The lesson from a monsoon-battered North India

Syllabus: GS1/ Geographical Features & their Location, Changes in Geographical Features, Floods

In Context

• Recently, parts of North India witnessed heavy rains that triggered flash floods and left a trail of destruction.
  • Several places in Haryana, Punjab and Himachal Pradesh reported record rainfall.
  • The rains triggered landslides which caused more damage.

About Flash Floods

• Flash Floods are highly localized events of short duration with a very high peak and usually have less than six hours between the occurrence of the rainfall and peak flood.
  • The flood situation worsens in the presence of choked drainage lines or encroachments obstructing the natural flow of water.
• Flash floods have a different character than river floods, notably short time scales and occurring in small spatial scales, which make forecasting of flash floods quite a different challenge than traditional flood forecasting approaches. 
• Urban areas are more likely to experience this type of “surface water” flooding because they have a lot of hard surfaces.
  • When rain hits them it can’t soak into the ground as it would do in the countryside.

Causes of recent flash floods in Northern India

• Three main factors can trigger such heavy rains in the region and the Himalaya. 
  • An active monsoon with strong winds in the lower air layers, bringing moisture into the region from the Bay of Bengal or the Arabian Sea.
  • A large-scale atmospheric forcing in the form of outflows in the upper layers of the atmosphere moving eastward through mid-latitude troughs. These troughs can also direct the flow of moisture towards the Himalaya. 
  • Deep convection triggered by orographic uplift combined with the steep terrain of the Himalaya.
    • All these conditions were present in the recent incident. The synoptic conditions were conducive to heavy rainfall.
• More examples:
  • The floods in Uttarakhand in 2013 were caused by similar synoptic conditions. 
  • Another good example is the 2010 floods in Pakistan.

Changing trends of rainfall

• Extreme Rainfall:
  • Recent studies show an increasing trend in extreme rainfall in many parts of the country, especially central India. 
  • The number of extreme rainfall events (more than 15 cm in 24 hours) has tripled in the region. 
• Duration of rainstorms:
  • The duration of rainstorms over central India has also tripled. The observations also indicate that during the monsoon, the total number of rainy days and rainy hours decreases. This indicates that when it rains, it rains very heavily. 
• Rainfall in Himalayan region:
  • The Himalayan region, with its complex topography and varied weather patterns, is prone to extreme rainfall events. 
  • A recent study shows that 65 percent of areas in the region have a positive trend in the frequency of daily rainfall extremes. 
  • Another study on the 2013 floods in Uttarakhand identified this region as one where deep, intense convective clouds are most likely to form. 

Causes of changing trends of rainfall

• Climate Change:
  • Instances of deep convection have increased over time. Climate change is thought to be one of the main causes of this. 
    • Warmer temperatures lead to increased evaporation, which, in turn, leads to more moisture in the atmosphere. 
    • This extra moisture leads to heavy rainfall when weather systems coincide with the unique geography of the region. 
• Changes in land use and land cover:
  • Changes in land use and land cover also appear to be reasons for the increase in extreme monsoon rainfall, especially its intensity. 
• Warming Arctic:
  • We know that the Arctic is warming and sea ice is receding due to human influence. 
  • There is growing evidence of the impact of Arctic warming on the monsoon climate through mid-latitude circulation. 
  • Observations and models suggest that due to Arctic warming, the frequency of occurrence of blocking highs and deep mid-latitude troughs (like the one last weekend) is likely to increase.

Mitigating floods

• Extreme rainfall events like the one last weekend can occur anywhere in India during the monsoon season. 
• To mitigate floods, we need a multi-pronged approach that includes both proactive measures and reactive strategies. These include: 
  • A robust early warning system that alerts people about heavy rains and possible flash floods.
    • This system can include meteorological observations including a Doppler weather radar (DWR) and a high-resolution numerical weather prediction model. 
    • Advanced methods such as AI/ML could be used to interpret the DWR and model forecast data. 
  • Continuous monitoring of rainfall patterns, river levels and an advanced flood warning system. 
  • Flood risk maps that take into account factors such as topography, historical flood data and hydrological modelling to assess vulnerability, identify high-risk zones and target actions. 
  • Improving and maintaining climate-resilient infrastructure, such as drainage systems and channels to prevent waterlogging. 
  • Proper implementation of land use planning and zoning regulations. 
    • For example, areas prone to flash floods can be designated as non-residential or restricted areas. 
  • The protection and restoration of natural ecosystems, such as forests and wetlands.
    • Vegetation acts as a natural buffer, absorbing rainfall and reducing runoff. 
  • Awareness campaigns can influence people to take the right actions during floods, including arranging evacuation, providing first aid and getting information from reliable sources.

Way ahead

• The IPCC’s scenarios for climate change indicate that these trends will continue. 
  • Multi-day flood events are projected to increase faster than single-day events in the future — this can have severe consequences.
• By recognising the increasing threat of extreme precipitation and implementing proactive measures, India can improve its resilience to extreme weather events.