South Carolina Drought Forecasting

Greg Carbone and Kirstin Dow

Department of Geography

University of South Carolina

Outline

Community water systems managers in South Carolina

Resampling methodology applied to drought forecasting

Sample products

Investigating CWS Managers

• 3 Focus groups

• 4 meetings with key informants

• Survey results from 269 managers (52%)

5 - Day Forecasts

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SRB

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5 - V

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SRB

3-Month Forecasts

Per

cent

age

Confidence in…

Survey Questions Included in Use of Forecasts for Planning

Percentage of “Yes” responses SC PAPlan future water storage needs for finished water? 16.8 13.1

Plan expanded distribution capability? 16.7 7.4

Plan when to bring new water supplies on line? 15.6 16.3

Adjust existing reservoir levels or back-up storage? 24.4 24.2

Anticipate inventory supply needs or guide purchasing decisions?

19.2 16.5

Schedule personnel, maintenance, or construction? 59.0 52.1

Schedule additional testing for water quality? 29.3 28.7

Help make budget projections? 22.2 10.8

Justify increased infrastructure investments? 18.9 11.7

Start a public information campaign to conserve water? 57.5 65.9

Summary of CWS Managers Views

• CWS managers’ have some confidence in climate forecasts, but……

• Confidence does not increase the likelihood that CWS managers will use forecasts

• Level of concern over risks and severity of consequences offers greater insight into uses of forecasts

Drought Stage

(SC Drought Response

Committee)

Palmer Drought Severity Index

(PDSI)

Standardized Precipitation Index (SPI)

Keetch-Byram Index

1 Incipient -0.50 to -1.49 0 to -0.99 300 to 399

2 Moderate -1.50 to -2.99 -1.00 to -1.49 400-499

3 Severe -3.00 to –3.99 -1.50 to -1.99 500-699

4 Extreme ≤ -4.00 ≤ -2.00 ≥ 700

South Carolina Drought Stages

Anticipating future drought indices

• Resample from climatology• Incorporate long-lead forecasts

Using Climatology (“equal chances”)

1/9 1/9 1/9

1/9 1/9 1/9

1/9 1/9 1/9

AboveNormalBelow

Temperature

Above

Normal

Below

Pre

cip

itatio

n

1934,1943,1960,1965,1975,1980,1993,1998

1944,1951,1952,

1964,1979,1983,

2003

1946,1948,1963,1973,1976,1977,1990,1997

1940,1942,1958,1962,1971,1984,1996,2001

1950,1954,1959,

1970,1972,1978,

1992,1994,2002

1935,1936,1938,1945,1953,1961,1968,1974,1997,2000

1931,1932,1933,1937,1941,1947,1969,1987,1999

1939,1949,1956,

1957,1966,1981,

1986,1988

1955,1967,1982,1985,1989,1995

AboveNormalBelow

Temperature

Above

Normal

Below

Pre

cip

itatio

n

1934,1943,1960,1965,1975,1980,1993,1998

1944,1951,1952,

1964,1979,1983,

2003

1946,1948,1963,1973,1976,1977,1990,1997

1940,1942,1958,1962,1971,1984,1996,2001

1950,1954,1959,

1970,1972,1978,

1992,1994,2002

1935,1936,1938,1945,1953,1961,1968,1974,1997,2000

1931,1932,1933,1937,1941,1947,1969,1987,1999

1939,1949,1956,

1957,1966,1981,

1986,1988

1955,1967,1982,1985,1989,1995

AboveNormalBelow

Temperature

Above

Normal

Below

Pre

cip

itatio

n

May 2002 drought prediction(made on January 1, 2002)

“El Nino Projections”(made 1 June 2002)

“El Nino Projections”

Final Thoughts• Seasonal temperature and precipitation

forecasts can be used for “secondary products” that address particular concerns and awareness– Risk aversion, past experience

• Since interannual variability swamps marginal probability shifts, exploit the historical climate record

• Purveyors need regional-scale appreciation for user knowledge base and requirements

Community Water Systems

• Provide water to at least 25 people or 15 service connections year round (EPA)

• Variety of water sizes, water sources

• Risk aversion: reliability/resilience built into management and systems

• Other management criteria: profitability, competitiveness, politically influenced

Drought Stage

(SC Drought Response

Committee)

Palmer Drought Severity Index

(PDSI)

Standardized Precipitation Index (SPI)

Keetch-Byram Index

1 Incipient -0.50 to -1.49 0 to -0.99 300 to 399

2 Moderate -1.50 to -2.99 -1.00 to -1.49 400-499

3 Severe -3.00 to –3.99 -1.50 to -1.99 500-699

4 Extreme ≤ -4.00 ≤ -2.00 ≥ 700

July Mean TemperatureGreenwood SC, 1895-2000

July Mean Temperature (°F)

70 72 74 76 78 80 82 84

July PrecipitationGreenwood SC, 1895-2000

July Precipitation (inches)

0 2 4 6 8 10 12