A thesis submitted in partial fulfilment of the requirements for the degree of Master of Science in Urban Water Engineering and Management Jointly offered by Asian Institute of Technology, Thailand and UNESCO - IHE, Delft Institute for Water Education the Netherlands

Thesis (M.Sc.) - Asian Institute of Technology - UNESCO-IHE, 2019

Impacts of climate and socio-economic changes affect water resources by altering the volume of water supply and demand, thus effective adaptation planning should incorporate the uncertainities of changing environment. The study applied Climate Risk Informed Decision Analysis (CRIDA approach) to assess impacts of climate and socio-economic changes on water supply system and develop adaptation pathways for Nairobi. With a boundary condition of Thika-Chania Sub- catchment as a source of supply and population growth as a socio-economic factor, assessment of system performance was attained through time series analysis, stakeholder engagement, development and calibration of hydrological model for period 1988-2013. With climate projections adopted for 4 RCM's under RCP 4.5 and RCP 8.5, and demand projections under low, medium and high scenarios for 30 years, stress testing was done on the system model under Cases of no climate change and under climate change considerations. Formulation and stress testing of the adaptation actions under different climate and demand scenarios was done to establish their robustness, after which pathways were developed for both cases using Adaptation Pathway Generator. Most promising and acceptable pathways were established through evaluation based on robustness, social and environmental acceptability, and implementation period using adaptation scorecard. From the results, it was established that the impacts of climate and socio-economic factors will affect the supply system by increased varied flows and increased demand due to population growth. On the evaluation of system performance, revealed that it's at high risk of failure due to socio-economic factors compared to climate change. Three most promising and acceptable pathways for the projection period were identified as (1) awareness campaigns, water metering, expansion & rehabilitation of treatment plant, and alternative source of supply. (2) water restrictions, policy regulations, expansion & rehabilitation of treatment plant, and alternative source of supply. (3) awareness campaigns, water metering, NRW reduction, and recycling of backwash water.