Quantifying the services of natural and built infrastructure in the context of climate change: The case of the Tana River Basin, Kenya

A study was conducted to explore the synergies and trade-offs between built and natural infrastructure in the Tana River Basin. A simple framework for better understanding the interactions and co-dependencies between water-related built and natural infrastructure was developed. To evaluate the costs and benefits associated with the current built infrastructure, empirical relationships were determined quantifying the links between river flow and ecosystem services. Depending on rainfall, river flow and other factors, the benefits vary from year to year, but a conservative estimate of the average cumulative value of six key waterdependent services (i.e., floodplain grazing, riverbank gardening and recession agriculture, freshwater fisheries, marine and estuarine fisheries, coastal shrimp fisheries and beach nourishment) in the lower basin is USD 152 million per year. The large dams built in the basin have significantly increased overall financial returns by creating new revenue streams (i.e., hydropower and irrigation) and by reducing the adverse impacts of large floods. Overall, average annual revenue has increased to USD 298 million. Nonetheless, the dams have also reduced the benefits that accrue from moderate floods with the greatest losses in the agriculture sector. Although they benefit from increased flood protection, impoverished pastoralists and smallholder farmers lose the most revenue; on average, USD 9.5 million per year. To improve the effectiveness and durability of future development initiatives, policy-makers and decision-makers should: (i) recognize that natural infrastructure in the Tana River Basin represents a national asset, providing valuable services to people living both in, and outside, the basin; (ii) adopt an ecosystem services approach to make clear the synergies and trade-offs between different sectors in different development scenarios; (iii) ensure that environmental and other issues associated with human well-being, such as equity and social inclusion, are considered in decisionmaking; and (iv) plan and manage natural and built infrastructure in tandem. © 2019, by IWMI. All rights reserved.

This research was carried out as part of the CGIAR Research Program on Water, Land and Ecosystems (WLE) and supported by Funders contributing to the CGIAR Trust Fund (https://www. cgiar.org/funders/).