Climate change adaptation through water portfolios planning in Alpine water systems

Climate change has significantly modified the water cycle worldwide, and projections confirm worsening trends over the next decades. In Alpine regions, glacier melting and shifts in rainfall regimes are critically accelerating the water cycle by anticipating the streamflow seasonal peak, steepening snow melt patterns, reducing the water available during the summer months while increasing winter flows, ultimately challenging water management and allocation across competing sectors. Storage capacity expansion seems to be a reasonable option to contrast the impact of such hydrological alteration as it allows to store additional seasonal water volumes by glacier melting and buffer extreme precipitation events, and associated flash floods. Yet, building new dams and/or heightening existing ones pose substantial environmental and economic concerns due to the lack of still valuable sites and aging of existing infrastructures. In this context, improving water productivity through multiple coordinated management measures, water portfolios hereafter, is an alternative solution worth investigating. In this study, we comparatively analyze multiple water portfolios for the Adda river basin, Italy, a complex Alpine water system, including several hydropower reservoirs in the upper part, a large regulated lake in the middle basin, and several downstream agricultural and industrial users. Portfolios are designed as combinations of three different measures: i) the re-negotiation of hydropower licenses for the three largest hydropower companies in the upper basin, ii) the re-operation of the regulated lake Como, and iii) the design of new constraints (lower and upper bounds) on the discretionary operating space of the lake. Results for different climate scenarios, including both downscaled and bias-adjusted CMIP5 and CMIP6 projections, show that while climate change is expected to exacerbate recently observed hydrological shifts, optimized water portfolios allow to restore an acceptable level of performance for all the sectors involved.