Besides extreme weather events, the geological structure of the watershed also needs to be taken into account so that a detailed risk assessment can be made before embarking on expensive water supply projects like Melamchi, and deciding on the location of future hydropower plants, bridges and roads.
Past studies had already declared many areas of the Melamchi watershed as a hazardous zone and not suitable for construction of houses and other infrastructure. If such warnings had been heard and timely precautions taken, the damage this monsoon would have been considerably less.
Based on the Department of Hydrology and Meteorology, all Nepal maximum and minimum air temperatures increased by 0.56 oC and 0.02 oC per decade from 1971 to 2014. The warming is higher in the Himalayan region than elsewhere. This means that even under the best-case scenario, the Himalaya could lose up to one-third more of its permanent ice during this century.
This means increased hazard from snow and ice avalanches, flash floods due to the discharge of supra-glacial lakes, or Glacial Lake Outburst Floods (GLOFs). There is a danger that these disasters to be more intense and frequent as weather systems change.
In October 2014, the power cyclone Hudhud which measured 2,000km in diameter spun out of the Bay of Bengal and made a direct hit on Central Nepal, dumping rain and snow in the Annapurna region, killing 43 people (including trekkers) in blizzards and avalanche.
Indian and Nepali meteorologists had sent out warnings and forecast heavy precipitation, however due to the lack of proper risk reduction mechanisms and safety management skills, casualties were high.
In January 2020, four Korean trekkers and three Nepali guides were swept away by an avalanche at Deurali on the Annapurna Base Camp trek. Although there has always been risk of avalanches in the Himalaya, very heavy snowfall with warming trends have increased the objective danger. Proper local forecasts could have warned trekkers in the area of the heightened risk.
In two of the worst disasters in recent times, 42 people, including 13 Japanese trekkers, were killed in November 1996 when the Gokyo region near Mt Everest was hit by an unprecedented blizzard. In October 2005, 18 people including trekkers were killed in snow storms and avalanches in Manang.
These and many other disasters show that post-monsoon cyclonic storms hitting Nepal at the peak of the trekking season must be more closely monitored and their local impact forecast accurately so early warning for specific areas can be issued. Fatalities can be reduced by finding ways to warn local communities, lodge owners, local governments, trekking outfits and guides, and build local capacity in search and rescue.
The importance of having high altitude weather and snow monitoring stations was also shown by the sudden increase in snow depth (1.65m) on the Rikha Samba Glacier in Mustang (5,200m) during the Hudhud cyclone on 15 October 2014. (See graph below.)