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Soon after the Wayanad landslides in July, which claimed over 400 lives, scientists with the World Weather Attribution, an international collaboration, unequivocally said that the disaster was exacerbated by nearly 11 per cent due to global warming. But for a handful of scientists closely monitoring the Western Ghats, global warming is responsible for almost every landslide in the region occurring in recent years.
“Landslides are happening throughout the eastern slopes of the Western Ghats, from Coorg district in Karnataka to Vellarimala in Kozhikode district of Kerala,” CK Vishnudas, director of Hume Centre for Ecology and Wildlife Biology in Kalpetta, Wayanad, told Down To Earth (DTE). “And these all are clearly linked to climate change.”
Usually areas that are urbanising fast have mines and a diminishing green cover are considered vulnerable to land-slides. But the eastern slopes are sparsely populated and have lush forests, Vishnudas said.
Since 2018, Vishnudas and his team have been collecting rainfall data for Wayanad district from historical weather logbooks of tea estates. They find that the number of rainfall events above 300 mm per day has increased since 2018. Records from the local agricultural weather station also show that Wayanad has warmed by 1.5°C over the past decade.
As many as six forested regions along the Western Ghats in Karnataka and Kerala found a place in the “climate change hotspots” map prepared by the Forest Survey of India (FSI), which indicated that the forests have recorded a temperature rise of more than 1.5°C along with a change in rainfall of 20 per cent or more in recent decades.
The FSI report, prepared in 2020, also classifies Arunachal Pradesh, southwestern Himachal Pradesh, southern Chhattisgarh, northeastern Andhra Pradesh and adjoining parts of Maharashtra, northern Tamil Nadu and the Jim Corbett National Park in Uttarakhand as climate change hotspot areas.
To assess the exact impact, DTE travelled to climate change hotspot forests in Kerala and Karnataka. And the crisis is widespread.
Hyder Ali, a former officer in the Kerala education department and a resident of Karulai village in Malappuram district, told DTE that over the past decade, there have been small landslides in forested areas upstream of Karulai village, locat-ed on the fringes of the New Amarambalam Wildlife Sanctuary along the perennial Karimpuzha stream of the Chaliyar river. “The muddiness of the river increases after a few heavy rain spells in June. This is evidence of landslides, and of the increase in soil erosion at the sanctuary due to the general degradation of hill slopes. When the rain stops for a few days, the river becomes clear again,” said Ali.
Adding that the river has never appeared muddy before the past decade, he said, “I see this as the beginning of a process of desertification of the for-ests in this region.”
“When there is extremely heavy rainfall, the soil, even on forested slopes, gets saturated and fractures at the weakest points which then come down as landslides,” said S Sandeep, scientist at the Kerala Forest Research Institute, Thrissur. Even a small patch of forest getting washed away destabilises the larger area, and with repeated heavy rains, the entire forest becomes primed for collapse.
Sandeep and his team are studying the impact of extreme rainfall on landslides in the Western Ghats. Their analysis suggests that 50-60 per cent of landslides since 2018 have occurred in fringe areas that separate human habitations from denser forested areas.
The threshold for the occurrence of a landslide in the region is 145-150 mm of rainfall in 24 hours. They have also come up with preliminary hazard zonation maps for the Western Ghats in Kerala to help in better decision making during development activities on forested slopes.
But despite the increase in brief heavy rainfall events, Kerala has in the past two years seen a drier-than-usual phase during both pre-monsoon and monsoon seasons. This has led to drought-like conditions inside forests and increased fire incidents. “With a greater number of dry periods in the future such forest fires could become more common,” said S Gopakumar, head of the Department of Forest Resource Management at the Kerala Agricultural University in Thrissur.
The dry conditions get more pronounced as one moves further up to the Western Ghats in Karnataka. Approaching Anshi National Park in Uttara Kannada district, several dry patches appear along the road, beginning from just 8 km from the first entry point of the semi-evergreen forest that comprises the Kali Tiger Reserve.
