Erratic rain patterns induced by global warming, coupled with land use change and unplanned development, are the main cause of the landslides in Wayanad
The Wayanad district in Kerala is reeling under the destruction wreaked by one of the most devastating landslides triggered by incessant Monsoon rains. During the wee hours of July 30, multiple landlines swept away several villages in the district. The tragedy has claimed over 250 lives, injured several and more than 200 are still missing.
Kerala receives the second-highest monsoon rainfall in India after its northeastern states. It records an average annual rainfall of about 3,107 mm, of which 75% is received during the monsoon months of June-September (JJAS).
However, the cumulative rainfall for Kerala from June 1 to July 30 stands at 1,222.5 mm against the normal average of 1,283.5 mm for the period, resulting in a deficit of -5%. According to meteorological criteria for districts during monsoon, a departure of +/-19% is considered to be normal rainfall.
“Whilst rainfall in Kannur district has been 21% above the average between 1 June and 30 July, it is 14% below the average in the neighbouring district of Wayanad, and up to 25% below average in Idukki and Ernakulam districts. The co-occurence of two extreme scenarios (landslides and rainfall deficit) in the same state reflect a strong spatial variability in this year’s monsoon rainfall. The expectation is that such a pattern would become more intense in the future if global warming continues,” said Akshay Deoras, research scientist, National Centre for Atmospheric Science and the Department of Meteorology, University of Reading, UK.
A brief history of extreme events
There has been a steady rise in extreme events in the state over the last decade. For example, Cyclone Ockhi wreaked havoc in 2017, followed by devastating floods in 2018, which were among the worst in the state’s history. In August 2019, the state experienced another spell of extremely heavy rainfall.
According to a report, ‘Climate Change Assessment over the Indian Region’, the interannual variability of summer monsoon rainfall is projected to increase throughout the twenty-first century. The increased frequency of localised heavy rainfall on sub-daily and daily timescales has enhanced flood risks across India.
Geographically, Kerala is bounded by Arabian Sea to its west and the Western Ghats to its east. This makes it highly susceptible for heavy rains during the season.
Orographic rainfall —precipitation produced when the mountains of uplands act as barriers to airflow, forcing the air to rise and the moist air moving upslope cool down by producing clouds and precipitation— has a strong effect on rainfall distribution in the mountainous region of Kerala. The rainfall potential of the region increases from the coastal belt towards the Western Ghats, reaching a maximum on the windward side of the Ghats and rapidly decreases on the leeward side.
The rainfall characteristics over Kerala are unique because of the influence of isolated steep-sloped structures separated by the wide Palghat gap.
Contrary to this climatology, the state has experienced severe floods in recent times due to intense precipitation during the SW monsoon. However, experts suggest that factors beyond the meteorological factors, such as climate change and unplanned development, are to blame for the catastrophic landslides.
“Monsoon patterns have definitely changed”
Numerous studies have established that the rise in global average temperatures due to human-induced climate change has led to an increase in the number of extreme rainfall events (ERE) associated with monsoon, thunderstorms and short-spanned local cloudbursts.
“Monsoon patterns have definitely changed and they now behave in an erratic manner. Despite these heavy showers, Kerala is yet to surpass its average rainfall so far. Also, with the rise in air as well as ocean temperatures, there has been a drastic increase in the moisture. The Arabian Sea has been warming at a faster rate, pumping moisture in the atmosphere, making it unstable. All these factors are directly linked to global warming,” said Mahesh Palawat, Vice President- Meteorology and Climate Change, Skymet Weather.
The number of heavy rainfall events is increasing, while the number of rainy days during the monsoon is decreasing. Contributing factors include the variability of low-level monsoon westerlies over the Arabian Sea, which drive surges of moisture supply, the trailing strength of monsoon circulation and the variation of vertical wind shear from the break phase to the active phase of an Indian Summer Monsoon (ISM) cycle.
Over 90% of the global warming is observed by oceans, which has led to significant rise in ocean heating. As per a new research by Nature, oceans have warmed by more than 1.5°C since the beginning of the industrial era, challenging previous estimates. The Indian Ocean is a hotspot for climate change and has seen the fastest surface warming since the 1950s. This rapid warming of the Indian Ocean has led to an increase in marine heat waves, which impact the monsoon by reducing the rainfall over the central Indian subcontinent while enhancing it over the southern peninsula.
According to the report ‘A review on the extreme rainfall studies in India,’ the frequency and intensity of extreme monsoon downpours in India have increased over the past 50 years, despite significant inter-annual variability.
A few studies have also suggested that changing climate, increased monsoon flow strength in the last two decades, and human-modified land cover changes have contributed to the increased frequency of the Heavy Rainfall Events (HRE).
Unplanned human interference
The Western Ghats are one of 36 global biodiversity hotspots, with forests in this region sequestering atmospheric carbon, thereby aiding in moderating the global climate and sustaining water and food security in peninsular India. An assessment of land-use land-cover (LULC) dynamics using temporal remote sensing data shows a 5% decline of evergreen forest accompanied by an increase in agriculture, plantations and built-up areas. Intact forests have declined by 10%, and are now largely confined to protected areas. Simulations of future changes indicate that the region will have only 10% evergreen cover, 17% agriculture, 40% plantations and 5% built-up areas.
Historically, from 1920 to 2013, the Western Ghats in Kerala experienced the highest forest cover loss, with a 62.7% reduction in forested area.
Deforestation, rapid urbanisation, unplanned development and poor planning are significant factors exacerbating the climate crisis in India. It is evident that development plans and human interference are not complementing the ecological balance of the mountainous terrain.
“We just see roads are being made or widened without taking proper measures such as no slope stability, lack of good quality retaining wall and rock bolting. All these measures can restrict the damage done by landslides up to some extent. There is a huge gap between planning and implementation. Policy and project implementation should consist of local geologists who understand the terrain well and how it responds,” said Professor Y P Sundriyal, Head of Department, Geology, HNB Garhwal University.
Call for an urgent need to deploy solutions
According to experts, resources and research to prepare for such events are already available. “Landslide-prone areas are mapped and available for Kerala. Panchayats with hazardous areas should be identified and sensitised. We need to monitor rainfall data in these hotspots and prepare early warning systems targeted at hazard prone areas. This is possible with current technology and know-how and could in fact save lives and livelihoods,” said Roxy Mathew Koll, climate scientist, Indian Institute of Tropical Meteorology (IITM).
The scientist also pointed out the need to evaluate the land use changes and development activities happening over landslide prone areas. Often landslides and flash floods occur over regions where the impact of both climate change and direct human intervention in terms of land use changes are evident, he said. “However, at the same time, there have been many severe landslides over regions with minimal land use changes also,” Koll added.
“Strengthening infrastructure by investing in climate-resilient bridges and roads will help withstand extreme weather events and facilitate quicker rescue operations. Promoting sustainable land management is also crucial; practices such as reforestation, controlled deforestation, and sustainable agriculture can maintain hillside stability and reduce soil erosion, thereby lessening the effects of heavy rains,” said Anjal Prakash, clinical associate professor (Research) and research director, Bharti Institute of Public Policy, Indian School of Business and IPPC Author.
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