Robustness Framework Leveraging Stochastic Dual Dynamic Programming in the Indus River Basin

Abstract

Water uses in the Indus River Basin (IRB) – agriculture, hydropower, etc. – primarily depend on meltwater from Himalayan glaciers, seasonal snow, and monsoon rains. This dependency makes the IRB vulnerable to climate change and associated deeply uncertain shifts in seasonal melt patterns, long-term glacier recession and erratic monsoon patterns. Therefore, there's a growing emphasis on creating robust adaptation plans suitable for various future scenarios, rather than focusing on a specific uncertain future. Our research aims to develop a robustness framework to capture the multi-reservoir system with multiple contributions to streamflow from various sources with unique characteristics for the IRB. Our methodology quantifies streamflow components across multiple reservoirs for the IRB into base flow, rainfall, snowmelt, and glacial melt. This breakdown enables us to model each individual component's impact under a changing climate. We use Fourier series transformations to represent shifts in magnitude and seasonality of each component. This then enables us to explore how these shifts impact the resilience of reservoir operating policies, typically based on static hydrological conditions. To determine operating policies in complex multi-reservoir systems, we use Stochastic Dual Dynamic Programming (SDDP), due to its ability to capture the stochastic nature of streamflow amidst dynamic and uncertain hydrological inputs. Running SDDP with historical flows yields policies whose robustness to streamflow change can be tested; alternatively, running SDDP with select climate change scenarios yields altered policies whose climate “niche” can then be determined. This approach enables the design of coordinated reservoir operation policy, optimal under different streamflow conditions, as well as their evaluation over a wide range of potential future conditions, enhancing the optimisation of water use and management policies for the IRB. Our findings are expected to offer valuable insights assisting policymakers, stakeholders, and water resource managers in developing more resilient and sustainable strategies to address the impacts of climate change on water resources.