Climate Change
My entry into the world of climate change began rather serendipitously during a trek in 1982 in the Nilgiri plateau in search of a dead elephant calf. I "discovered" peat bogs which I realized were archives of past vegetation change. After several years I was able to work on this system and make links with glacial climate cycles. Since then my lab has not only advanced this work but also ventured into the Himalaya to investigated past climate change from tree rings.
Quaternary climate change: The Nilgiri plateau in the Western Ghats features montane stunted forest ("sholas") and extensive grasslands. Peat bogs located at over 2000m in the Nilgiri plateau are archives of past vegetation and climate change going back to tens of thousands of years before present. With the help of Rengaswamy Ramesh in measuring stable carbon isotopes, I showed that past global climatic events such as the peak ice age and the end of the glaciation are also recorded in these bogs. Geeta Rajagopalan extended our record from 20,000 to 40,000 years BP. Ramya Bala Prabhakaran made high resolution radio-carbon dating of the Sandynallah bog and found that the shola forests and grasslands existed in "alternative stable states."
Climate change and human migration: Perhaps one of the most exciting outcomes of our work on palaeoclimate of the montane Nilgiri region in the Western Ghats has been unearthing evidence from a number of proxies for human presence on the plateau at about 3500 years before present, or about 1500 years prior to what historians and anthropologists have believed. It is most likely that a pastoral community, the Todas, migrated to the higher elevations of the Nilgiris with their buffalo herds in response to a major drying event.
Climate change in the Himalaya: Dendrochronology or tree rings in the Himalayan fir trees have helped reconstruct past climates. Masaki Sano analyzed oxygen isotopes in fir tree rings to infer that rainfall has been decreasing in the Nepal Himalaya over the past two centuries. Rayees Malik used conventional tree ring analysis of fir trees and inferred climatic factors influencing the onset of cambial growth in trees along an elevation gradient in the Kashmir Himalaya. The ongoing analysis is not only reconstructing past climates of the Himalaya but also providing insights into how trees would respond to future climate change in this region.
Climate change impacts on Indian forests: I assisted NH Ravindranath in conceptualizing and developing some of the early models of how climate change would impact the various forest biomes in the country. Rajiv Chaturvedi further refined this understanding by using Dynamic Global Vegetation Models to quantify the nature and extent of possible change in India's forests as well as accompanying changes in processes such as carbon sequestration. This research has contributed to India's National Communication on Climate Change.
Climate and wildfires: The initial work on fires began in conjunction with the long term monitoring of forest dynamics in Mudumalai. Nandita Mondal derived fire-climate relationships for this tropical dry biome in the Western Ghats, showing not only that fire frequencies are related to rainfall, temperature and humidity as expected but also that they peak in the intermediate rainfall zone. Jaideep Joshi developed a global model of wildfires using machine learning which greatly improved prediction of fires in space and time.
