Effects of Land Cover on Streamflow Variability in a Small Iowa Watershed: Assessing Future Vulnerabilities

Agricultural expansion and urbanization, coupled with climate change represent major threats to the sustainability of river ecosystems and infrastructure. In this study, we evaluated how subbasins with different dominant land covers within the 27.5 km² Clear Creek, IA watershed affect key hydrologic indicators. Hydrologic output from two stream gages and a calibrated Soil Water Assessment Tool (SWAT) model were used as input to the Indicators of Hydrologic Alteration (IHA). Study results indicated that land cover plays a dominant role in controlling hydrologic variability at the subbasin level within a watershed. Subbasins dominated by urban development had nearly 30 more reversals than row crop or grass-dominated subbasins and the duration of small and large flood events were half as long. Row crop dominated subbasins had greater water yield and maximum flows and higher peak flows, whereas grass-dominated subbasins had lower rise and fall rates, fewer zero days and fewer reversals. Hydrologic variations from land cover differences were more prominently expressed at the subbasin level than at the watershed level, as the dominant land cover represented a greater percentage of the total land area. Study results suggest that future changes in LU/LC and climate will have significant effects on the hydrology of Clear Creek Watershed.