Udaipur . The catastrophic flood and debris-flow event in Nepal on August 26, 2026, together with the severe urban flooding witnessed in Udaipur on September 6 last year, should serve as a warning that in an era of climate change, development undertaken without understanding natural drainage, hills and catchment systems can substantially increase flood risk. Environmentalist & Principal of Vidya Bhawan Polytechnic Dr. Anil Mehta said that the geographical and geological conditions of the Himalayas and the Aravallis are fundamentally different. However, the underlying hydrological principle is the same: a mountain or hill is not an isolated piece of land; it is an integral part of a larger watershed system. Dr. Mehta said the lesson for Udaipur is not that the Aravallis face a Himalayan-type hazard, but that upstream disturbances can have consequences far downstream. The entire chain—hill–catchment–stream–river–lake– river - groundwater —must therefore be treated as one interconnected ecological and hydrological system. Historical rainfall averages are no longer enough: Dr. Mehta said that Udaipur's and other cities future flood risk cannot be assessed merely on the basis of historical rainfall averages. “With climate change, we have to increasingly examine short-duration, high-intensity rainfall events , rather than relying only on seasonal or long-term rainfall averages. Urban and watershed planning must therefore be designed not merely for ‘normal rainfall’, but for extreme rainfall, rapid runoff and flash-flood conditions” he said. In Udaipur, the September 6, 2025 episode had already demonstrated this vulnerability. According to media reports, the Gogunda and Madar areas received around four inches of rainfall each within just three hours, causing both Madar reservoirs to overflow and triggering strong flows in the downstream drainage system. Dr. Mehta said that when intense rainfall occurs over a disturbed or highly urbanised catchment, the problem is not simply the volume of water, but also the speed at which water reaches downstream areas. When natural drainage is narrowed, water creates its own pathway : Dr. Mehta said that the lessons emerging from Himalayan disasters, including those in Nepal and Uttarakhand, are particularly relevant to the planning of vulnerable landscapes. In Udaipur, seasonal streams, minor drainage channels, valleys and the Ayad river constitute the natural pathways for stormwater. They cannot be treated as vacant land available for roads, colonies, hotels, resorts, landscaping or other construction. “If we cut hills, we alter runoff. If we disturb the catchment, sediment increases. If we narrow or obstruct streams, rivers and flood channels, flood risk increases.” Where natural drainage channels are constricted, filled, diverted or encroached upon, water during an extreme rainfall event may be forced through a smaller cross-sectional area, increasing flow depth and velocity and potentially inundating areas that were previously considered safe. Udaipur's lakes are also receiving the warning through sediment : Dr. Mehta said that the same degradation of catchments is already becoming visible in Udaipur's lakes. The catchments of Madar, Badi, Fateh Sagar and Pichola are delivering substantial quantities of sediment during rainfall. Hill cutting, loss of vegetation, exposed soil and unplanned development increase surface runoff and soil erosion. Many check dams, anicuts and small water-harvesting structures that previously acted as sediment traps have themselves become filled with silt. Once their storage and sediment-retention capacity is exhausted, sediment moves downstream into the lakes. The consequence is two fold: sedimentation progressively reduces the effective storage capacity of lakes, while the sediment also transports nutrients, agricultural chemicals and other pollutants into the lake system. This is why lake conservation cannot be reduced to removing silt from the lake after every monsoon. The more fundamental intervention is to prevent the soil from leaving the catchment in the first place. Catchment Impact Assessment should precede major development : Dr. Mehta said that environmentally sensitive development proposals in the Aravalli and Udaipur region should be evaluated at the catchment scale, rather than merely at the individual plot or project boundary. The correct planning unit is not merely the plot of land; it is the watershed,” Dr. Mehta said. Natural drainage is ecological infrastructure : Dr. Mehta emphasised that Udaipur's natural drainage network should be treated as critical public ecological infrastructure. “Roads and bridges can be reconstructed, but once a natural drainage system is blocked, diverted or destroyed, restoring its original hydrological function can be extremely difficult.” He said that development must therefore adapt to the landscape rather than forcing the landscape to adapt to development The solution is early action, not merely post-disaster relief : Dr. Mehta said Udaipur needs to move from conventional flood response to risk-informed watershed management. This should include protection of hill slopes and natural drainage corridors; restoration of degraded catchments; soil and water conservation; regular desilting of check dams and anicuts; protection of lake flood pathways; village-level sewage and solid-waste management; and real-time monitoring of rainfall, stream flow and lake levels. The city should also develop high-resolution flood-hazard and drainage maps identifying natural streams, flood-prone areas, critical infrastructure and vulnerable settlements. Nepal should not be dismissed as a Himalayan problem : Dr. Mehta cautioned against drawing a simplistic comparison between the Himalayas and the Aravallis. "Nepal does not tell us that Udaipur will experience a Himalayan glacial disaster. It tells us something more fundamental: natural systems are interconnected, and disturbance in an upstream landscape can amplify risk downstream." The warning for Udaipur is therefore clear: Cut the hill, and runoff changes. Degrade the catchment, and sediment increases. Narrow the stream, and flood depth and velocity can increase. Fill the drainage corridor, and water loses its natural pathway. Reduce lake storage through sedimentation, and the system loses its capacity to absorb future inflows. Dr. Mehta said the September 2025 flooding in Udaipur and the recent Nepal catastrophe should therefore be viewed as warnings for better planning, not merely as isolated natural events. Nepal's tragedy should not be dismissed as a Himalayan problem. Udaipur must learn before a disaster forces us to learn. Development has to become nature-based, watershed-sensitive and climate-resilient. The fundamental principle is simple: protect the hill before protecting the property, protect the catchment before building on the valley, and protect the natural drainage before attempting to engineer it away. A disaster becomes a catastrophe when a natural hazard meets an exposed and vulnerable landscape. Udaipur still has the opportunity to reduce that vulnerability—before the next extreme rainfall tests the city again.