In ecoregions across western USA streamflow increases during post-wildfire recovery

Abstract

Continued growth of the human population on Earth will increase pressure on already stressed terrestrial water resources required for drinking water, agriculture, and industry. This stress demands improved understanding of critical controls on water resource availability, particularly in water-limited regions. Mechanistic predictions of future water resource availability are needed because non-stationary conditions exist in the form of changing climatic conditions, land management paradigms, and ecological disturbance regimes. While historically ecological disturbances have been small and could be neglected relative to climatic effects, evidence is accumulating that ecological disturbances, particularly wildfire, can increase regional water availability. However, wildfire hydrologic impacts are typically estimated locally and at small spatial scales, via disparate measurement methods and analysis techniques, and outside the context of climate change projections. Consequently, the relative importance of climate change driven versus wildfire driven impacts on streamflow remains unknown across the western USA. Here we show that considering wildfire in modeling streamflow significantly improves model predictions. Mixed effects modeling attributed 2%−14% of long-term annual streamflow to wildfire effects. The importance of this wildfire-linked streamflow relative to predicted climate change-induced streamflow reductions ranged from 20%−370% of the streamflow decrease predicted to occur by 2050. The rate of post-wildfire vegetation recovery and the proportion of watershed area burned controlled the wildfire effect. Our results demonstrate that in large areas of the western USA affected by wildfire, regional predictions of future water availability are subject to greater structural uncertainty than previously thought. These results suggest that future streamflows may be underestimated in areas affected by increased prevalence of hydrologically relevant ecological disturbances such as wildfire.

Optimizing Forest Management Stabilizes Carbon Under Projected Climate and Wildfires

“…In the case of the Santa Fe Fireshed and other forested watersheds of the southwestern United States, a century of fire-exclusion, nearly 2 decades of extreme drought, and warming have increased high-severity wildfire risk (Hurteau et al, 2014;Singleton et al, 2019;Swetnam & Brown, 2011). In this water-limited region, streamflow invariably increases following high-severity wildfires due to decreased infiltration and decreased vegetation water use (Bart, 2016;Wine et al, 2018;Wine & Cadol, 2016). However, the measured increase in water yield from severely burned watersheds following precipitation events is paired with a significant detriment to water quality, which has cascading negative impacts on wildlife, riparian biodiversity, and ultimately the provision of municipal water from forested landscapes (Cooper et al, 2015;Jackson et al, 2012;Jones et al, 2016;Murphy et al, 2018).…”

Nonlinear Long‐Term Large Watershed Hydrologic Response to Wildfire and Climatic Dynamics Locally Increases Water Yields

“…The objective of this study was to predict wildfire impacts on streamflow across ungauged watersheds in seven ecoregion divisions within the western United States over a three‐decade period (1986–2015). To accomplish this objective, we first relate wildfire impacts to m within 39 gauged wildfire‐affected reference watersheds, as quantified by the wildfire impact index (WII) suggested by Wine et al (). The 39 watersheds include all gauged U.S. Geological Survey (USGS) reference watersheds with at least 20% burned area within a consecutive 5‐year period.…”

“…Up to this point studies of postwildfire hydrologic response have ranged from point (Krammes & Debano, ) to large watershed—6,800 km 2 (Wine et al, ) scales but typically have been limited to gauged reference watersheds (Hallema et al, , ; Wei & Zhang, ), which are sparsely distributed. Due to the sparse nature of this measurement network, hydrologic effects of western United States wildfires at large scales remain largely unknown (Shakesby et al, ), with the possible exception of coarse spatial resolution global studies (Li & Lawrence, ).…”

Changes in Climate and Land Cover Affect Seasonal Streamflow Forecasts in the Rio Grande Headwaters

“…Here, only one high‐elevation wildfire affecting 9% of the basin was analyzed. Regions with multiple basins experiencing fires may consistently see streamflow increases (Wine et al 2018) and require frequent postfire investigations. Additionally, insect‐induced tree mortality may not be of concern unless mortality crosses a threshold where expected streamflow increases are considerable and contribute to prediction bias.…”