Urban Thermal Influence on the Background Environment of Convective Precipitation

Abstract

 Does the cities enhance precipitation? It is an unsettled question and the comprehensive answer has not been archived for it. This study focuses on the urban heat excess and evaluates its influence on atmospheric instability which is the background condition for the convective precipitation. A simple approach was developed that involved calculating the daytime evolution of the mixed layer over homogeneous ground surface. Calculations were based on the ensemble average of observations. The convective available potential energy (CAPE) was evaluated for both urban and rural land cover. Urban heat excess, which was 200 W m^-2 higher in the urban than rural area, increased CAPE by 75 % comparing to the rural CAPE of 513 J kg^-1. Results show that cities could cause favorable stratification of the atmosphere for convective precipitation.