We know that urban development strongly affects the amount of water in streams after a storm, but urban impacts have mostly been documented in cities with wet climates. We don’t know as much about how streams are affected by urbanization in cities with dry climates. We used the Denver metro area as a case study to understand these patterns. Denver has a dense network of rain and streamflow monitoring through the Mile High Flood District and US Geological Survey, and in nearby Rocky Flats grasslands monitored by the Department of Energy.
We paired over 3,000 rain events with their corresponding streamflow responses in 21 streams across a range of levels of urban development from grassland (Rocky Flats watersheds) to dense urban (Harvard Gulch in Denver).
We found that in the Denver area, urbanization:
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- reduced the time that streams are dry from greater than 50% of the summer for grassland streams down to 0% (always flowing) for most urban streams
- increased the responsiveness of streamflow to small rain events, resulting in more frequent stormflow in urban streams
- increased peak streamflow after a storm and shortened the length of time that streamflow was elevated after a storm. This can be seen from an example comparison of the streamflow response to a similar sized rain event in an urban and rural stream:
These findings help us understand how streamflow changes with urban development in a semi-arid setting, which is important to managing the effects of these altered patterns of streamflow on infrastructure, water availability, and stream health.
Further information is available from: , , , , , & (2022). Urbanization of grasslands in the Denver area affects streamflow responses to rainfall events. Hydrological Processes, 36( 10), e14720. https://doi.org/10.1002/hyp.14720