Cloudbursts and Landslides in Himachal Pradesh

18 Aug 2023

In the aftermath of torrential downpours on 14^th August, 2023, Himachal Pradesh confronts a tragic aftermath with catastrophic landslides due to cloudbursts and heavy rainfall.

Factors behind Heavy Rains in Himachal and Uttarakhand

The northward shift of the monsoon trough and its interaction with a mild western disturbance contribute to the intense rainfall in Himachal Pradesh and Uttarakhand.
The monsoon trough extends from Pakistan's "heat low" to the Bay of Bengal region. It's a semi-permanent feature in India's monsoon system.
Currently, the monsoon trough lies north of its usual position, over the Himalayan foothills.
A gradual southward shift of the monsoon trough is expected, leading to reduced hill rainfall and increased rainfall over east-central India.

About Cloudburst

A cloudburst signifies concentrated, intense rainfall that typically transpires in hilly locales.
Though not all instances of heavy rainfall constitute cloudbursts, they embody unique criteria: rainfall exceeding 10 cm within an hour across a roughly 10 km x 10 km zone.
Under this parameter, 5 cm rainfall within half an hour in the same region qualifies as a cloudburst.

Trends in Cloudburst

A surge in cloudbursts, as per IMD's definition, isn't evident in long-term trends.
However, extreme rainfall occurrences, along with other weather extremes, are mounting globally, not confined to India.
Although India's overall rainfall hasn't drastically changed, a larger proportion now occurs in shorter durations.
In Himachal Pradesh, cloudbursts are frequent, especially during the monsoon from June to September.
The unique topography, wind dynamics, and temperature variations in the Himalayan region contribute to their prevalence.
Presently, the monsoon trough is centered over Uttarakhand and Himachal Pradesh, intensifying rainfall patterns.
This pattern, attributed to climate change, indicates a possible increase in cloudburst events.

Understanding Landslides and Their Causes

Landslides entail the movement of rock, debris, or earth down a slope, classified under "mass wasting," involving gravity-induced soil and rock movement.
Mainly found in mountainous regions, conducive conditions of soil, rock, geology, and slope prompt landslides.
Natural triggers include heavy rainfall, earthquakes, snow melting, and slope undercutting due to flooding.
Human activities like excavation, deforestation, overdevelopment, and overgrazing can also induce landslides.
In India, rainfall-induced landslides are common.

Unpredictability and Challenges

Cloudbursts are renowned for their capricious nature, arriving suddenly and unexpectedly.
Preferring secluded and inaccessible regions, these localized occurrences frequently initiate flash floods that imperil settlements downstream.
The task of predicting cloudbursts remains arduous, particularly within the small valleys of the Himalayas.
Despite the potential utility of Doppler radar, which offers velocity insights on objects, forecasting these events remains intricate.

Impact of Cloudbursts

Due to the terrain's nature, heavy rainfall frequently triggers landslides and flash floods, inflicting extensive damage downstream.
While these events occur in small, instrument-scarce areas, their repercussions extend beyond these confines.

Key Points from NDMA's National Landslide Risk Management Strategy Report

Urban Overload in Shimla: The National Disaster Management Authority (NDMA) report highlights the strain of overpopulation in Shimla, originally designed for 25,000 but now accommodating around 300,000 residents.
Inappropriate Planning and Copied Blueprints: The report points to unsuitable planning for hilly regions and the adoption of Delhi Master Plans, criticized for neglecting environmental factors.
Plan Implementation Shortcomings: Even existing plans suffer from poor execution, resulting in unsafe buildings and non-compliance with design codes.
Environmental Challenges in Himalayan Cities: The report identifies issues such as untreated sewage, garbage accumulation, water scarcity, urban sprawl, and air pollution.
Water Scarcity and Vulnerable Infrastructure: Shimla grapples with water shortages due to landslides, silt deposition, and power outages disrupting water supply systems.
Comprehensive Development Solutions: The report advocates for planned development in Himalayan towns, suggesting measures like banning plastics and sustainable waste management.
Prioritizing Systemic Solutions: Authorities should focus on systemic fixes instead of quick remedies for issues like landslides, as long-term benefits outweigh upfront costs.
Investment in Long-Term Solutions: The report urges a shift from short-term engineering approaches to more sustainable solutions for landslide prevention.