Shantaram Kamat, an expert on forest ecology from Kumbarwada village on the periphery of Anshi, attributes this to the decreased rainfall over the past few years. “We always got ample rainfall around Holi and Gudi Padwa festivals during the pre-monsoon season, but that has not been the case for the past few years,” Kamat said, adding that both Anshi and Dandeli, a nearby moist deciduous forest, showed shift in character.
MD Subash Chandran of Centre for Ecological Sciences, Indian Institute of Science, Benguluru, an expert on the ecology of the Western Ghats, said this shift has been brought on by weeds like Eupatorium and uncontrolled fire due to the change in vegetation and increasing dryness. Such increase in forest fires is also being reported from Dakshina Kannada, the other climate change hotspot district. In Pairodi village of the district, 62-year-old Sushila says that temperatures have risen in recent years and rainfall has been dwindling. “In 2023, we did not have enough water for household use, let alone for my arecanut farm,” she said.
The erratic rainfall patterns in Karnataka have impacted food production in forests, which is crucial for wildlife as well as communities. In July 2021, heavy downpour led to a landslide near Teloli village, located inside the core forest area of Anshi. “The landslide washed away the hillside forest. I had never seen anything like this before,” said 55-year-old resident Suresh Babu Gavada. The landslide decimated the vegetation to such an extent that it has not yet grown back.
Then in the 2023 pre-monsoon season (March-May), Uttara Kannada district received 59 per cent less rains than nor-mal, according to data from the India Meteorological Department. This affected the growth and collection of monkey jack fruits, known as wate wadi in the local language and used as a condiment with tubers. “There has been next to no collec-tion of monkey jack fruit,” said Kamat, who runs a farmer producer organisation in Kumbarwada village.
Prashant Bhatt from Honnavar town in the district, a contractor of forest produce, told DTE, “While fruits like kokum and upagi mara (pot tamarind) have not been impacted much by increasing temperatures and changing rainfall patterns in the region, other produce like wild nutmeg and Malabar tamarind have been heavily impacted in the past few years.”
But Ratnakar Naik of Hosagod village, who collects forest produce for Bhatt and earns around Rs 5,000 per season, notes that even kokum collection has reduced because of lower rainfall and hot temperatures. “I collected 30 per cent less kokum fruits in 2023. Upagi mara collection decreases in the years when there is heavy rainfall before the monsoon,” said Naik, adding that the collection of honey has reduced by almost 90 per cent in recent years.
Kamat explained that honey production needs good pre-monsoon showers, as the liquid thickens when there is no rain. Half a decade ago, a single honeycomb would yield about 20 kg of honey. This has now reduced to 5-10 kg, mainly due to the decline in the number and variety of flowers inside and outside the forest.
Forest tubers and other edible species also need good pre-monsoon rains for germination, along with ample monsoon showers to aid their growth. “Though we do not venture into the core forest, I am certain that the situation there would be no different,” he added.
Back in Kerala, Ali noted that the lifecycle of tubers, which are both cultivated as crops and grow wild in forests, has been gradually shifting over the past decade. This coincides with the time when landslides started occurring in the region. “Local tuber crops are planted in April, around the time of Vishu. But in 2023, I planted the crops in the first week of May, around three weeks later than usual, because of the lack of rainfall,” Ali told DTE.
Like in Karnataka, honey production has also reduced, particularly in the Nilambur forest area, notes Ali. Some 90 km away in Palakkad, tribal communities such as the Kurumba tribe report a decline in medicinal plants, honey and gooseberries with decreased rainfall.
To worsen the matter, people living near Muthanga wildlife sanctuary and other areas of Wayanad, report proliferation of Senna spectabilis weed, an invasive species that has originated in Central and Latin America. “This weed takes over a landscape in ways that other weeds do not and does not let any other vegetation grow at all. Animals do not eat the weed, which helps it spread even further,” said N Badusha, a resident of Naikatty village on the fringes of the sanctuary.
The spread of Senna spectabilis has decreased food availability in the forests, increasing interaction and conflict be-tween humans and animals. Wayanad has a dense population of tigers. “At the Wayanad Wildlife Sanctuary, the wild cats are cramped into a small area of 344 sq km, which is further being restricted by rampant development activities,” said Badusha. In several areas, tigers have taken over farmlands where herbivores are abundantly available. Rampant devel-opment, and abandonment of farmlands by younger generations, has exacerbated the problem.
