NEW DELHI: Hours after a flash flood hit the Himalayan village of Dharali in Uttarkashi district, IMD on Tuesday claimed that it has been issuing regular warnings to Uttarakhand for the past four days about expected “heavy to extremely heavy” rainfall over the state from August 3 till August 5.The MeT department, however, kept mum on whether the flash flood was due to a cloudburst— a short lived extreme weather event in which heavy rainfall occurs over very small areas (20-30 sq km) at a very fast rate (100 mm per hour).Though more clarity on the cause of the flash flood will come up later, the 24-hour accumulated rainfall data from six meteorological stations in Uttarkashi district does not show at this stage the possibility of it being triggered by a cloudburst.Cloudbursts are highly localised and are of a very short duration. Since most cloudbursts occur over very remote inaccessible sites in hilly regions, a number of such events remain unobserved and unreported due to lack of sufficient real-time data.In India, cloudbursts occur during monsoon over orographically dominant regions like Himalayan region, northeastern states and Western Ghats.Since such an event is mainly attributed to sudden development of thunderstorms and also due to the complexity of associated atmospheric processes, its prediction is a challenging task across the world.Nevertheless, IMD has repeatedly been warning the state about “heavy to extremely heavy” rainfall in the region since August 1 and repeated it more specifically on Monday — enough for district authorities to remain alert.In the weather warning for the next five days, IMD on Tuesday predicted “isolated heavy rainfall” over Uttarakhand during August 6-9.
