Guwahati: The India Meteorological Department (IMD) had forecast the heavy to very heavy rainfall that led to flooding across parts of Upper Assam in July, with warnings issued up to seven days in advance, the Centre informed the Lok Sabha on Wednesday.
In a written reply, Minister of State (Independent Charge) for Earth Sciences Dr Jitendra Singh said the IMD issued district-level rainfall forecasts and colour-coded warnings for all districts in Upper Assam, including Jorhat, Golaghat, Sivasagar and Charaideo, before and during the period of intense rainfall from July 18 to 20.
The forecasts included daily warnings covering the following seven days, according to the ministry.
The heavy rainfall was linked to a combination of weather systems, including a low-pressure area over Gangetic West Bengal and adjoining regions and an upper-air cyclonic circulation over Northeast Assam. The circulation later moved towards Central Assam and adjoining Nagaland and remained active until July 20.
The ministry said the IMD assesses the performance of its extreme rainfall forecasts across different regions of Assam using indicators such as forecast accuracy, probability of detection, false alarm ratio and the Critical Success Index.
Northeast Assam recorded the highest detection performance among the four regions assessed. Its Probability of Detection was 0.7229 for forecasts issued one day in advance, falling to 0.1857 for forecasts issued five days ahead. The False Alarm Ratio increased from 0.3913 on Day 1 to 0.5538 on Day 5, while the Critical Success Index declined from 0.4275 to 0.19 over the same period.
The figures indicate that the accuracy of rainfall forecasts generally decreases as the forecast period becomes longer.
The Centre also said seasonal rainfall forecasts consider wider climate patterns, including the El Niño-Southern Oscillation (ENSO) and the Indian Ocean Dipole (IOD). However, these factors alone cannot determine flood risks in the Northeast, where short-duration extreme rainfall, river levels and local catchment conditions are also important.
Flood forecasting itself is carried out by the Central Water Commission, which uses IMD rainfall forecasts along with river gauge readings, hydrological information and forecasting models.
The government said work is also underway to improve weather forecasting at the sub-district level in the Northeast. The high-resolution Bharat Forecasting System (BharatFS), with a resolution of 6 km, has been operationalised to provide forecasts at block and panchayat levels.
Under Mission Mausam, the government has introduced the Multi-Hazard Early Warning-Decision Support System (MHEW-DSS) to support real-time monitoring and forecasting. The weather observation network across the Northeast is also being expanded with additional monitoring systems.
The Centre’s response comes against the backdrop of severe floods that affected Upper Assam in July, particularly Sivasagar, Charaideo, and Jorhat. Intense rainfall and rapid rises in river levels caused widespread disruption and affected thousands of people across the region.