| THE BYRAM-KEETCH DROUGHT INDEX (BKDI) & DROUGHT FACTOR (DF) |
The The Byram-Keetch Drought Index (BKDI) attempts to measure the amount of precipitation necessary to return the soil to
full field capacity. It is a closed system ranging from 0 - 800 and represents a moisture regime from 0 to 203 millimetres (0 - 8 inches)
of water through the soil layer.
At 203 millimetres (8in) of water, the KBDI assumes saturation. Zero is the point of no moisture deficiency and 800
is the maximum drought that is possible. At any point along the scale, the index number indicates the amount of net rainfall that is required to reduce the index to zero, or saturation.
The inputs for KBDI are weather station latitude, mean annual precipitation, maximum dry bulb temperature, and the last 24 hours of rainfall. Reduction in drought occurs
only when rainfall exceeds 5mm (0.20 inch) (called net rainfall).
| BKDI RANGE |
GENERAL DESCRIPTION |
| 700-800 |
Upper soil and surface litter are extremely dry. Live understory vegetation burns actively and contributes to fire potential. Fire behavior is unpredictable with crowing and downwind spotting.
Associated with extreme drought and increased wildfire occurrence. |
| 500-700 |
Upper soil and surface litter are very dry. Above 600 is associated with severe drought. Surface litter and organic soil material contribute to fire intensity.
All surface litter and most of organic layer are consumed by fire leaving excessive site damage. Above 600 fire suppression is a significant undertaking. |
| 300-500 |
Upper soil and litter are dry and may contribute to fire intensity.Fire consumes most surface litter along with significant loss in organic soil material.
Although escaped fire is difficult to control, fire behavior is somewhat predictable. |
| 150-300 |
Upper soil and litter are moist and do not contribute to fire intensity. Some surface litter remains damp and undisturbed following the fire. Fire behavior is predictable |
| 0-150 |
Upper soil and litter are wet. Fire potential is minimal. |
Drought Factor (DF): A key component of the FFDI is the modelling of the dryness of the fuel. This is expressed by the Drought Factor (DF), which ranges from 0 to 10.
If this is multiplied by 10 and called a percent, it gives the percentage of fine fuel that would be removed by a fire under the current conditions.
The DF is based on recent rainfall and on the Byram-Keetch Drought Index (BKDI).
|