Urbanization-induced land and aerosol impacts on sea-breeze circulation and convective precipitation

Jiwen Fan,Daniel Rosenfeld,Jiaxi Hu,Yuwei Zhang,Zhanqing Li

doi:10.5194/acp-20-14163-2020

Abstract

Abstract. Changes in land cover and aerosols resulting from urbanization may impact convective clouds and precipitation. Here we investigate how Houston urbanization can modify sea-breeze-induced convective cloud and precipitation through the urban land effect and anthropogenic aerosol effect. The simulations are carried out with the Chemistry version of the Weather Research and Forecasting model (WRF-Chem), which is coupled with spectral-bin microphysics (SBM) and the multilayer urban model with a building energy model (BEM-BEP). We find that Houston urbanization (the joint effect of both urban land and anthropogenic aerosols) notably enhances storm intensity (by ∼ 75 % in maximum vertical velocity) and precipitation intensity (up to 45 %), with the anthropogenic aerosol effect more significant than the urban land effect. Urban land effect modifies convective evolution: speed up the transition from the warm cloud to mixed-phase cloud, thus initiating surface rain earlier but slowing down the convective cell dissipation, all of which result from urban heating-induced stronger sea-breeze circulation. The anthropogenic aerosol effect becomes evident after the cloud evolves into the mixed-phase cloud, accelerating the development of storm from the mixed-phase cloud to deep cloud by ∼ 40 min. Through aerosol–cloud interaction (ACI), aerosols boost convective intensity and precipitation mainly by activating numerous ultrafine particles at the mixed-phase and deep cloud stages. This work shows the importance of considering both the urban land and anthropogenic aerosol effects for understanding urbanization effects on convective clouds and precipitation.

Highlights

Urbanization has been a significant change in the earth’s environment since industrialization and is expected to further expand during the coming decades (Alig et al, 2004)
To answer the science question, we employ the Chemistry version of the Weather Research and Forecast (WRF) model coupled with the spectral-bin microphysics (WRF-Chem-SBM) scheme, a model we previously developed and applied to warm stratocumulus clouds (Gao et al, 2016), to simulate a deep convective storm case that occurred over the Houston region and produced heavy precipitation
We have investigated the Houston urbanization effects on convective evolution, convective intensity, and precipitation of a sea-breeze-induced convective storm using WRF-Chem coupled with SBM and the BEM-BEP urban canopy model

Summary

Introduction

Urbanization has been a significant change in the earth’s environment since industrialization and is expected to further expand during the coming decades (Alig et al, 2004). Urbanization could impact storm properties through two major pathways. The most typical and extensively studied effect is the increase in surface temperature compared to the surrounding rural area, known as the urban heat island (UHI) effect (e.g., Bornstein and Lin, 2000; Shepherd, 2005; Hubbart et al, 2014). Convective storms may be initiated at the UHI convergence zone, created through a combination of increased temperature and mechanical turbulence resulting from complex urban surface geometry and roughness (Bornstein and Lin, 2000; Shepherd, 2005; Hubbart et al, 2014). Urban landscapes impact sensible and latent heat flux, soil moisture, etc., affecting thunderstorm initiation (Haberlie et al, 2015) and changing the location and amount of precipitation compared to the Published by Copernicus Publications on behalf of the European Geosciences Union

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