Impacts of Urbanization on Convective Storms through Urban Land and Aerosol effects

Tuesday, 15 December 2020: 08:34
Jiwen Fan1, Yun Lin2, Yuwei Zhang1, Jong-Hoon Jeong2, Zhanqing Li3 and Cameron R Homeyer4, (1)Pacific Northwest National Laboratory, Richland, WA, United States, (2)Pacific Northwest National Laboratory, Richland, United States, (3)University of Maryland, Atmospheric and Oceanic Sciences Department, College Park, MD, United States, (4)University of Oklahoma, School of Meteorology, Norman, OK, United States
There has been a rapid increase in urbanization in recent decades and a further increase in the coming decades. Urbanization effect on weather and climate is not well understood yet, particularly about how urban land cover change and anthropogenic aerosols jointly affect them. Here, using WRF-Chem in which the spectral-bin microphysics (SBM) is coupled with the Model for Simulating Aerosol Interactions and Chemistry (MOSAIC) at cloud-resolving scale (1 km), we studied the urbanization effects on two different types of convective storms: a supercell storm influenced by Kansas City producing hail, tornado, and strong wind during PECAN campaign and

a sea-breeze induced thunderstorm occurring near Houston. We find that the joint effect of urban land and anthropogenic aerosols plays an important role in affecting storm dynamics, evolution, precipitation, and hail frequency and size. The relative importance of the urban land effect to the aerosol effects strongly depends on storm types and associated environmental conditions, emphasizing resolving storm dynamics is key for accurately simulating their effects.

Specifically, for the Kansas City supercell storm, the urban land effect initiates a much stronger convective cell and the storm gets much intensified when interacting with stronger turbulence. The urban land effect diverts the storm toward the city. The joint effect enhances the occurrences of both severe hail and significant severe hail by ~ 20%. Overall the urban land effect on convective intensity and hail is larger than the aerosol effect. However, for the Houston storm, the joint effect drastically enhances storm intensity and precipitation, with the anthropogenic aerosol effect more significant than the urban land effect. The urban land effect strengthened sea breeze circulation, leading to faster development of the deep storm and earlier rain.