| Climate resilience


Italy’s Lake Como Lake Como in Italy is a natural reservoir mainly used


for irrigation and hydropower generation, but with flood protection becoming an increasingly important additional purpose. As live storage of the reservoir is only 5% of the lake’s mean annual inflow volume, combined with the control gates’ small discharge capacity, reservoir management is described as being ‘challenging’. Back in 1997, an adaptive reservoir management


approach was implemented to incorporate short term predictive probability density forecasting information into decision making. Despite conflicting management objectives of the multipurpose reservoir, the decision support system demonstrated significant operational improvements, such as: ● Reducing the frequency of flooding in the city of Lake Como by more than 30%.


● Reducing water deficit by 110 million m3 on average by 12%.


/year -


● Increasing hydropower generation by an average 3%.


The decision support system aims at optimising conflicting operational objectives with an advanced flood forecasting system. Whereas the system’s operating rules focus on maximising long-term benefits, it also guides operators on the amount of water to be released from the reservoir during floods in order to reduce dam failure and downstream flooding risks. Furthermore, the system makes extensive use of


probabilistic forecasts, stochastic optimisation, and Bayesian decision techniques implemented in a user- friendly environment. It also illustrates the importance of collaboration among reservoir managers, scientists, and other stakeholders for developing an advanced rainfall and flood forecasting system integrated with a system for optimising reservoir operation.


Shift in US policy


In a significant policy shift back in 2017, the US Army Corps of Engineers co-developed the Forecast Informed Reservoir Operations (FIRO) programme. Its aim is to better inform decision making on retaining or releasing water, by integrating additional flexibility in operation policies and rules based on enhanced monitoring and improved weather and flow forecasts, in order to maximise various development objectives, such as water supply, hydropower generation, and flood attenuation. The FIRO system uses Ensemble Forecast Operations (EFO) - a risk-based approach of reservoir flood control operations that incorporates ensemble streamflow predictions made by the California-Nevada River Forecast Centre.


One of FIRO’s first applications was for the Coyote


Valley Dam on Lake Mendocino in California. A dual-use reservoir with a capacity of 137 million m3, it is owned and operated by the United States Army Corps of Engineers and Sonoma Water. However, over time, it became clear it was meeting neither water resources nor flood control demands efficiently. The Corps was to pilot test the system during water years 2019 and 2020 - a period of time which coincided with an extreme drought in the region. Whereas WY 2019 was a relatively wet year, WY 2020 was the third driest year on record for 127 years. Indeed, FIRO enabled a 19% (more than 13.6 million m3


) increase in water storage by


the end of March which allowed the service provider to maintain water supplies throughout the subsequent very


www.waterpowermagazine.com | January 2026 | 37


dry period in the region. The case of Lake Mendocino demonstrates the importance of introducing advanced technologies, building the capacity of responsible agencies, and ensuring close collaboration among key stakeholders, including technical and research agencies for climate and hydrometeorology.


Japan


In Japan, many metropolitan areas have been developed in highly flood-prone areas at the downstream ends of river basins. Therefore, the country has established a river basin–based comprehensive and integrated flood management system, upon which river basin administrators provide guidance regarding dam operations to dam owners and operators during floods. Non-government owners of dams that do not have flood control functions are also requested to contribute to flood management at the basin scale, with the aid of an advanced rainfall and flood forecasting system. The case study is given of the 140m high Kusaki Dam, a concrete gravity structure which impounds a 60.5 million m3


reservoir. Commissioned in 1976


and managed by the Japan Water Agency, the project serves several purposes, including 20MW of hydropower generation, water supply to the Tokyo metropolitan area, and irrigation and flood control of the downstream Tone and Watarase Rivers. During Typhoon Hagibis from October 11–13, 2019, the Kusaki Dam conducted an emergency pre-flood reservoir drawdown based on weather and flood forecasting information. Without this, the dam would have had to move into emergency operation, requiring the dam operator to discharge the full amount of inflow to prevent the reservoir level from exceeding the maximum surcharge flood water level and to ensure dam safety. Instead, the operator was able to limit the maximum outflow to about 600m3 about 1700m3


/sec compared with /sec and, accordingly, the maximum flood


reservoir level was reduced by about 2.6m. Without such operation, critical downstream areas protected by embankment dikes could have been flooded as a result of breaches.


India In India, research shows a clear increasing trend in


PMP across the country. Specifically, 84% of the Indian mainland exhibits an increasing trend in PMP, about a 35% increase from 1971–2010 compared with the 1901–70 period. This indicates the significant impact of climate change, demonstrating that it must be factored into the revised planning and design of water resources and hydropower engineering projects.


Below: Kusaki Lake and dam in Japan. A pre-flood reservoir drawdown during Typhoon Hagibis in 2019 helped to reduce extensive flooding


Above: Lake Mendocino in California, US, played an instrumental role in the development of the Forecast Informed Reservoir Operations programme


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