Details

Autor(en) / Beteiligte

• McPhillips, L. E.
• Earl, S. R.
• Hale, R. L.
• Grimm, N. B.

Titel

Urbanization in Arid Central Arizona Watersheds Results in Decreased Stream Flashiness

Ist Teil von

• Water resources research, 2019-11, Vol.55 (11), p.9436-9453

Ort / Verlag

Washington: John Wiley & Sons, Inc

Erscheinungsjahr

2019

Quelle

Wiley-Blackwell Journals

Beschreibungen/Notizen

• There is broad consensus that urbanization results in dramatic changes in stream hydrology, such as higher peak flows and greater flashiness. However, this has not been definitively tested for aridlands, which are characterized by these very same hydrograph properties. We analyzed streamflow records from 19 watersheds of central Arizona, USA, to determine how hydrograph characteristics varied with urban development. Using linear mixed effects models, which factored in imperviousness along with other watershed characteristics, we evaluated influences on streamflow regime metrics calculated from daily and subdaily flow data. We found that flashiness, coefficient of variation, zero‐flow days, and hydrograph rise and fall rates decreased with extent of imperviousness—the opposite pattern to that observed in previous studies primarily in humid regions. Engineered retention basins are one explanation for this observation though novel urban sources of dry weather flows are likely also playing a role. We also found strong relationships between these hydrologic metrics and mean area‐weighted discharge, watershed area, and annual precipitation. Like in humid systems, we did observe more high flow events in the urban desert streams compared to nonurban desert streams. However, this was only at the lower flood threshold; there was no increase in larger floods with urban development. Overall, the urban stream syndrome manifests differently in this arid system: Urbanization increases water retention and leads to less variable flows in stream ecosystems. Plain Language Summary As humans have developed landscapes using hard surfaces like buildings and parking lots, we have noticed that flooding and “flashier” conditions characterize streams in many of these developed areas. By flashiness, we are referring to the tendency of streamflow to quickly rise or fall. Here, we use data on streamflow in desert streams in Arizona, USA, to see how development in deserts may or may not have similar impacts on flooding. We did find that there were more small floods in the more urban desert watersheds. However, we also found that desert streams located in more developed areas tended to be less flashy than those in more rural areas. This is interesting because it is opposite of the patterns we see in the wetter cities. One reason for this pattern is that there are more places where water can be held back during storms instead of flowing directly to the stream. These places might be accidentally created or may be engineered features like storm water retention basins. Streams in cities also have other sources of water besides rain, such as runoff from car washes or irrigated lawns, that help to maintain more constant flows in these arid urban streams. Key Points Urbanization in arid central Arizona watersheds results in decreased flashiness and fewer zero‐flow days These urban arid watersheds have increased retention of storm water, partially due to increased engineered retention Impacts of urbanization on stream flashiness in arid central Arizona watersheds are opposite those observed in more humid regions