Terrestrial Water Budget Data Archive:
Monthly Time Series (1950 - 1999)
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
Archive (Version 1.02) released July 1, 2001
GRIDDED DATA SOURCES:
Time series of gridded monthly average air
) and total precipitation (P
) were taken from
the Terrestrial Air
Temperature and Precipitation: Monthly and Annual Time Series
archive, which also is available through this web site.
The length of each grid-point time series is 50 years (from 1950 through 1999)
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
(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 (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.
There are seven tar files, one for each water-budget
variable. Each tar file includes 50 yearly files.
|E150.tar:||actual evapotranspiration |
|Eo150.tar:||adjusted potential evapotranspiration |
|M150.tar:||snow melt |
|w150.tar:||mid-monthly soil moisture |
|ws150.tar:||mid-monthly snow cover |
All yearly files have the same structure (once they are uncompressed).
||1 - 8
||Longitude (decimal degrees)
||9 - 16
||Latitude (decimal degrees)
||17 - 112
||Monthly values (mm)
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,