Calculator
Example Data Table
Sample conditions and exposure index outcomes for comparison.
| Scenario | Max/Min (°C) | Wind (km/h) | RH (%) | Rain (mm) | UV | Sun (hrs) | Shelter | Sensitivity | Typical Index |
|---|---|---|---|---|---|---|---|---|---|
| Hot, dry afternoon | 40 / 22 | 18 | 28 | 0 | 10 | 11 | 0.30 | High | 78–92 |
| Mild coastal day | 26 / 18 | 14 | 65 | 1 | 6 | 7 | 0.70 | Medium | 22–38 |
| Cold clear morning | 12 / 2 | 8 | 55 | 0 | 3 | 5 | 0.55 | Medium | 35–55 |
| Stormy wet period | 22 / 16 | 32 | 82 | 35 | 4 | 2 | 0.60 | Low | 45–65 |
Formula Used
This calculator builds a single index from six component risks: Heat, Cold, Wind, Dryness, Rain, and UV. Each component produces a 0–100 score.
- Heat risk rises as max temperature exceeds 18°C, peaking near 45°C.
- Cold risk rises as min temperature drops below 10°C, peaking near −10°C.
- Wind risk uses a 0–60 km/h scale, clamped above that.
- UV risk maps UV index 0–11+ to a 0–100 score.
- Rain risk scales 0–50 mm/day for waterlogging and splash risk.
- Dryness risk blends (100−RH), sun hours, and wind.
The weighted base index is:
The index is a practical planning score, not a forecast.
How to Use This Calculator
- Enter temperatures, wind, humidity, rainfall, UV, and sun hours.
- Set shelter and canopy cover to match your site.
- Choose season and plant sensitivity for realistic stress.
- Adjust weightings if one factor dominates locally.
- Press Calculate Exposure to view the index.
- Use the tips and drivers to plan protection steps.
- Download CSV or PDF for record keeping and sharing.
Practical Guide
Index bands and what they signal
The Weather Exposure Index runs from 0 to 100 and groups results into five bands: Low (0–19), Moderate (20–39), High (40–59), Very High (60–79), and Extreme (80–100). Use the band to decide how aggressively to protect crops. A Moderate day may only need routine watering, while Very High often warrants shade, wind protection, or delayed planting. For routine beds, aim to keep results below 40 during establishment and transplanting stages.
Temperature and UV are fast-moving drivers
Heat risk is anchored to maximum temperature, with stress accelerating beyond the upper comfort zone and approaching full risk near 45 °C. Cold risk rises as minimum temperature drops below 10 °C and becomes critical near −10 °C. UV is scaled from 0 to 11+, so an index jump from 6 to 9 can noticeably increase overall exposure for young seedlings.
Dryness blends humidity, sun hours, and wind
Dryness is calculated from three measurable inputs: relative humidity, daily sun hours, and wind speed. Low humidity pushes the dryness component upward, and long sun hours (up to 14 hours in the model) compound leaf water loss. Wind amplifies transpiration and mechanical stress, so even mild heat can score higher when wind exceeds 20 km/h.
Shelter and canopy reduce direct exposure
The calculator applies shielding using two site controls: shelter level (0–1) and canopy cover (0–100%). Together they can reduce the base index by up to roughly 50% in the model, reflecting shade cloth, walls, hedges, and trees. If your plot is exposed, lowering shelter and canopy values will highlight how quickly risk increases under full sun.
Duration and sensitivity help plan operations
Exposure duration scales the final index so a short task window can be safer than an all-day workload. Sensitivity adjusts for hardy versus tender plants, making transplants and soft herbs more responsive to the same weather. Track a few days of outputs, export CSV for records, and compare driver lists to prioritize irrigation, mulching, and protection.
FAQs
1) What does the index represent?
It is a planning score that combines heat, cold, wind, dryness, rain, and UV into a single 0–100 value for garden exposure and stress.
2) Do the weightings need to total 100?
No. The calculator automatically normalizes weightings, so you can set priorities without manual balancing. Avoid setting every weight to zero.
3) How should I estimate shelter level?
Use 0.0 for open fields, 0.5 for partial barriers like hedges, and 0.8–1.0 for protected areas near walls, pergolas, or dense windbreaks.
4) Why can the same temperature produce different results?
Humidity, sun hours, wind, rainfall, UV, and site shielding change plant water loss and damage risk. Those factors can raise or reduce exposure.
5) Is rainfall always “bad” in the index?
Rain risk reflects heavy-rain issues such as splash disease and waterlogging. Light rain often has low risk and may reduce dryness outside this model.
6) How can I use exports effectively?
Export CSV or PDF after calculations to keep a site log. Compare top drivers across days to decide whether shade, mulch, drainage, or windbreaks gives the best return.