Monsoon systems are crucial for the survival of the Indian subcontinent, but they are threatened by climate change.
We are all familiar with climate change headlines including fear-inducing topics concerning extreme weather events and the shifting of the climate. Climate change impacts weather equilibriums and phenomena, and understanding how it occurs and may develop is essential for its mitigation. Monsoons are seasonal weather events that have a large impact on people’s livelihoods and water availability. Any slight changes in environmental factors already have a noticeable effect on people and the planet. Monsoon systems influence the climate in a majority of India. Understanding monsoons can help us make better climate policy decisions in the affected regions.,
What are monsoons?
Monsoons can be defined by the stark differences in precipitation during winter and summer, and the yearly switching of surface winds. They result from the annual movement of the Intertropical Convergence Zone, where the northeastern and the southeastern trade winds meet. Monsoons usually occur in tropical and sub-tropical climatic zones. Climate zones can be differentiated based on weather characteristics such as precipitation, temperature, humidity, and seasonal trends. Additionally, the presence of a large oceanic surface is essential for their formation, due to the contrast in temperature between the ocean and land.
Heated water from the ocean evaporates and moves over the land, which has heated up more than the water during the day and the area above it has a lower pressure. As the air parcels containing water move over the terrain with a higher temperature, precipitation occurs. Monsoons were previously geographically linked to the eastern hemisphere, specifically South Asia. Nonetheless, thanks to a new definition of the phenomenon, monsoons can also be identified in the Western hemisphere. The strongest monsoon system does however exist across Asia, with South Asia being one of its subsystems and impacting India. Above you can see a map of the Southwest Monsoon over India and the difference between the actual and usual days of onset.
Monsoon systems are complex with many variables at play, however, there are a few key drivers that define them. The main drivers of monsoons are solar radiation (heating), topography, differences between land and sea, and ocean circulations. There are variations of monsoon systems, caused by external (large scale, long term) and internal (regional, short term) factors. Regional variations in monsoons are caused by topographic features and variations in region-specific interactions between the land and ocean. For example, the Tibetan Plateau heats during the summer months and reinforces the temperature differences with the land in the south. Variations in circulation, such as trade winds and jet streams as well as upwelling in the west of the Arabian Sea which is partly caused by incoming winds from Eastern Africa are other examples of this.
How do monsoons influence humans?
Many people die each year due to flooding, houses are destroyed, and lives are turned upside down as a result of monsoons. Moreover, monsoons have impacted the livelihood of people, the migration, and the establishment of human populations since the start of settlements. Water availability - especially freshwater - and local temperature influence the distribution of populations by driving the availability of resources, local ecology, and ease of agriculture. Summer rains resulting from the monsoon have played a large role in the location, creation, and collapse of human settlements. During the late Holocene, the Indus Valley hosted thriving settlements, thanks to the availability of water and fertile soils, which were maintained by summer rain from the monsoons. 4,200 years BP there was a decline in summer monsoon rains caused by global changes in the climate, which halted the development in the Indus Valley. Changes in precipitation and temperature impact the feasibility of an area as an ideal settlement. Understanding how variations in the monsoon systems impacted civilisations in the past is fundamental for predicting how future changes might impact humanity in the future.
How might monsoons change in the future?
Solar radiation is the main determining factor of monsoon systems because the creation of the monsoon rides on large contrasts in temperature. Thus, monsoon systems are highly sensitive to temperature differences and human-induced global warming and are highly susceptible to alteration. To what extent monsoons will be impacted on a larger time scale depends on how much the temperature increases. Depending on which emission projection, and thus temperature projection, the effects can vary. One example of altered monsoon ecosystems is the changing monsoon patterns in Mumbai. In the past cyclones formed in the central Arabian Sea but steered clear of Mumbai due to steering winds that would direct the cyclones towards Oman and Yemen. However, ocean warming has weakened the steering winds that control these mechanisms, and thus the direction of cyclones has changed.
An increase in temperature will impact the water cycle and hydrological balance. Researchers predict that there will be an increase in the average rainfall, caused by an increase in water vapor coming from the ocean. Furthermore, at a higher temperature, the air can retain more moisture, therefore, rainfall is likely to be more intense and there will be a larger quantity of rainfall over a short period of time. Rainfall during the monsoon season in India varies by around 10% each year, however, it is estimated that with an increased temperature this would add another 5-10% of variability making water availability for personal consumption, sanitation, and agriculture even less predictable. These changes are evident in heavy spells of rain causing severe landslides in regions like Wayanad, Kerala earlier in 2024.
