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Oklahoma Comprehensive Water Plan


 

Drought Indicators

Palmer Drought Severity Index

The percent of normal precipitation, as presented in the Oklahoma Rainfall Update, is one of the simplest and most useful indicators of drought. It may be calculated over a variety of time periods -- for a single month, a growing season, or an annual or water year. The homepage of the Oklahoma Climatological Survey provides a wide array of this and related information garnered primarily from the Oklahoma Mesonet, a network of 115 automated stations located throughout the state.

The Palmer Drought Severity Index uses precipitation, air temperature, soil moisture, evapotranspiration and previous indices to generate a positive or negative number, with a value of 0 being normal, -4 and below an extremely dry condition, and 4 and above an extremely wet condition. The PDSI is most effective in measuring impacts sensitive to soil moisture conditions, such as agriculture. However, the PDSI is slow to respond to rainfall events and subsequent runoff and it may underestimate or overestimate the severity of ongoing dry periods. The PDSI is updated weekly.

The Standardized Precipitation Index, more sensitive than the PDSI, provides a comparison of precipitation over a specified period with precipitation totals from that same period for all years included in the historical record. The 3-month SPI provides a seasonal estimation of precipitation which, primarily in agricultural regions, might be more applicable in highlighting available moisture conditions than the PDSI. The 6-month SPI can be very effective in showing precipitation over distinct seasons. The SPI is updated around the 15th of each month.

The Keetch-Byram Drought Index, an excellent tool to monitor drought-related fire conditions, is a soil/duff index that ranges from 0 (no drought) to 800 (extreme drought) and is based on a soil capacity of 8 inches of water. The KBDI is calculated 11 times each day as an integral product of the Oklahoma Fire Danger Model.

The Crop Moisture Index uses a meteorological approach to monitor crop conditions from week to week. Unlike the Palmer Drought Severity Index, which monitors long-term wet and dry spells, the CMI is designed to evaluate short-term moisture conditions in major crop-producing regions, such as Oklahoma. The CMI is issued weekly. A representation of crop moisture by climate division is available.


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Page last updated: August 08, 2006

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