Uncertainty about the regional impacts of climate change and rapidly changing socio-economic conditions make long-term planning of water resources problematic. Robust Decision Making (RDM) approaches seek to identify strategies that work reasonably well across large ranges of uncertain future conditions. We develop qualitative and quantitative RDM approaches to identify robust water management strategies (e.g. waste water recycling, micro-irrigation, river water transfer, more extraction for cities) against future climatic and socio-economic uncertainty. We apply these approaches to the Cauvery River Basin in Karnataka (population ~23 million) in India.
We developed climate narratives of the plausible future evolutions of the Indian Summer Monsoon through a structured expert elicitation. We also developed socio-economic narratives to reflect potential future changes in urban and agricultural water demand. In the qualitative RDM approach, the first stakeholder workshop helped elicit key vulnerabilities, water resources adaptation options and performance criteria for evaluating options. In the second workshop, stakeholders constructed adaptation pathways by sequencing options till 2050. In the quantitative RDM approach, a Water Evaluation And Planning (WEAP) model was driven by quantitative data coherent with the climatic and socio-economic narratives to develop plausible scenarios of future water availability and demand. Individual adaptation options and adaptation pathways were applied across scenarios to assess their robustness.
In this predominantly agricultural basin, we find that options which address agricultural water demand, such as micro-irrigation and agricultural water pricing reduce the pressure on water resources. Urban water demand options are also important for the rapidly expanding cities of Bangalore and Mysore. Agricultural water demand options demonstrate ability to satisfy legal instream flow requirements for downstream riparian states across a larger range of scenarios, indicating robustness. Adaptation pathways demonstrate differential value across scenarios, depending on timing and sequencing of options, thus illustrating the need to design them carefully. We suggest that iteratively combining qualitative and quantitative RDM approaches can help plan for a changing climate under conditions of deep uncertainty.