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Average Annual Precipitation



Citation Information

Title: Average Annual Precipitation

Source: Willmott and Matsuura (2001)

Date: 2001

Citation: Willmott CJ, Matsuura K (2001) Terrestrial Air Temperature and Precipitation: Monthly and Annual Climatologies (Version 3.02).  pp Page, Center for Climatic Research, Department of Geography, University of Delaware. [online] URL: http://climate.geog.udel.edu/~climate/html_pages/README.ghcn_clim2.html


Average annual precipitation (mm yr-1) from 1950-1999 compiled from a number of sources. Native resolution is 30 arc minute projected in Geographic Coordinate System WGS 1984.

Data Transformation

The data was transformed using a logarithm transformation to reduce the skew of the raw data.


Raw precipitation data (left) versus log-transformed precipitation data (right).

Processing Procedure

1. In ArcMap 10.0, convert native data to 30 arc second resolution.

2. Extrapolate existing data using a 360×360 cell rectangular neighborhood.

3. Use zonal statistics to calculate mean values within each GLU.

Data Coverage

Data is coded by the number of cells covered by the native data (1), data extrapolation (2), and not covered by either (3).

DGG Cell Coverage Report
Coverage Codes Frequency Percent Valid Percent Cumulative Percent
Valid 1 1428763 98.9 98.9 98.9
2 13644 .9 .9 99.8
3 2557 .2 .2 100.0
Total 1444964 100.0 100.0
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