Sunday, April 20, 2014

National Drought Mitigation Center

Comparison of Major Drought Indices: Reclamation Drought Index

Description: Like the SWSI, the RDI is calculated at the river basin level, incorporating temperature as well as precipitation, snowpack, streamflow, and reservoir levels as input.

Who uses it: The Bureau of Reclamation; the State of Oklahoma as part of their drought plan.

Pros: By including a temperature component, it also accounts for evaporation.

Cons: Because the index is unique to each river basin, interbasin comparisons are limited.

Developed by: The Bureau of Reclamation, as a trigger to release drought emergency relief funds.

RDI Classifications
4.0 or more extremely wet
1.5 to 4.0 moderately wet
1 to 1.5 normal to mild wetness
0 to -1.5 normal to mild drought
-1.5 to -4.0 moderate drought
-4.0 or less extreme drought

The Reclamation Drought Index (RDI) was recently developed as a tool for defining drought severity and duration, and for predicting the onset and end of periods of drought. The impetus to devise the RDI came from the Reclamation States Drought Assistance Act of 1988, which allows states to seek assistance from the Bureau of Reclamation to mitigate the effects of drought.

Like the SWSI, the RDI is calculated at a river basin level, and it incorporates the supply components of precipitation, snowpack, streamflow, and reservoir levels. The RDI differs from the SWSI in that it builds a temperature-based demand component and a duration into the index. The RDI is adaptable to each particular region and its main strength is its ability to account for both climate and water supply factors.

Oklahoma has developed its own version of the RDI and plans to use the index as one tool within the monitoring system designated in the state’s drought plan. The RDI values and severity designations are similar to the SPI, PDSI, and SWSI.

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