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Variable streamflow response to forest disturbance in the western US: A large-sample hydrology approach
  • Sara A Goeking,
  • David Gavin Tarboton
Sara A Goeking
USDA Forest Service, USDA Forest Service

Corresponding Author:sara.goeking@usda.gov

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David Gavin Tarboton
Utah State University, Utah State University
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Forest cover and streamflow are generally expected to vary inversely because reduced forest cover typically leads to less transpiration. However, recent studies in the western US have found no change or even decreased streamflow following forest disturbance due to drought and insect epidemics. We investigated evidence for cases where forest cover loss leads to decreased streamflow using hydrologic, climatic, and forest data for 159 watersheds in the western US from the CAMELS dataset. Forest change and disturbance were quantified in terms of net tree growth (total growth volume minus mortality volume) and mean annual rate of tree mortality, respectively, from the US Forest Service’s Forest Inventory and Analysis database. Annual water budget components were analyzed using multiple methods: Mann-Kendall trend analysis, time trend analysis to quantify change not attributable to precipitation and temperature, and multiple regression. Many watersheds exhibited decreased annual streamflow even as forest cover decreased. Time trend analysis identified decreased streamflow not attributable to precipitation and temperature changes in many disturbed watersheds, yet streamflow change was not consistently related to disturbance, suggesting that factors other than disturbance, precipitation, and temperature are driving streamflow changes. Finally, multiple regression analysis indicated that although change in streamflow is positively related to tree mortality, the direction of this effect is dependent upon aridity. Specifically, forest disturbances in wet, energy-limited watersheds (i.e., where potential evapotranspiration is less than precipitation) tended to increase streamflow, while post-disturbance streamflow more frequently decreased in dry water-limited watersheds (where the potential evapotranspiration to precipitation ratio exceeds 2.35).
Jun 2022Published in Water Resources Research volume 58 issue 6. 10.1029/2021WR031575