Movement of elephants has also become more frequent in Wayanad, as well as in Palakkad and Ernakulam districts. “Change in rainfall patterns and increasing temperatures in forests have affected the quality of forage available, which pushes elephants towards human habitations,” said Gopakumar. “However, I do not consider this interaction as a con-flict, but rather an attraction towards human settlements,” he added.
One of the places elephants appear to be attracted to is Kottappady village in Malayatoor forest division in Ernaku-lam district. A night before DTE visited Kottappady in May 2023, a herd of elephants had visited the banana, rubber and arecanut plantations between the village and the forest, damaging trees and boundary walls. “We have been witnessing such attacks by this herd almost every day for the past three-four years. Before that it was not as common,” said Reji, a farmer in the village, who lost `4 lakh worth of crops to elephants in 2022-23.
The behavioural changes are not confined to wildlife. Ali, an avid bird watcher, said that the Indian pitta bird usually arrives in the Nilambur area around December. It has become much rarer now. As has the Eurasian golden oreole that migrates from Europe and Central Asia. These regular visitors have been replaced by other species that were rarely or never seen earlier, such as peacocks.
In Wayanad, peacocks seem to have invaded the forests. The State of India’s Birds 2023 report found that the number of peacocks in Kerala has increased by 150 per cent since 2000, with the birds expanding their earlier habitats in Idukki, Palakkad, Thrissur and Wayanad. “The increase in the population of peacocks has meant that the populations of snakes and other small reptiles have decreased, disturbing the balance of the food web in the area,” said Badusha, who heads the Wayanad Prakriti Samrakshana Samiti, a local non-profit that works on issues such as human-animal conflicts and consequences of rampant development.
Similarly, in the Dandeli forest area in Karnataka, known for its forest grasses, cattle herders and birds like the great hornbill and the Malabar pied hornbill, ecological niches and livelihoods are being disrupted. “There has been a significant decrease in forest grass in the area, which is being replaced by the weed Eupatorium that is prone to fires and is not eaten by the cattle,” GE Umesh, a local wildlife expert and photographer, told DTE.
Reduced grass availability inside the forest appears to have led to a decline in herbivorous animals such as spotted and barking deer. “Consequently, the incidences of attacks on cattle by leopards and tigers have increased in the nearby villages in recent years,” said Umesh. Located at an altitude of 475 m, Dandeli used to receive continuous rainfall as a drizzle, but this has now been replaced by dry periods or excess rainfall.
The impact on the fruiting of trees is evidenced by the changing nesting behaviour of the Malabar pied hornbill, a bird species that Umesh regularly photographs. “I have been studying one particular nest for the past 20 years. For three con-secutive years till 2023, the nest had no eggs. Hornbills need 40-45 varieties of fruits, mainly figs, for their nutrition. Perhaps they are not able to find the fruits and hence abandoning the nests,” said Umesh.
Changes in rainfall patterns, vegetation and biodiversity are just three of the many indicators of climate impact on forests. But there is a huge dearth of ground-level observational data on forest processes and health to determine the exact impacts.
One aspect that needs greater analysis is the role of forests as carbon sinks. Forests are the most essential means to absorb excess carbon emissions in the atmosphere due to anthropogenic activities. According to the 2020 FSI report, at present, Indian forests store 3,121 Giga-tonnes of carbon (GtC), with an additional 4,003 GtC stored as soil organic carbon. The total storage is equivalent of 26,145 billion tonnes of carbon dioxide.
But only healthy and productive forests will have enough organic matter for soil microorganisms to decompose and enrich the soil with carbon. This then calls for analysis into the most vital process to keep a tree healthy — photosynthesis, the process by which plants and trees convert the Sun’s light energy and carbon dioxide into glucose and oxygen.
Photosynthesis generally decreases with increasing temperatures since processes such as fixing carbon dioxide into the plant and water transport cannot occur effectively in hotter conditions.
