Modeling Forest Thinning Effects on Water Yield for the Four Forest Restoration Initiative

Forests in Arizona are increasingly affected by persistent drought conditions due to global warming. The Four Forest Restoration Initiative (4FRI) researched the effects of climate variability and accelerated forest thinning on watershed-scale runoff, aiming to improve water flows and reduce forest mortality. The focus was on ponderosa pine forests. Researchers designed a forest runoff model to predict annual flow based on climate variability (winter precipitation), changes in forest basal areas due to thinning, and years since thinning treatment. The model estimated that thinning could increase downstream runoff by approximately 20%, although these effects may be transient. Researchers are now exploring management tools to sustain these benefits.