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Desertification is regarded as one of the major global environmental problems of the 20th century and the African Sahel is often quoted as the most seriously affected region. Previous attempts to map the occurrence and severity of desertification in the Sahel have been unsatisfactory, mainly because of the lack of any readily measured, objective indicators. We explore here the properties of the ratio of net primary production (NPP) to precipitation – the rain‐use efficiency (RUE) – calculated from remotely sensed vegetation indices and rain gauge data. Negative deviations from the normal range of RUE values are shown to be an indicator of desertification. Observations of NPP of the entire Sahel were possible using satellite platforms for the period 1982–90, including the 1984 drought. The results suggest that NPP was remarkably resilient, a fact that was reflected in only little variation in the RUE during the period of study. Thus, in much of the region, NPP seems to be in step with rainfall, recovering rapidly following drought and not supporting the fears of widespread, subcontinental scale desertification taking place in the 9‐year period that is studied. In fact the results show a small but systematic increase in RUE for the Sahel as a whole from 1982 to 1990, although some areas contained within the region did have persistently low values.

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We report herein the publication and evaluation of the International Satellite Land Surface Climatology Project (ISLSCP) Initiative II global interdisciplinary data record. The record consists of 52 data sets, with a common series in the 10‐year period 1985 to 1996. Selected data series extend well beyond this period. All series are coregistered to a common grid and gap‐filled for continuity using uniform procedures. We describe briefly the individual data sets within the collection; provide user guidance; and contrast, compare and evaluate those data sets containing similar parameters (land cover, NDVI, albedo, precipitation and near‐surface meteorology). We also describe the process used to develop the Initiative II collection which involved a broad international scientific community focused on addressing a well‐defined set of carbon, water and energy cycle questions within the context of a specific set of analysis tools. The communities that drove the definition of the Initiative II collection were investigators within the international scientific communities of the Global Energy and Water cycle Experiment, GEWEX, program (http://www.gewex.org/); the International Geosphere/Biosphere Program IGBP (http://www.igbp.kva.se); and the U.S. Global Change Research Program, USGCRP (http://www.usgcrp.gov/). Finally, we report usage statistics based on access and download of files from the ISLSCP Initiative II collection available at http://www.daac.ornl.gov.