Effective wildfire prevention begins before smoke rises. Yet one of the factors influencing fire danger – the moisture content of vegetation – remains difficult and costly to measure in the field. Researchers at King’s College London and the University of Salford have developed a portable optical sensor that assesses leaf water content within seconds. Built by modifying a £70 car window tint meter at a total prototype cost of approximately £140, the device could help fire services and forestry authorities identify increasingly dry vegetation before ignition occurs. It does not detect fires, but offers a potentially valuable tool for assessing the conditions in which they are more likely to start and spread.

As prolonged droughts and extreme weather place growing pressure on forests and agricultural landscapes, reliable information about vegetation moisture is becoming increasingly important for preventive fire management. Conventional methods generally require plant samples to be collected, dried and weighed in a laboratory. Although reliable, the procedure is time-consuming and destroys the material being examined. Specialist field instruments can also cost tens of thousands of pounds.

Researchers led by Dr Luke Brown of King’s College London and Professor Mark Danson of the University of Salford have developed a considerably more accessible alternative. Their starting point was a commercially available light-transmission meter designed to assess tinted vehicle windows. By modifying its optical components, they created a handheld instrument capable of estimating leaf moisture rapidly and without damaging the plant.

The original meter costs approximately £70, while the complete modified prototype can be assembled for around £140, including the additional components. The latter figure represents an estimated construction cost rather than a commercial selling price.

Measuring Water Content with Infrared Light

The technology exploits the different ways in which water absorbs light at specific wavelengths. The researchers replaced the instrument’s original light sources with two infrared LEDs operating at 940 and 1,450 nanometres.

Water absorbs light strongly at 1,450 nanometres but comparatively weakly at 940 nanometres. Comparing transmission at both wavelengths allows the instrument to estimate leaf water content while accounting for other characteristics of plant tissue.

To evaluate the approach, the team first simulated light transmission through 1,000 virtual leaves using a physics-based model. Experimental measurements followed at Rothamsted Experimental Farm in Hertfordshire between April and June 2026.

Six plant species were examined, including wheat, oilseed rape, beech, birch, hazel and sycamore. Their leaves were progressively dried under controlled conditions and repeatedly measured to establish the relationship between optical readings and actual moisture levels.

Promising Accuracy – with Important Limitations

The results, published in the scientific journal Methods in Ecology and Evolution, demonstrated a strong relationship between sensor readings and measured leaf water content.

Across the species examined, the optical method explained at least 81 per cent of the observed variation in fuel moisture content, a key parameter in assessing vegetation flammability. For water content relative to leaf area, the corresponding figure reached at least 85 per cent.

These findings suggest that relatively simple optical technology could provide useful moisture estimates at a fraction of the cost of specialist equipment.

However, the researchers identified limitations. The instrument requires calibration for individual plant species, while measurement accuracy decreases when leaves become extremely dry. This is particularly relevant to wildfire prevention, as low vegetation moisture levels can coincide with elevated fire danger.

Further validation across different vegetation types, seasons and environmental conditions will therefore be necessary before the device can be considered suitable for routine operational use.

Early Warning of Dry Vegetation – Not Fire Detection

For fire services and forestry authorities, the sensor’s potential lies in identifying changes in vegetation moisture before a fire starts.

Repeated measurements at selected locations could help monitor drying trends, identify areas requiring closer assessment and support decisions on preventive vegetation management.

Such information could complement established fire danger rating systems, which take account of meteorological conditions, combustible vegetation and other factors influencing ignition and fire behaviour.

The distinction between risk monitoring and fire detection is essential. The instrument does not detect smoke, flames, smouldering material or heat from an emerging fire. Nor does a low moisture reading establish that ignition is imminent.

Instead, it provides information about one of the environmental conditions that influence how readily vegetation may burn.

Unlike automated wildfire detection networks, the prototype requires measurements to be taken directly from leaves. It therefore supplies localised observations rather than continuous surveillance of forested areas.

If validated for operational use, the technology could complement weather observations, satellite-based monitoring and established vegetation assessment methods. Its relatively low cost may also make more frequent field measurements feasible for organisations managing extensive forested areas.

Applications Beyond Wildfire Prevention

The researchers also see potential applications in agriculture, where rapid measurements of plant water status could support more precise irrigation decisions.

By identifying developing moisture stress, farmers may be able to adjust watering schedules according to crop conditions rather than relying exclusively on predetermined intervals.

According to King’s College London, agriculture accounts for approximately 70 per cent of global freshwater use. More accessible monitoring technology could therefore contribute to improved water efficiency, particularly in regions facing increasing pressure on available resources.

Its practical value will depend on how reliably individual leaf measurements reflect irrigation requirements across different crops and growing conditions.

From Experimental Device to Preventive Monitoring Tool

The development demonstrates how inexpensive, commercially available technology can be adapted for environmental monitoring and preventive fire safety.

With a total prototype cost of approximately £140, the modified instrument could make leaf moisture measurements more accessible than conventional specialist equipment. Its operational reliability, however, remains to be established.

For fire services and land managers, the decisive question will be whether the device can deliver sufficiently consistent results under variable field conditions, particularly when vegetation reaches critically low moisture levels.

If these challenges can be addressed, the technology could strengthen local wildfire risk assessments and help authorities recognise deteriorating vegetation conditions at an earlier stage.

Its early-warning value is therefore indirect but potentially significant. Rather than signalling that a fire has started or is imminent, the sensor provides evidence of increasing vegetation dryness – information that could support earlier risk assessment and more targeted preventive measures.

Editorial sources: King’s College London, “Scientists turn £70 gadget into wildfire early-warning tool”, 7 October 2026; Luke A. Brown and F. Mark Danson, “Rapid non-destructive assessment of leaf water status with low-cost transmittance meters”, Methods in Ecology and Evolution, 12 August 2026, DOI: 10.1111/2041-210x.70388; pressetext, “Modifiziertes Gerät erkennt Waldbrandgefahren”, 12 October 2026.