In the context of India, depleted groundwater levels are a national concern, with the variations in precipitation due to monsoons already causing irregularities in water supplies. To what extent changes in the climate due to global warming will impact the monsoon is still unclear and there are still a lot of unanswered questions. Nevertheless, research has shown that the distribution of the monsoon system and rainfall has already shifted. In Northern India, a pattern of less precipitation during the monsoon period has been observed in addition to higher temperatures during the winter. This has caused a reduction in groundwater that is expected to further increase with higher temperatures. An increase in temperatures will also require a larger input for irrigation while at the same time reducing groundwater stocks, this will further deteriorate water security and ask for creative and sustainable solutions to be implemented
Future impact
Hydrological cycles: Monsoons are an essential component of the planet’s hydrological cycle, and they have also been seen as factors of climate change in the past. Past changes in the monsoon system have caused changes in precipitation patterns and have led to flooding and droughts. If major, these changes have caused the deterioration of civilisations in the Indus Valley in the past. Although we live in the age of modern technology and there are options for retrieving water from other sources and/or importing it, a decline in water available, especially in areas that are already under stress and don’t have easy access to other sources will have grave effects. Subsistence farmers and people living in rural areas are more dependent on monsoon rains for water and would suffer more under droughts and floods. The Kedarnath flood which occurred in 2013 and the glacial outburst in Uttarakhand from 2021 are examples of how even slight changes in temperature and the climate can lead to knock-on effects. However, there are emerging solutions to combat water shortages such as the use of bunds to capture rainfall during monsoons.
Climate change will increase evaporation rates which will also intensify drought and desertification in certain areas. Combined with changes in monsoons, temperatures and equilibriums between the sea and land, this may also increase the areas that suffer from droughts. Since the turn of the 21st century, the monsoon system has already changed, exhibiting more floods in the south of India and more droughts in the north and Northeast. Loss of mangroves in coastal regions and loss of forest covers in the Northeast are worsening the effects of altered hydrology. There is a high possibility that this trend will intensify leading to further changes in hydrological equilibriums and potentially also shifts in climatic zones.
Nutrient cycling: In the northern Arabian Sea, an alternation in monsoon winds may cause increased upwelling of nutrients which could also impact coastal ecosystems. Changes in the hydrology will impact erosion, soil stability, and nutrient cycles as well. Heavier rainfall could lead to more nutrient losses, as nutrients such as nitrogen and phosphorus which are essential for plants will be leached out of the soil and flushed into water systems. The increased influx of nutrients into water bodies also leads to algal blooms that may lead to eutrophication. With a higher risk of erosion and a higher density of rainfall, surface runoff and the risk of flooding are increased. On the other hand, a decrease in rainfall, such as can be further expected in northern India, reduces the release of nutrients into the soil due to a lack of moisture and thus decomposition.
As previously mentioned climate change will increase evaporation rates which will also intensify drought and desertification in certain areas. If the range of the monsoons is changed due to changes in temperature and equilibriums between the sea and land, this may also increase the areas that suffer from droughts. Since the beginning of this century, the monsoon system has already changed, exhibiting more floods in the south of India and more droughts in the north. There is a high possibility that this trend will intensify leading to further changes in hydrological equilibriums and potentially also shifts in climatic zones.
Way forward
As with many issues related to climate change, there are a plethora of unknowns. Climate systems are innately complex and impacted by a large variety of factors. However, keeping an eye on the driving factors can help us predict extreme weather events like cyclones and floods, and these warnings should be taken seriously by world leaders. It is also essential for the monsoon predictions to be taken into account during urban planning, city management, and governmental decisions. How much the temperature changes depends on human advancements towards a net-zero emission world and the use of carbon capturing and nature-based solutions. Unfortunately, the temperature will increase regardless of the changes we make — but we can significantly reduce how far it increases and reduce its impact.
It has become clear that monsoon systems will be impacted by an increase in temperature and change in climate dynamics, and that this will impact human civilizations just like it has done in the past. It is crucial that we better understand the monsoon systems and develop detailed models for how they may change. Having more precise information about how the monsoon system will change will help prepare the most affected areas.
References
Fernandes, S. (2020, June 2). How Mumbai steered clear of cyclones. Hindustan Times. https://www.hindustantimes.com/mumbai-news/how-mumbai-steered-clear-of-cyclones/story-LKPqsXxe1beBuyL6DdhX7K.html
Laskar, A. H., & Bohra, A. (2021). Impact of Indian summer monsoon change on ancient Indian civilizations during the Holocene. Frontiers in Earth Science, 9. https://doi.org/10.3389/feart.2021.709455
Mishra, V., et. al. (2024). Summer monsoon drying accelerates India’s groundwater depletion under climate change. Earth S Future, 12(8). https://doi.org/10.1029/2024ef004516
The Indian Monsoon in a Changing Climate. (n.d.). RMetS, Royal Meteorological Society. https://www.rmets.org/metmatters/indian-monsoon-changing-climate
Wang, B., et. al. (2021). Monsoons Climate Change Assessment. Bulletin of the American Meteorological Society. 102), E1–E19. https://doi.org/10.1175/BAMS-D-19-0335.1
Wang, P. X., et.al. (2017). The global monsoon across time scales: Mechanisms and outstanding issues. Earth-Science Reviews, 174, 84–121. https://doi.org/10.1016/j.earscirev.2017.07.006
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