Corsicana Daily Sun, Corsicana, Texas

July 1, 2013

Burn ban in effect, but fireworks not restricted

From Staff Reports
CNHI

Corsicana — A burn ban is now in effect for Navarro County after commissioners enacted the measure in a special called meeting Monday morning. Fireworks have not been banned.

The KBDI drought index is now at 575 in the county. The ban will remain in effect until it is repealed by the court.

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Keetch and Byram (1968) designed a drought index specifically for fire potential assessment. It is a number representing the net effect of evapotranspiration and precipitation in producing cumulative moisture deficiency in deep duff and upper soil layers. It is a continuous index, relating to the flammability of organic material in the ground.

Keetch-Byram Drought Index MapThe KBDI attempts to measure the amount of precipitation necessary to return the soil to full field capacity. It is a closed system ranging from 0 to 800 units and represents a moisture regime from 0 to 8 inches of water through the soil layer. At 8 inches 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 0.20 inch (called net rainfall). The computational steps involve reducing the drought index by the net rain amount and increasing the drought index by a drought factor.