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Diagnostic analysis of future climate scenarios applied to urban flooding in the Chicago metropolitan area

TitleDiagnostic analysis of future climate scenarios applied to urban flooding in the Chicago metropolitan area
Publication TypeManual Entry
AuthorsMarkus, Momcilo, Donald J. Wuebbles, Xin-Zhong Liang, Katharine Hayhoe, and David A. R. Kristovich
Date PublishedAPR

Past heavy precipitation events in the Chicago metropolitan area have caused significant flood-related economic and environmental damages. A key component in flood management policies and actions is determining flood magnitudes for specified return periods. This is a particularly difficult task in areas with a complex and changing climate and land-use, such as the Chicago metropolitan area. The standard design storm methodology based on the NOAA Atlas 14 and ISWS Bulletin 70 has been used in the past to estimate flood hydrographs with variable return periods in this region. In a changing climate, however, these publications may not be accurate. This study presents and illustrates a methodology for diagnostic analysis of future climate scenarios in the framework of urban flooding, and assesses the corresponding uncertainties. First, the design storms are calculated using data downscaled by a regional climate model (RCM) at 30-km spacing for the present and 2050s under the IPCC A1Fi (high) and B1 (low) emissions scenarios. Next, the corresponding flood discharges at six watersheds in suburban Chicago are estimated using a hydrologic event model. The resulting scenarios in flood frequency were first assessed through a set of diagnostic tests for precipitation timing and frequency. The study did not reveal any significant changes in the 2050s in the average timing of heavy storms, but their regularity decreased. The average timing did not exhibit any significant spatial variability throughout the region. The precipitation frequency analysis revealed distinct differences between the northern and southeastern subregions of the Chicago metropolitan area. The quantiles in the northern subregion averaged for 2-year, 5-year, and 10-year return periods exhibited a 20% and 16% increase in daily precipitation for scenarios B1 and A1Fi, respectively. The southeastern subregion, however, exhibited a decrease of 12% for scenario B1 and a minor increase of 3% for scenario A1Fi. The hydrologic effects of changing precipitation on the flood quantiles were illustrated using six small watersheds in the region. The relative increases or decreases in precipitation translated into even larger relative increases or decreases in flood peaks, due to the nonlinear nature of the rainfall-runoff process. Simulations using multiple climate models, for longer periods, finer spatio-temporal resolution, and larger areal coverage could be used to more accurately account for numerous uncertainties in the precipitation and flood projections.

Citation Key1137
Community Notes

"The main goal of this research is to develop and illustrate a methodology for diagnostic analysis of heavy precipitation, in particular, the magnitude and frequency under future climate scenarios in the framework of urban flooding. Future precipitation time series were based on a regional climate model, described in Liang et al. (2001, 2004b). The corresponding floods were calculated using the methodology described in FEMA (2003), based on the design storm approach (Singh 1992)."

RCM used for future projections was the fifth generation Pennsylvania State University-National Center for Atmospheric Research Mesoscale Model (MM5).  The driving GCM simulations were from the PCM model.  SRES A1Fi (high) and B1 (clean and resource-efficient) emissions scenarios were used.

"Timing of precipitation events can be calculated using circular statistics: mean daily value (MDV) and regularity"

Differences in future extreme precipitation were found between the north and south regions of Chicago.

There are so many sources for uncertainty that it is necessary to validate the dipole changes with additional models before trusting the results of this individual study.