Water storage and irrigation practices associated with cannabis production drive seasonal patterns of water extraction and use in Northern California watersheds

Abstract

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...

Can cannabis go green?

“…But these California studies didn't take into account differences in cultivation practices, whether farms relied on watersheds or how plants' needs changed as they grew. When Butsic and Graham examined data reported by legal growers enrolled in a California state programme, as part of their preprint study, they found that most farms relied on wells and stored water for irrigation 1 .…”

“…The researchers also learnt that although the cannabis grew from June to October, the plants actually required 22 litres of water each day only for about three months of the year 1 . "That amount probably overestimates use earlier and later in the growing season, " Grantham says.…”