Stormwater Runoff Response Under Changing Climate and Land uses Across Gradients of Inland and Coastal Urban-Natural Basin

Abstract

Climatic variability has caused significant shifts in the magnitude, frequency and spatiotemporal distribution of precipitation, generating excessive runoff that leads to frequent occurrences of extreme hydrologic events such as the pluvial (rainfall accumulation) and fluvial (riverine) floods. The conversion of natural areas into urban lands is further exacerbating the rainfall accumulation by increasing surface imperviousness that hinders infiltration of water into the soil. This dissertation predicts and characterizes potential shifts in the future annual stormwater runoffvolumes and runoff extremes under the standalone and coupled changes in climate and land use across inland and coastal urban-natural settings. The research was performed by considering Southwest Florida Basin (28,530 km2) and Kissimmee River Basin (10,686 km2) as the test beds of, respectively, coastal and inland urban-natural environments. Process-based hydrologic modelswere developed for these two basins by using the Storm Water Management Model (SWMM) of U.S. Environmental Protection Agency (EPA). The models were calibrated and validated to successfully predict the daily mean streamflow observations (Nash Sutcliffe Efficiency, NSE =0.70 to 0.86) during 2004-2013 (2010s). The models were then employed to investigate runoffsensitivities to synthetic changes in climatic and land use variables in the two basins. Further, changes in the annual runoff volume, as well as in the extreme runoffs of 1-7 day durations with 2, 5, 10, 25, 50, and 100 year return periods, were computed for the future time-frames of 2050s (2044-2053) and 2080s (2076-2085) based on the climatic projections from 20 Global Circulation Models and land use projections from EPA. Results suggested higher, but comparable changes inannual stormwater runoff volume under standalone climatic and land use changes in the coastal urban-natural basin. In contrast, the inland urban-natural basin exhibited much higher changes in runoff due to climatic changes than that due to land use changes. Simultaneous changes in climatic and land use variables led to much higher, non-linear changes in annual runoff volume for both basins. The annual runoff volume in the coastal urban-natural basin was projected to increaseby 18 to 62% under climatic changes, 24 to 39% under land use changes, and by 60 to 114% under concurrent climatic and land use changes during 2050s to 2080s, compared to that of the 2010s. The inland urban-natural basin had a comparable projected increase (11 to 30%) in annual runoff volume under land use changes. However, much higher increases in annual runoff volume wereprojected in the inland urban-natural basin during 2050s and 2080s