How is Climate Change Altering India’s Monsoon Rainfall Patterns?

REPORT

Decoding India’s Changing Monsoon Patterns

A Tehsil-level Assessment

17 January, 2024 | Climate Resilience

Shravan Prabhu and Vishwas Chitale

Suggested citation: Prabhu, Shravan and Vishwas Chitale. 2024. Decoding India’s Changing Monsoon Patterns: A Tehsil-level Assessment. New Delhi: Council on Energy, Environment and Water.

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Overview

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. We do this climatological analysis by employing established statistical criteria and indices endorsed by the World Meteorological Organization (WMO) and the India Meteorological Department (IMD).

Recognising the micro-climatic variabilities of Indian monsoons, this study 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 in annexure format that can be used for mapping of monsoon performance at tehsil levels.

Key findings

In the past forty years (1982-2022), 23 per cent 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.
55 per cent of tehsils witnessed an increase and 11 per cent witnessed a decrease in southwest monsoon rainfall in the past decade (2012-2022), by more than 10 per cent 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 per cent tehsils that saw a decrease in southwest monsoon rainfall, 68 per cent experienced reduced rainfall in all months from June to September, while 87 per cent 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.
64 per cent 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 (OND) 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 per cent of tehsils in India saw an increased rainfall in October by over 10 per cent, which could be due to the delayed withdrawal of the southwest monsoon from the subcontinent.

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Shravan Prabhu

Research Analyst

[email protected]

"The Indian monsoons, which inherently show high variability, are now seeing even more rapid changes across seasons and geographies due to climate change. This poses significant risks to critical sectors such as agriculture, water, and energy. To build resilience against these evolving rainfall patterns, there is a need to mainstream local-level decision-making based on granular climate risk assessments. Our study not only maps these changes but also empowers decision-makers with open-access tehsil-level information."

Executive summary

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 (GDP) (Gadgil and Gadgil 2006; Wang, Gadgil, and Kumar 2006; Gulati, Saini, and Jain 2013).

In 2022 alone, Asia witnessed over 81 natural hazards, with 83 per cent of them being hydro-meteorological. India, in particular, incurred significant losses, primarily due to floods caused by the monsoons (WMO 2023). While the Indian monsoons, by nature, show high variability through space and time, current climate change trends indicate that we are likely to breach global warming records earlier than expected (WMO 2023). Thus, we 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.

Existing literature predicts intensifying monsoon seasons with 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). Yet, capturing short-term granular spatial variabilities has been a challenge, especially beyond the district level. Existing assessments often focus on prolonged long-term trends at coarse resolutions and have not been able to account for intricate nuances within seasons, spanning across months and days, or even variations within a single district.

To fill this gap in enhanced analyses of short-term variabilities and to untangle the intricacies of the Indian monsoons, we conducted India’s first sub-district -level monsoon variability assessment. Sub-districts in India are known as tehsils, talukas, mandals, circles and sub-divisions. However, we refer to them as tehsils in our study to align with the prevalent usage of the nomenclature across the majority of the country for these administrative units. We answer 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).

For this assessment, we utilised the most recent 12-km high-resolution reanalysis data sourced from the Indian Monsoon Data Assimilation and Analysis project (IMDAA). The 12-km spatial grid covered 4419 tehsils out of 4723 tehsils as per the Survey of India shapefile obtained. Our assessment delves into trends spanning the past four decades (1982–2022), with a specific emphasis on quantifying changes in rainfall patterns in the past decade (2012–2022) during the southwest monsoon (referred to as JJAS, since it occurs from June to September) and the northeast monsoon (referred to as OND, since it occurs from October to December). We undertook a geospatial climatological analysis, employing established statistical criteria and indices endorsed by the World Meteorological Organization (WMO) and the India Meteorological Department (IMD), to accurately assess and quantify these changes.

