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Drought ??
Jim Broderick Monday, January 24, 2005
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Questions?Does your community have a drought plan?When was it developed? Is it current?What indicators/indices are used to monitor water supply/drought conditions?Do you have voluntary and mandatory water restrictions?What triggers are used to initiate these restrictions?
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Questions?When did the current drought begin?How does it compare to historical droughts?Did you experience water supply shortages in 2002, 2001, or 2000?What steps has your community taken to improve drought management in 2003?
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: a deficiency of precipitation from expected or “normal” that, when extended over a season or longer period of time, is insufficient to meet the demands of human activities and the environment.
Drought is:a temporary aberrationa relative condition aggravated by temperature, high winds, and low RH
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Spatial Extent
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Types of Drought
MeteorologicalPrecipitation
AgriculturalSoil moisture
HydrologicalSurface/subsurface water supplies
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Components of Drought Risk Management
(natural event) (social factors)
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Components of Drought Plans
Monitoring, early warning and predictionFoundation of a drought mitigation plan Indices linked to impacts and triggers
Risk and impact assessment Who and what is at risk and why
Mitigation and responseActions/programs that reduce risk and impacts and enhance recovery
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The Importance of Drought Monitoring Systems
Allows for early drought detection
Allows for proactive (mitigation) and reactive (emergency) responses
“Triggers” actions within a drought plan
Bottom line—provides information for decision support
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Key Indicators for Monitoring Drought
Climate data (precip, temp)Stream flowGround waterReservoir and lake levelsSoil moistureSnow packShort, medium, and long range forecastsVegetation health/stress and fire danger
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Drought Assessment Tools
Percent of Normal
Deciles
Palmer Drought Severity Index (PDSI)
Crop Moisture Index (CMI)
Surface Water Supply Index (SWSI)
Standardized Precipitation Index (SPI)
U.S. Drought Monitor
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Importance of Drought Indices
Simplify complex relationships and provide a good communication tool for diverse audiencesQuantitative assessment of anomalous climatic conditions
IntensityDurationSpatial extent
Historical reference (probability of recurrence)Planning and design applications
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Approaches to Drought Assessment
Single index or indicator
Multiple indices or indicators
Composite index
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Triggers
Triggers: thresholds determining specific, timely actions by decision makers. Link impacts to index or indicator values.
AppropriateConsistent with impactsAdaptable
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What is the PDSI?A commonly used indicator of the status of the environmental demand for precipitation with respect to what has actually been received (supply). Includes
Average temperatureTotal precipitationParameterization of soil type and water holding capacity of the top layers of the soil.
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Surface Water Supply Index (SWSI)
River basin, watershed approachHydro/climate index for mountainous regions relying on snowpackIndicators: precipitation, reservoir levels, snowpack, and streamflowComputed seasonallyData normalized, probability of non-exceedance computed for each componentIndex unique for each basin, limits comparison
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Characteristics of the SPI
Developed by McKee et al. in 1993Simple index—precipitation is the only parameter (probability of observed precipitation transformed into an index)Being used in research or operational mode in over 40 countriesMultiple time scales allow for temporal flexibility in evaluation of precipitation conditions and water supply
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6-month SPI through the end of April 2001
Copyright © 2001 National Drought Mitigation Center
+ 2.0 and above (extremely wet)
+ 1.50 to + 1.99 (very wet)+ 1.0 to + 1.49 (moderately wet)-0.99 to + 0.99 (near normal)-1.00 to -1.49 (moderately dry)-1.50 to -1.99 (severely dry)-2.0 and less (extremely dry)
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http://drought.unl.edu/dm
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SummaryMonitoring drought effectively requires multiple indicators or indicesExperiences from other states and water utilities can be helpful and will avoid “reinventing the wheel”U.S. Drought Monitor is an important tool to provide a national and regional perspectiveLocal, more site specific information is essential to evaluate local conditions and trends
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SummaryHistorical climate information is readily available to help determine the “drought of record” for your locationCommunicating timely and reliable information on drought severity to the public is criticalDeveloping appropriate triggers for the start-up and shut-down of phased voluntary and mandatory response actions for water users is a critical element of a drought plan