Changes In Dominant Streamflow Drivers As Network-Scale Flow Regime Shifts From Intermittent To Ephemeral Across A Multi-Year Drought
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https://doi.org/10.1002/hyp.70413 ← shared paper
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H/T @Lauren Giggy | Postdoctoral Researcher, Hydrologist, Geologist
“This work leverages a theoretically simple dataset: weather + a handful of sensors recording whether they are submerged in water or not, to explore why streamflow persists in some regions of headwater catchments longer than others across several years of drought. While simple in theory, the resulting data set was quite large and complex to analyze… [the authors were] glad [they] pushed through!
HIGHLIGHTS:
1) At the onset of the study, when storage conditions were relatively high, flow persistence was related to physical landscape characteristics (rock type, slope, catchment area, curvature, etc.); however, with ongoing drought, flow persistence declined across the network, and physical landscape characteristics were no longer predictive of persistence.
2) With ongoing drought, flow activation events were controlled more by the timing, intensity, and depth of precipitation than by antecedent storage conditions.
3) [They] present a simple conceptual framework (inspired by many others before us) that demonstrates how this system shifts along an ephemeral-to-intermittent continuum within each water year and across the drought period, due to the combined effect of increasing storage deficits, punctuated by high-intensity, high-depth winter precipitation events…”
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“Dynamic surface water wetting and drying are characteristic of most headwater stream networks, influencing ecological function and downstream water quality. While topography and subsurface properties have been shown to influence spatial surface water persistence, it is unclear how sensitive non-perennial stream network flow regimes are to persistent drought conditions. To address this unknown, [they] monitored surface water presence and absence for three consecutive drought years at 31 locations across a 0.25 km² non-perennial headwater stream network in central coastal California. [They] coupled these observations with landscape characteristics and climatic conditions to examine both physical and climatic drivers of spatiotemporal flow activation and persistence. [They] observed non-stationarity in flow regimes throughout the stream network; reaches that were characterised by seasonal flow in 1 year became ephemeral as the drought conditions progressed. [They] observed declining spatial variability in surface water persistence and declining correlations between persistence and landscape attributes with ongoing drought. From year one to year three, as drought conditions intensified, correlation coefficients between surface water persistence and topographic wetness index declined from r = 0.60 to r = 0.17, stream channel slope declined from r = 0.47 to r = 0.21, profile curvature declined from r = −0.51 to r = −0.21, and elevation declined from r = −0.33 to r = −0.06. A principal component analysis suggests that, unlike prior years, flow activation events after several years of drought were more closely associated with precipitation event characteristics than antecedent storage states. This work suggests semi-arid landscapes such as central coastal California may see shifts in the flow regimes of aquatic systems as landscape aridity intensifies with climate change. As predictive indicators of flow may shift from physical to climatic factors, the timing, intensity and frequency of individual storm events may play increasingly larger roles in driving annual-scale flow conditions…”
#GIS #spatial #mapping #water #hydrology #fluvial #pluvial #precipitation #extremeweather #California #USA #semiarid #watershed #headwaters #weather #metrology #spatialanalysis #spatiotemporal #model #modeling #geostatistics #monitoring #sensors #instrumentation #insitu #drought #streamflow #ephemeral #intermittent #catchments #waterresources #watermanagement #watersecurity #planning #coast #coastal #hydrogeomorphic #geology #climate