Every monsoon, it is the same scene in Kathmandu that every resident knows well. Roads that were packed with traffic just moments ago begin to disappear. Water rises above knee level, leaving pedestrians stranded on shop doorsteps. Motorcycles begin to stall, and vehicles crawl through what resembles shallow rivers. Everyone’s immediate reaction is to blame the rain. Kathmandu Valley has experienced these downpours for generations, but the city has not always responded to them in the same way.

To understand why our streets flood so quickly today, we have to look at the basic way nature handles water. In a natural environment, the ground acts like an enormous, highly efficient sponge. When rain falls on open fields, forested hillsides, wetlands, or backyard gardens, the loose soil absorbs it. This process is called infiltration. The water seeps downward, replenishing underground water reserves. What cannot be absorbed flows gently into rivers over time.

Before Kathmandu expanded into the dense urban landscape we know today, it was once rich in exactly these kinds of natural systems. Ponds were scattered across the valley. Orchards and open courtyards surrounded old neighbourhoods. These were functional features that helped absorb rainwater, slow its movement, and allow it to seep naturally into the ground.

Over the past three decades, much of that has changed drastically. According to urban satellite tracking data published in 2017, built-up concrete areas in the Kathmandu Valley alone have expanded by more than 400 percent over the last thirty years, which has nearly wiped out 31 percent of the valley's highly fertile agricultural land. 

As more surfaces have become covered with concrete and asphalt, rainwater has fewer places to soak into the ground. Instead, it redirects towards drains and gutters designed decades ago for a much smaller city. When those drains cannot keep up, it results in water gathering on the roads and low-lying areas simply because it has nowhere else to go. Urban flooding in Nepal is not simply a rainfall problem. It is an urban planning problem.

Too Much Water, Too Little Water

One of Kathmandu's greatest contradictions is that it floods during the monsoon and faces severe water shortages during the dry season.

As the city's population has grown, many households, businesses, and institutions have increasingly relied on groundwater extracted through boring machines drilling hundreds of feet into the earth to meet their daily water needs, filling the gap where municipal supplies become limited. This reliance on groundwater is both understandable and, increasingly, unsustainable. Underground aquifers are not bottomless. They are recharged over time through natural infiltration.

At the same time, because we have paved over our open spaces, we are blocking the very mechanism that refills these deep underground storage spaces. The monsoon rain that should be soaking through the earth to recharge our deep aquifers is instead being swept out across paved surfaces and into drains. Then, when the monsoon ends, the city finds its underground reserves depleted because it received so little water during the wet season.

The flood damage during the monsoon and water scarcity in the dry months both these problems should not be viewed as separate issues. Groundwater depletion and urban flooding are two symptoms of the same urban planning decisions.

Who Pays the Price?

Flooding disrupts daily life for everyone, but its impacts are rarely experienced equally. 

In Kathmandu, as in most cities, it tends to hit hardest in the places where land is cheapest, and infrastructure is the weakest. Settlements along riverbanks are often home to low-income families who had few other options when they arrived in the city. These areas flood first and drain last. When the water recedes, it often leaves behind damage to belongings, health risks from contaminated water, and the quiet loss of another working day.

Daily wage workers like construction labourers, vegetable vendors, for them, a flooded road means losing an entire day’s income. For a small shop owner operating out of a basement or ground-floor shutter, a single flash flood can destroy electronics, textiles, or food stocks, wiping out months of hard-earned savings in a matter of hours. 

This is not to say that flooding spares the better-off entirely; waterlogged roads inconvenience everyone. But the difference lies in the ability to recover. Poor urban planning does not impact every resident in the same way; those with fewer financial resources often have less capacity to recover from repeated flooding or invest in protective measures. 

Understanding these unequal impacts shows that poor urban planning is not only about buildings and roads, it's also about creating a city that is safe, resilient, and inclusive.

What Is a Sponge City, and Could Kathmandu Become One?

In recent years, as cities around the world are facing growing challenges from urban flooding and climate change, urban planners have been talking about a different way of designing cities known as a ‘Sponge City’.

A sponge city is designed to work with nature rather than against it. The concept is straightforward: instead of rushing rainwater off surfaces and into drains as fast as possible, a sponge city slows water down, absorbs it, filters it, and stores it for later use. Permeable pavements let water pass through road surfaces into the ground below, replacing solid concrete ones. Rain gardens capture and filter stormwater. Parks, wetlands, green roofs, and restored waterways help slow the movement of water while replenishing groundwater and reducing flood risk. Rooftop rainwater harvesting systems capture rain before it ever hits the street.

Although the term "sponge city" is relatively new, the idea is not completely unfamiliar to Kathmandu. 

Before rapid urbanisation began, the valley had a remarkably important role in managing water. The pukhuris (traditional step ponds) collected rainwater, recharged groundwater, and supplied water for religious rituals and daily life. Many were maintained by guthis, the community associations that organised civic life in Newar towns. Open courtyards in traditional Newari architecture served a similar function, allowing rainwater to pool and percolate rather than run off. 

The valley's paddy fields, which once covered large areas of the floor of the valley, also acted as seasonal water storage. During the monsoon, flooded paddies held vast quantities of water that would slowly drain and recharge the soil. As those fields became housing estates and industrial plots, that storage capacity simply disappeared.

Many of these traditional water systems still exist, though often in neglected condition. Some pukhuris have been encroached upon or filled in. Others are choked with waste. But they have not disappeared entirely.

Transforming a congested city like Kathmandu into a more water-resilient city requires recognising what the valley already understood and restoring those functions in a contemporary urban context. Restoring degraded ponds. Planting trees along roads and river corridors. Mandate requiring permeable surfaces in new construction. Creating policies that require new residential and commercial buildings to maintain a specific percentage of unpaved, open green soil within their compounds, which can significantly scale up infiltration. Encouraging rooftop rainwater harvesting to make it the norm rather than the exception. Protecting the remaining open spaces. 

This does not mean Kathmandu can simply transform into a sponge city overnight. Dense development, existing infrastructure, and limited space present significant challenges. But cities across Asia have shown that sponge city principles can be implemented gradually, neighbourhood by neighbourhood, even within dense urban environments. The pressure of population growth does not pause while planners deliberate. Nevertheless, the city can still adopt principles that make it more water-sensitive. 

Conclusion

Every monsoon, flooded streets remind us that water always follows its natural course. When we pave over every square inch of green ground, restrict our rivers into narrow concrete jackets, and build over our natural wetlands, we are essentially declaring war on the water cycle. It is a war that our cities are bound to lose every summer. 

Urban flooding is often treated as an unavoidable consequence of heavy rainfall. Yet the growing frequency of waterlogged roads and overwhelmed drainage systems suggests a deeper issue. As Kathmandu and other Nepali cities continue to expand, the challenge is not simply moving rainwater away faster but creating urban environments that allow water to be absorbed, stored, and returned to the ground. The decisions made now will shape how these cities manage water for generations.

The idea of a sponge city offers more than a technical solution. It encourages a different way of thinking about urban development, one that recognises water as an essential part of the city's natural system rather than an obstacle to be removed. 

By blending modern sustainable urban drainage practices with our country’s rich heritage of traditional water management, we can design smarter, more resilient cities. As Nepal’s urban centers continue to grow, we must shift our perspective. We need to stop viewing the monsoon as an annual enemy to be fought with taller concrete walls, and start viewing it as a valuable resource to be managed, captured, and respected.