Is assessing climate change impacts adequate for water security planning?

For water resources planning, development and management, it is imperative to assess water sufficiency and its sensitivity to low flows. This study assesses water sufficiency at a watershed in central Nepal under current and future climate scenarios and evaluates its sensitivity to low flows across the local government units (Palikas) in the watershed. Water availability was simulated using a hydrological model, future climate was projected based on global climate model outputs, remains highly vulnerable at the times of low flow sectoral water demands were estimated as per the government’s guidelines, water sufficiency ratio (WSR) was computed as a ratio of water availability to demands, and low flow was estimated using Bayesian approach. Results showed that WSR for current and future climate change conditions are above one, reflecting sufficient water availability, however, anticipated future low flows based on non-parametric approach is only 0.374 m³/s, lower than the lowest flow projected with future climatic conditions, leading to WSR of only 0.16. This disparity reveals the watershed even though WSR is above one with climate change context. Such a discrepancy highlights a substantial risk of water sufficiency that is overlooked by analysis that only considers mean and annual flow. This research demonstrates how integrating low flow analysis using Bayesian approach can add value in water security planning. This approach offers a more robust foundation for climate resilient water resources planning particularly in area with limited data.