Why Urban Flooding Is Not Caused by Rain Alone

The myth of the rain disaster

When Pakistani cities flood, the easiest explanation is also the least complete one: heavy rain. But the evidence from recent monsoon seasons tells a more troubling story. During the 2024 and 2025 monsoons, areas receiving only moderate rainfall of 50 to 70 millimetres still flooded, according to NDMA monsoon reports, specifically because outfalls were entirely blocked. As Dr Noman Ahmed of NED University has argued, urban flooding in Pakistan is better understood as an engineered disaster, the product of systematically destroyed natural hydrology rather than rainfall alone.

The NDMA's own 2025 assessment reached a similar conclusion: rainfall intensity is increasing, but drainage capacity is, in effect, being artificially decreased through neglect and encroachment. This distinction matters. Conflating every flood with climate change alone risks obscuring the governance failures that are, in many cases, the more immediate and more fixable cause of damage.

Garbage in the veins of the city

Karachi generates an estimated 12,000 to 14,000 tonnes of solid waste daily, according to the Sindh Solid Waste Management Board's 2024 figures, and a substantial share of it ends up choking the city's major storm drains, known locally as nullahs. Over 50 major natural storm drains in Karachi, including the Gujjar and Orangi nullahs, have been severely narrowed by illegal concrete structures, according to 2024 data from the Karachi Metropolitan Corporation and NDMA.

The result is a drainage network that, even when structurally intact on paper, functions at a fraction of its designed capacity in practice. Sewerage systems in most major Pakistani cities are combined with stormwater drains, according to 2025 WASA data, meaning that during heavy rain, toxic sewage overflow compounds the flooding rather than simply adding clean rainwater to the mix.

Building on the drains

Encroachment is not a marginal contributor to this problem; it is central to it. Land mafias and unauthorised construction have repeatedly built directly on or beside natural waterways, narrowing channels that were never designed to accommodate reduced capacity. In Rawalpindi, the Lai Nullah's flood risk is compounded by the dumping of municipal waste and raw sewage, according to WASA Rawalpindi's 2025 assessment, making it one of the country's most persistent urban flood risks.

Even premium real estate has not been immune. DHA Karachi experienced flooding in 2022 and again in 2024 linked to engineering failures in stormwater outfalls, a reminder that the problem is not confined to informal or low-income areas, even if those areas bear the worst consequences.

The human and economic toll

The costs of urban flooding fall hardest on those least equipped to absorb them. Slums built along nullah edges face immediate destruction and exposure to toxic sewage floodwater when drains overflow. Daily wage earners lose income whenever a city's transport network is paralysed, while post-flood outbreaks of dengue, cholera and typhoid place additional strain on already stretched public health systems.

The economic scale is considerable even beyond individual hardship. World Bank and local chamber of commerce estimates from 2024 put the economic losses from a single severe urban flood day of transport paralysis in Karachi in the billions of rupees, reflecting just how disruptive these events are to a city's functioning economy, not only its physical infrastructure.

Institutional chaos

Part of what makes the problem so persistent is the fragmented governance around drainage itself. Responsibility is split between the Karachi Metropolitan Corporation, district municipal corporations, cantonment boards and other civic agencies, often with little coordination between them. It is frequently unclear, in practice, which body is accountable for maintaining a given stretch of drain, a gap that encroachers and illegal dumpers have effectively exploited for years.

The Supreme Court has mandated anti-encroachment drives as one response, and the 2024/2025 clearance of the Gujjar Nullah in Karachi stands as the clearest recent example, though it also produced significant resettlement disputes that remain unresolved. The human cost of clearing decades of encroachment is real, even where the underlying flood risk reduction is necessary.

Distinguishing the roles of rain and governance

None of this is an argument that rainfall does not matter. Extreme rainfall events remain capable of overwhelming even a well-maintained drainage network, and Pakistan's monsoon variability, discussed elsewhere in this collection, is a genuine and growing factor. The distinction that matters for policy is one of trigger versus severity: rain triggers flooding, but the extent of damage, how many homes are destroyed, how long transport networks stay paralysed, how much sewage overflows into residential streets, is overwhelmingly determined by drainage capacity, waste management and encroachment control. Treating every flood as an unavoidable act of nature lets governance failures escape scrutiny they should not escape.

Fixing the flow

The NDMA has shifted towards more proactive nullah clearing drives ahead of the monsoon season starting in 2025, an attempt to get ahead of the problem rather than simply respond to it. Lahore, meanwhile, began constructing underground water storage tanks in 2024 designed to capture rainwater and reduce street-level flooding, an infrastructure-based approach that treats stormwater as a resource to be managed rather than simply a hazard to drain away.

None of this diminishes the role of increasingly intense rainfall in a warming climate. But the honest picture is one of compounding failures: moderate rains today cause the kind of flooding that thirty years ago required genuinely extreme storms, precisely because the natural hydrology that once absorbed and channelled that water has been so extensively dismantled. Restoring drainage capacity, enforcing anti-encroachment rules and modernising solid waste collection would meaningfully reduce flood damage even without any change in rainfall itself.

Key Facts

•Karachi generates 12,000 to 14,000 tonnes of solid waste daily, much of which chokes storm drains (2024, Sindh Solid Waste Management Board).

•Moderate rainfall of 50 to 70mm caused flooding during 2024/2025 monsoons due to blocked outfalls (2025, NDMA).

•Over 50 major storm drains in Karachi have been narrowed by illegal construction (2024, KMC/NDMA).

•Lahore has paved over 40 percent of previously permeable surfaces in the last two decades (2025, Urban Unit Punjab).

•Only 15 to 20 percent of planned stormwater infrastructure in new housing societies meets peak rainfall capacity (2024, NDMA/Engineering Development Board).