120°W 100°W 80°W
50°N
30°N
One Year Moisture Surplus/ Deficit
Extreme Drought (<-2)
Severe Drought (-2 to -1.5)
Moderate Drought (-1.5 to -1)
Mild Drought (-1 to -0.5)
Near Normal Conditions (-0.5 to 0.5)
Mild Moisture Surplus (0.5 to 1)
Moderate Moisture Surplus (1 to 1.5)
Severe Moisture Surplus (1.5 to 2)
Extreme Moisture Surplus (>2)
Map produced by FHTET, IL
Fort Collins, CO on 2-8-2012
0 100 200 400 600 800
Kilometers
Albers Equal Area Conic Projection
1,000
One year moisture surplus and deficit for 2010 developed from PRISM climate data resampled to 1km resolution. Moisture index values for a given location represent the deviation from the 100 year moisture average.
Koch, F.H.; Smith, W.D.; Coulston, J.W. In press. Recent drought conditions in the conterminous
United States. Chapter 4 in Potter, K.M.; Conkling, B.L. (eds.) Forest Health Monitoring 2011 National
Technical Report. Gen. Tech. Rep. SRS-xxx. Asheville, NC: U.S. Department of Agriculture, Forest
Service, Southern Research Station.
100°W 80°W
30°N

Moisture Surplus and Deficit Map and Data Summary
The Moisture Surplus and Deficit maps represent the departure from typical moisture conditions over a 1-, 3-, and 5-year time period (Koch 2011).
PRISM climate grids (4km resolution) were used to calculate a moisture index value for each location across the contiguous U.S. (CONUS), with the final product resampled to 1km resolution. Moisture index values incorporate both precipitation and potential evapotranspiration, giving an accounting of a location’s water balance. Typical (i.e., long-term) moisture conditions are represented by the 100 year average and standard deviation. Moisture conditions over a 1-, 3-, or 5-year window are compared to the corresponding 100 year conditions to classify an area as having moisture deficit, surplus, or near normal conditions during the time period of interest (Table 1).
Data Source:
Gridded precipitation data developed using the Parameter-elevation Regression on Independent Slopes (PRISM) Climate Mapping System, and available from the
PRISM Climate Group web site ( http://www.prism.oregonstate.edu/ ). Potential evapotranspiration grids calculated in part using gridded temperature data, also from the PRISM Climate Group web site. For additional details on the PRISM method: Daly, C.; Gibson, W. P.; Taylor, G. H. [and others]. 2002. A knowledgebased approach to the statistical mapping of climate. Climate Research. 22: 99-113.
Reference:
Koch, F.H.; Smith, W.D.; Coulston, J.W. In press. Recent drought conditions in the conterminous United States. Chapter 4 in Potter, K.M.; Conkling, B.L. (eds.)
Forest Health Monitoring 2011 National Technical Report. Gen. Tech. Rep. SRS-xxx. Asheville, NC: U.S. Department of Agriculture, Forest Service, Southern
Research Station.
Table 1: Moisture surplus deficit scores classified Point of Contact
into nine moisture status classes.
Frank H. Koch
Moisture
Score Moisture Status
Research Ecologist
USDA Forest Service,
<-2 Extreme drought
-2 to -1.5 Severe drought
Southern Research Station
Eastern Forest Environmental
-1.5 to -1
-1 to -0.5
Moderate drought
Mild drought
Threat Assessment Center
3041 Cornwallis Road
-0.5 to 0.5 Near normal conditions
Research Triangle Park, NC 27709
Phone: (919) 549-4006
0.5 to 1 Mild moisture surplus
1 to 1.5
1.5 to 2
> 2
Moderate moisture surplus
Severe moisture surplus
Extreme moisture surplus
Email: fhkoch@fs.fed.us
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