News and Updates!
Hemp a Thirsty Crop? New South African Research Measures the Water Cost of Cannabis Farming
Original source:
The Conversation – “Is hemp a thirsty crop? New research measures just how much water cannabis farming can use”
Key research links retained:
• Study DOI / related publications referenced in the original
• University of KwaZulu-Natal & Rhodes University collaboration
• Water Research Commission funding acknowledgement
• National Water Act context
Suggested media to retain / pair:
• Cannabis / hemp plant field imagery (original Raw Pixel credit style)
• Research tower photograph (Courtesy Trevor Hill)
• Hemp field aerial or ground shots from the KwaZulu-Natal study site
• Simple water-use comparison graphic (hemp vs young eucalyptus)
Hemp is frequently marketed as a climate-friendly, multi-purpose crop — a source of fibre, seed, building materials, and, in low-THC forms, a legally distinct cousin of high-THC cannabis. In South Africa the plant has attracted growing interest from small-scale farmers, investors and policymakers looking for new agricultural opportunities after the 2018 Constitutional Court judgment and the subsequent development of hemp permitting pathways.
Yet South Africa is a water-constrained country. Any crop that expands at scale must be assessed for its impact on rivers, dams and downstream users. A new study by researchers from the University of KwaZulu-Natal and Rhodes University, working with Masters graduate Gary Denton, provides the first detailed, field-based measurement of how much water a commercial hemp crop actually uses under local conditions. The findings, summarised in The Conversation, offer a necessary reality check for the “green gold” narrative.
Why Water Use Data Matters
South Africa’s National Water Act allows the regulation of land-based activities that noticeably reduce the water reaching rivers and dams. Commercial forestry has long been managed under this framework because trees can be significant stream-flow reduction activities. Until now, hemp has lacked equivalent local data. Without measured numbers, regulators cannot make evidence-based decisions about where and at what scale the crop should be encouraged or restricted.
The KwaZulu-Natal Midlands study fills that gap. Researchers installed a sensor tower in the middle of a commercial hemp field to measure water vapour released by the plants (transpiration) together with wind speed. They combined these continuous ground measurements with drone flights carrying thermal and infrared cameras. Healthy, well-watered plants cool their leaves through transpiration; water-stressed plants run warmer. By mapping leaf temperature and feeding the data into a model (QWaterModel), the team produced spatial maps of water use across the field.
The Numbers
Over a four-month growing season the hemp crop used the equivalent of 377 mm of water. On average, the area occupied by each plant used about 28 litres of water per day. That figure includes water taken up by the hemp itself, by weeds growing between the rows, and evaporation from the soil surface.
For comparison, a young eucalyptus (gum) tree — widely recognised as a high water-use species — typically consumes 30–50 litres per day. Hemp therefore sits in a similar range to other large, relatively thirsty plants rather than in the low-water category sometimes claimed in promotional material.
Rainfall during the season totalled 452 mm. The farm also used drip irrigation. Soil moisture, temperature, wind and sunlight were monitored throughout, giving a fuller picture of the water balance.
What the Spatial Data Revealed
Water use was not uniform across the field. Terrain, soil depth and soil water-holding capacity created clear variation. Drone thermal maps made these differences visible, pointing to a practical application: precision irrigation. Farmers who can identify which zones are stressed can apply water more efficiently instead of treating the entire field as a single unit.
A second important finding was the role of weeds. A substantial share of the measured water use was attributable to vegetation growing between the hemp rows rather than to the crop itself. Weed control therefore emerges as a direct water-management issue, not merely an agronomic one.
The QWaterModel produced higher overall water-use estimates than the ground sensors. The researchers attribute the difference largely to evaporation from bare soil and the contribution of weeds — a reminder that models must be calibrated against real measurements.
Implications for South African Hemp Ambitions
The study was conducted on a commercial planting near Pietermaritzburg where plants were managed for flowering (apical dominance removed, males eliminated to protect bud quality). Water use itself was not materially altered by these management choices, but the results remain specific to the Midlands climate, soils and management regime. Extrapolation to the Eastern Cape, Limpopo, North West or Western Cape will require additional site studies.
Nevertheless, the baseline is now established. Expanding hemp in catchments that are already stressed cannot be treated as automatically sustainable. Licensing and support programmes will need to incorporate water-availability assessments, just as they already consider soil suitability, market access and compliance capacity.
For small-scale and emerging farmers the picture is mixed. Hemp’s versatility remains attractive. The water data does not make the crop unviable; it makes the crop’s requirements visible. Farmers and support organisations can use the numbers to plan irrigation systems, choose appropriate sites, and budget for water costs or restrictions. Precision tools — drones, soil sensors, improved scheduling — will become more valuable as the industry grows, even if they are currently out of reach for many smaller operators.
Broader Cannabis and Hemp Context
South Africa’s hemp pathway has been deliberately separated from high-THC cannabis. Permits under the agricultural framework, the recent adjustment of the THC threshold for hemp, and ongoing work on seed varieties all aim to create a distinct industrial and low-THC sector. Medical cannabis, by contrast, remains under SAHPRA and is oriented toward controlled cultivation and export. Private adult use of higher-THC cannabis is constitutionally protected but commercially constrained.
Water cuts across all these categories. A medical greenhouse, an outdoor hemp fibre crop and a small private plot have different water footprints, but none is exempt from the country’s overall scarcity. The KwaZulu-Natal study supplies the first robust outdoor hemp number against which other production systems can eventually be compared.
What Needs to Happen Next
The researchers themselves describe the work as a vital first step. Further studies in different climatic zones, under different irrigation regimes, and with different cultivars will refine the picture. Weed-management trials that quantify water savings would deliver immediate practical value. As drone and sensor technology becomes cheaper, the precision-agriculture approach demonstrated here can move from research plots into ordinary farming practice.
Policymakers should treat the 377 mm / ~28 litres-per-plant-per-day figures as a planning baseline, not a final verdict. The National Water Act already provides tools to manage high-impact crops. Applying those tools intelligently to hemp will protect both the resource and the long-term credibility of the emerging industry.
Conclusion
Hemp is not a magical low-water crop. Under the conditions measured in the KwaZulu-Natal Midlands it uses water on a scale comparable to other substantial plants. That finding does not end the case for hemp; it improves it by replacing assumption with evidence. Farmers, investors and regulators now have a local number to work with. The next task is to expand the data, tighten management practices — especially weed control and precision irrigation — and ensure that the expansion of hemp occurs in places and at scales that South Africa’s water resources can sustain.
“Green gold” remains possible. It will simply have to be grown with a clear-eyed understanding of its thirst.
