Running dry: Cannabis farming is changing streams in California, experts warn

Research

Running dry: Cannabis farming is changing streams in California, experts warn

by Robyn Stubbs

Groundwater pumped to irrigate cannabis crops in California's Emerald Triangle can cause some streams that normally run year-round to dry up entirely during summer, say researchers from Simon Fraser University, the University of California, Berkeley and the United States Department of Agriculture.

A new study reveals how groundwater pumping in the region's rugged mountain headwaters may reduce streamflow that support salmon habitat and feed larger river systems downstream.

"People often think of groundwater or aquifers as a separate resource from streams. But in many landscapes, they're connected parts of the same system," says Jesse Hahm, assistant professor of geography and co-author of the study.

"During heat waves and droughts, demand for irrigation often increases at the same time stream ecosystems are under the greatest stress. What matters is not only how much water is used, but when and where it is taken," he explains. "We found that in these upland, mountainous landscapes, pumping water from underground can affect streamflow in ways that may not be immediately obvious."

Published in the Journal of Hydrology, the study examined how groundwater pumping affects headwater streams in two watersheds in California's Emerald Triangle, a globally recognized cannabis-growing region that is increasingly vulnerable to water shortages.

Using a new modelling approach, the team analyzed 580 scenarios to understand how groundwater pumping and environmental conditions converge to influence streamflow.