Costing of nature-based vs grey solutions for water management: cases from Nairobi

Abstract

Climate change adaptation in urban Africa is a critical development issue of this century. Informal and low-income neighbourhoods in African cities are particularly vulnerable as they are often located on flood pathways. Nature-based Solutions (NbS) have been put forward as an approach to enhance flood and climate resilience in urban settings. While social and environmental benefits of urban NbS are increasingly well documented, a key gap in the literature is robust data on the cost of implemented NbS, particularly from African cities. In this paper, we compare lifecycle costs of two significant implemented NbS projects against hypothetical equivalent grey solutions, in two different informal settlements in Nairobi, Kenya. We apply comparative Life Cycle Costing (LCC) for both cases and a Cost Benefit Analysis (CBA) for one case study where historical data is available. In one of the two cases NbS was significantly cheaper, while in the other higher costs were attributed to costs required to create understanding of the new approach. We find that the cost of any solution is highly context dependent, although the NbS approach shows competitive lifecycle costs, potential for cost-optimisation as the concept matures, and highly attractive for investment when the documented co-benefits are considered.