Monsoon hits Nepal with a bang
Extreme rainfall over the past three days on Himalayan foothills that were ravaged by wildfires just four months ago have led to dangerously high water levels in the Gandaki Basin in Central Nepal.
Major damage has been reported after a flash flood on the Melamchi River that has left eight people missing. Nepal Army helicopters rescued people marooned on the tops of homes in Melamchi Bazar. Many bridges, parts of the highway and some of the headworks of the Melamchi Water Supply project were also damaged.
The southwest monsoon arrived on schedule earlier this week, propelled by a massive low pressure system over the Bay of Bengal, and as the moisture-laden clouds rose over the Himalaya they dumped above-average rainfall from Makwanpur to Dolpo.
As a result, the Narayani River at Bharatpur is flowing above the danger mark as the flood waters race towards the Indian border. Most of the tributaries of the Narayani upstream have also seen floods.
Manang district, which suffered a wildfire that lasted three months and ravaged most of the forests in its southern region, saw flash floods on Tuesday morning on the Timang Khola and Syalkhyu Khola that washed away a 32kW hydropower plant, and put homes at risk in the district capital of Chame. Fifty families have reportedly been displaced.
The rivers feed into the Marsyangdi, which is now in spate as it rushes past several of Nepal’s major hydroelectric plants downstream.
In Kaski district, high water on the Madi river damaged a 44MW hydropower plant under construction. The powerhouse and headworks were damaged, while 15 excavators, tipper trucks and other vehicles were washed away.
Interestingly, areas of the Himalayan rain shadow which usually lie north of the mountains and receive scanty rainfall, saw the worst floods after continuous rain for 24 hours from Monday till Tuesday afternoon.
In Mustang, people in the village of Lupra had to move to higher ground after a tributary of the Kali Gandaki brought down a viscous paste of water and mud from the glaciers in the mountains above.
In southern Dolpo, a newly-built bridge on the Thulo Bheri River was washed away by raging flood waters. The rainfall chart of the Department of Hydrology and Meteorology (DoHM) showed between 150-200mm of rainfall in 24 hours right across Myagdi, Kaski, Tanahu, Lamjung, Gorkha, Chitwan, and Makwanpur.
The DoMH had been sending out persistent warnings about heavy rainfall all this week, but even it seems to have been caught by surprise by the intensity of the rainfall and the location of some of the heaviest precipitation in the trans-HImalayan districts of Manang, Mustang and Dolpo.
The highest rainfall in the past 24 hour period was recorded in Syangja with 214mm, and 30 of the Department’s 200 rainfall recording stations measured precipitation above 100mm in the past 24 hours. Nearly all of these were in the Gandaki watershed in Central Nepal.
Raging muddy flood waters on the Kali Gandaki forced the Nepal Electricity Authority to open all sluice gates on the Kali Gandaki A hydropower project, which means that some of the settlements downstream in Syangja are at risk.
Last week, the National Disaster Risk Reduction and Management Authority (NDRRMA) had cited weather modelling by the South Asian Climate Outlook Forum that had projected heavier than normal rainfall this monsoon over most of Nepal. But no one expected the monsoon to hit with such a bang so early into the season.
“We are now bracing up for the 2021 monsoon season, and it is predicted to be much more intense than last year," NDRRMA’s Anil Pokhrel wrote in Nepali Times last week. He predicted that this year’s monsoon comes after the worst wildfire season ever, and it could make it even more destructive.
“Wildfires that raged for months burnt through forest-shrub cover, undermining the ability of mountain slopes to absorb rainfall and prevent soil erosion. This could potentially result in more landslides and floods,” Pokhrel said.
Besides heavier than usual rainfall, what made the floods more destructive in Melamchi and other rivers are: poorly constructed roads triggering landslides, slopes scorched in the spring wildfires unable to soak in water, mountains still unstable from the 2015 earthquakes, as well as rampant sand and boulder mining along rivers that increased the velocity of the rivers.