Climate change and India’s monsoon pattern

A recent study ‘Decoding India’s Changing Monsoon Patterns: A Tehsil-level Assessment,’ was carried out by the Council on Energy, Environment and Water (CEEW). In the Executive Summary, researchers Shravan Prabhu and Vishwas Chitale point out that while the Indian monsoons, by nature, show high variability through space and time, current climate change trends indicate that global warming records would be breached earlier than expected. Hence, the need to answer the crucial question of how these changes are likely to affect the variability of India’s most critical climatic phenomenon – the monsoons.

The researchers highlight that the monsoons are crucial for the Indian economy and are often regarded as the backbone of the agricultural sector, which employs over half of India’s population. They also play a pivotal role in the management of water resources and the generation of hydro-based clean energy. However, the variability of the Indian monsoons and the associated wet and dry conditions have direct impacts on socio-economic aspects of the country, including the gross domestic product. In 2022 alone, Asia witnessed over 81 natural hazards, with 83% of them being hydro-meteorological. India too incurred significant losses, primarily due to floods caused by the monsoons.

This study undertakes a pan-India sub-district level (tehsil-level) assessment of changing monsoon patterns during the southwest monsoon (June to September) and northeast monsoon (October to December). It delves into trends spanning the past four decades (1982–2022), with a specific emphasis on quantifying changes in rainfall patterns in the past decade. This climatological analysis employed established statistical criteria and indices endorsed by the World Meteorological Organization and the India Meteorological Department. Recognising the micro-climatic variabilities of Indian monsoons, it recommends development of local-level climate action plans. It aims to support local-level decision makers and administrators by providing granular information of monsoon statistics that can be used for mapping of monsoon performance at tehsil levels.

The CEEW website states the southwest monsoon is the primary monsoon affecting India. Around June, the monsoon hits Kerala on southwestern coast, gradually progressing across the country. The monsoon’s arrival marks the end of scorching summer heat, providing relief and contributing significantly to India’s diverse ecosystems and economy, especially the growing of kharif crops. India is also impacted by the northeast monsoon, also known as the winter monsoon or retreating monsoon. This monsoon is less intense compared to its southwestern counterpart but plays a crucial role in growing rabi (winter) crops and helps recharge groundwater.

The key findings of the report as listed on the CEEW website state that in the past 40 years (1982-2022), 23% of districts such as New Delhi, Bengaluru, Nilgiris, Jaipur, Kachchh, and Indore, witnessed both a high number of deficient and excessive rainfall years. 55% of tehsils witnessed an increase and 11% witnessed a decrease in southwest monsoon rainfall in the past decade (2012-2022), by more than 10% each compared to the climatic baseline (1982–2011). A statistically significant rainfall increase was observed in the traditionally drier tehsils of Rajasthan, Gujarat, central Maharashtra, and parts of Tamil Nadu.

Of the 11% tehsils that saw a decrease in southwest monsoon rainfall, 68% experienced reduced rainfall in all months from June to September, while 87% showed a decline during the initial monsoon months of June and July, which are crucial for the sowing phase of kharif crops. These tehsils are in the Indo-Gangetic plains, which contribute to more than half of India’s agricultural production, northeastern India, and the Indian Himalayan region.

Also, 64% of Indian tehsils experienced an increase in the frequency of heavy rainfall days in the past decade during the southwest monsoon. This pattern is prominent in the tehsils of states with the highest GDPs – Maharashtra, Tamil Nadu, Gujarat, and Karnataka. Over the past decade, the northeast monsoon has increased in Tamil Nadu, Andhra Pradesh and Telangana. Notably, tehsils in Maharashtra and Goa on west coast and Odisha and West Bengal on the east coast show a significant rise in October to December rainfall, contrary to their usual dry conditions. 48% of tehsils in India saw an increased rainfall in October by over 10%, which could be due to the delayed withdrawal of the southwest monsoon from the subcontinent.