The rapid urbanization of past decades is expected to continue, with an approximately six-fold increase in urban land by the end of the century. Changes in land cover and the anthropogenic aerosols caused by urbanization could impact the weather and climate, but the current scientific understanding of their influence remains poor. Past studies focused solely on the effects of either urban land change or anthropogenic aerosols but not their joint effects. Researchers led a study aimed at understanding the combined effects of coastal urban land development and anthropogenic aerosols on convective storm evolution and precipitation while ascertaining their individual roles. They found that urban land and anthropogenic aerosols in the Houston area work together to drastically enhance storm intensity and precipitation rate. This work improves the fundamental understanding of how urbanization impacts thunderstorms over the Houston area.
Urbanization has rapidly increased in recent years, with further urbanization expected in upcoming decades. Urbanization causes changes in land cover and land use while drastically boosting anthropogenic aerosols, which can influence weather and climate. Understanding how these factors jointly affect convective storms and precipitation can help reduce uncertainties in weather and climate predictions. While this study specifically looked at the Houston area, the insights gained about urbanization effects might also apply to other warm and humid coastal cities.
The researchers investigated the impacts of Houston urbanization on convective storm evolution and precipitation by focusing on changing land cover and anthropogenic aerosols. To do this, they employed detailed models: the Chemistry version of the Weather Research and Forecasting model coupled with a bin microphysics model and a multilayer urban model with a building energy model. Simulations were run at very high resolution with 0.5 km grid spacing. The researchers first evaluated simulations of aerosol, radar reflectivity, and precipitation properties using observations before carrying out model sensitivity tests. In these tests they replaced urban land with surrounding cropland and shut off anthropogenic emissions, allowing them to specifically examine the effects of urban land and anthropogenic aerosols. They found that the joint changes in urban land and anthropogenic aerosols notably enhanced storm intensity, radar reflectivity (by up to 10 dBZ), peak precipitation rate (by ~ 45%), and accumulated rain (by ~ 26%), with anthropogenic aerosol effects playing a dominant role. However, the urban land effect strengthened sea breeze circulation, leading to faster development of warm clouds into mixed-phase clouds and an earlier start of rainfall. Aerosol effects accelerated the development of storms into deep convection events and play a dominant role in enhancing storm intensity and precipitation at the deep cloud stage. This work also shows the importance of considering both urban land and anthropogenic aerosol effects to understand how urbanization affects convective clouds and precipitation.