Confusing the Definition (part 2): Unraveling the Confusion

Ships from the East India Trading Company (source:

Ships from the East India Trading Company (source:

In my first snack in this series, I wrote that we need clearly defined concepts in science if we are going to carry out transparent and comparable research. The monsoon research community still disagrees about how to define the monsoon. This confusion can quickly propagate into decision-making practices, policy development and even further scientific research design.

In this snack I want to delve into this confusion in more detail and discuss how it has come about, and why it is still a problem. Why is there no universal definition for the monsoon? Why do scientists still disagree? The next few quotes illustrate the situation in monsoon science:

[…] early studies dealt with monsoon in terms of wind frequency (e.g. Ramage, 1971). Nowadays, monsoon is more generally applied to tropical and subtropical seasonal reversals in both the atmospheric circulation and associated precipitation (Zhang and Wang, 2008)

we defined the […] monsoon onset […] as the first pentad (5-day mean) in which the […] precipitation exceeded 5 mm/day [plus] the […] January mean. (Ashfaq et al, 2009)

[…] the occurrence of heavy rainfall during the seasonal transition period does not necessarily represent the Asian Summer Monsoon (ASM) onset. (Zhang et al, 2004)

Irrespective of the confusion, rainfall is obviously an important parameter and many researchers use rainfall or precipitation indices to define the monsoon (eg. Ashfaq et al, 2009 Zeng and Lu, 2004). However, it hasn’t always been this way. As the first quote illustrates, wind was previously the main monsoon-defining parameter. What has brought about this change? I would argue that the needs of society have played a role. I think it is sciences response to these changing needs that is our first source of confusion.

A wind-based definition of the monsoon may have previously dominated for very good reasons. It was the Romans and Greeks who first discovered the Monsoon’s potential for oceanic trade as early as 45-50 AD (Tripati and Raut, 2006; D’Souza, 2008). The power of this trade was further fuelled by colonialism, slavery and the rise of consumerism during the second half of the last millennium. The rich and wealthy aristocrats in Europe pined for the newly discovered luxuries: Coffee and tea from Asia, Ivory from Africa and spices from Arabia. For better or worse, the Monsoon played a huge part in the making of the modern world. Wilbur Smith vividly describes how dependent this trade was on the monsoon winds:

[Zanzibar] lay full in the track of the monsoon winds, which reversed themselves with the change of the seasons. The south-easterly monsoon carried shipping from India to Africa, and when the season changed, the north-westerly monsoon facilitated the return trip. (p.235)

If you had asked someone at the East India Company -which traded from Europe to India via Zanzibar in the 1700’s- what the monsoon was, I would put money on the fact that they would relate it to wind. Back in those times, Britain was the Empire. Britain was rich and powerful. The monsoon winds made Britain and other trading countries a lot of money. Therefore, if Britain had researched the monsoon, then wind and circulation patterns would have been the focus.

Today, the monsoon winds have (relatively) little influence on global trading success. Nowadays, it’s difficult to think of a more important parameter for a rain-dependent agricultural economy (like India and Bangladesh) than rainfall itself. Definitions change and science adapts to cater for the needs of society. But if we agree on that, why is there still confusion?

Catering for the needs of society is but one of the main objectives of science. I think science has two main (but not mutually exclusive) goals. One goal is societal advancement (research for the sake of society) and the other goal is scientific advancement (research for the sake of science itself). I believe that confusion about these objectives has also leads to much confusion concerning how we define the monsoon, and not least for whom.

The problem for monsoon science is that the two objectives (societal and scientific advancement) can lead to research with very different scales of focus. For the sake of advancing science, we may want to look at the large-scale meteorology in order to understand the dynamics of the whole monsoon system. For the sake of society, we may want to look at the local-scale rainfall in order to provide information that can be used by local communities.


Trends in total May-October rainfall for northern India and Bangladesh between 1978-2007. The trends are calculated from APHRODITE rainfall data. The trends are simply given as +ve and -ve to illustrate the variations over the whole region. The trends for Beriyarpur and Kirnapur are discussed in the text.

If these different objectives lead to research at different scales, then how can this affect the information that is produced? If we take a closer look at some climatological features from the South-East Asia monsoon region we can see that the large-scale situation does not necessarily correspond to what happens at the local level. We illustrate the complexity by looking at the trends in total May-October rainfall between 1978-2007 as shown for northern India and Bangladesh (see the figure above). The average trend over the whole region was +1.0 mm/year (not statistically significant). This information is meaningless to someone in Bariyarpur in northern Madhya Pradesh where the monsoon months seem to have become wetter by an average of +12.5 mm/year (statistically significant to 95%). The large-scale trend seems equally meaningless to someone from Kirnapur in south-east Madhya Pradesh, where the trend was -13.4 mm/year (statistically significant to 90%) during the same period. While the information about the large-scale trend might be insightful, it is clear that it cannot necessarily be applied to local communities. The link between the large-scale and society is weak at best. With respect to the question of how we define the monsoon, a large-scale approach/framework may result in an inapplicable definition at the local-scale and vice versa.

It was very recently stated in a paper yet again that ‘There is currently no universally accepted definition of monsoon onset […]’ (Adamson and Nash, 2013). Confusion about how to define the monsoon is therefore still prevalent. I have presented two interlinked reasons for this: firstly, that the changing needs of society and secondly, the intertwined objectives of science.

Even if the needs of society and the objectives of monsoon science are clear in our heads, I think confusion would still prevail for a single important reason: communication, or lack of it. It is possible that poor communication is the root and good communication is the solution to all the previous confusion. I will be deliberating on this in more detail in my next snack where I will propose some solutions and discuss how important it is to accurately frame our scientific articles.


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Mathew Stiller-Reeve

I am a postdoc researcher at NORCE Climate and the Bjerknes Centre for Climate Research. I research the monsoon in Bangladesh and I am the founder of ClimateSnack; a community that hopes to give all young and early career climate scientists an opportunity to practice and improve their scientific communication skills.

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