of urban rainfall enhancement and impacts from urban expansion are highly dependent on both the microphysics scheme used to represent cloud processes and the prevailing synoptic regime.


Urbanization is a global trend. Quantifying feedbacks to hazards associated with deep convection can aid planning for building climate-resilient cities of the future.


A range of multi-year observational data sets are used to characterize the hydroclimate of the Dallas Fort-Worth area (DFW) and to investigate the impact of urban land cover on daily accumulated precipitation, RADAR composite reflectivity (cREF), and cloud top height (CTH) during the warm season months. Analyses of observational data indicate rainfall rates (RR) in a 45° annulus sector 50-100 km downwind of the city are enhanced relative to an upwind area of comparable size consistent with the majority of past literature that has indicated urban rainfall enhancement (URE). Further, the probability of high cREF and CTH are also increased downwind of DFW. However, enhancement of mean precipitation intensity in the downwind annulus sector is not observed on days with spatially averaged RR > 6 mm/day. Two deep convection events that passed over DFW are simulated with the Weather Research and Forecasting model at 1km grid spacing using a range of microphysical schemes and evaluated using RADAR observations. Model configurations that exhibit the highest fidelity in these control simulations are used in a series of perturbation experiments where the areal extent of the city is varied between zero (replacement with grassland) and eight times its current size. These perturbation experiments indicate a non-linear response of Mesoscale Convective System properties to the urban areal extent and a very strong sensitivity to the microphysical scheme used. The impact on precipitation from the urban area, even when it is expanded to eight times the current extent, is much less marked for deep convection with stronger synoptic forcing. These results imply great caution needs to be used in extrapolating from studies that employ WRF with only one microphysics scheme and/or that do not stratify data by the prevailing atmospheric conditions. 

Point of Contact
Professor Sara C Pryor
Cornell University
Funding Program Area(s)
Additional Resources:
NERSC (National Energy Research Scientific Computing Center)