The Drought Factor Calculator helps determine the current dryness level of soil based on temperature, rainfall, and past conditions. It’s used widely in fire weather forecasting, agriculture, forestry, and environmental monitoring. The calculator produces a key output known as the Keetch-Byram Drought Index (KBDI), which measures drought severity and fuel moisture levels.
This tool belongs to the Environmental and Agricultural Calculator category. It supports critical decision-making in fire management, irrigation planning, and land use policies. When drought conditions rise, the calculator becomes an essential tool for alert systems and resource allocation.
The drought factor is especially useful in predicting wildfire behavior and planning controlled burns. High KBDI values indicate extremely dry ground conditions, which can be hazardous.
formula of Drought Factor Calculator
KBDI = Previous KBDI + (0.968 × (Max Temp - 0.13 × P)^1.65 × 10^-3 × (10.88 - Rainfall)) × DF
Where:
KBDI ranges from 0 to 800
P is the annual precipitation in inches
Max Temp is the daily maximum temperature in °F
Rainfall is the daily rainfall in inches
DF is the drying factor, based on soil type and vegetation
Assumptions:
- No rain during the previous 24 hours increases dryness
- Higher temperatures and lower rainfall cause faster KBDI increase
- DF varies depending on soil absorption, vegetation cover, and climate
This equation is widely used by environmental agencies for its reliability and scientific basis.
Drought Factor Quick Reference Table
The table below helps users estimate general drought severity based on calculated KBDI values:
| KBDI Range | Drought Severity Level | Typical Conditions |
|---|---|---|
| 0 - 200 | Low | Moist soil, low fire risk |
| 201 - 400 | Moderate | Drying trend, increased plant stress |
| 401 - 600 | High | Very dry, vegetation highly flammable |
| 601 - 800 | Extreme | Severe drought, dangerous fire potential |
This table is useful for quick field assessments and decision support.
Example of Drought Factor Calculator
Suppose a region has the following data:
- Previous KBDI = 300
- Max Temp = 95°F
- P (annual precipitation) = 40 inches
- Rainfall (today) = 0.1 inches
- DF = 1.2 (based on dry sandy soil)
Now apply the formula:
KBDI = 300 + (0.968 × (95 - 0.13 × 40)^1.65 × 10^-3 × (10.88 - 0.1)) × 1.2
KBDI = 300 + (0.968 × 89.8^1.65 × 0.001 × 10.78) × 1.2 ≈ 314.31
The new KBDI is approximately 314, which falls into the Moderate drought range.
Most Common FAQs
It means the soil is very dry and vegetation is more likely to catch fire. A value over 600 indicates extreme drought.
Yes, the drying factor (DF) depends on soil type, vegetation, and climate, so it must be adjusted for local conditions.
Absolutely. It helps fire agencies assess fire risk and plan prevention or control measures.