Terrestrial Water Budget Data Archive:
Monthly Time Series (1900 - 2008)

(Version 1.03)

produced and documented by
Kenji Matsuura and Cort J. Willmott
(with support from IGES and NASA)

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 1.03) released August 21, 2009

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GRIDDED DATA SOURCES:

Time series of gridded monthly average air temperature (T) and total precipitation (P) were taken from the Terrestrial Air Temperature: 1900-2008 Gridded Monthly Time Series (Version 2.01) and Terrestrial Precipitation: 1900-2008 Gridded Monthly Time Series (Version 2.01) archives, which also are available through this web site. The length of each grid-point time series is 109 years (from 1900 through 2008) and the grid points cover the global land surface 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 85,794.

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 85,794 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 (E^o), 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 (E^o- E) in mm, mid-monthly soil-moisture depth (w) in mm, mid-monthly water equivalent of the snow pack (w^s) in mm, monthly snow melt (M) in mm, and monthly surplus (S) in mm.

ARCHIVE STRUCTURE:

There are seven gzipped tar files, one for each water-budget variable. Each tar file includes 109 yearly files.

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