According to a new study, by the end of this century the vast, dense forests that define much of the Indian landscape could undergo a dramatic transformation, shifting into open, grassy savannas. A team of researchers from the Indian Institute of Technology (IIT) Bombay, alongside colleagues from the Max Planck Institute for Biogeochemistry, has found that global warming is significantly increasing the likelihood of this ecological tipping point. Their study warns that while total rainfall might remain steady in some regions, the increasing unpredictability and seasonality of that rain are making it harder for dense forests to survive. Between 2001 and 2020, India has already seen its total tree cover grid decline from 30% to 28%, with many regions transitioning from thick forest to more sparse, savanna-like conditions.

To arrive at these conclusions, the team employed a space-for-time substitution approach. They used 20 years of high-resolution satellite data from the Moderate Resolution Imaging Spectroradiometer (MODIS) sensor aboard NASA’s Terra and Aqua satellites. They used the data to track changes in tree cover nationwide. By examining current vegetation patterns and matching them with climate data, they could project how these ecosystems would behave in the future if temperatures continue to rise. 

The researchers focused on a mathematical concept known as alternative stable states. In simple terms, they viewed ecosystems as a point on a graph with a series of valleys. Currently, the system remains stable within a valley. However, if climate stress, like erratic rainfall, changes the factors too much beyond a tipping point, the point could roll into a neighbouring valley on the graph, which coincides with a savanna. Once we reach this point, it might become too difficult to return to the earlier state.

The team also examined the hydroclimate, which examines how water cycle processes (precipitation, evaporation, runoff) are influenced by atmospheric conditions and, in turn, influence them, focusing on precipitation variability and seasonality. They discovered that forests are surprisingly sensitive to how rain is distributed throughout the year. Even if a region receives plenty of rain, if that rain arrives in short, violent bursts followed by long dry spells, the forest loses its resilience. The researchers used potential landscape modelling, a technique often used in physics to describe how systems move between stable and unstable states, to show that nearly half of India’s landscape currently exists in a state where it could potentially be either forest or savanna, depending on environmental pressures.

Their work also represents an improvement over earlier ecological models by integrating human intervention as a key variable. The researchers found that while climate change is a massive threat, the non-climatic drivers, such as government-led reforestation programs and stricter conservation laws, have actually helped increase forest cover in some areas between 2001 and 2020. This suggests that humans are not just spectators to environmental decline but can actively offset the damage caused by global warming through strategic policy. By including factors like CO2 fertilisation and human-led planting, the study provides a much more holistic view of the environment than models that only look at temperature and rain.

This research provides a vital blueprint for society. By identifying which regions are most unstable and likely to tip into savanna states, the study allows the government and conservationists to target their efforts where they are needed most. In a warming world, this knowledge is a critical tool, showing that while the climate may be shifting the ground beneath our feet, strategic human action can still safeguard the vital carbon-storing forests that regulate our water and air.