Key findings

In the past 40 years during the southwest monsoon, we found that India as a whole experienced 29 ‘normal’, 8 ‘above-normal’, and 3 ‘below-normal’ monsoon years. However, analysis of these trends at the district level showed that approximately 30 per cent of India’s districts witnessed a high number of deficient rainfall years and 38 per cent witnessed a high number of excessive rainfall years. Of this, 23 per cent 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.
Decoding these trends at an even more granular level, we found that 55 per cent of tehsils witnessed an increase in southwest monsoon rainfall in the past decade (2012-2022), by more than 10 per cent compared to the climatic baseline (1982–2011). A statistically significant JJAS rainfall increase was observed in the traditionally drier tehsils of Rajasthan, Gujarat, central Maharashtra, and parts of Tamil Nadu.
While the decreasing trends in southwest monsoon were not statistically significant continuously over forty years, we found that nearly 11 per cent of the Indian tehsils witnessed a decrease particularly in the past decade (2012-2022), by more than 10 per cent compared to the climatic baseline (1982– 2011). These are in the Indo-Gangetic plains, which contribute to more than half of India’s agricultural production, northeastern India, and the Indian Himalayan region. These regions also host fragile but highly diverse ecosystems. Of these tehsils, approximately 68 per cent experienced reduced rainfall in all months from June to September, while 87 per cent showed a decline during the initial monsoon months of June and July, which are crucial for the sowing phase of kharif crops.
In our study of localised wet rainfall extremes, we found that nearly 64 per cent of Indian tehsils experienced 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 of states with the highest GDPs – Maharashtra, Tamil Nadu, Gujarat, and Karnataka. Furthermore, we found that in the tehsils experiencing an increase in rainfall during the southwest monsoon, the excess is coming from short-duration, heavy rainfall events
The rainfall associated with the northeast monsoon (OND), which primarily impacts peninsular India, has increased by more than 10 per cent 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. While the remaining Indian states are usually dry during this period, we found a statistically significant increasing trend in the OND rainfall 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.
Further, the analysis of monthly variability indicated that nearly 48 per cent of tehsils in India saw an increased rainfall in October by more than 10 per cent, which could be due to the delayed withdrawal of the southwest monsoon from the subcontinent.

Figure ES1 The JJAS rainfall has increased in majority of the country, but decreased over Indo-Gangetic plains, north-eastern India and Indian Himalayan region in the last decade

Source: Authors’ analysis

Figure ES2 Both the western and eastern coasts of India have seen an increase in OND rainfall in last decade

Source: Authors’ analysis

Figure ES3 Majority of India’s tehsils in the north and east zones show high variabilities in monthly rainfall

Source: Authors’ analysis

Note: The states and UTs of Jammu and Kashmir, Ladakh, Arunachal Pradesh and Lakshadweep have not been included here due to lack of availability of tehsil-level name attributes in administrative boundary shapefile.

Conclusions and way forward

Mapping monsoon performance at more localised level based on our findings: Considering the evolving complex trends such as high month-to-month variability and increasing occurrence of wet extremes, localised decision-making is crucial for building resilience against monsoon variability. Presently, IMD provides monsoon information at country, zonal, state, meteorological sub-division, and district scales, which is based on existing observation stations. However, this network lacks the density needed to map the monsoon at a more granular administrative level. Therefore, we utilised reanalysis data from IMDAA to map monsoon variability for all tehsils in India for both JJAS and OND seasons. We have provided the coefficient of variation (CV) and long-period average (LPA) for all tehsils considered in this study in Annexure 1, following the WMO and IMD guidelines. Local level decision-makers should use these metrics for analysing local-level monsoon performance. This will provide comprehensive, actionable insights, enhancing disaster preparedness and response.
Development of district-level climate action plans incorporating tehsil-level climate risk assessments: In line with the MoEFCC’s 2019 directive, all the Indian States and UTs are revising their State Action Plans on Climate Change (SAPCCs) up to 2030. While the current plans focus on districtlevel climate risk analysis, our findings reveal availability of tehsil-level climate information. We recommend developing district-level climate action plans, integrating this information with socioeconomic and sector-specific data for detailed climate risk assessments in critical sectors like agriculture, water, and energy. The Global Goal on Adaptation requires updated climate risks assessments by 2030. However, current SAPCCs rely on prolonged climate projections upto 2050 and 2100 for adaptation strategies for the next decade. Hence, prioritising short-term projections, especially with advanced global weather prediction models at a 12-kilometre resolution as outlined in Ministry of Earth Sciences’ (MoES) Atmosphere & Climate Research-Modelling Observing Systems & Services (ACROSS) scheme, is crucial. Further, to make this climate information more accessible for a diverse range of stakeholders, collaboration among research institutions, meteorological agencies, and civil society is key, drawing inspiration from global best practices like California’s Cal-Adapt platform for tailored climate action plans aligning with local needs.
Investing in automatic weather stations and community-based recordings to capture rainfall variabilities at a hyper-local level: Our analysis highlights diverse monsoon patterns at the tehsil level, emphasising the need for hyperlocal climate adaptation strategies. The current, most-refined long-term observational rainfall data available, at a spatial resolution of 25 km, lacks the granularity required for precise climate models and local action plans. Alternative sources such as the 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.

