Past precipitation, watershed characteristics, and drought: interactive effects on watersheds of Northern California.

Abstract

Forested watersheds in Western North America are experiencing more frequent drought due to climate change, which impacts drinking water resources and stresses vulnerable aquatic species. Watershed properties, such as aspect, elevation, soil type, vegetation composition, and stand age, are known to impact runoff through differences in evapotranspiration and storage. Drought may further change the hydrological function, or precipitation-runoff relationship of a watershed. In this study, I investigated how watershed properties provide resilience against drought in forested watersheds. Precipitation and streamflow data from twelve sub-watersheds in the Caspar Creek Experimental Watersheds (California, USA) were collected from 2001-2017. Sub-watershed mean aspect, mean stand density index, and maximum soil depth correlated significantly with annual runoff ratios. To assess the hydrological functioning of sub-watersheds at different timescales, streamflow and runoff ratios were correlated to lags of past precipitation at annual, seasonal, and monthly timescales. Past precipitation was found to be an insignificant driver of streamflow or runoff ratios at annual and seasonal timescales, and significant for streamflow up to three months. These results may help in understanding the drivers of watershed resilience to aid in adaptive land management decisions.