Abstract
Non-perennial streams are widespread, critical to ecosystems and society, and the subject of ongoing policy debate. Prior large-scale research on stream intermittency has been based on long-term averages, generally using annually aggregated data to characterize a highly variable process. As a result, it is not well understood if, how, or why the hydrology of non-perennial streams is changing. Here, we investigate trends and drivers of three intermittency signatures that describe the duration, timing, and dry-down period of stream intermittency across the continental United States (CONUS). Half of gages exhibited a significant trend through time in at least one of the three intermittency signatures, and changes in no-flow duration were most pervasive (41% of gages). Changes in intermittency were substantial for many streams, and 7% of gages exhibited changes in annual no-flow duration exceeding 100 days during the study period. Distinct regional patterns of change were evident, with widespread drying in southern CONUS and wetting in northern CONUS. These patterns are correlated with changes in aridity, though drivers of spatiotemporal variability were diverse across the three intermittency signatures. While the no-flow timing and duration were strongly related to climate, dry-down period was most strongly related to watershed land use and physiography. Our results indicate that non-perennial conditions are increasing in prevalence over much of CONUS and binary classifications of ‘perennial’ and ‘non-perennial’ are not an accurate reflection of this change. Water management and policy should reflect the changing nature and diverse drivers of changing intermittency both today and in the future.
Highlights
Non-perennial streams—referring to streams and rivers that do not flow continuously, including intermittent rivers and ephemeral streams (Busch et al 2020)—are present across all global continents, ecoregions, and climate types (Messager et al 2021) and provide many ecosystem services such as agricultural and domestic water supply while sustaining the ecological integrity of river networks (Datry et al 2018a, Kaletova et al 2019, Stubbington et al 2020)
Changing stream intermittency Half the continental United States (CONUS) non-perennial gage network had a significant trend in no-flow duration, dry-down period, and/or no-flow timing over the study period
Shifts towards more intermittent flow dominated the southern half of CONUS, while decreased intermittency indicating wetter conditions was prevalent in the northern half of CONUS
Summary
Non-perennial streams—referring to streams and rivers that do not flow continuously, including intermittent rivers and ephemeral streams (Busch et al 2020)—are present across all global continents, ecoregions, and climate types (Messager et al 2021) and provide many ecosystem services such as agricultural and domestic water supply while sustaining the ecological integrity of river networks (Datry et al 2018a, Kaletova et al 2019, Stubbington et al 2020). Recent efforts have quantified spatial patterns of stream intermittency at regional (Datry et al 2016, Allen et al 2019, Jaeger et al 2019), national (Snelder and Booker 2013, Beaufort et al 2018, Hammond et al 2021, Sauquet et al 2021), and global (Messager et al 2021) scales. These studies provide a useful framework for classifying and understanding spatial patterns in stream intermittency during a particular study period. Given the strong influence of stream intermittency on aquatic biodiversity (Jaeger et al 2014, Datry et al 2014b) and water quality (Datry et al 2018b, Gómez-Gener et al 2020), a pressing question remains: is stream intermittency changing at regional to continental scales, and if so, what are the characteristics and causes of this hydrologic change?
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