Attributing the Human Influence on Precipitation Changes over India

Variations in rainfall over India -much of which is received during the summer monsoon season (June-September) - influences the economy of the country as nearly 50% of the population is engaged in the agricultural sector which constitutes 17.4% of the GDP of India. The agriculture and economy of India is highly vulnerable to any changes in the monsoon rainfall is well recognised. Recent decades have seen decreasing monsoon rainfall in various parts of India. Whether these are a consequence of natural monsoon variations or are caused by specific anthropogenic factors is an important question to answer in formulating the right policy response to these changes. Understanding the physical changes is also a first step towards being able to attribute downstream impacts due to rainfall changes. We have carried out an optimal fingerprint based Detection & Attribution analysis to study the changing rainfall patterns. We make use of outputs from 7 models in the Coupled Model Intercomparison Project Phase-5 (CMIP5) database that carried out single forcing experiments with, Natural, GHG, Anthropogenic Aerosols, and historical (All) forcings. We use multiple observational datasets of rainfall (CRU 3.22 and IMD gridded) to account for observational uncertainty to analyse seasonal (JJA and DJF) and annual mean rainfall over the 1906-2005 period. Our analysis shows the dominant role of GHG and Anthropogenic Aerosol forcings on the observed rainfall changes.