Decoding the moody monsoon

Indian monsoon, crucial for the economy

The southwest (June to September) and northeast (October to December) monsoons are crucial for India’s agriculture and economy with more than 50 percent of the net sown area in the country depending on the rain, which contributes to 40 percent of the total production. More than half of India’s population (55 percent) is engaged in agricultural and allied sectors, and well-distributed rainfall during the kharif and rabi seasons is essential for agricultural production in the country.

Monsoons are also crucial for meeting the growing water needs of the population and will play an important role in meeting India’s clean energy aspirations in the future.

The monsoon is changing

But the Indian monsoon is changing in recent years. While the monsoon is known to be  highly variable, climate change is bringing about unexpected changes in monsoon patterns and decoding these changes to know how it will impact monsoon variability in the years to come is crucial for the Indian economy and sustainable development argues this report titled 'Decoding India's changing monsoon patterns: A Tehsil level assessment' by Council on Energy, Environment and Water (CEEW).

Available literature on monsoon predicts increased rainfall in core monsoon regions in both the medium term (up to 2050) and long term (up to 2100) under different representative concentration pathways (RCPs). However, the report argues that these assessments have focused on long term trends at coarse resolutions and have not been able to look at intricate variations within seasons and across months and days and within individual districts. 

The report discusses the outcomes of a study that has conducted India’s first sub-district -level monsoon variability assessment namely at the level of tehsils, talukas, mandals, circles and sub-divisions. The study refers to them as tehsils to align with the nomenclature used across the country to refer to administrative units. 

The study aimed at understanding how rainfall patterns are changing across India during the southwest and northeast monsoon in terms of inter-annual variability (year-to-year variability) and intra-annual variability (changes within months and wet and dry extremes). The most recent 12-km high-resolution reanalysis data sourced from the Indian Monsoon Data Assimilation and Analysis project (IMDAA) was used for the analysis.

Findings

The study found that:

• India as a whole experienced 29 ‘normal’, 8 ‘above-normal’, and 3 ‘below-normal’ monsoon years In the past 40 years during the southwest monsoon. Analysis at the district level showed that approximately 30 percent of India’s districts witnessed a high number of deficient rainfall years and 38 percent witnessed a high number of excessive rainfall years. Twenty three percent of districts such as New Delhi, Bengaluru, Nilgiris, Jaipur, Kachchh, and Indore, witnessed both a high number of deficient as well as excessive rainfall years.
• Fifty five percent of tehsils show a 10 percent increase in southwest monsoon rainfall in the past decade (2012-2022). A significant JJAS (south-west monsoon) rainfall increase was observed in the drier tehsils of Rajasthan, Gujarat, central Maharashtra, and parts of Tamil Nadu.
• Eleven percent of the Indian tehsils have witnessed a 10 percent decrease in the southwest monsoon during 2012-2022. These include those in the Indo-Gangetic plains, which contribute to more than half of India’s agricultural production, northeastern India, and the Indian Himalayan region, which have extremely fragile and diverse ecosystems. 
• Nearly 64 percent of Indian tehsils show an increase in the frequency of heavy rainfall days by 1-15 days per year in the past decade during the southwest monsoon. This pattern is prominent in the tehsils in  Maharashtra, Tamil Nadu, Gujarat, and Karnataka. The frequency of heavy rainfall is characterised by short duration, but heavy rainfall events. 
• The northeast monsoon (OND), which primarily impacts peninsular India, has increased by more than 10 percent in the past decade (2012-2022) in approximately 80 per cent of tehsils in Tamil Nadu, 44 per cent in Telangana, and 39 per cent in Andhra Pradesh, respectively.
• It was found that even in the normally dry states, an increasing rainfall trend was found along the tehsils of Maharashtra and Goa on the west coast and Odisha and West Bengal on the east coast. This increase could partially be attributed to the cyclonic activities in the Arabian Sea and Bay of Bengal.
• Nearly 48 percent of tehsils in India saw an increased rainfall in October by more than 10 percent, which could be due to the delayed withdrawal of the southwest monsoon from the subcontinent.

The report argues that:

Mapping monsoon performance at more localised level is essential

The increasing variability of monsoon and extreme rainfall events call for the need for localised decision-making to build resilience against monsoon extremes. While IMD provides monsoon information at country, zonal, state, meteorological sub-division, and district scales based on existing observation stations, this network lacks information on the monsoons at a more granular level. It is thus essential that local level decision-makers should use granular metrics used in this study for analysing local-level monsoon performance to help action and enhance disaster preparedness and response. 

Development of district-level climate action plans that include tehsil-level climate risk assessments are needed 

Making district-level climate action plans and integrating them with socioeconomic and sector-specific data can be greatly useful for detailed climate risk assessments in critical sectors like agriculture, water, and energy. Collaboration among research institutions, meteorological agencies, and civil society is important to make this climate information more accessible for a diverse range of stakeholders. 

Investing in automatic weather stations and community-based recordings to capture rainfall variabilities at a hyper-local level can be a useful strategy 

Diverse monsoon patterns at the tehsil level call for the need to have hyperlocal climate adaptation strategies. The current available long-term observational rainfall data lacks the granularity required for precise climate models and local action plans. 

The report states that alternative sources such as the Automatic Weather Stations (AWSs) and citizen science can help in expanding the network of observation stations. Initiatives such as the national Weather Information Network and Data System (WINDS) and community efforts such as school students in Kerala recording micro-weather data offer promising avenues to enhance the assessment of micro-climatic rainfall variations and inform effective local strategies, which should be scaled up, argues the report.