On the other hand, increased car-bon dioxide in the atmosphere leads to more absorption by plants, resulting in a process called carbon fertilisation that increases the rate of photosynthesis and makes plants produce more vegetation. “But this can only be beneficial for plants up to a certain level, varying from one species to the other,” K Sreejith, scientist at the Kerala Forest Research Institute, told DTE. “Warming is a more crucial factor than rise in carbon dioxide levels, but its impact cannot be general-ised. It must be studied at an individual species level,” said Sreejith.
According to research led by Subimal Ghosh at the Indian Institute of Technology, Bombay and Rajiv Kumar Chaturvedi at the Birla Institute of Technology and Science, Goa campus, forests in several regions of the country see a net decrease in carbon dioxide absorption, mainly due to decreased photosynthesis.
These are also regions where temperatures have increased in the last few decades, according to the study published in Nature in December 2023. The scientists studied satellite data of leaf area index, which provides the measure of the total green cover of a region and has increased by 18.51 per cent between 2001 and 2019 across India. They also analysed the gross pri-mary productivity (GPP), or the amount of carbon dioxide captured by plants in unit time during photosynthesis, and the net primary productivity (NPP) or the total carbon dioxide absorbed by plants after accounting for respiration (which involves taking in oxygen and releasing carbon dioxide to generate energy).
“There is a 6.19 per cent decrease in NPP over forests in northeast India, Western Ghats and some other parts of peninsular India in the last two decades (2001-19),” said Ghosh, who is also lead author for the AR6 Working Group I report, published by the Intergovernmental Panel on Climate Change (IPCC). This is despite a 6.75 per cent in-crease in the leaf area index over the same regions during the same period. This data indicates that with rising temperature, the rate of photosynthesis decreases but respiration rate keeps on increasing, thus reducing the net carbon uptake.
This analysis has some caveats. For example, the calculation of leaf area index is only based on satellite imagery and is thus incomplete. “The species of trees, whether they are evergreen or deciduous, the duration of the seasonal shed-ding and the type of canopy must be taken into account as well,” said Subash Chandran. Such factors can only be known if extensive ground level data is available for each type of forest, he adds.
Further, Ghosh and his team only looked at regions that have been continuously under forests, without major changes to land cover and land use. Finally, the research has not taken into account carbon fertilisation. “So we do not know the direct impact of carbon dioxide levels on forests, we only have an indication of the indirect impacts through warming on photosynthesis,” said Ghosh.
Other research provides more clues on the link between photosynthesis and warming. A research paper published in the journal Nature in August 2023 stated that the photosynthetic ability of tropical forest trees area in Brazil, Puerto Rico and Australia starts to fail when the leaf temperature reaches 46.7°C. It said that at an average atmospheric temperature rise of 4°C, tropical trees will cross a point of no return for photosynthesis.
Similar research has been conducted to check the thermal tolerance of species. Sreejith’s team studied mangrove forests in Kerala and found them to be the most tolerant to increasing temperatures and to droughts of all ecosystems across the world.
A more recent study published in Science of The Total Environment in September 2024 analysed 13 mangrove species from Kerala and found that estimated maximum leaf temperatures of the species were higher than the surrounding air temperatures, but well below their own heat tolerance limits. This indicated high resilience to future warming.
Chaturvedi is also studying how changes in temperatures influence plant phenology — flowering, fruiting and leaf-related phenomena impacted by the lack of photosynthesis — in the Netravali forest area of Goa, where his team is using near surface camera-based instruments known as phenocams. The data or analysis from the plots, which began in 2022, is being shared with the Indian Space Research Organisation (ISRO) in real time.
The rainfall in Goa is usually concentrated in the monsoon months from June to September, but in 2021 it rained throughout the year. This affected the cashew crops, both inside and outside the forests, because the trees require seamless sunlight during the summer for their growth and productivity, with cloudy days also inviting fungal infections, said Chaturvedi. Similarly, mango and honey production in the region had also dropped in 2021.
Despite these advancements, current research needs to be ramped up to understand the status of forests in the country in terms of the impacts of climate change. More observations, dedicated satellite imagery and better modelling could change the scenarios further and give a more holistic understanding of how global warming and consequential cli-mate change will change the fate of the forests in India.
(This story was first published in the 1-15 November, 2024 print edition of Down To Earth.)