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Changes in the water-surface area occupied by the Cuitzeo Lake, Mexico, during the 1974-2001 period are analysed in this study. The research is based on remote sensing and geographic information techniques, as well as statistical analysis. High-resolution satellite image data were used to analyse the 1974-2000 period, and very low-resolution satellite image data were used for the 1997-2001 period. The long-term analysis indicated that there were temporal changes in the surface area of the Cuitzeo Lake and that these changes were related to precipitation and temperatures that occurred in the previous year. Short-term monitoring (1997)(1998)(1999)(2000)(2001) showed that the Cuitzeo Lake surface is lowering. Field observations demonstrated also that yearly desiccation is recurrent, particularly, in the western section of the lake. Results suggested that this behaviour was probably due to a drought period in the basin that began in the mid 1990s. Regression models constructed from long-term data showed that fluctuations of lake level can be estimated by monthly mean precipitation and temperatures of the previous year.

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The accuracy of the Mexican National Forest Inventory (NFI) map is derived in four distinct ecogeographical areas, using an assessment design tailored for the project. A main achievement of the design was to integrate the high diversity of classes encompassed at the most detailed subcommunity level of the classification scheme within a cost-controlled statistically sound assessment. A hybrid double sampling strategy was applied to the 2.5 million-ha study area. A total of 5955 reference sites were verified against their NFI map label. The availability of detailed quasisynchronous reference data for the 2000 Landsat-derived NFI and the high diversity of mapped classes allowed a careful thematic analysis on the selected regions, relevant for national extrapolation. Global accuracy estimates of 64-78 per cent were registered among the four ecogeographical areas (two with mainly temperate climate and the other two with mainly tropical climate), with the lower accuracy levels found in areas more densely covered with forests. According to the estimates, the NFI map tends to underestimate the presence of temperate forest (especially oak) and overestimate the presence of tropical forest in the areas investigated. The analysis of confusions reveals difficulties in unambiguously interpreting or labelling forests with secondary vegetation, herbaceous and/or shrub-like vegetation as well as distinguishing between aquatic vegetation types. The design proved useful from the perspective of accuracy assessments of regional maps in biodiverse regions.