Average global temperatures show a similar trend, and all of the top 10 warmest years on record worldwide have occurred since 2005. Nine of the top 10 warmest years on record have occurred since 1998. Average temperatures have risen across the contiguous 48 states since 1901, with an increased rate of warming over the past 30 years. While increased precipitation can replenish water supplies and support agriculture, intense storms can damage property, cause loss of life and population displacement, and temporarily disrupt essential services such as transportation, telecommunications, energy, and water supplies. ![]() More frequent and intense extreme heat events can increase illnesses and deaths, especially among vulnerable populations, and damage some crops. More extreme variations in weather are also a threat to society. For example, warmer average temperatures could increase air conditioning costs and affect the spread of diseases like Lyme disease, but could also improve conditions for growing some crops. Long-term changes in climate can directly or indirectly affect many aspects of society in potentially disruptive ways. This chapter focuses on observed changes in temperature, precipitation, storms, floods, and droughts. Scientific studies indicate that extreme weather events such as heat waves and large storms are likely to become more frequent or more intense with human-induced climate change. Live fuels can also be expected to burn actively at these levels.Rising global average temperature is associated with widespread changes in weather patterns. Intense, deep burning fires with significant downwind spotting can be expected. KBDI = 600 - 800: Often associated with more severe drought with increased wildfire occurrence. Lower litter and duff layers actively contribute to fire intensity and will burn actively. KBDI = 400 - 600: Typical of late summer, early fall. Lower litter and duff layers are drying and beginning to contribute to fire intensity. KBDI = 200 - 400: Typical of late spring, early growing season. Typical of spring dormant season following winter precipitation. ![]() KBDI = 0 - 200: Soil moisture and large class fuel moistures are high and do not contribute much to fire intensity. The computational steps involve reducing the drought index by the net rain amount and increasing the drought index by a drought factor. Reduction in drought occurs only when rainfall exceeds 0.20 inch (called net rainfall). The inputs for KBDI are weather station latitude, mean annual precipitation, maximum dry bulb temperature, and the last 24 hours of rainfall. 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. Zero is the point of no moisture deficiency and 800 is the maximum drought that is possible. At 8 inches of water, the KBDI assumes saturation. 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. ![]() The KBDI attempts to measure the amount of precipitation necessary to return the soil to full field capacity. It is a continuous index, relating to the flammability of organic material in the ground. It is a number representing the net effect of evapotranspiration and precipitation in producing cumulative moisture deficiency in deep duff and upper soil layers. Keetch and Byram (1968) designed a drought index specifically for fire potential assessment.
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