Water security is fundamental to the sustainable economic development of countries. Ensuring sufficient and good quality water for the population and the freshwater ecosystem (Sustainable Development Goal 6 - Clean Water and Sanitation) is interconnected with other SDGs, and failure to achieve SDG6 may affect the achievement of other sustainable goals.

Policymakers always face the dual challenge of meeting human and environmental water security. The economic developments and land use transformation on a river basin scale, combined with the impact of climate change on water resource systems, intensify the human and ecosystem threats to the catchments. Accelerated investments are required to mitigate these risks to human and environmental water security, stemming from many anthropogenic and non-anthropogenic factors. With the rise in water-hard infrastructure investment costs, particularly in developing countries' river basins, it is challenging to meet the investment needs. There is a knowledge gap in pinpointing priority areas and optimal timing for investment, which can allow the reduction of the risks in a cost-minimised way.

This thesis aimed to develop an Economic Water Security Assessment Modelling framework to assess and track water security threats and assets in a river basin and construct an optimal spatial and temporal pathway of investments to mitigate these risks, illustrating a case study in Brazil and Australia.

The thesis adds value to the water resources planning and management on a river basin scale because provides information to improve the steps of water resources planning, The method presents a better understanding of the water security vulnerabilities influenced by climate change and the ideal spatial and temporal distribution of water investments, contributing with the optimal distribution allocation of the financial resources available. [...]