African Water Development Report 2006 - United Nations Economic ...

African Water Development Report 2006The GLCC study was able to arrive at 18 classifications of vegetation and other land cover types using these dataproduct through the following steps:1. AVHRR data preparation: In this step the daily satellite data are composited into one monthly value so as toprovide higher-quality, cloud-free images. Masks are applied to screen out built-up areas, water bodies, permanentice, and barren areas, all areas where NDVI is not a useful indicator of land cover type.2. Unsupervised classification: Those areas not screened out are classified using an automated classification approachcalled unsupervised clustering, often used where location and characteristics of specific classes are unknown.3. Preliminary Labelling: After clusters are determined, the characteristics of each are investigated to determinethe land cover type or types falling within it. Statistics and graphs of each are generated and are then interpretedand a land cover type or types are assigned to each class.4. Postclassification Stratification: This step separates classes containing two or more disparate land cover types.This step is important because disparate land cover types, usually natural and agricultural land cover types, areoften clustered together due to spectral similarities.5. Final Land Cover Characterization: The final step is to derive a collection of attributes that describe the characteristicsof each seasonal land cover region. The classifications are then labeled according to various commonlyusedschemes and published. WRI publishes the version labeled according to the International Geosphere-BiosphereProgramme (IGBP).Following publication of the GLCC database, a number of scientific teams assessed the accuracy of the GLCC’sapproach by comparing the results with higher-resolution satellite imagery. These teams found that the accuracyof the GLCC’s approach was, depending on the assessment approach, in a range from 60 to nearly 80 per cent,meaning that the assessment teams’ classification of a given area agreed with the GLCC’s classification between60 and 80 per cent of the time.Source: Loveland el al. 2000Human activities encroach on the natural habitatsof many species. The loss, fragmentation andconversion of natural areas due to the spread ofcultivation and pasture are a major factor contributingto the loss of Africa’s biodiversity (ECA,2001). While Africa currently makes a relativelysmall contribution to global climate change, it isextremely vulnerable to the results of it. A significantchange in climate over the next 50 to 100years is likely to result in conditions under whichmany natural populations of wild organisms maybecome incapable of existing within their naturalranges. Changes in temperature and precipitationare likely to seriously affect the present distributionof many species. Thus, climate changeis an additional factor threatening the survival ofspecies. Some species - such as mosquitoes andother disease vectors and some pests may flourishand expand their ranges (ECA, 2001).Population, Urbanization and EcosystemAfrica has undergone major social, economic andpolitical transformations. At the turn of the 20thcentury, the total population was only 118 million,7.4 per cent of the world population. By 1997, thepopulation was estimated at 778.5 million, morethan 13 per cent of the world population (UNEPGEO-2000; United Nations Population Division1996). It is projected that by the year 2025,the population of Africa will almost double to 1453 million, representing about 18 per cent of theprojected world population (ibid). This high rateof population growth should be expected for thefuture and is a very important factor of the humanimpact on the hydrological regime of water bodiesand on renewable freshwater resources. In spite ofthe seemingly intensive population growth of the146