The Role of Urbanization in Modifying Post-Landfall Hurricane Rainbands

The continuous growth of urban development in the coastal regions of the southeastern and southwestern United States, combined with projections of increased intense hurricane occurrences, raises concerns about the impact of urbanization on hurricane post landfall characteristics, specifically inland precipitation. The existing literature lacks studies that thoroughly investigate the impact of realistic, multi-decadal urban land cover changes on landfalling hurricanes. To bridge this gap, this study employs realistic urban change over the Houston region and used WRF simulations to simulate the hurricane Harvey (2017) under LULC from 2001 and 2017. This study used a combination of observational analyses, mesoscale modeling through the Weather Research and Forecasting (WRF) model, and idealized simulations employing the Cloud Model (CM1) to understand the dynamics of hurricane rainbands and changes associated with the underlying land surface characteristics. Specifically, this research focuses on three significant hurricane events – Harvey 2017, Rita 2005, and Ike 2008 – that made landfall around the Houston city, enabling a comprehensive exploration of their rainband characteristics. The experiments are being done by replacing the model surface properties like LULC and greenfrac from 2001 and 2017 so that the model can simulate the realistic land surface characteristics to simulate hurricane rainbands. Modeling analysis shows the enhancement of rainbands which eventually leads to increase in precipitation over the urban area and the similar characteristics found in all the three hurricanes, and similar rainband characteristics are also supported by the sensitivity experiments done by altering the water vapor mixing ratio.

Furthermore, this study incorporates idealized experiments facilitated by the CM1 model, wherein variations in surface roughness are manipulated. Several idealized experiments using the CM1 model by changing the surface roughness have also been performed to support the conclusion from the WRF model, and found the same dynamics behind the enhancement of rainbands. Urbanization significantly influences precipitation patterns with a shift in both location and intensity. It plays a vital role in decelerating rainband propagation, resulting in short-lived rainbands with slower speeds and modified precipitation patterns, particularly near cities where significant urban growth has been noticed. Despite changes in land surface characteristics, they don't substantially affect hurricane track and intensity after landfall. Urban-induced changes in wind, moisture content, and vertical motion lead to more intense and persistent rainbands, showing the urban changes have a significant influence on hurricane precipitation.

This study presents a comprehensive analytical framework which uses the observational insights and numerical modeling, which collectively deepen our understanding of the dynamics of hurricane rainbands. As cities keep growing near the coasts, this research is really important for getting ready for disasters, planning cities, and coming up with ways to lessen the problems caused by heavy rain during hurricane landfall.