Urbanization in Arid Central Arizona Watersheds Results in Decreased Stream Flashiness

Abstract

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.

Spatial Patterns and Drivers of Nonperennial Flow Regimes in the Contiguous United States

“…Streams dry down significantly slower in nonreference watersheds across CONUS, and particularly in Mediterranean California and the Southern Great Plains (Figure 3). Impervious cover was higher in nonreference gages for these regions (Table ), consistent with previous research that has observed flashier runoff in human‐impacted watersheds (Kaushal & Belt, 2012), although these impacts vary regionally (McPhillips et al., 2019). Human‐derived impacts that we observed varied with region and metric and highlight the need for more in‐depth understanding of how human modifications impact drying processes.…”

Classifying Streamflow Duration: The Scientific Basis and an Operational Framework for Method Development

“…Disturbances other than stream drying can reduce discriminatory ability of flow duration indicators if responses are indistinguishable or complex (e.g., synergistic, antagonistic; [105,106]. High impervious cover increases the frequency of moderate-sized stormflow events in arid streams [107,108], so differences among flow duration classes in sedimentary characteristics and channel form may be diminished. A major flood reduced the abundance and diversity of the macroinvertebrate assemblage to a greater extent at a downstream perennial reach than at upstream intermittent reaches in a tallgrass prairie stream network because flood magnitude downstream was~30X greater than at intermittent reaches [109].…”

Ungaged inflow and loss patterns in urban and agricultural sub‐reaches of the Logan River Observatory

“…For example, the adoption of high efficiency irrigation technologies may significantly reduce shallow groundwater recharge and tailwater (i.e., excess runoff), reducing these agricultural contributions to streamflow (Grafton et al, 2018; Scott et al, 2014). Similarly, stormwater treatment or engineered retention of stormwater may decrease both urban groundwater recharge and discharge and/or surface water contributions (Hale et al, 2014; McPhillips et al, 2019). As exemplified in our case study, a net flow balance that only accounts for large tributaries and diversions across a reach does not effectively represent the exchanges occurring within the reach.…”