What is the news?

• Last weekend, parts of North India witnessed heavy rains that triggered flash floods and left a trail of destruction, tragically it resulted in at least 50 reported deaths. Himachal Pradesh was the worst affected. Several places in Haryana, Punjab and Himachal Pradesh reported record rainfall.

Central idea

• Last weekend, North India faced a calamity as torrential rains triggered flash floods and wreaked havoc across the region. Understanding the factors that led to this catastrophe is crucial in developing effective strategies to mitigate the impact of such extreme weather events in the future.

Fundamental characteristics of monsoon rainfall in the region

• Concentrated Timeframe: Monsoon rainfall in the region is not evenly distributed throughout the year. Instead, it occurs within a specific timeframe. All the seasonal rainfall (about 80-100 cm) falls within 130-150 hours, which is a relatively short period.
• Heavy Rain Contribution: The heavy rains play a significant role in contributing to the overall seasonal precipitation. Half of the seasonal rainfall (40-50 cm) occurs in only 30-40 hours.
• Runoff: When heavy rains occur, most of the rainwater drains away as runoff, particularly when the soil is already wet. This indicates that a substantial amount of rainfall does not get absorbed into the ground but flows off as surface runoff.

Factors attributed to the Heavy Downpour in north India

• Active Monsoon and Moisture Influx: An active monsoon season with strong winds in the lower air layers brought in moisture from the Bay of Bengal and the Arabian Sea. These moisture-laden winds contributed to the heavy rainfall in the region.
• Atmospheric Forcing and Eastward Moving Troughs: Large-scale atmospheric forcing, in the form of outflows in the upper layers of the atmosphere, moved eastward through mid-latitude troughs. These troughs directed the flow of moisture towards the Himalayan region, exacerbating the intensity of the rainfall.
• Orographic Uplift and Steep Terrain: The steep terrain of the Himalayas, combined with orographic uplift, played a significant role in intensifying the precipitation. When air masses encounter the mountains, they are forced to rise, resulting in enhanced rainfall.
• Synoptic Conditions and Moisture Intrusion: The synoptic conditions during the period were conducive to heavy rainfall. The monsoon was active, with strong moist easterly winds entering the region. Additionally, there was moisture intrusion from the North Arabian Sea, further augmenting the rainfall.

Increasing Trend of Extreme Rainfall

• Tripled Number of Extreme Rainfall Events: Recent studies indicate that the number of extreme rainfall events, defined as rainfall exceeding 15 cm in 24 hours, has tripled in many parts of the country.
• Prolonged Duration of Rainstorms: The duration of rainstorms has also tripled, indicating that rainfall events are lasting longer, potentially leading to higher rainfall accumulation.
• Decreased Number of Rainy Days and Hours: The total number of rainy days and hours during the monsoon season has decreased. This means that when it does rain, it tends to be in the form of heavy downpours rather than spread out over more frequent but lighter rainfall events.
• Regional Variation: Central India has been particularly affected by the increasing trend of extreme rainfall events, with a significant rise in both frequency and intensity.
• Himalayan Region Prone to Extreme Rainfall: The Himalayan region, with its complex topography and varied weather patterns, is prone to extreme rainfall events. Studies indicate that 65 percent of areas in the region show a positive trend in the frequency of daily rainfall extremes.

Impact of Arctic Warming on Monsoon Climate

• Increased Frequency of Blocking Highs and Mid-latitude Troughs: Arctic warming has been observed to influence the monsoon climate through changes in mid-latitude circulation. As the Arctic warms and sea ice recedes, there is growing evidence of an increased frequency of blocking highs and deep mid-latitude troughs. These atmospheric patterns can affect weather systems and contribute to extreme rainfall events during the monsoon season.
• Influence on Circulation Patterns: Observations and models suggest that Arctic warming can alter circulation patterns, including the movement of air masses, pressure systems, and wind patterns. These changes can have cascading effects on the monsoon climate, including the transport of moisture and atmospheric conditions that contribute to heavy rainfall events.
• Impact on Monsoon Dynamics: The warming of the Arctic and subsequent changes in circulation patterns can affect the dynamics of the monsoon. This can lead to shifts in moisture inflow, atmospheric stability, and the timing and intensity of rainfall during the monsoon season.
• Potential for Future Changes: As Arctic warming continues; it is expected that the impacts on the monsoon climate will persist and potentially intensify. This suggests that the influence of Arctic warming on the monsoon may contribute to further changes in extreme precipitation patterns and associated impacts in the future.

Way forward: Mitigation Strategies for Flooding

• Robust Early Warning System: Implement a comprehensive early warning system that utilizes meteorological observations, including Doppler weather radar and high-resolution numerical weather prediction models. Advanced technologies like artificial intelligence and machine learning can aid in interpreting the data, enhancing the accuracy and timeliness of alerts.

• Continuous Monitoring and Flood Warning Systems: Continuously monitor rainfall patterns, river levels, and deploy an advanced flood warning system. This integrated approach allows for timely response and evacuation plans to safeguard vulnerable communities.
• Flood Risk Maps: Develop flood risk maps incorporating topography, historical flood data, and hydrological modeling. These maps can identify high-risk zones and guide targeted actions to enhance preparedness and resilience.
• Climate-Resilient Infrastructure: Improve and maintain climate-resilient infrastructure, including robust drainage systems and channels, to prevent waterlogging and minimize flood damage.
• Land Use Planning and Zoning Regulations: Implement effective land use planning and zoning regulations, designating flash flood-prone areas as non-residential or restricted zones to mitigate potential risks.
• Protection and Restoration of Natural Ecosystems: Prioritize the protection and restoration of natural ecosystems such as forests and wetlands. These natural buffers can absorb rainfall and reduce runoff, mitigating the intensity of floods.
• Public Awareness Campaigns: Conduct widespread awareness campaigns to educate individuals on flood response and preparedness. Encourage actions such as evacuation planning, first aid knowledge, and reliance on credible sources of information during emergencies

Conclusion

• Recognizing the escalating threat of extreme precipitation events and implementing proactive measures are pivotal in improving India’s resilience to climate-induced disasters. Building resilience is crucial to safeguarding vulnerable communities and ensuring a sustainable future for the nation.

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[Burning issue] Urban Floods in India

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