7. Materials and Methods

All geographic analysis was done in Arc Info Grid version 7.0. All data layers were projected in UTM Zone 18 a common map coordinate.

7.1 Climate data

Climatic data was obtained from ZedX, Boalsburg, PA. The following data were obtained for total monthly precipitation and mean monthly; maximum and minimum temperature and monthly mean daily solar radiation and evaporation. Data on precipitation, mean maximum temperature and solar radiation from October was used to assess harvest conditions. Extreme minimum temperature (10 year interval) and length of growing season were also obtained. The later was based on the time interval between the last 29^oF (-1.7^oC) day in spring and the first 29^oF (-1.7^oC) in fall. Data were available at a 1km² resolution and were based on a 30 year average. Accuracy of the temperature data in comparison with actual stations was +/- 1^oF (0.56^oC). The data are derived from an elevation based interpolation of climatic records from weather stations across the North East of America. The accuracy of the data is thus dependent upon the density of stations, the variation and height of topography in the grid, the proximity of large bodies of water and the quality of the original data.

More details on ZedX data are avialable

Table 2. Values for construction of climate suitability map

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7.2 Soil data

Soil data was obtained from the Penn State Universities Earth Science Systems Center .The data is derived from the state scale base STATSGO which consists of georeferenced digital map data and associated digital tables of attribute data. The compiled soil maps were created with the USGS 1-degree by 2-degree topographic quadrangles (1:250,000 scale, Albers Equal Area projection) as base maps which were then merged on a state basis. The data was reformatted by ESSC and supplied as a 1km raster database.

Available water holding capacity

The mean available water capacity for each STATSGO map unit was computed by calculating the mean available water capacity for each layer using the AWCL(low) and AWCH (high) values from the Layer table. The averages were then summed over the layers for each component. The component values were then weighted by the COMPPCT value in the Component table to determine an AWC value for each map unit. Units of AWC are in centimeters (more properly cubic centimeters of water per square centimeter of soil). Calculations are based on a total 250 cm soil profile or the depth-to-bedrock if less than 250 cm

Drainage

The Hydrologic Soil Group (HSG) class is contained in the HYDGRP variable of the STATSGO Component Table. Possible HYDGRP values include A, B, C,D, A/D, B/D, and C/D. The percentage of each HSG class represented by the components within a map unit was calculated. Mixed classes (A/D, B/D, and C/D) were converted to HSG D during processing. The percentages of each HSG class within a map unit is then placed in a table that can be used to determine the runoff CN for each map unit. Preserving the percentages of the relevant HSG's in each component of each map unit allows the production of a "weighted" CN for each map unit.

Depth to bed rock

The mean depth-to-bedrock for each STATSGO map unit was computed by calculating the mean depth-to-bedrock for each component using the ROCKDEPL (low) and ROCKDEPH (high) values from the Component table. A weighted average of the mean component values was calculated for each map unit. The map unit polygons were then gridded at a resolution of 1 km.

Soil pH

The soil pH map was obtained from the IRIS at Cornell University. The mean PH for each STATSGO map unit was computed by calculating the mean pH for each component using the pH (low) and pH (high) values from the Component table. A weighted average of the mean component values was calculated for each map unit. The map unit polygons were then gridded initially at a resolution of 1 ha and later resampled to 1km.

Table 2. Values for construction of soil suitability map

* Percentage of grid unit in either well or moderately well drained drainage classes.

** pH is composed of three classes; I) less than 5, ii) between 5 and 6; and iii) between 6 and 7.3. There were no soils in the state over 7.3.

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7.3 Land use data

Land use data was also provided as a USGS 1:250,000 base map Each polygon in the data base represents a homogenous area and has a minimum area of 4 ha for urban or man-made features and 16 ha for non-urban features Anon (1991). The Land Use and Land Cover map is compiled to portray the Level II categories of the Land Use and Land Cover classification system documented by Anderson and others (1976). More details on the land cover data are available from the USGS condensed users guide.

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7.4 Elevation data

The source of digital elevation data was a USGS1:250,000 DEM which has a data point every 3 arc seconds (approx. 92m) with a horizontal accuracy of 130m and a vertical accuracy of 30m (Anon, 1987). The data was projected in lat./long. Due to the size of the data file, it was resampled to provide horizontal resolution of approximately 930m. This DEM was used to calculate aspect and slope information. More information is available from the USGS condensed users guide.

Return to New York Elevation

7.5 Analysis

A simple macro was designed to incorporate threshold values, rescale and weight data values. A slice function was used to assign grid values into a specified number of classes between threshold values, and classes were then scaled between zero and one. A weighting value was then added so that each grid could be given a relative importance in comparison with other grids. The final suitability map was constructed by overlaying a final climatic map, with the final soil map and land use map. Suitable land uses were either agriculture or forest classes.

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