Table of Contents
- History & Background
- Annual & monthly rainfall pattern in India
- How unpredictable are India’s monthly rainfall patterns?
- Decadal rainfall pattern in India
- Seasonal rainfall pattern in India
- How unpredictable are India’s seasonal rainfall patterns?
- Anomalies observed in rainfall pattern in India
- Strategies and Supportive Measures
- References
History & Background
In ancient India, it was believed that the sun causes rainfall, encapsulated in the saying “Aditya Jayate Vrishti.” Good rainfall during the rainy season was essential for abundant agriculture and food supply. Kautilya’s Arthashastra includes records of scientific rainfall measurements and their implications for the country’s revenue and relief efforts. In his seventh-century epic ‘Meghdootam, ‘ the poet Kalidasa,’ mentioned the onset of the monsoon over central India and traced the path of the monsoon clouds. Indian classical music also celebrates the monsoons through several ragas.
Rainfall measurement is one of the key aspects of India’s meteorological studies, which significantly influences the country’s agriculture, water resources, and overall economy. The measurement is typically expressed in millimetres and recorded using rain gauges deployed across various regions. In this crucial process, the Indian Meteorological Department (IMD) plays a pivotal role in collecting, analyzing, and disseminating rainfall data, ensuring the nation’s preparedness and resilience.
Analyzing rainfall patterns is one of the crucial tools for disaster preparedness. It helps understand the distribution and intensity of precipitation across different regions and seasons, which is vital for agricultural planning and management. Monsoon rains, which account for most of the annual rainfall, are crucial for the country’s agricultural sector, which employs a significant portion of the population and contributes substantially to the GDP. Moreover, rainfall analysis aids in predicting droughts and floods, enabling better disaster preparedness and management. Accurate rainfall data is also fundamental for managing water resources and ensuring sufficient water supply for domestic, industrial, and irrigation purposes. Therefore, a comprehensive understanding and analysis of rainfall are vital for sustainable development and the resilience of India’s socio-economic framework.
The categorization of monsoon rainfall for the country as a whole depends on its deviation from the long-period average for the season of June to September. When rainfall is within 10% of this average, it is termed a “Normal” monsoon. An “Excess” monsoon occurs if rainfall exceeds 110% of the average, while a “Deficient” monsoon occurs when it falls below 90%. Monitoring smaller areas involves evaluating departures from the norm for each meteorological sub-division and district, classifying rainfall as excess, normal, deficient, or scanty based on specific criteria: Excess (+20% of normal or more), Normal (+19% to -19% of normal), Deficient (-20% to -59% of normal), and Scanty (-60% of normal or less).
Annual & monthly rainfall pattern in India
Table: 1
Table: 2
January and February show relatively low rainfall between 2001 to 2023, averaging 16.6 mm and 20.1 mm respectively. As the year progresses, rainfall gradually increases, reaching an average of 26.8 mm in March and 38.4 mm in April. May sees a more substantial rise to 62.5 mm, leading into the monsoon season. The monsoon months from June to September exhibit the highest rainfall, with averages of 162.1 mm in June, peaking at 276.8 mm in July, and then slightly decreasing to 245.1 mm in August and 174.8 mm in September. Post-monsoon, rainfall diminishes, with October averaging 74.4 mm and November dropping significantly to 27.0 mm. December records the least rainfall at 13.4 mm. This data underscores the monsoon’s pivotal role in India’s rainfall, highlighting July as the peak month and illustrating the stark contrast between monsoon and non-monsoon periods (fig: 1).
Fig: 1
Annual rainfall demonstrates considerable variability, ranging from a low of 953.7 mm in 2009 to a high of 1289.6 mm in 2020. Notably, 2019 and 2020 recorded the highest rainfall, exceeding 1280 mm. The early 2000s, specifically 2003 and 2005, also experienced significant rainfall with totals around 1242.8 mm and 1208.1 mm respectively. In contrast, 2002 and 2009 were relatively dry years with totals below 1000 mm (fig: 2).
Fig: 2
How unpredictable are India’s monthly rainfall patterns?
Decadal rainfall pattern in India
Between 2001 and 2010, the average annual rainfall was 1124.8 mm, which saw a slight uptick to 1135.2 mm in the subsequent decade (2011-2020). However, the period spanning 2021 to 2023 experienced a more notable increase to 1197.5 mm, despite covering only three years. This indicates an overall trend of rising rainfall, with a more pronounced acceleration in recent years. The initial increase from 2001-2010 to 2011-2020 was modest at 0.92%, whereas the leap from 2011-2020 to 2021-2023 was more significant, likely influenced by the condensed timeframe of just two years (fig: 4).
Fig: 4
From 2001 to 2010 and 2011 to 2020, the rainfall patterns showed remarkable similarity, except for August. However, between 2021 and 2023, significant fluctuations were observed both before and after the monsoon season, particularly in May, July, August, and September (fig: 5).
Fig: 5
Seasonal rainfall pattern in India
Table: 4
How unpredictable are India’s seasonal rainfall patterns?
