Impacts of Green Infrastructure on the Water Budget and Other Ecosystem Services in Subhumid Urban Areas

Abstract:

Green infrastructure (GI) measures have been well established as part of low-impact development approaches for stormwater (SW) management. The origin of the concepts, practices and the preponderance of research have taken place in humid climates. Recent work has begun to explore and adapt GI to subhumid and semi-arid climates, which experience warmer and drier periods. But much remains unknown about effects of GI on the water cycle and how to effectively implement to maximize ecosystem benefits. This research synthesizes observation and modeling to address questions related to changes in evapotranspiration (ET), SW runoff volume, and other water cycle processes from GI introduction in Salt Lake City, Utah, USA. First, the water budget of green roofs is being studied via weighing lysimeter systems on two rooftop gardens on the University of Utah campus. ET, outflow, and soil moisture have been measured for approximately one year. Up to this early summer, average ET rates for lysimeters of pure medium, Sedums, and Bluegrass are 1.85±1.01, 1.97±0.94, and 2.31±0.91 mm/d respectively; the maximum ET rate could reach 6.11 mm/d from Sedums. Over 2/3 of total rainfall and irrigation were slowly consumed via ET from green roof. Second, the observation studies are leading to new ET modeling techniques that are being incorporated into the U.S. EPA Storm Water Management Model (SWMM). The modified SWMM has been used to simulate ET, SW runoff volume, and overall water budget changes from GI implementation. Preliminary result shows that ET could account for 10% of the total inflows into bioretentions, and 25% of the inflows into landscapes; potential ET rates could vary up to 0.95 mm/hr across 53 subcatchments in the 29 acres catchment. The influence of various design factors for GI on SW runoff reduction and the water budget is also to be estimated. The application of the research is to analyze the water budget of the Red Butte Creek Watershed in Salt Lake City and to explore the necessary GI elements to approach pre-development water budget conditions.