Planning and adaptation measures for urban slum communities in West Africa : stochastic rainfall modeling applied to domestic rainwater harvesting and climate change adaptation

Over half of the world’s population is living in urban settlements, and most urban growth is occurring in developing countries. These countries’ economies are often unable to accommodate these rural-urban immigrations, resulting in millions of people settling in insecure communities known as urban slums. Current efforts to prevent urban slums include UN-HABITAT strategies to upgrade slums and stimulate urban/regional development. Urban metabolism analysis, which studies material and energy flows/stocks through urban processes, help decision-makers better understand their urban system. Nine lessons from past urban metabolism studies are presented to assist in finding answers on how to best solve urban slum challenges. Worldwide, improved water access rates are lowest for Sub-Saharan Africa and these low rates have important implications on the health and economy of the region. Domestic rainwater harvesting (DRWH) is proposed as a potential mechanism for water supply enhancement, especially for the poor urban households in the region, which is essential for development planning and poverty alleviation initiatives. Several parsimonious stochastic rainfall models are developed and compared for application to DRWH assessment in West Africa. A first-order Markov occurrence model with a mixed exponential amount model is selected as the best option for unconditioned Markov models. However, there is no clear advantage in selecting Markov models over spelllength models for DRWH, with each model having distinct strengths and weaknesses. It is clear DRWH can be successfully used as a water enhancement mechanism in West Africa for significant portions of the year. Climate model output is used to determine climate change impacts to DRWH and to assess the technology as an adaptation measure to climate change. Several statistical downscaling methods are used to downscale multiple climate models to the local level. Climate change is expected to have little impact on DRWH reliability in West Africa by the mid-21st century, with only slight temporal shifts in rainfall. Developing communities in this region can invest with confidence in DRWH systems for drinking water enhancement. Study results also suggest that community improvements toward implementing DRWH systems should be focused on increasing water storage, due to storm size frequency changes