FAQs

When is the monsoon season in India? Which type of monsoon is mostly seen in India?

The southwest monsoon is the primary monsoon affecting India, which occurs from June to September. Around June, the monsoon hits Kerala on southwestern coast, gradually progressing across the country. The monsoon's arrival is eagerly awaited as it 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, which affects the peninsular India and occurs from October to December. This monsoon is less intense compared to its southwestern counterpart but plays a crucial role in growing rabi (winter) crops and helps recharge groundwater.
How has the monsoon pattern changed in India?

The natural variability of Indian monsoons is further influenced by climate change, as revealed in our study. Traditionally monsoon-rich regions like Northeast India, the Indo-Gangetic plains, and the Indian Himalayan region experienced a decrease in the past decade. Conversely, traditionally drier areas, including Rajasthan, Gujarat, central Maharashtra, and Tamil Nadu, witnessed an increase in southwest monsoon rainfall. The northeast monsoon intensified in Tamil Nadu, and states such as Odisha and West Bengal on the east coast, as well as Maharashtra and Goa on the west coast, observed heightened October to December rainfall.
What are the factors affecting monsoons in India?

Several factors influence the monsoon patterns in India. The primary driver is the differential heating of the land and sea. During summer, the Indian subcontinent heats up, creating low-pressure areas. Meanwhile, the surrounding oceans maintain relatively lower temperatures, creating high-pressure zones. The resulting pressure gradient triggers the southwest monsoon, drawing moist air from the Indian Ocean. Other factors include the El Niño-Southern Oscillation (ENSO), with El Niño leading to drier conditions and La Niña enhancing the monsoon. The Indian Ocean Dipole (IOD) also plays a role, impacting sea surface temperatures. Additionally, features like the Tibetan Plateau, Western Ghats, and Himalayan mountains influence wind patterns, affecting rainfall distribution across regions.
How will the Indian monsoon change in the future?

As Earth's surface temperatures rise globally, the scientific understanding is that increased evaporation leads to a rise in overall precipitation. This phenomenon is anticipated to result in increased rainfall in various regions globally due to a warming climate. Projections over India align with this trend and an increase in both southwest and northeast monsoon rainfall in the country is expected, accompanied by more heavy rainfall days. Climate change projections for India indicate a substantial 10-14 per cent rise in southwest monsoon rainfall by the close of the twenty-first century.
How can India adapt to changing monsoon patterns?

Adapting to the evolving monsoon patterns necessitates a comprehensive approach, integrating policy, research, and citizen science. Initially, fostering more localised decision-making is essential, emphasising the creation of district and city-level climate action plans. These plans should incorporate climate risk assessments tailored for key sectors like agriculture, water, and energy. Secondly, critical sectors must undergo a strategic reevaluation and adjustment of their approaches in response to the shifting patterns. This entails recalibrating crop cycles and disaster management calendars, to align with the dynamic nature of the changing monsoons.