heat_stress_index: heat stress index (Heat Index) — calculated based on temperature, humidity, and wind, °C (degrees Celsius) [More details]

The heat stress index (or "apparent temperature in heat") shows how hot the air feels at a given temperature and humidity. It accounts for high humidity, which slows sweat evaporation and impairs body cooling. It also considers wind effects.

Application:
Can be used to assess the risks of heat exhaustion, dehydration, and overheating, especially during physical activity.

High values may indicate dangerous conditions:

• 27–32°C: discomfort possible
• 32–41°C: heat stress
• 41–54°C: danger of overheating
• >54°C: extremely dangerous

fire_risk_index: fire risk index (Fire Risk Index) — assessment of natural fire risk based on air temperature and relative humidity [More details]

The fire risk index is a simple empirical indicator that assesses the risk of wildfires (in forests, fields, etc.) based on weather conditions. It is calculated using air temperature and relative humidity. Values above 30 indicate increased fire risk.

Unit of measurement: relative, dimensionless.

Interpretation:

• <10: low risk. Minimal fire danger. Humid and cool weather
• 10–20: moderate. Local fire outbreaks are possible in presence of fuel (dry grass)
• 20–30: increased. Conditions are favorable for fire spread. Campfires are not recommended
• 30–40: high. High risk of wildfires. Precautionary measures required
• >40: extreme. Ignitions are likely even with minimal flame sources

The icing risk index (Icing Risk Index) is an approximate assessment of conditions conducive to surface icing (roads, power lines, vessels, etc.).

• High risk (high): Temperature from -2 to +2°C, humidity above 90%, wind ≥2 m/s — high likelihood of ice formation.
• Moderate risk (moderate): Temperature from -5 to -2°C, humidity above 80%, wind ≥1.5 m/s.
• Low risk (low): Temperature below -5°C, humidity above 70%, wind ≥1 m/s.
• No risk (none): Other conditions are considered safe, no icing expected.

This index is especially useful for predicting black ice, icing on power lines, ships, or aviation equipment.

Values:

• 0–20 - low risk
• 21–40 - low risk
• 41–60 - moderate
• 61–80 - high risk
• 81–100 - very high risk (dangerous driving conditions)

Growing Degree Days (GDD) is calculated as the sum of positive exceedances of air temperature above the base plant growth temperature. It is used in crop science to estimate development phases. Unit: °C·day.

!!! The base temperature is set via the tbase_gdd parameter (default: 5°C).
!!! GDD is calculated only when the request specifies forecast dates without time (hours).
Request example:
https://projecteol.ru/api/spec/?lat=47.074&lon=42.631&date=2025-05-15&token={YOUR_TOKEN}&tbase_gdd=10

Calculated using the formula:
GDD = max(0, (Tmax + Tmin) / 2 - Tbase)
where:
Tmax, Tmin — forecasted daily maximum and minimum air temperatures;
Tbase (API parameter — tbase_gdd) — the base temperature below which plant growth slows down or stops.

Application:
The index is widely used to assess planting dates, plant phenophases, frost risk, and harvest times.

GDD interpretation, °C·day:

• 0–5 - insufficient warmth, little or no growth
• 5–15 - moderate growth
• 15–25 - active growth
• >25 - very rapid development (possible drought stress)

Different crops may use different base temperatures (tbase_gdd):

• Winter wheat — 5 °C
• Buckwheat — 5 °C
• Corn — 10 °C
• Sunflower — 6–8 °C
• Potato — 5 °C
• Soybean — 10 °C

!!! GDD is calculated only when the request specifies forecast dates without time (hours).

Criteria:

• < 0.2 — humid conditions
• 0.2–0.4 — normal conditions
• > 0.5 — drought risk

!!! The calculation is made when only the forecast days are specified in the request, without hours.

Photosynthetically Active Radiation (PAR) is an important indicator that determines the availability of sunlight for photosynthesis. It is especially useful for assessing agricultural productivity.

Criteria:

• < 0.1 - almost no photosynthetic activity
• 0.1–0.3 - insufficient light for most crops
• 0.3–0.6 - acceptable for shade-tolerant plants
• 0.6–1.2 - good conditions for photosynthesis
• >1.2 - maximum photosynthesis, overheating possible

!!! The calculation is made when only the forecast days are specified in the request, without hours.

The dry wind index reflects the number of hours per day when the following conditions occur simultaneously:
- high air temperature (≥ 25 °C),
- низкая относительная влажность воздуха (≤ 30 %),
- high wind speed (≥ 5 m/s).

Meaning:
Dry wind is an adverse agrometeorological phenomenon that causes increased evaporation from soil and plants. Such conditions may lead to:
- rapid drying of the topsoil,
- reduced agricultural productivity,
- increased drought risk,
- plant stress during flowering and fruiting stages.

How it is used:
The index shows how many hours per day dry wind conditions were observed.

Examples:
dry_wind_index = 0: no dry winds during the day;
dry_wind_index = 6: dry wind conditions occurred for 6 hours;
dry_wind_index ≥ 10: high agrometeorological stress, potential crop damage.