A GIS-based method of modeling water input from rain-on-snow storms for management and regulation of clearcut forest harvest

Timber harvest has helped transform the Northwest into a patchwork of cities, farms, clearcuts, plantations, and mature trees, surrounding fragments of primeval forest. Forest canopy affects snow accumulation and melt, particularly during rain-on-snow storms; harvest has thus caused changes in water systems at various scales. The management environment has also changed, with increased attention to protection of woodland resources.DNR now regulates harvest with regard to water input during R/S events. The key layer of our GIS-based system is a map of precipitation zones, based on snow available for melting (used partly to determine which forest-practice applications are examined for R/S implications). Modeling of snowmelt during hypothetical events allows estimation of water reaching the soil in each polygon. Differences between inputs under fully-forested and current vegetation suggest changes in effective storm frequency. Results are used to predict hydrologic effects of harvest scenarios.