Why in news?
During the monsoon season of 2023, heavy precipitation caused widespread flooding and landslides in Northern India, primarily affecting residents of Himachal Pradesh, Punjab, Chandigarh, Uttarakhand, Jammu and Kashmir, Haryana, Rajasthan, and Delhi.
 
North India's monsoon chaos is the result of a convergence of factors:  
Every climatic event today is influenced by global warming. Additionally, one must pay close attention to the weather patterns that emerge as a result of other factors. El Nio has dominated news coverage this year, but it is unclear whether the monsoon chaos has had much to do with El Nio thus far.
Unnoticed is the fact that this year's wildfires have already consumed more than three times the normal area and released roughly three times as much carbon dioxide. This has contributed to the warming as well.

Multiple contributors:  
·                     The warming of the Arabian Sea:
Since January, the Arabian Sea has warmed approximately 1.5 degrees Celsius, which is consistent with the excess rainfall over northwest India. This was anticipated, according to a study the author conducted last year.
June contributes only about 15% of the season's total precipitation. Typically, the distribution of monsoon precipitation is irregular. As the Sun crosses into the northern hemisphere in March, the Indian subcontinent heats up like a cauldron of popcorn. Rainfall resembles corn kernels erratically popping around a kettle.
During the pre-monsoon season, the atmospheric instabilities that cause convection are not intense enough to cause widespread precipitation.
Due to a combination of the balmy Arabian Sea and an unusually high number of western disturbances, pre-monsoon precipitation was above average. As a consequence, the soils were left with a higher level of moisture than usual, which influenced the development of the monsoon. 
Despite averaging rainfall over a month, a season, or even multiple seasons, the distribution of rainfall remains unequal. The probable culprits are heterogeneous land-use patterns and irregular topography.

·                     Atlantic Ocean and upper atmospheric circulation  
The monsoon is also influenced by the Atlantic Ocean and upper atmospheric circulation. Since March, the entire Atlantic Ocean has been warmer than normal. While the so-called Atlantic Nio, characterised by a warm tropical Atlantic, tends to reduce monsoon precipitation, it is unclear what the effects will be when the entire Atlantic is as warm as it has been this year.
When they encounter mountainous terrain, such as the Himalaya, the fiercest winds in the upper atmosphere can spontaneously form clockwise and anticlockwise patterns. Strong clockwise winds, with air flowing out from the centre, in the upper atmosphere necessitate an anticlockwise circulation near the surface to fuel the upper level outflow. Such a convergence at the surface can result in excessive precipitation.

·                     Rising temperatures over the Himalaya  
Lastly, warming over the Himalaya has also not been uniform. A portion of the mountain range is exacerbating global warming, resulting in rapid local warming. Due to the wind's expansion and contraction as it races up and down the narrow valleys, irregular monsoon weather patterns are superimposed on these geographical features. Depending on the local flow patterns, the result can be cloudbursts, torrential rainfall, or even heat waves. Such disparate weather patterns can also occur simultaneously.

·                     Urbanisation in India:   
As India reaches the tipping point in its transition from a predominantly rural to an urban society, urbanisation is intrinsic to development and frequently functions as a significant driver of economic growth. By 2030, it is anticipated that 40.76 percent of the country's population will reside in urban areas.
However, urban planning tools have not evolved at the same rate as urbanisation and technological progress. Numerous tragic occurrences, such as urban inundation, are caused by unplanned urbanisation and climate change, which necessitates serious consideration.
During the flooding in Hyderabad in 2020, thousands of homes were submerged. The Chennai deluge of 2015 is a stark reminder of how rapid urbanisation makes cities more susceptible to urban flooding. During this monsoon season, Bengaluru has recently been the site of numerous inundation incidents.

·                     What is urban inundation?  
Urban flooding is the inundation of land or property in a built environment, especially in densely populated areas (such as cities), as a result of rainfall exceeding the capacity of drainage systems.
Unlike rural flooding (heavy rain over a flat or low-lying area), urban flooding is caused not only by higher precipitation but also by unplanned urbanisation (catchments), which: o increases flood peaks by 1.8 to 8 times; o increases flood volumes by up to 6 times.

·                     What factors contribute to urban flooding in India?  
Invasion into Drainage Channels: In Indian cities and villages, land prices have increased and there is less land available in the city centre. New developments are appearing in low-lying areas, typically as incursions over lakes, wetlands, and riverbeds.
o Ideally, the natural drains should have been widened (similar to road widening for increased traffic) to accommodate the higher stormwater volumes. o However, large-scale encroachments have occurred without the natural drains being widened. As a consequence, the capacity of the natural drains has diminished, leading to flooding.

Climate Change:   
Extreme events that are exacerbated by climate change. The frequency of short-duration, intense rainfall has increased as a result of climate change, resulting to greater water runoff.
o According to NASA studies, the urban heat island effect also contributes to increased rainfall over urban areas, which leads to inundation.
• Whenever rain-bearing clouds pass over an urban heat island, the hot air forces the clouds upward, causing highly localised precipitation that is sometimes intense.

