WATCH forcing data (WFD) - 20th century Qair (specific humidity) 1901-2001

The WATCH Forcing data is a twentieth century meteorological forcing dataset for land surface and hydrological models. It consists of three/six-hourly states of the weather for global half-degree land grid points. It was generated as part of the EU FP 6 project "WATCH" (WATer and global CHange") which ran from 2007-2011. The data was generated in 2 tranches with slightly different methodology: 1901-1957 and 1958-2001, but generally the dataset can be considered as continuous. More details regarding the generation process can be found in the associated WATCH technical report and paper in J. Hydrometeorology. To understand how the data grid is formed it is necessary to read the attached WFD-land-long-lat-z files either in NetCDF or DAT formats. The data covers land points only and excludes the Antarctica. Qair or 2m specific humidity (instantaneous) is the instantaneous specific humidity at 2m measured in kg/kg at 6 hourly resolution and 0.5 x 0.5 degrees spatial resolution.

Publication date: 2011-08-01

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Format of the dataset : netCDF

Please note that these data are based on climate reanalysis data, plus a spatial interpolation (from one-degree to half-degree), elevation correction and monthly-correction based on gridded observations. As such the WATCH Forcing data are designed for use in modelling (e.g. hydrological modelling) and for where good meteorological observations are not readily available.

Please reference the use of the WATCH forcing data in any work published using


Study area
Temporal extent
1911-01-01    to    2001-12-31

Supplemental information

Other useful information regarding this dataset:

An educational website using the data generated by the WATCH project and providing extra contextual information regarding 18 key river basins
More information regarding the data variable resources is available on the WATCH project website data format pages
Weedon, G.P.; Gomes, S.; Viterbo, P.; Shuttleworth, W.J.; Blyth, E.; Osterle, H.; Adam, J.C.; Bellouin, N.; Boucher, O.; Best, M.. 2011 Creation of the WATCH forcing data and its use to assess global and regional reference crop evaporation over land during the twentieth century. Journal of Hydrometeorology, 12 (5). 823-848.
THE WATCH FORCING DATA 1958-2001: A METEOROLOGICAL FORCING DATASET FOR LAND SURFACE- AND HYDROLOGICAL-MODELS. Author names: Weedon, G.P., Gomes, S., Viterbo, P., Osterle, H., Adam, J.C., Bellouin, N., Boucher, O., and Best, M. Date: February 2010

Provenance & quality

These data were created as part of the EU FP6 project WATCH which was coordinated by NERC-CEH and ran from 2007-2011. The data were generated in two tranches according to time interval. The data from 1958-2001 were based on ECMWF (European Centre for Medium Range Weather Forecasting) "ERA-40" reanalysis data via interpolation, elevation correction and monthly bias correction from gridded observations. The data from 1901-1957 were created via re-ordering of the ERA-40 reanalysis one year at a time. For full details of the process see the WATCH technical report No 22 and Weedon (2011, J. Hydrometeorology).

Correspondence/contact details

Dr. Tanya Warnaars
Centre for Ecology & Hydrology
Maclean Building, Benson Lane, Crowmarsh Gifford
OX10 8BB
United Kingdom

Other contacts

Environmental Information Data Centre


Spatial representation type
Spatial reference system
WGS 84


Topic categories
Climatology / Meteorology / Atmosphere
3-hourly,  Atmosphere,  Hydrology,  land surface,  Land surface modelling,  meteorology,  Modelling
Atmospheric Conditions
Meteorological geographical features