In South Africa, growing hemp—a low‑THC variety of Cannabis sativa—has been legal for personal use for several years after legislative changes. Interest is rising not only for its medicinal properties but also for industrial applications such as fibre for clothing, building insulation, and paper. Many view it as a potential “green gold” for small‑scale farmers looking to diversify.
However, hemp is a water‑dependent crop, and South Africa already faces tight water supplies. Expanding hemp cultivation could further strain limited resources, especially in arid regions where every litre counts.
Our team, comprising researchers from the University of KwaZulu‑Natal and Rhodes University together with recent MSc graduate Gary Denton, deployed drones and ground‑based sensors to quantify hemp’s water consumption in the KwaZulu‑Natal Midlands. This work delivers South Africa’s first direct measurement of how hemp farming influences local water resources.
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Understanding a crop’s water footprint is essential in a water‑scarce nation. The National Water Act permits regulators to limit crops that demonstrably diminish runoff to rivers and dams—a power already exercised in commercial forestry. Without solid data on hemp’s water use, policymakers cannot assess its impact or devise appropriate management strategies.
Our study establishes a baseline for hemp’s water consumption, giving regulators the evidence needed to evaluate the crop’s effect on water supplies and to shape informed policies.
Using drones and sensors to measure hemp’s thirst
As hemp grows, it draws water from the soil and releases vapour through leaf transpiration. To capture this flux, we erected a central tower in the field equipped with sensors that continuously recorded water vapour loss and wind speed.
The research tower.
Courtesy Trevor Hill
This setup let us calculate daily water use without disturbing the plants. While earlier estimates relied on satellite imagery or intra‑plant water tracking, our approach is the first to apply this high‑resolution technique directly to hemp.
Next, we flew drones fitted with thermal and infrared cameras over the plot. Healthy, well‑watered hemp displays cooler leaf temperatures due to vigorous transpiration, whereas water‑stressed plants show warmer leaves. Because transpiration also drives growth, leaf‑temperature measurements from the aerial sensors enable us to infer the crop’s water consumption.
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We processed the drone imagery with a computer model named QWaterModel to generate spatial maps of water use across the field.
The trial took place on a commercial farm near Pietermaritzburg. To promote flowering, we removed the tops of the plants, and we eliminated male individuals to prevent pollination of females. While pollination lowers the yield and quality of medicinal buds, it does not alter the plant’s water demand.
One of the hemp fields studied.
Courtesy Trevor Hill
Our findings indicate that the hemp crop consumed the equivalent of 377 mm of water over its four‑month growing season. On average, each plant’s footprint accounted for roughly 28 litres of water per day, a figure that also incorporates water taken by inter‑row weeds and soil evaporation.
For context, a young eucalyptus (gum) tree—known for high water uptake—uses 30‑50 litres daily, placing hemp’s thirst in the same range as other large, water‑intensive species.
Beyond the primary flux measurements, the team logged additional environmental variables:
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temperature, wind and sunlight
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rain: 452 mm fell during the season
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soil moisture: water stored in the root zone
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irrigation: supplemental water supplied via drip lines
These datasets helped us untangle the factors driving water use and provide a template for comparing hemp performance under different climatic conditions in future research.
What we found
The analysis yielded several insights crucial for managing hemp cultivation:
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Water use varied across the field because topography influences soil depth, water‑holding capacity, and plant vigor. Drone‑derived maps pinpoint zones under moisture stress, allowing growers to target irrigation more efficiently.
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A substantial portion of the measured water loss originated from weeds growing between hemp rows rather than the crop itself.
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The QWaterModel proved useful for visualising spatial patterns but tended to overestimate total water use, likely because it counted evaporation from bare soil and weed foliage.
What needs to happen next
As the inaugural study measuring hemp’s water footprint, our results provide a baseline that can be extrapolated to other South African regions, supporting the development of sound water‑management plans for prospective expansion.
Establishing or scaling hemp plantations in water‑limited areas must be guided by robust scientific evidence. We urge farmers, extension officers, and policymakers to deepen their understanding of how hemp planting affects local water balances and to prioritise weed control between rows.
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Our methodology relied on high‑end drone platforms, specialised thermal/infrared cameras, and costly ground sensors—tools that may be out of reach for small‑scale or subsistence growers. Nevertheless, the workflow showcases the promise of precision agriculture, where GPS, sensors, and data analytics tailor inputs to specific field zones.
As sensor costs decline and modelling improves, drone‑based precision farming could become standard practice, helping producers adapt to a changing climate while conserving vital water resources.
This project received funding from the Water Research Commission.
