Green-Gray Analysis (GGA) is a cost-benefit analysis method that compares the present value of costs and benefits of two or more water management options involving natural “green” infrastructure and conventional “gray” infrastructure. It can be scenario-driven and coupled with sensitivity analysis for robust results.

The GGA builds on existing case studies of green and grey infrastructure analysis and is rooted in classic decision and public investment theory already employed by water managers, planners, and practitioners. It couches valuation of green infrastructure within a broader analysis of portfolios of green and grey options to meet a specific water management investment objective.

The method consists of six key components for an effective general methodology that optimizes performance and financial benefits:

1. Clearly define the investment objectives and constraints;
2. Specify investment portfolios that include both green and gray investments;
3. Model the outcomes of the portfolios;
4. Conduct the economic valuation of the portfolios;
5. Compare the cost-benefit analyses between portfolios; and
6. Conduct a risk and uncertainty analysis.