Observed Land Surface Precipitation Data:
1850-1995 (GISS/Dai)

The datasets here contain monthly and annual anomaly precipitation analyses (relative to the 1951-1979 period), in millimeters. 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:

Grid Resolution

In the datasets, resolution is 2.5° × 2.5°. The center of grid cell (I,J) is at longitude = -180.+(I-1)*2.5, latitude = -90.+(J-1)*2.5. Negative longitude (latitude) is for western (southern) hemisphere.

First Dataset

This dataset may be downloaded by anonymous ftp as a single 48-Mb file.

The station data source is Eischeid et al. (1991) and the data cover the period from Jan. 1900 to Dec. 1988 (data for 1989 are incomplete). Boxes with no data have a real value of -99999. 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.

The data file is in FORTRAN binary format (of IBM RISC 6000 AIX machines). The following code snippet might be used to read one record. Note that IYEAR runs 1900, 1901, ..., 1988 and MONTH runs 1, 2, ..., 12, 13 (where 13 represents the annual value).

      CHARACTER*80 TITLE
      INTEGER IYEAR, MONTH
      REAL PREC(144,73)

      READ(10) TITLE, IYEAR, MONTH, PREC

Second Dataset

This is an updated version of the first dataset and is available by anonymous ftp as a single 78-Mb file. (The most recent update of this file is dated 1998-03-17.)

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.

Each record is a map of a monthly or annual precipitation anomalies (relative to the 1951-1979). The following code snippet might be used to read one record:

      CHARACTER*80 TITLE
      INTEGER IYEAR, MONTH, N
      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

Shea Dataset

This is a related dataset described by Shea (1986) and is available by anonymous ftp as a single 500-kb file.

      CHARACTER TITLE*80
      REAL PRC(144,73)

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

Note that in this dataset, record 13 is for annual precipitation. Units are mm, and the "missing value" is -1000.0.

Anonymous FTP

Please note that the files described above are very large and that you may enjoy a more stable download if you use an FTP client program instead of your web browser. If you do so, connect to ftp.giss.nasa.gov, login as user anonymous (using your e-mail address as the password), and cd into the direcxtory /pub/adai.

Additional Data

Monthly precipitation data for January 1979 onwards are available by anonymous ftp from ftp.ncep.noaa.gov, in the directory /pub/precip/cmap/monthly. Data file names in this directory look like cmap_mon_vYYMM_yy.txt.Z, where "YYMM" indicates the date when the datasets were prepared (most recently listed as "0207" for July 2002) and the "yy" indicates the year which the data describe (e.g., "83" for 1983 or "01" for 2001).

Contacts

Please address any questions you may have regarding these data to:

• Dr. Aiguo Dai, adai@ucar.edu

Other GISS scientists who participated in this research were:

• Dr. Anthony Del Genio
• Dr. Inez Fung

References

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.