Gridded Monthly Climatologies

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 August 1, 1999

Climatic means of monthly air temperature (*T*) and unadjusted
(for raingage undercatch) precipitation (*P*) were taken from the
station and oceanic-grid-point records compiled by Legates and
Willmott (1990a and b). These in-situ averages then were used to
spatially reinterpolate average-monthly *T* and *P*
fields to a 0.5x0.5
degree spatial grid, which covers the entire globe. The
interpolations were, in part, based on Willmott et al.'s (1985a)
spherical implementation of Shepard's spatial-interpolation
algorithm, although an average of 20 nearest stations influenced
each grid-point estimate, instead of the seven suggested by
Shepard. Two separate sets of gridded *T* fields were alternately
interpolated, first using "traditional" interpolation alone
(Willmott et al., 1985a, as outlined above), and second by "DEM-assisted"
interpolation as described by Willmott and Matsuura
(1995). It is likely that the DEM-assisted *T* fields are more
realistic over the land surfaces, with regional and seasonal
exceptions. These gridded *T* and *P* data fields are available from
this site (Global Air Temperature and Precipitation: Regridded
Monthly and Annual Climatologies, V. 2.01). Our estimates
of the average-monthly moisture indices from *T* and *P*
(see below) were made at (and are available for) only the land-surface
grid points, which number 86,609.

Average-monthly water-balance fields first were estimated from the
gridded average-monthly *T* and *P* fields according to
Willmott et al.'s (1985b) modified version of the Thornthwaite
water-balance procedure. The computational algorithm was derived
from Willmott (1977). Climatic water-balance calculations were
separately made for each of the 86,609 grid nodes, thereby
conserving mass (in z only) at each grid node. Two complete sets
of water-balance estimates were produced and archived: one based on the
traditionally interpolated average-monthly *T* fields; and the other
based on a DEM-assisted gridding of average-monthly *T*. These
0.5-degree resolution water-balance estimates also are
available through this site (Terrestrial Water Balance Data Archive:
Regridded Monthly Climatologies, V. 1.01). Using our estimated average-monthly
potential evapotranspiration (*Eo*) and *P* values,
average-monthly moisture indices were calculated according to Willmott
and Feddema (1992) at the same resolution as the water-balance
fields. Two sets of moisture indices were estimated and archived: one
based on Eo from traditionally interpolated air temperature and
other based on DEM-assisted, interpolated air temperature
(mentioned above).

There are two sets of files in this archive. One based on Eo calculated
from traditionally interpolated air temperature and the other
based on *Eo*calculated from DEM-assisted, interpolated air
temperature. Please note that each mean-annual moisture index
was computed from the 12-month total *Eo* and *P*.

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 Moisture Indices | 12F8.2 |

15 | 113 - 120 | Annual Moisture Indices | F8.2 |

Legates, D. R. and C. J. Willmott, 1990a. Mean Seasonal and Spatial Variability in Gauge-Corrected, Global Precipitation.

Legates, D. R. and C. J. Willmott, 1990b. Mean Seasonal and Spatial Variability in Global Surface Air Temperature.

Willmott, C. J., 1977. WATBUG: A FORTRAN IV Algorithm for Calculating the Climatic Water Budget.

Willmott, C.J. and K. Matsuura, 1995. Smart Interpolation of Annually Averaged Air Temperature in the United States.

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. T

Willmott, C. J., C. M. Rowe, and Y. Mintz, 1985b. Climatology of the Terrestrial Seasonal Water Cycle.

Willmott, C. J. and J. J. Feddema, 1992. A More Rational Climatic Moisture Index.