Improved understanding and prediction of extreme precipitation in multiple urban systems

Cities are becoming increasingly vulnerable to flooding because of changes in the heavy precipitation patterns caused by climate warming and urbanization. There has been an increase in heavy rain occurrences and associated risk of urban flooding in the past decade worldwide especially in rapidly expanding cities in densely populated developing countries like India and China. Since 1991, according to the 2014 National Climate Assessment, the biggest storms have produced 30 percent more rain than the 1901-1960 average in the Northeast, Midwest, and Upper Great Plains. Even with better planned and mature urban cities, urban areas in Europe and North America are not immune to vagaries of extreme precipitation. Hence, impacts of climate warming are expected to increase the risk of urban flooding. Urbanization itself can exacerbate the occurrence of heavy precipitation in and around cities, through modifying the physical properties of land-surface characteristics and regional and local atmospheric circulations. Recent meta-analysis revealed that cities substantially modified the patterns and amount of summer storms, and that sub-daily extreme rainfall was intensified by urban heat islands (UHIs). However, there is limited concerted effort that has been undertaken by an interdisciplinary team to integrate multiscale multi-sensor datasets, and detailed urban models to enrich our understanding of the change trend associated with UHI and urban extreme precipitation (EP).

Therefore, we propose to integrate NASA satellite products, high-resolution urban-specific simulations, and detailed diagnostics to assess the impact of urban physical processes on EP in urban areas, especially sub-daily extremes, and its relationship with larger-scale climate warming and regional urbanization for multiple urban systems located in various geographical and climate regimes. Overall, this research will bring together interdisciplinary expertise in information science, urban-climate dynamics, urbanization-effect modeling, and regional climate simulations to address the following three principal questions:

  • Is there a significant observed relationship between urban heat islands and urban extreme precipitation for cities with different climate regimes and paces of urbanization?
  • How does current climate warming and urbanization individually and collectively contribute to the plausible intensification of urban extreme precipitation?
  • How will such intensification evolve in future climate warming and further urban development?

Specifically, the following tasks will be undertaken to address the above questions:

  • Integrate satellite and in-situ data to understand the evolution of urban EP and its relationship with UHI and associated aerosol interactions for selected cities.
  • Utilize fine-scale satellite data to assess the evolution (before and after a rapid urbanization) of detailed characteristics of aerosol emissions, urban forms, morphology, land-surface properties, and anthropogenic heating that contribute to changes in UHI; develop more realistic urban model parameters for improving the representation of urbanization in earth system models.
  • Implement the new urban parameters and physics in the Weather Research and Forecasting (WRF) urban modeling system (WRF-Urban) and evaluate the model performance for both UHI and urban precipitation simulations for different cities and under different conditions (local convection, frontal storms, large scale systems).
  • Conduct high-resolution seasonal simulations for selected cities to explore the individual and collective effects of urbanization and climate warming on the intensification of urban EP.
  • Assess effects of future climate warming and urban expansion on urban EP.