Environmental Cluedo

It's like environmental Cluedo; we have the victim - Harappan Society, we have the location - the Indus Valley, we just need to find out who did it...The Holocene has played host to some of the most iconic civilisations seen on Earth, evidence of which litters the globe, but many have found their demise at the hands of Mother Nature (McMichael, 2012; Figure 1). Today I want to look at human civilisation in the South Asian monsoonal regions through the Holocene, with a focus on the Harappan Civilisation.

Comparison of historical and climate events since 8 ka (Clift and Plumb, 2008:199)

The earliest evidence of human settlement in the Indian subcontinent is all found in western Pakistan and eastern Afghanistan and dates from 7000 BCE. These settlements, known as the Mehrgarh Culture, were Neolithic in their nature and there is evidence of farming of wheat and barley alongside herding of livestock (Clift and Plumb, 2008:207). The bulk of the evidence, or distinct lack of, points towards a hunter-gatherer society during the Early Holocene (Clift and Plumb, 2008:200) until the Mid Holocene (~7000 - 6000 BCE), when the climate became much drier and human societies formed as a result of the need to work together to find food (deMenocal, 2001; Clift and Plumb, 2008:200). 

It is from the Mehrgarh Culture that the Harappan Civilisation emerged around 3300 BCE during a period of increasing aridity (Madella and Fuller, 2005); by 2600 BCE it had become a complex civilisation with grid format cities, written script, water supply systems and the world's first urban sanitation systems (Clift and Plumb, 2008:227). Along with well developed agricultural systems, complex trade is also evident in Harappan society, an example of which are the ruins of Lothan Port (Figure 2). Indeed, Harappan artefacts such as carnelian, pearls, lapis-lazuli and woods have been found as far as the Akkadian empire of Mesopotamia (MacDonald, 2009). 
  

The Harappan engineers must have possessed great knowledge of tides and hydrology as they built this structure (assumed to be a port) on the Sabarmati river and included both inlet and outlet flows and wooden gate systems to maintain the water levels (Image).

Then an apparent threshold was breached around 2200 BCE...the 'Urban Harappan' period, where the population lived in organised cities, moved to the 'Post-Urban Harappan' period, where the population moved to smaller settlements and migrated south-eastward (Clift and Plumb, 2008:208). Madella and Fuller. (2006) have also suggested an increase in Harappan rural settlements in the wetter foothills of the Himalayas and also the Ganges watershed. It was also at this time that the ancient civilisations of Egypt and Mesopotamia came near to or did collapse (Straubwasser et al., 2003) so what was the cause? 

A common suggestion is an intense drought associated with a weakened monsoon. Straubwasser et al. (2003) explored this possibility, with the use of oxygen isotope analysis (δ¹⁸O) of planktonic foraminifera from cores around the Indus delta mouth. They linked a change in the δ¹⁸O to increased salinity in the ocean around the Indus delta, the cause of which was identified as reduced flow from the Indus river linked to a rapid weakening of the SW monsoon. Solar variability (from ¹⁴C records) has been proposed as a driver for this (Straubwasser et al., 2003) and earlier events (Neff et al., 2001), as has changes in the Pacific Ocean in the form of ENSO events (MacDonald, 2009) but both still have uncertainties attached. 

Another interesting possibility involves the disappearance of rivers...the Saraswati River in particular. This river ran sub-parallel to the Indus and drained the western Himalayas, transporting water to the Arabian Sea. The river is mentioned in the Sanskrit Hindu holy text - Rig Veda - 72 times and is noted to be of a similar size to the Indus itself, and yet this river does not exist today. Of the 2600 Harappan sites discovered thus far, 2000 of them were located on on the palaeo-channel of the Saraswati River (Clift and Plumb, 2008:210). Regardless of what drove this change, the results of the drainage piracy/drainage capture of the Saraswati River would have impacted the populations it sustained dramatically, although further study is again needed to calibrate this to the historic events (Figure 3). 

Satellite map of the Indus River Valley with the modern day Indus River and the palaeo-channel of the Saraswati River. The hexagons are Harappan sites and the triangles are early farming sites of the Mehrgarh Culture (Clift and Plumb, 2008:206)

Undoubtedly the change in climate would have had a detrimental affect upon the ability of the Harappan Civilisation to sustain themselves, but how much impetus we place on environmental determinism is open to debate. To definitively say that climate caused the collapse is impossible as it is merely an assumption of the proxy data, but I tend to air towards climate being a major influence with its effects dependent upon societal susceptibility and exacerbated by a mix of other factors. Two big questions remain...firstly, how will future changes in the monsoon impact upon relations between various nations and secondly, do you think we have solved the clues and won the game....or is the culprit still out there?

