Contextualizing cannabis water demand and potential for streamflow impacts relative to residential and agricultural users in Northern California

This study examines the relative water demand and potential streamflow impacts of cannabis cultivation, residential use, and non-cannabis agriculture in rural northern California watersheds. While cannabis has received much attention for its potential impact on sensitive aquatic species, the relative contribution to overall water demand in watersheds where cannabis is farmed remains poorly understood. Using spatial and temporal analyses across multiple watersheds, this study assesses how water use for cannabis cultivation compares to other major water users in terms of total demand, spatial distribution, and interannual fluctuations. Cannabis was more rarely the top water user in a given catchment (1.6% of observations) than were residential users (34.6%) or non-cannabis agriculture (29.8%). Cannabis water demand was more seasonal, with greater interannual variability, and more evenly spread among catchments than other water use types. Residential and non-cannabis agriculture had the potential to impair streamflow at annual timescales, while cannabis water use impacts was only evident at the monthly scale. Overall, findings suggest that water demand for residential and non-cannabis agriculture has a greater impact on streamflow than cannabis, but that demands from cannabis may cause additive impacts when all uses are considered. Additionally, the potential for cannabis demand to cause streamflow alteration varied year-to-year, with greater potential for impairment during dry years. Given these dynamics, we recommend adoption of holistic approaches that manage all human water uses to protect sensitive natural resources in cannabis-producing watersheds.