Kathmandu: With the arrival of the monsoon, residents of the Kathmandu Valley face a familiar concern: Will the roads be flooded by the time they return home? Even after sunny afternoons, sudden evening downpours frequently leave major roads—including Maitighar and Anamnagar—underwater within minutes, disrupting traffic and daily life.

Experts say the problem is no longer limited to heavy rainfall. Instead, a combination of intense short-duration rain, clogged drainage systems, rapid urbanisation, and weak coordination among government agencies has made urban flooding a recurring challenge.

Short, Intense Rainfall Overwhelms Drainage System
According to Binu Maharjan, a meteorologist at the Department of Hydrology and Meteorology, rainfall patterns have changed significantly in recent years.

He explained that rain which once fell gradually over two or three days is now often concentrated within a single hour. Recently, 47 millimetres of rainfall were recorded in just one hour in the Babarmahal area—far beyond what Kathmandu's ageing drainage network can efficiently handle.

Dr. Maheshwar Dhakal, Head of the Climate Management Division at the Ministry of Forests and Environment, said these increasingly intense rainfall events are consistent with the impacts of climate change. While such events strengthen Nepal's case for international climate financing, they also increase the frequency of urban disasters.

Plastic Waste and Construction Debris Blocking Sewers
Officials say clogged drainage systems are another major cause of flooding.

According to Prakash Kumar Rai, spokesperson for Kathmandu Upatyaka Khanepani Limited (KUKL), plastic bags, bottles, and other waste frequently block sewer inlets, preventing rainwater from flowing freely.

Construction activities during the monsoon further worsen the situation, as soil, sand, and debris are washed into drains, reducing their carrying capacity. Experts also point to poor coordination among agencies responsible for roads, sewerage, and water supply, resulting in infrastructure that is often built without adequate planning.

Concrete Expansion Has Reduced Natural Water Absorption
Geologist Dr. Subodh Dhakal says Kathmandu's natural ability to absorb rainwater has been severely reduced by rapid urban development.

As open land has been replaced with concrete roads, buildings, parking areas, and paved courtyards, rainwater can no longer seep into the ground. Instead, it runs directly into the drainage system, quickly overwhelming its capacity.

Dr. Dhakal recommends that new buildings be required to leave open ground wherever possible and install rainwater recharge systems or collection tanks to allow roof water to infiltrate underground. He believes widespread adoption of such measures could significantly reduce urban flooding.

Authorities Begin Long-Term Mitigation Efforts
Government agencies say efforts are underway to improve flood management.

According to Santosh Baral, Information Officer at the Kathmandu Valley Water Supply Management Board, more than 300 rainwater recharge structures have already been installed in schools, colleges, and public buildings across the valley. A recharge system at Tri-Chandra Campus near Ranipokhari has been cited as a successful example.

Meanwhile, Kathmandu Metropolitan City spokesperson Naveen Manandhar said the city has cleaned rivers and drainage channels ahead of the monsoon and has emergency response teams on standby. However, he acknowledged that the increasingly intense nature of rainfall makes it difficult to eliminate flooding immediately.

Experts Call for Comprehensive Urban Planning
Urban planning experts argue that traditional sewer cleaning alone is no longer sufficient. They say Kathmandu needs larger-capacity drainage infrastructure, stronger plastic waste management, mandatory rainwater harvesting and groundwater recharge systems, and better coordination among government agencies.

Without long-term planning and investment, they warn, flooding during even moderate rainfall is likely to remain a recurring reality for Kathmandu Valley residents.