| Global urbanization presents enormous challenges for planners of water and sanitation infrastructure systems in the twenty-first century. In Africa, urbanization will push over a billion new residents into cities before 2100. In order to plan for these residents, it is necessary to disaggregate national population forecasts into smaller spatial units to determine where future needs will be the greatest. To achieve this, a methodology is needed for estimating future urban populations at the sub-national level. Remote sensing of human populations provides a means of distributing present day national totals across space. Combining urban growth modeling and Zipf's Law as applied to urban settlement distributions, urban populations to 2100 are forecast based on present day population location. Once urban and rural populations are estimated to 2100, the numbers of urban and rural unserved residents are estimated for each category of infrastructure in each subnational spatial unit. Average per-capita construction costs are also applied to the projected unserved populations of Africa, yielding the magnitude of the challenge facing Africa and the world if adequate water and sanitation are to be provided for all. Capital costs for water and sanitary infrastructure in the first decade of the twenty-first century alone will comprise approximately 0.1% of the total continental GDP over that period. |
