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<br />Monitoring
<br />
<br />
<br />Colorado Drought Indicators
<br />
<br />Throughout the water year (October through
<br />September), the Water Availability Task Force (WATF)
<br />collects data on snowpack, soil moisture, reservoir
<br />levels, stream flow, precipitation and temperatures, The
<br />members meet quarterly, or monthly during dry
<br />periods, to share the information, discuss projections,
<br />and assess the water situation, Chairs of the Impact
<br />Task Forces comment on any observed or potential
<br />impacts within their area of responsibility, The group
<br />then recommends what actions, if any, should be taken,
<br />The chair of the WATF relays this information to the
<br />Office of the Governor, Upon recommendation, the
<br />Governor may elect to issue a memorandum ordering
<br />an assessment of impacts,
<br />
<br />Figure 2.3
<br />
<br />~
<br />Monitors conditions.
<br />
<br />Members
<br />Colorado Water Conservation Board (Chair)
<br />Colorado Office of Emergency Management
<br />Office of the State Climatologist
<br />Colorado Division of Water Resources
<br />National Weather Service
<br />Natural Resources Conservation Service (USDA)
<br />United States Geological Survey
<br />Bureau of Land Management
<br />Bureau of Reclamation
<br />Private Parties
<br />
<br />Tasks
<br />· Monitor drought forecasts and climate conditions
<br />
<br />· Make projections by basin on:
<br />. Snowpack . Precipitation
<br />. Soil Moisture . Temperatures
<br />. Stream flow . SWSI
<br />. Reservoir levels . SPI
<br />. Ground water levels . Palmer indexes
<br />· Determine requirements for routine and special
<br />reports,
<br />· Provide other task forces with this information,
<br />· Identify resource information gaps and make
<br />recommendations to address them.
<br />· Coordinate and respond to special data requirements
<br />of the other Task Forces,
<br />
<br />Data Sources:
<br />Monthly water supply report, monthly climate report,
<br />modified Palmer Index, monthly Standardized
<br />Precipitation Index (SPI), Surface Water Supply Index
<br />(SWSI), historical norms, weather forecasts, reservoir
<br />levels, stream flow data, rain gauge sites, snow course
<br />sites,
<br />
<br />PAGE 12
<br />
<br />Drought indicators synthesize complex water
<br />availability data for planners and decision-makers.
<br />Since drought is not easily assessed by a single
<br />indicator, Colorado utilizes three indicators: the
<br />Standardized Precipitation Index (SPI), the Surface
<br />Water Supply Index (SWSI), and the Palmer
<br />Drought Index (POI), A brief description of these
<br />indicators follows, '
<br />
<br />Standardized Precipitation Index (SPI)
<br />The SPI measures the precipitation deviation from the
<br />average for a particular location, The SPI can quantify
<br />the precipitation deficit over multiple time scales-
<br />typically three, six, twelve, and twenty four month
<br />periods. Developed in Colorado by the Colorado
<br />Climate Center (McKee et al. 1993), the SPI provides
<br />an early warning of drought and an intensity level for
<br />each month in which the drought occurs.
<br />
<br />Surface Water Supply Index (SWSI)
<br />The SWSI is an indicator of surface water condi-
<br />tions for each major river basin in the state. The
<br />index summarizes snowpack, streamflow, precipita-
<br />tion, and reservoir storage for a particular month.
<br />The weighting factors change from winter to
<br />summer as follows:
<br />November-April SWSI - observed reservoir
<br />storage + precipitation + snowpack + Apr-Jul
<br />streamflow forecast (USDA-NRCS calculation)
<br />
<br />
<br />May-October SWSI - observed reservoir storage +
<br />precipitation + streamflow (CO DWR calculation)
<br />
<br />Palmer Drought Index (POI)
<br />The Palmer Index is widely used across the United
<br />States primarily to gauge impacts on agriculture. It is
<br />based on precipitation and temperature data and the
<br />local available water content of the soil. Since this
<br />index was developed for areas of the country with
<br />more homogeneous climates, the Colorado Climate
<br />Center has adapted the index by separating the state
<br />into twenty-five climatically similar regions, Thus, we
<br />have the Colorado Modified Palmer Drought Index,
<br />
<br />Figure 2A SPI, SWSI, POI Classification and Comparison
<br />
<br />SPI SWSI, POI Drought Category
<br />
<br />2.0+
<br />1.5 to 1,99
<br />1.0 to 1.49
<br />0.99 to 0,99
<br />-1,0 to -1,49
<br />-1,5 to -1,99
<br />-2 and less
<br />
<br />4.0+
<br />3,0 to 3,9
<br />2,0 to 2,9
<br />1,9 to 1,9
<br />-2.0 to -2,9
<br />-3.0 to -3.9
<br />-4,0 and less
<br />
<br />extremely moist
<br />very moist
<br />unusually moist
<br />near normal
<br />moderate drought
<br />severe drought
<br />extreme drought
<br />
<br />JANUARY 2001
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