Unplanned Tourism Activities:   
Water bodies have been utilised for decades as a tourism development attraction. In order to preserve tourism, water plants that reduce discharge speed are being removed from rivers and lakes.
o Religious and cultural activities that involve the disposal of non-biodegradable matter into rivers and lakes degrade the water quality. In the event of flooding, suspended particles and pollutants travel into cities, posing a threat to public health.
• Example: oil spillage from vessels polluted Ashtamudi Lake in Kollam, Kerala.

Unplanned and abrupt Release of Water from Dams:   
Unplanned and abrupt releases of water from dams and lakes cause urban flooding without giving the public sufficient time to react.
o Example: the 2015 flooding in Chennai was caused by the discharge of water from Chembarambakkam Lake.
Illegal mining of river sand and quartzite for use in construction depletes the natural substrate of rivers and lakes.
o It causes soil erosion and diminishes the water-retention capacity of the water body, thereby increasing the velocity and magnitude of water flow.
o Example: the Jaisamand Lake in Jodhpur and the Cauvery river in Tamil Nadu.
 
What Effects Does Urban Flooding Have? 
Loss of Life and Property: Urban flooding is frequently accompanied by loss of life and physical injury, either directly as a result of the flooding or indirectly as a result of the spread of water-borne diseases during the inundated period.
o Urban flooding has regional consequences such as structural damage to buildings, property, and agriculture. In addition, it disrupts the water supply, sewage system, electricity and transmission lines, communications, road and rail traffic, and other infrastructure.
Ecological Effects: During extreme flood events, trees and vegetation are washed away, and riverbank erosion is caused by swift flood water.  
Effects on Animal and Human Health: The stagnation of runoff in urban areas and the contamination of potable water lead to a variety of health issues that result in plagues and epidemics.
o Sewage and solid waste washing into homes and communities also contribute to the spread of various diseases.
Psychological Consequences: The mental health of the stranded is adversely affected by the loss of shelter and family members. The recovery process following such incidents is arduous and time-consuming, frequently resulting in long-term psychological trauma.
  
Way Forward:   
Developing Blue Green Infrastructure: Blue Green Infrastructure is an efficient means of providing a sustainable natural solution to urban and climatic issues.
o Equal emphasis should be placed on water management and infrastructure development in order to create more pleasurable, less stressful living environments.  
o Ensuring that every structure in the city has Rainwater Harvesting as an integral part of its utility system
• Blue represents bodies of water such as rivers and ponds. 
• Green represents trees, parks, and gardens.  
Flood Vulnerability Mapping: Vulnerable areas can be identified by analysing topography and historical inundation data at the city level.
o Maintaining a record of all water bodies and wetland areas at the city and village levels is crucial for flood-prevention, tolerance, and resiliency.
Construction of flood walls and elevated platforms along flood-prone river basins, as well as expeditious cleaning and deepening of drainage channels, should be undertaken along the entire river basin, not just in urban areas.
o Bioswales can be constructed alongside roads so that road runoff flows into them and percolates into the earth.
o Additionally, catchment areas of water bodies must be well-maintained and free of encroachment and contamination in order to keep the flow of water unobstructed.
Public facilities such as hospitals and schools, as well as essential services such as food, water, health, and sanitation, should be made resilient to natural disasters.
o They should be positioned or relocated so that they can operate without interruption during floods.
Sensitization and Rehabilitation: Along with response exercises, awareness should be raised about flood preparedness and mitigation measures.
o It is necessary to educate residents on the hazards associated with illegal constructions along drains and water bodies. Additionally, the government should contemplate relocating the poor to other regions.  
Institutional Arrangements - It is essential to establish a unified flood control implementing agency at the city level, comprised of city administrative officials, physicians, police, firefighters, non-governmental organisations, and other emergency service providers.

NDMA Guidelines:  
In 2010, NDMA had issued guidelines on Urban Flood Management in India
·      Create a National Hydro-meteorological Network.
·      The guidelines say that for providing early warning, the Central Water Commission (CWC) should maximize the real-time hydro-meteorological network to cover all urban centres to effectively deal with the problem of urban flooding
·      Use of Doppler Weather Radarsto be expanded to cover all urban areas in the country
·      An inventory of the existing stormwater drainage system to be prepared. The inventory will be both watershed-based and ward-based.
·      Catchment to be the basis for planning and designing the stormwater drainage systems in all ULBs
·      All future road and rail bridges in cities crossing drain to be designed such that they do not block the flows resulting in backwater effect
·      Every building in an urban area must have rainwater harvesting as an integral component of the building utility.
·      Low-lying areas in cities have to be reserved for parks and other low-impact human activities.
·      Encroachments on the drain should attract penal action.
·      Pre-monsoon desilting of all major drains to be completed by March 31 each year.
·      Urban Flooding has to be dealt as a separate disaster, de-linking it from riverine floods which affect the rural areas.
·      Suitable interventions in the drainage system like traps, trash racks can be provided to reduce the amount of solid waste going into the storm sewers.
·      Inlets to be provided on the roads to drain water to the roadside drains and these have to be designed based on current national and international practices.
·      Every building in an urban area must have rainwater harvesting as an integral component of the building utility.
·      Concept of Rain Gardens to be incorporated in planning for public parks and on-site stormwater management for larger colonies and sites that are to be developed.
·      Flood hazard assessments should be done on the basis of projected future scenarios of intensities and duration of the rainfall and land-use changes.

Mains practice question:
  Q. Urban floods are wake-up calls to treat rain with respect. Comment.