Using the Storm Water Management Model to predict urban headwater stream hydrological response to climate and land cover change

摘要

Streams are natural features in urban landscapes that canprovide ecosystem services for urban residents. However, urban streams areunder increasing pressure caused by multiple anthropogenic impacts,including increases in human population and associated impervious surfacearea, and accelerated climate change. The ability to anticipate thesechanges and better understand their effects on streams is important fordeveloping and implementing strategies to mitigate potentially negativeeffects. In this study, stream flow was monitored during April–November(2011 and 2012), and the data were used to apply the Storm Water ManagementModel (SWMM) for five urban watersheds in central Iowa, USA, representinga gradient of percent impervious surface (IS, ranging from 5.3 to 37.1%).A set of three scenarios was designed to quantify hydrological responses toindependent and combined effects of climate change (18% increase inprecipitation), and land cover change (absolute increases between 5.2 and17.1%, based on separate projections of impervious surfaces for the fivewatersheds) for the year 2040 compared to a current condition simulation. Anadditional set of three scenarios examined stream response to differentdistributions of land cover change within a single watershed. Hydrologicalresponses were quantified using three indices: unit-area peak discharge,flashiness (R-B Index; Richards–Baker Index), and runoff ratio. Stream hydrology was stronglyaffected by watershed percent IS. For the current condition simulation,values for all three indices were five to seven times greater in the mostdeveloped watershed compared to the least developed watershed. The climatechange scenario caused a 20.8% increase in unit-area peak discharge onaverage across the five watersheds compared to the current conditionsimulation. The land cover change scenario resulted in large increases forall three indices: 49.5% for unit-area peak discharge, 39.3% forR-BIndex, and 73.9% for runoff ratio, on average, for the five watersheds.The combined climate and land cover change scenario resulted in slightincreases on average for R-B Index (43.7%) and runoff ratio (74.5%)compared to the land cover change scenario, and a substantial increase, onaverage, in unit area peak discharge (80.1%). The scenarios for differentdistributions of land cover change within one watershed resulted in changesfor all three indices, with an 18.4% increase in unit-area peak dischargefor the midstream scenario, and 17.5% (downstream) and 18.1%(midstream) increases in R-B Index, indicating sensitivity to the locationof potential additions of IS within a watershed. Given the likelihood ofincreased precipitation in the future, land use planning and policy toolsthat limit expansion of impervious surfaces (e.g. by substituting pervioussurfaces) or mitigate against their impacts (e.g. by installing bioswales)could be used to minimize negative effects on streams.