Can We Use the Water Budget to Infer Upland Catchment Behavior? The Role of Data Set Error Estimation and Interbasin Groundwater Flow. Issue 9 (19th September 2022)

• Record Type: Journal Article
• Authors: Gordon, Beatrice L.; Crow, Wade T.; Konings, Alexandra G.; Dralle, David N.; Harpold, Adrian A.
• Is Part Of: Water resources research. Volume 58:Issue 9(2022)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2022-09-19
• Subjects: Budyko hypothesis -- catchment -- water budget -- uncertainty -- streamflow -- snow; Hydrology -- Periodicals; 333.91
• DOI: 10.1029/2021WR030966
• Languages: English
• ISSNs: 0043-1397

Abstract

Abstract: Water budgets are essential for characterizing water supplies from snow‐dominated upland catchments where data are sparse, groundwater systems are complex, and measurements are prone to error ( ε ). One solution is imposing water budget closure (CWB) by ignoring difficult‐to‐measure variables, including inter‐basin groundwater fluxes ( G ) and ε . However, conventional CWB‐based analyses, which derive evapotranspiration ( ET ) from precipitation ( P ) and streamflow ( Q ) (e.g., the Budyko hypothesis), are limited in their ability to take advantage of recent advances in ET products, physically‐based frameworks for improving inferences about G, or tools to statistically characterize ε (Triple Collocation [TC]); all of which offer promise for improved water supply predictions via open water budgets (OWB). We clarify the value of these advances in upland settings by comparing standard land surface model, Ensemble Mean, and TC‐Merged P and ET products in 114 upland catchments. When compared against a long‐term OWB, we find that the CWB assumptions are unsupported in 75%–100% of our 114 catchments, depending on the product. We then show how applying these CWB assumptions in snowy, steep catchments where ε is large can inflate inferences about streamflow response to climate change by up 9 times more than independent (OWB) estimates of ET using TC. Finally, we demonstrate how advances in OWB analysis reveal that high, arid settings with deep permeable substrate are groundwater exporters while most other basins are groundwater importers. Our results highlight the advantages of OWB analyses that harness new products, tools, and frameworks for characterizing inter‐basin groundwater fluxes in critical upland settings. Plain Language Summary: Hydrologists use calculations about the inputs, outputs, and stores of water to anticipate changes in water supply from higher elevation, snow‐dominated (upland) regions. To avoid challenges related to data limitations, it is common to make simplifying assumptions about negligible measurement error and groundwater storage and flow to close the annual water budget. However, the implications of these assumptions are rarely assessed. We investigate the support for these assumptions over a 15‐year period and find that when invalid, they can over inflate the expected sensitivity of streamflow to precipitation falling as snow. We filter some error through optimized averaging (using a method called triple collocation) to illustrate how an open water budget approach that allows for measurement error and groundwater storage and flow can improve our understanding of water resources. This approach illustrates that higher, drier catchments with a deep subsurface provide a groundwater subsidy to lower catchments that is not apparent using other common techniques. Key Points: Closed water budget assumptions about groundwater flux and measurement error are widely unsupported in upland catchments Triple Collocation (TC) indicates groundwater export in high arid catchments with deep substrates consistent with a framework by Fan (2019, https://doi.org/10.1002/wat2.1386 ) The Fan (2019, https://doi.org/10.1002/wat2.1386 ) framework, TC‐based merging, and independent estimates of evapotranspiration advance upland water budget understanding