New study predicts urban development and greenhouse gases will fuel urban floods

Sustainability scientist Matei Georgescu, associate professor in ASU’s School of Geographical Sciences and Urban Planning, is lead author of a new study, Precipitation response to climate change and urban development over the continental United States, published in the journal Environmental Research Letters.

When rain began falling in northern Georgia on Sept. 15, 2009, little did Atlantans know that they would bear witness to epic flooding throughout the city. Georgia’s busiest expressway was underwater, as were roads and bridges; untreated sewage mingled with rising flood waters; cars and people were swept away. Moisture from the Gulf of Mexico fueled the flood of 2009.

A decade later, Arizona State University researchers are asking whether a combination of urban development — and climate change fueled by greenhouse gases — could bring about comparable scenarios in U.S. cities. Based on a just-published study, the answer is yes. Read the full story in ASU News. The abstract follows.

Appropriately characterizing future changes in regional-scale precipitation requires assessment of the interactive effect owing to greenhouse gas-induced climate change and the physical growth of the built environment. Here we use a suite of medium resolution (20 km grid spacing) decadal scale simulations conducted with the Weather Research and Forecasting model coupled to an urban canopy parameterization to examine the interplay between end-of-century long-lived greenhouse gas (LLGHG) forcing and urban expansion on continental US (CONUS) precipitation. Our results show that projected changes in extreme precipitation are at least one order of magnitude greater than projected changes in mean precipitation; this finding is geographically consistent over the seven CONUS National Climate Assessment (NCA) regions and between the pair of dynamically downscaled global climate model (GCM) forcings. We show that dynamical downscaling of the Geophysical Fluid Dynamics Laboratory GCM leads to projected end-of-century changes in extreme precipitation that are consistently greater compared to dynamical downscaling of the Community Earth System Model GCM for all regions except the Southeast NCA region. Our results demonstrate that the physical growth of the built environment can either enhance or suppress extreme precipitation across CONUS metropolitan regions. Incorporation of LLGHGs indicates compensating effects between urban environments and greenhouse gases, shifting the probability spectrum toward broad enhancement of extreme precipitation across future CONUS metropolitan areas. Our results emphasize the need for development of management policies that address flooding challenges exacerbated by the twin forcing agents of urban- and greenhouse gas-induced climate change.