Terrestrial Water Budget Data Archive:
Monthly Time Series (1950 - 1996)

(Version 1.01)

produced and documented by

Cort J. Willmott and Kenji Matsuura
(with support from NASA's Seasonal to Interannual ESIP)

For additional information concerning this archive,
please contact us at:

Center for Climatic Research
Department of Geography
University of Delaware
Newark, DE 19716
(302) 831-2294

or

kenjisan@udel.edu


Archive (Version 1.01) released January 31, 2000


GRIDDED DATA SOURCES:

Time series of gridded monthly average air temperature (T) and total precipitation (P) were taken from the Terrestrial Air Temperature and Precipitation: Monthly and Annual Time Series (1950 - 1996) (version 1.01) archive, which also is available through this web site. The length of each grid-point time series is 47 years (from 1950 through 1996) and the grid points cover the globe at a 0.5x0.5 degree resolution. Our spatial interpolations were based on Willmott et al.'s (1985a) spherical implementation of Shepard's spatial-interpolation algorithm, and they also incorporated DEM (digital elevation model)-assisted and Climatologically-Aided interpolation methods (see the related references below). Our estimates of the climatic water budget from T and P (see below) were made at (and are available for) the land-surface grid points, which number 86,609.

GRIDDED WATER-BUDGET ESTIMATES:

Monthly water-budget fields were estimated from the gridded monthly-average T and total P fields according to Willmott et al.'s (1985b) modified version of the Thornthwaite water-budget procedure. The computational algorithm was derived from Willmott (1977). Climatic water-budget calculations were separately made for each of the 86,609 grid nodes, thereby conserving mass (in z only) at each grid node. These 0.5-degree resolution water-budget estimates are based on semi-empirical relationships between observed monthly total P and an estimated monthly potential evapotranspiration (Eo), derived from a monthly average T. Available soil water-holding capacity (w*) was held constant at 150 mm for these calculations. Time-series fields with different w*s may be added in the future. A snow-cover water budget also was evaluated and coupled with the soil-moisture budget according to Willmott et al. (1985b). Water-budget variables estimated and archived here include: monthly Eo in mm, monthly actual evapotranspiration (E) in mm, average-monthly deficit (def) in mm, mid-monthly soil-moisture depth (w) in mm, mid-monthly water equivalent of the snow pack (ws) in mm, monthly snow melt (M) in mm, and monthly surplus (S) in mm.

ARCHIVE STRUCTURE:

There are seven tar files, one for each water-budget variable. Each tar file includes 47 yearly files.

def150.tar: deficit
E150.tar:actual evapotranspiration
Eo150.tar:adjusted potential evapotranspiration
M150.tar:snow melt
S150.tar:surplus
w150.tar:mid-monthly soil moisture
ws150.tar:mid-monthly snow cover


All yearly files have the same structure (once they are uncompressed).

Field Columns Variable Fortran Format
1 1 - 8 Longitude (decimal degrees)
F8.3
2 9 - 16 Latitude (decimal degrees)
F8.3
3-14 17 - 112 Monthly values (mm)
12F8.1


SELECTED REFERENCES:

Legates, D. R. and C. J. Willmott, 1990a. Mean Seasonal and Spatial Variability in Gauge-Corrected, Global Precipitation. International Journal of Climatology, 10, 111-127.

Legates, D. R. and C. J. Willmott, 1990b. Mean Seasonal and Spatial Variability in Global Surface Air Temperature. Theoretical and Applied Climatology, 41, 11-21.

Willmott, C. J., 1977. WATBUG: A FORTRAN IV Algorithm for Calculating the Climatic Water Budget. Pubs. in Climatology, 30, 1-55. (Also published as Report 1 in The Use of the Climatic Water Budget in Water Resources Management and Control. Newark, DE: University of Delaware, Water Resources Center, 1977).

Willmott, C.J. and K. Matsuura, 1995. Smart Interpolation of Annually Averaged Air Temperature in the United States. Journal of Applied Meteorology, 34(12), 2577-2586.

Willmott, C.J., C.M. Rowe, and W.D. Philpot, 1985a. Small-Scale Climate Maps: A Sensitivity Analysis of Some Common Assumptions Associated with Grid-Point Interpolation and Contouring. The American Cartographer, 12, 5-16.

Willmott, C. J., C. M. Rowe, and Y. Mintz, 1985b. Climatology of the Terrestrial Seasonal Water Cycle. Journal of Climatology, 5, 589-606.