Baltimore Ecosystem Study Institute of Ecosystem Studies

2015 BES Annual Meeting Presentation and Poster Abstracts

Type and timing of stream flow changes in urbanizing watersheds
Hopkins, Kristina
Co-Authors: Kristina G. Hopkins, Nathaniel B. Morse, Daniel J. Bain, Neil D. Bettez, Nancy B. Grimm, Jennifer L. Morse, and Monica M. Palta

Abstract: Linking the type and timing of hydrologic changes with patterns of urban growth is essential to identifying the underlying mechanisms that drive declines in urban aquatic ecosystems and to understanding the drivers of regional variability in hydrologic changes. We characterized stream flow changes in nine U.S. cities (including Baltimore) using two approaches 1) urbanization gradients and 2) long-term (>40 years) watershed studies. Hydrologic changes were characterized using USGS stream flow records and a suite of hydrologic indices. Results from the gradient approach indicated heterogeneity in the type and magnitude of hydrologic responses to urbanization, with watersheds in glaciated terrains having less frequent high-flow events and longer high-flow durations compared to similarly developed watersheds in non-glaciated terrains. Our result suggested differences in physical characteristics associated with low relief and high water storage capacity likely buffer the severity of hydrologic changes. Results from the long-term approach indicated significant increases in high-flow frequency and runoff efficiency, with rapid (10-15 years) shifts toward more frequent high-flow events between 1969 and 1976 in three watersheds. Results suggested the intensity of development during the peak growth period had the strongest association with the magnitude of high-flow changes, while the timing of high-flow changes was mainly driven by the development trajectory of each watershed. Our results underscore the need to refine urban stream syndrome theory to incorporate the impact of gradual versus rapid urbanization, as well as recognize that the dominant drivers of hydrologic changes are heterogeneous among urban watersheds and change through time.