IPCC Headlines

What’s the latest…The IPCC released the Assessment Report 5 (AR5) at the end of September 2013 and I thought it apt to take a quick look at the monsoon headlines from the Summary For Policymakers to better equip ourselves with the latest global projections before venturing onwards…

• “Some important climate phenomena are now better reproduced by models. There is high confidence that the statistics of monsoon and El Niño-Southern Oscillation (ENSO) based on multi-model simulations have improved since AR4.”

• “Globally it is likely that the area encompassed by monsoon systems will increase over the 21^st century.”

• “While monsoon winds are likely to weaken, monsoon precipitation is likely to intensify due to the increase in atmospheric water.”

• “Monsoon onset dates are likely to become earlier or not to change much.”

• “Monsoon retreat dates will likely be delayed, resulting in lengthening of the monsoon season in many regions.”

...so what does this mean for the South Asian monsoon in particular...well that's our stop in a couple of posts time...all aboard!! 

Life goes on in Mumbai during the monsoon (BBC)

NB: In all of the above quotes from the AR5 report, likely indicates the assessed likelihood of an outcome or a result at 66-100%. The IPCC AR5 also has sections on all of the global sub-system monsoons and it's well worth a read if you're interested!

At the mercy of demonic powers

Religion...monsoons…not necessarily a link that would immediately spring to mind, however the two are intrinsically entwined and have been since the dim and distant past. Today I thought we’d look past the science for a moment and better equip ourselves to understand not only what the monsoon means to the population, but what it ‘means’ to the population. 

Praying to the gods to provide rain to sustain crops and livestock is not a practice limited to the bounds of Asia, though it is here that the rains and the rivers themselves have gained immortal status (Clift and Plumb, 2008:223). The monsoon is a time of celebration; one festival, Kumbh Mela, is held every three years with millions attending (Figure 1). It is also a time associated with fear; during the four month monsoon season in India, it is said that Vishnu heads below the ocean to sleep and thus the Earth is under threat from demonic powers (Clift and Plumb, 2008:225).

Figure 1 - Bathing in the holy water of the Ganges on Makar Sankranti, the
first day of Maha Kumbh Mela, Allahabad, India (Daily Telegraph, AU)

The River Ganges, whose flow is fed by the monsoon, is one such sacred river and the tale of its formation is an interesting one…

   

The Ganges is personified by the Goddess Ganga (Figure 2) who is integral to the formation of the River Ganges. In one such tale she was formed after Brahma (the creator god) had washed the feet of Vishnu (the sustainer god) and it was from this water that Ganga emerged. Our tale progresses to a time where King Sagara, a Vedic King, magically attained sixty thousand sons and performed a ritual for the good of his kingdom; a ritual requiring a horse. Upon finding the horse had been stolen, King Sagara sent his sons out to search, and they discovered the creature in the underworld beside a meditating sage. Accusations of theft and insults rained down causing the sage to open his eyes for the first time in years, upon which all sixty thousand were burnt to death and their souls bound to walk the Earth as ghosts (The Life of Ganga)

Figure 2 - The Goddess Ganga standing upon a lotus
(British Museum Collection)

Some time later, Bhagiratha, a Hindu King and descendent of one of the unfortunate souls wandering the Earth, prayed to Brahma that his ancestors souls could be freed to proceed to heaven. Brahma sent Ganga down, first to the Earth to free Bhagiratha's ancesters, and then onto the nether regions. Ganga, somewhat aggrieved by this turn of events, vowed to destroy the Earth as she fell from the heavens. Bhagiratha, upon discovering this, prayed once more, this time to Shiva (the destroyer god) for help. Ganga’s decent was interrupted as she fell onto Shiva’s head and became bound within his hair, where Shiva broke Ganga up into smaller streams and saved the Earth. Ganga for her trouble, ended up passing into the nether regions but left a different stream on the Earth, one that would serve to purify souls and thus the Ganges was born, its heritage to the gods and link to the monsoon cemented (Clift and Plumb, 2008:225). For many the monsoon and the rivers it feeds are not just the life-blood of the land, but so much more. I think to truly understand the monsoon, you must have an appreciation of how ingrained it is in both the daily lives and the culture of millions...

Whats, Whys, Wheres & Hows…

Before delving any further into this blog, I thought it might be worth a quick review of the whats, whys, wheres and hows of the Asian monsoon...

The Asian monsoon system, sometimes referred to as the Asia-Australian monsoon, affects almost two-thirds of the world’s population and demonstrates the influence of Mother Nature on mankind (Clift and Plumb, 2008: vii). The South Asian monsoon is a sub-system of the Asian monsoon, affecting the Indian subcontinent and its surroundings, and is formed of two distinct periods; the South-west monsoon and North-east monsoon (retreating monsoon).

