SINDHUPALCHOWK, NEPAL - Critics of a massive project to build a 26-km tunnel to channel water from the Melamchi River to Nepal's water-starved capital Kathmandu were vindicated when the tunnel was damaged by heavy flooding last year.

The same critics are now questioning whether other phases of the project should be built while also suggesting solutions to Kathmandu's water shortage problem.

Experts have long criticised the huge investment of US$500 million in the Melamchi Water Supply Project, questioning its suitability for a country like Nepal, which is extremely vulnerable to climate change.

The tunnel had taken two decades to build, and was two months in operation when its headworks were damaged by debris from a landslide caused by unexpectedly heavy rainfall in June last year that also caused severe flooding in the area.

The headworks are structures for diverting the river water towards the water tunnel.

Freelance climate change and senior watershed expert Madhukar Upadhya said the unprecedented heavy rainfall at high altitudes atop the Himalayan mountains could be a symptom of global warming, with rain clouds forming at much higher altitudes than before as a result of higher temperatures

He added: "Mega projects are not suitable for our landscapes, especially in the mountains where landslides are extremely common during the monsoon. This could only worsen with climate change."

Dr Basanta Raj Adhikari, deputy director of the Centre for Disaster Studies at the Institute of Engineering in Nepal's Tribhuvan University, said the way in which climate change is impacting the entire Himalayan mountain chain is not well understood, but its adverse impacts have already been clear.

"If you look at (the) Chamoli floods in India last year, which occurred due to an avalanche, and then the Melamchi flooding, followed by the flash floods in a remote mountain camp in Bhutan last month... climate change impacts can be very adverse at high altitudes," he said.

The Chamoli floods had swept away two hydropower dams in India while 10 people died in the Bhutan flash floods.

The floods in Nepal killed 25 people and damaged 200 homes and large swathes of farmland.

"The government actually closed the Melamchi Water Supply tunnel at the time, one day before the floods hit, so the destruction was only at the headworks. We were lucky in that sense," he added.

The tunnel was designed to divert 170 million litres of fresh water daily from the Melamchi river to Kathmandu.

The second phase of the project - which has yet to be constructed - will divert through two tunnels, an additional 340 million litres of fresh water from the Yangri River and Larke River in the same district.

To ensure that the tunnel can be better protected against similar events, Dr Adhikari said that modelling would need to be done to understand the potential damage from falling debris, so that a flood warning system can be created and the tunnels can be closed in time.

Another solution would be to conduct impact-based forecasting, which would involve planning for different scenarios to reduce the socio-economic impact of these climate-related hazards.

He said that the Asian Development Bank (ADB) is expected to launch a report detailing how the water project can be better adapted to climate change.

A spokesman from ADB told The Straits Times that Nepal's Ministry of Water Supply is currently in the final stage of its hazard mapping of the upper catchment of the Melamchi river with the support of ADB.

This will help to identify strategic options to support the system's medium to long-term mitigation against similar natural hazard events.

"We also have to rethink whether we should even continue with the (second phase) of the project, and if we do, to study very carefully the climatic conditions in this area which is changing very quickly," said climate change expert Raju Pandit Chhetri.

To help meet Kathmandu's water scarcity, Mr Upadhya proposes alternative, small-scale solutions that work as closely with nature as possible.

One such solution would be to recharge groundwater resources which Kathmandu relies upon by creating small ponds to allow rainwater to re-enter the earth.