During the winter season, the mean rainfall is relatively low at 36.7 mm, but it exhibits a high coefficient of variation (CV) of 38.4%, indicating considerable unpredictability in rainfall amounts. Conversely, the summer season, with a mean rainfall of 127.7 mm, shows a lower CV of 17.7%, suggesting more consistent rainfall patterns compared to winter. The monsoon season, characterized by the highest mean rainfall of 858.8 mm, has the lowest CV at 8.7%, reflecting the most reliable and predictable rainfall period. In contrast, the post-monsoon season, with a mean rainfall of 114.8 mm, has a higher CV of 27.6%, indicating moderate variability. This data underscores the pronounced differences in rainfall stability across seasons, with monsoon rains being the most dependable, while winter and post-monsoon periods exhibit greater unpredictability (fig: 6).
Fig: 6
Anomalies observed in rainfall pattern in India
The All-India Summer Monsoon Rainfall (AISMR) anomalies data from 2001 to 2023 show notable variability in the monsoon performance, with several years experiencing significant deviations from the mean rainfall. There is a high degree of variability in the AISMR anomalies over the years. The anomalies range from a low of -18.7% in 2009 to a high of 13.1% in 2019. Years with notable negative anomalies (drier conditions) include 2002 (-14.2%), 2004 (-9.2%), 2009 (-18.7%), 2014 (-9.0%), and 2015 (-10.8%). Years with notable positive anomalies (wetter conditions) include 2003 (10.3%), 2007 (10.0%), 2013 (9.2%), 2019 (13.1%), and 2020 (11.6%) (fig: 7).
Fig: 7
Strategies and Supportive Measures
The detailed analysis of rainfall patterns from 2001 to 2023 underscores the need for comprehensive and adaptive policy measures to address the challenges posed by India’s dynamic climate. By implementing these policy recommendations, India can enhance its resilience to climate variability, ensuring sustainable development and improved quality of life for its population.
India faces several critical challenges related to its rainfall patterns, significantly impacting water resource management, agriculture, and climate resilience. High variability and unpredictability in rainfall, particularly in January, February, March and November, create difficulties in agricultural planning and water resource management. The concentration of a substantial portion of annual rainfall during the monsoon months (June to September) exacerbates water scarcity during non-monsoon periods. It increases the risk of flooding during the monsoon. The recent trend of increased rainfall, particularly between 2021 and 2023, suggests a rise in extreme weather events, further straining infrastructure and livelihoods.
To tackle these challenges, India has the potential to implement a range of effective solutions. Enhanced water management systems, such as rainwater harvesting and improved irrigation infrastructure, can ensure water availability during dry periods. Promoting climate-resilient agricultural practices, including using drought-resistant and flood-resistant crop varieties and encouraging crop diversification, can mitigate the impacts of extreme weather. Investment in advanced meteorological technologies and forecasting models, along with the establishment of early warning systems, will provide accurate weather predictions and alerts for extreme events. Integrated Water Resource Management (IWRM) practices should be adopted for coordinated water management across sectors and regions, and infrastructure development, such as dams, reservoirs, and robust urban drainage systems, is essential for managing floodwaters and storing excess rainwater. Policy and regulatory measures aimed at sustainable water use and conservation and incentives for water-saving technologies will support these efforts. Public awareness campaigns and community-based water management initiatives will further enhance these strategies’ effectiveness. By adopting these multi-faceted solutions, India cannot only improve its resilience to climate variability but also ensure sustainable water resource management and support agricultural productivity, instilling a sense of hope and optimism for the future.
References
- Kumar, V., Jain, S. K., & Singh, Y. (2010). Analysis of long-term rainfall trends in India. Hydrological Sciences Journal–Journal des Sciences Hydrologiques, 55(4), 484-496.
- Jagannathan, P., & Parthasarathy, B. (1973). Trends and periodicities of rainfall over India. Monthly Weather Review, 101(4), 371-375.
- Singh, R. N., Sah, S., Das, B., Potekar, S., Chaudhary, A., & Pathak, H. (2021). Innovative trend analysis of spatio-temporal variations of rainfall in India during 1901–2019. Theoretical and Applied Climatology, 145(1), 821-838.
- Imd_It_Team. (n.d.). Rainfall Information | India Meteorological Department. https://mausam.imd.gov.in/responsive/rainfallinformation.php
- Subrahmanyam, K. V., Ramana, M. V., & Chauhan, P. (2023). Long-term changes in rainfall epochs and intensity patterns of Indian summer monsoon in changing climate. Atmospheric Research, 295, 106997.
About Author: Pankaj Chowdhury is a former Research Assistant at the International Economic Association. He holds a Master’s degree in Demography & Biostatistics from the International Institute for Population Sciences and a Bachelor’s degree in Statistics from Visva-Bharati University. His primary research interests focus on exploring new dimensions of in computational social science and digital demography.
Disclaimer: The views expressed in this article are those of the author and do not necessarily reflect the views of 360 Analytika.
Acknowledgement: The author extends his gratitude to the India Meteorological Department, Ministry of Earth Sciences for providing data support.
This article is posted by Sahil Shekh, Editor at 360 Analytika.