Kerala is once again in the news for an extreme weather event, as its Wayanad district reels from 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 hundreds of lives and injured several.
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 per cent is received during the monsoon months of June-September.
Geographically, Kerala is bounded by the Arabian Sea to its west and the Western Ghats to its east. This makes it highly susceptible to heavy rains during the season. Orography 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 decreasing 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.
“Whilst rainfall in Kannur district has been 21 per cent above the average between 1 June and 30 July, it is 14 per cent below the average in the neighbouring district of Wayanad, and up to 25 per cent below average in Idukki and Ernakulam districts. The co-occurrence of two extreme scenarios (landslides and rainfall deficit) in the same state reflects 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, a research scientist at the National Centre for Atmospheric Science and the Department of Meteorology, University of Reading, UK.
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.
Role of climate change and the science behind it
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 associated with monsoons, thunderstorms and short-spanned local cloudbursts.
These events, ranging from a few hours to a few days, have become more frequent in recent decades over the subcontinent.
The effects of climate change have led to changes in monsoon trends due to the weakening of synoptic activity within the Indian monsoon and the moistening of the tropical troposphere.
“Climate change is drastically changing rainfall patterns in Wayanad. What was once a cool, humid environment with year-round drizzles and monsoon rains, is turning into one marked by drier, hotter summers and intense downpours during the monsoons. This change has increased the risk of landslides. Dry soils absorb less water and heavy rainfalls cause run-offs that can lead to landslides,” said Mariam Zachariah, research associate, at Imperial College London.
Over 90 per cent of global warming is observed by oceans, which has led to a significant rise in ocean heating. As per new research by Nature, oceans have warmed by more than 1.5 degrees Celsius 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.
Trends indicate that extreme rainfall events are likely to continue increasing in the coming decades. 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.
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 Heavy Rainfall Events (HRE).
Role of Unplanned Development
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.
“Construction of roads should be done with all scientific techniques. At present, we just see roads being made or widened without taking proper measures such as no slope stability, lack of good quality retaining walls and rock bolting. All these measures can restrict the damage done by landslides up to some extent. ” said Prof. Y P Sundriyal, head of the department of Geology, at HNB Garhwal University.
The Western Ghats have been classified as an ecologically fragile region. According to recent research by the Indian Institute of Science, the 1.6 lakh sq km of hats in six states have been divided into four ecologically sensitive regions (ESR): very high ecological fragility (63,148 sq km), high ecological fragility (27,646 sq km), moderate ecological fragility (48,490 sq km) and low ecological fragility (20,716 sq km).
Roxy Mathew Koll, climate scientist, Indian Institute of Tropical Meteorology (IITM), Pune called for early warning systems to curtail the damage from natural disasters, “Roughly half of Kerala are hills and mountainous regions where the slope is more than 20 degrees and hence these places are prone to landslides when heavy rains occur. 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 the current technology and know-how and could in fact save lives and livelihoods. Other than climate change, we also need to evaluate the land use changes and development activities happening in 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.”
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 per cent decline in evergreen forests accompanied by an increase in agriculture, plantations and built-up areas.
Intact forests have declined by 10 per cent, and are now largely confined to protected areas. Simulations of future changes indicate that the region will have only 10 per cent evergreen cover, 17 per cent agriculture, 40 per cent plantations and 5 per cent built-up areas.
“The devastating landslides in Wayanad, a direct consequence of excessive monsoon rains, highlight the urgent need to address climate change. Kerala has been increasingly hit by such events, which are closely linked with global warming and consequent climate change as a significant factor behind the irregular, heavy rainfall patterns. Several measures can be taken to mitigate the impact of landslides and excessive rains linked to climate change. 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 Prof. Anjal Prakash, clinical associate professor (research) and research director, Bharti Institute of Public Policy, Indian School of Business and IPPC author.