Forest Management and Warming Effects on a Century of Salt River Streamflow (November 2017)

Recent studies suggest that climate change has altered the flow and provision of water from western US rivers to downstream cities and natural communities, but fewer studies have examined hydrological influences related to a century of fire suppression. This study evaluated the effects of changing forest and temperature conditions on 20th century flow patterns in the Salt River in central Arizona. Seasonal and annual flows declined by 8-29% in the first half of the century which coincided with a 10-fold increase in ponderosa pine forest densities. Based on a scientific review, there is strong evidence that changes in forest structure contributed to these flow declines. In the 2nd half of the century, warmer temperatures led to earlier timing of peak spring flows of almost 2 weeks but had negligible direct effects on flow magnitudes. These results suggest that forest change had effects on flow well before anthropogenic warming and that large-scale restoration projects hold some promise of recovering seasonal flows.

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