In its simplest form, the South-west monsoon is driven by seasonal cycles of solar heating whereby the land undergoes much more rapid warming than the adjoining seas, therefore developing a large scale temperature gradient (Turner and Annamalai, 2012). In the case of the South Asian monsoon, temperatures in the interior of the subcontinent regularly exceed 40°C, creating a north-south pressure gradient as shown in Figure 1.

Figure 1 - Formation of the Indian monsoon circulation with strong heating over Tibet in Summer, causing the rising of air that flows equator-wards aloft, which then causes moist air to be drawn in from the equator (Clift and Plumb, 2008: 17)

Coupled with this, the northern Indian Ocean, especially the Arabian Sea and the Bay of Bengal, SSTs (sea surface temperature) have warmed and can provide the moisture-laden winds required to drive the monsoon. Deep convection still does not occur though as the MSE (moist static energy) over the land surface is still less than that over the oceans. Once overcome, deep convection and rainfall occurs fairly rapidly (Figure 2) up to approximately 20° N and the South-West monsoon circulation is established.

Figure 2 - Evolution of the wind speed over the Arabian Sea throughout the year (day 1 is January 1st). The vertical lines represent the rapid onset of circulation between day number 142 and 160 (Clift and Plumb, 2008: 17) .

The temperatures in the subcontinent decrease somewhat and as a result cooler air, that is full of moisture, moves inland and the monsoon rain belt moves northwards (Figure 3).  This process contributes 80% of annual rainfall to South Asia between the four months of June-September (Turner and Annamalai, 2012). The North-west, or retreating, monsoon occurs around October when the winds reverse direction and is a much more gradual process than the onset of the monsoon and lasts to the end of November.

Figure 3 - Wind currents and ITCZ in the time frames for the onset of the Indian monsoon (Burroughs, 1999:138)

Orography of the Himalayas and Tibetan Plateau have a profound impact upon the monsoon and arguably have done so since the Indian and Asian plates collided around 45-55 Ma, forming the landscape we recognise today. Prior to this the monsoon would have existed but it is believed that the intensity would have been much lower, as Asia was both smaller and less elevated (Clift and Plumb, 2008: 29). Prell and Kutzbach (1992) note from General Circulation Modelling experiments, that  the elevation of Tibet-Himalaya has to be at least half of today's value to have a strong monsoon that is driven by solar forcing. The shear scale of the Himalayas means that they are able to disrupt atmospheric circulation and in the case of the South Asian monsoon, act as a barrier causing the uplift of moisture-laden air over a large depth of the troposphere and "anchoring the monsoon onset and intensity" (Turner and Annamalai, 2012). 

The take home message from all of the above...the Asian monsoon really is a "fully coupled ocean-land-atmosphere system" (Turner and Annamalai, 2012), and it is the interactions between processes on a global scale that make it one the the most dramatic phenomena on the planet. It's a highly sensitive system, both to short term variations such as ENSO/snow cover and by orbital forcing on even longer timescales (something I'll come back to another time!). Humanity has become a force perhaps as great as nature and I think that given that the phrase 'low confidence' appeared in the IPCC AR5 a total of 295 times, there is still much that is not fully understood and thus the consequences of our actions could be catastrophic. 

Today I'll finish off with this...

"For millennia, humans have behaved as rebels against a superpower we call "Nature." In the 20th century, however, new technologies, fossil fuels, and a fast-growing population resulted in a "Great Acceleration" of our own powers. Albeit clumsily, we are taking control of Nature's realm, from climate to DNA. We humans are becoming the dominant force for change on Earth. A long-held religious and philosophical idea - humans as the masters of the planet Earth - has turned into a stark reality. What we do now already affects the planet of the year 3000 or even 50,000." (Crutzen and Schwägerl, 2011).

Gathering Clouds

First and foremost, welcome to my blog! As a complete blogging newbie, it is with a little apprehension and a lot of excitement that I dive off of the metaphorical cliff into the depths of this subject (perhaps stepping out into the storm may well be more apt). This blog has been set up for the Global Environmental Change module at UCL, as an attempt to explore a wealth of information and put across my, and of course your own should the mood take you, opinion on a subject that I find compelling – the South Asian monsoon.

In this blog I hope to answer and better understand the potential effects of climate change on the Asian monsoon and what this could mean for the physical geography, biodiversity and future generations dwelling within its influence alongside its wider scale implications. I am sure that over the course of the blog I will lead you on various interesting tangents, however to propel myself in reasonably the right direction and allow you all to understand the wider context of my posts I aim to review:

Where to start? Why at the beginning…