Sri Lanka received an extraordinary warning on 12 November 2025 from both meteorological and hydrological authorities: the island was likely to be hit by a “once-in-50-years” rainfall event in the days ahead. This level of forecast signalled rainfall far beyond historical norms, with the potential to unleash widespread flooding, reservoir overflows, flash floods, and major downstream devastation.
Sri Lanka’s water management system is anchored by a network of roughly 1,840 reservoirs, including 73 major irrigation reservoirs formally overseen by the Irrigation Department. These major reservoirs—with a collective surface area of nearly 70,850 hectares—serve as the country’s strategic hydrological backbone, regulating irrigation, drinking water supply, hydropower generation, and moderating flood flows. Among them, several stand out for their vast storage capacities: Senanayake Samudraya (~950 MCM), Randenigala (~861 MCM), Victoria (~723 MCM), Maduru Oya (~598 MCM), Moragahakanda (~570 MCM), and others ranging between 173 and 278 MCM.
With such an extensive system, international and local best practices dictate that when extreme rainfall is forecast, reservoir levels must be reduced in advance to create spare capacity. This pre-emptive buffer is vital to absorb sudden inflows and prevent dams from reaching dangerous spill levels.
Ordinarily, Sri Lankan technical agencies—including the Irrigation Department, Mahaweli Authority, Central Environmental Authority, Disaster Management Centre, and the Meteorological Department—follow a widely accepted protocol. Once a credible extreme-rainfall alert is issued, engineers increase monitoring, assess current reservoir levels against Full Supply Levels and maximum flood thresholds, and begin gradual controlled releases. These releases are carefully timed to ensure downstream rivers can handle the additional flow, while local authorities coordinate warnings and evacuation readiness. Real-time monitoring of rainfall, river gauges, reservoir inflows, and dam safety parameters continues throughout the high-risk period.
However, the days following the 12 November alert were especially critical. The anticipated rainfall was expected to hit major river basins—including the Mahaweli, Walawe, Walawe, Deduru Oya, and Malwathu Oya—with volumes exceeding typical monsoon patterns. Without timely drawdown, reservoirs such as Victoria, Kotmale, Randenigala, and others risked fast and uncontrolled rise to spill level. Unplanned emergency spills of this nature typically produce devastating outcomes downstream, particularly in districts such as Polonnaruwa, Anuradhapura, Mannar, Kurunegala, as well as vulnerable low-lying communities in the Eastern Province including Kinniya, Muttur, Manampitiya, and Elahera.
Experts note that a timely pre-emptive drawdown could have provided 10–30% additional storage buffer in some reservoirs—reducing peak river flows at the height of the storm, preventing sudden flash flooding, protecting agricultural zones, and significantly lowering economic and infrastructural disruption. More importantly, it would have strengthened dam safety and demonstrated proactive risk-management aligned with international hydrological standards.
Yet despite the exceptional warnings and the well-established protocols, Sri Lankan authorities did not initiate the expected pre-emptive releases in the critical window after 12 November. This omission has now emerged as a major policy concern, raising questions about decision-making failures, communication breakdowns, or operational hesitations at a time when decisive action was required.
Given the scale of the forecast and the proven value of reservoir drawdown during extreme-rainfall threats, the lack of timely action has intensified scrutiny of Sri Lanka’s disaster-risk governance—and the price paid when preventive measures are delayed.