DW AngolaAnalysis of Angolan historic rainfall data

Analysis of Angolan historic rainfall data


This paper reports on a component of Development Workshops’ research project “Water resource management under a changing climate in Angola’s coastal settlements”. It sets out why recovery and analysis of historic rainfall data is important, as well as the challenges of using rainfall data in Africa. It shows why these difficulties are greater in the case of Angola, where there are significant gaps in the records before 1940 and after 1975. It lists the sources of data and the analyses carried out in this component of the research. It discusses the mean annual rainfall in different regions of Angola and then goes on to discuss the issue of rainfall variability, which is particularly important in the context of Angola. It presents two measures of variability and demonstrates that rainfall variability is high along the Atlantic coast of Angola and some adjacent areas inland. Rains in this area tend to fall as very heavy, isolated storms late in the rainy season and a high percentage of the mean annual rainfall can fall in one day. This creates the conditions for flooding in the rapidly growing cities of the coastal regions of Angola. Heavy rainfall splashes fine particles on bare soil surfaces in coastal river basins and deposits them as a water-repellent crust. This increases run-off and water level in rivers rises quickly. Cities can also be affected by rainstorms in the urban area itself. Flooding and erosion are common in coastal urban areas in Angola. The high variability of rainfall makes it difficult to judge whether the climate is changing. However under future climate regimes it is unlikely that variability will be less, and adaptation to the current variability will be a useful step in step to adaptation to climate change.