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Observed Land Surface Precipitation Data: 1850-1995 (Dai et al. 1997)

The datasets here contain monthly and annual anomaly precipitation analyses. Dataset 1 covers the period 1900-1988, while the extended and updated Dataset 2 covers the period 1850-1995.

Details of the analysis are described in the paper "Surface observed global land precipitation variations during 1900-1988" (Dai et al. 1997). Following are a few major specifics:

Anomalies are calculated relative to the 1951-1979 period. Values are in millimeters.

Resolution of the longitude-latitude grid is 2.5° × 2.5°. The center of grid cell (I,J) is at longitude (east) = -180.+(I-1)*2.5, latitude = -90.+(J-1)*2.5.

Dataset 1: 1900-1989

The station data source is Eischeid et al. (1991) and the data cover the period from January 1900 to December 1988 (data for 1989 are incomplete). Five-sigma gross screening and discontinuity-correction were performed on the station data before the gridding. An inverse-distance weighted averaging was used during the gridding, which was carried out on the anomalies relative to the 1951-1979 mean.

One may add the gridded anomalies to a climatology of monthly precipitation of the 1951-1979 period such as that of Shea (1986) to obtain the total precipitation values for each month. This may result in negative values for a small number of grid boxes. We suggest that these values should be set to zero.

This dataset is available in two formats:

Sample FORTRAN code for reading the binary is given below.

Dataset 2: 1850-1995

The dataset uses the quality-controlled NOAA Baseline precipitation station data and latest station data from NOAA NCEP, covers the period from 1850 to 1995 (data for 1996 are incomplete). The same analysis procedure (including the discontinuity correlation) was used for the updated dataset. The most recent update of this file is dated 1998-03-17.

This dataset is available in two formats:

Shea Dataset

A related dataset described by Shea (1986) is available as:

Reading Binary Datasets

The binary files were written by FORTRAN programs running on a big-endian RISC 6000 computer. The following code snippet demonstrate how their contents may be read. In all cases, the months run from 1 to 13, where 13 represents the annual value.

For dataset 1,, the following might be used read one record. The value "-99999." represents missing data.

      REAL PREC(144,73)


For dataset 2,, the following code snippet might be used to read one record. The value "-99999." represents missing data.

      REAL PREC(144,73)

      IYEAR = 1850 - 1
      N = 0
  10  READ(10) TITLE, PREC
      N = N + 1
      MONTH = MOD(N,13)
      IF (MONTH.EQ.1) IYEAR = IYEAR + 1
      GOTO 10

For the Shea dataset, the following code snippet might be used to read one record. The value "-1000." represents missing data.

      REAL PRC(144,73)

      DO MONTH =1, 13
      READ(1) TITLE, PRC
      END DO

As further examples of FORTRAN code that can be used to read these files, the programs used to convert them to netCDF format are also available:

Additional Data

Monthly precipitation data for January 1979 onwards are available from NOAA by anonymous ftp. Data file names in this directory look like cmap_mon_vYYMM_yy.txt.Z, where "YYMM" indicates the date when the datasets were prepared (e.g., "0411" for November 2004) and the "yy" indicates the year which the data describe (e.g., "83" for 1983 or "01" for 2001). These data are also available in netCDF from the CMAP webpage.


Please address any questions you may have regarding these data to Dr. Aiguo Dai, currently (2014) at the University of Albany.

Other GISS scientists who participated in this research were Dr. Anthony Del Genio and Dr. Inez Fung.


Papers and reports which describe the datasets include:

  • Dai, A., I.Y. Fung and A.D. Del Genio 1997. Surface observed global land precipitation variations during 1900-1988. J. Climate 10, 2943-2962.
  • Escheid et al. 1991. A comprehensive precipitation data set for the global land areas. DOE Technical Report No. TR051, DOE ER-69017T-H1, 81 pages.
  • Shea, D.J. 1986. Climatological Atlas: 1950-1979. NCAR TN-269+STR. National Center for Atmospheric Research, Boulder, CO.