No abstract

ssessing the environmental impacts of the cannabis industry in Northern California has been notoriously difficult (Carah et al. 2015; Short Gianotti et al. 2017). The federally illegal status of cannabis has prevented researchers from obtaining funding and authorization to study cultivation practices (Arnold 2013; Kilmer et al. 2010). Fear of federal enforcement has also driven the industry into one of the most sparsely populated and rugged regions of the state (Bauer et al. 2015; Butsic and Brenner 2016; Corva 2014; Leeper 1990; Thompson et al. 2014), further limiting opportunities for research. The result has been a shortage of data on cultivation practices and their environmental risks (Short Gianotti et al. 2017). An improved understanding of cannabis cultivators' water use practices is a particularly pressing need. Given the propensity of cannabis growers to establish farms in small, upper watersheds, where streams that support salmonids and other sensitive species are vulnerable to dewatering (Bauer et al. 2015), significant concerns have been raised over the potential impacts of diverting surface water for cannabis cultivation. The

26Concerns have been raised over the impacts of cannabis farms on the environment and 27 water resources in particular, yet data on cultivation practices and water use patterns and have 28 been limited. Estimates of water use for cannabis cultivation have previously relied on 29 extrapolated values of plant water demand, which are unable to account for differences in 30 cultivation practices, variation across the growing season, or the role of water storage in 31 altering seasonal extraction patterns. The current study uses data reported by enrollees in 32 California's North Coast Regional Water Quality Control Board (Regional Water Board) Cannabis 33 Program to model how variation in cultivation practices and the use of stored water affect the 34 timing and amount of water extracted from the environment. We found that the supplemental 35 use of stored water resulted in a seasonal pattern of water extraction (i.e. water withdrawals 36 from the environment) that was distinct from water demand (i.e. water applied to plants). 37 Although water input to storage in the off-season months (November through March) reduced 38 water extraction in the growing season (April through October), farms generally did not have 39 sufficient storage to completely forbear from surface water extraction during the growing 40 season. Beginning in 2019, forbearance will be required during this period for those in the 41 regulated cannabis industry. The two most important predictors of storage sufficiency (type of 42 storage infrastructure and seasonality of water source) also had reliable effects on seasonal 43 extraction patterns, further emphasizing the link between water storage and extraction 44 profiles. These findings suggest that resource managers and policy makers should consider the 45 ways in which cultivation practices drive water extraction patterns and how these practices 46 may be influenced by participation in the regulated cannabis industry. 58 California are located in rural landscapes with no access to municipal water supplies, cultivators 59 generally obtain water directly from the environment, relying on local springs, streams, and 60 groundwater wells [10]. Stream flow has been identified as an important limiting factor to 61 salmon, and other sensitive aquatic species in the region, particularly given the seasonal 62 drought of California's Mediterranean Climate [11][12][13][14]. Because cannabis water demands 63 coincide with the summer dry season, agricultural water diversions in the North Coast Region 64 have the potential to reduce stream flows [15][16], increase stream temperatures [17], or even 65 dewater streams during critical life stages of aquatic species [18][19]. Although these streams 66 are highly sensitive to variability in flow rates [20][21], there is a dearth of information 67 surrounding cannabis water use practices, making it difficult to quantify potential 68 environmental impacts. 69 An accurate baseline assessment of water use by cannabis cultivation is particularly 70 import...