Paradoxical Drought...

Palaeoclimatic evidence suggests with medium confidence that there have been megadroughts associated with the Asian monsoon system throughout the Holocene (AR5; Cook et al., 2010). Additionally, Levermann et al. (2009), defined the two stable states of the monsoon; wet or dry. Despite the increased frequencies of extreme precipitation events (Goswami et al., 2006) and models predicting an overall increase in precipitation (Turner and Annamalai, 2012), drought through monsoon failure and/or over-usage of water resources, remains a risk to the South Asian regions and thus is the focus today...

Figure 1 - During the dry months, lack of storage
facilities means many have to walk kilometres to
find clean water (Times of India; Image source).

The Paradox - Cherrapunji, Meghalaya state, India. This village holds the world record for the most rainfall in one calendar month - July 1861 at 9300 mm, and over a 12-month period - August 1860 to July 1861 at 26461 mm. The 40 year average (1973-2012) still puts the value at 11859.4 mm, with the majority falling Mar-Oct and no or nominal rainfall Nov-Feb (Indian Meteorological Department). Despite this, during Nov-Feb the region experiences acute drought (Figure 1). Locals point to large-scale deforestation for drying up local springs but the main issue, reminiscent of so many areas in South Asia, is the lack of water capture and storage facilities.

The Himalayan/Karakoram mountain ranges feed many of Asia's greatest rivers, supporting over a billion people, and are thus known as 'Asia's Water Towers' (The Economist). In GHGs, Aerosols and Cookfires, I mentioned the reduction in black carbon through utilisation of cleaner cookfires, as a saviour of the glaciers. This may have been a little optimistic! IPCC AR5, suggests that despite a few glaciers advancing, the majority are in retreat (High Mountain Asia = losses of 26 ± 12 Gt yr⁻¹). In addition to this the levels of snowfall cover also appear to be reducing (AR5). Immerzeel et al. (2010) note that the contribution of glacial melt to the discharge of the Indus and Ganges is at 40%, using the Normalised Melt Index. Thus, in the short term discharge values will increase. However in the long-term, unless any action is taken it could result in far reduced discharge rates and the rivers becoming even more seasonal, causing further reductions in water security (Immerzeel et al., 2010).

Figure 2 - Villagers crowing around a well to gather water during 
a drought in Natwarghad, Gujarat state, India (Source)

Approximately 85% of all India's freshwater is utilised for agriculture, with groundwater forming the backbone of the agricultural sector, accounting for 59% (35,372,000 hectares) of all irrigated land in 2005-06. Approximately 85% of the population rely upon groundwater for drinking, which combined with agricultural use, make India the largest global groundwater user at 230 km³/yr. Rains account for ~67% of annual groundwater recharge, thus drought can severely impact upon water security of the country (Tyagi et al., 2012; Figure 2). Furthermore, a recent article in National Geographic, shows the impact of agriculture upon the Indus river as it flows through Pakistan; the heavy demands placed upon it have caused a 90% reduction of water reaching the delta over the last 60 years, impacting upon biodiversity such as Indus River Dolphin and the delta human populations. As with India, additional stress through drought may be catastrophic.

Next up...putting this and Dark Clouds - Silver Linings into context...agriculture 

Dark Clouds - Silver Linings...

And the rain rain rain, came down down down...

• Increased extreme events and fewer weaker events (Goswami et al., 2006)
• Lengthening of the monsoon season with earlier onset and later retreat (AR5). 

The nature of the future monsoon could have a variety of effects, aside from the more obvious incantations seen in The Himalayan Tsunami. Extreme precipitation events will lead to flooding, with Guha-Sapir et al. (2011) noting in their study, that over half of disasters were accounted for through flooding between 2001-2010. This is the focus of this post...

  

Figure 1: Monsoon flood driven infrastructure damage (ABC News)

Infrastructure damage is an annual by-product of the monsoon (Figure 1). It is often the indirect impacts of such things as road damage, that can isolate areas from medical/aid facilities, exacerbating the situation (SREX Report). In India for example, 845 million people live in areas defined as rural, thus infrastructure damage has a large influence (World Bank). Impacts are often greater due to the number of the population residing in at risk areas; globally 800 million people live in flood-prone areas - 10% of these experiencing annual flood risk (Peduzzi et al., 2011 in SREX Report). River evolution/erosion is also intensified due to land-use change; deforestation and increased soil saturation due to irrigation, can increase run-off and destabilise river banks, thus the associated risks increase (Niyogi et al., 2010; BBC: River Erosion). Lack of long-term planning is exposed during disaster response with a focus on rapid rebuilding, which can "recreate or even increase existing vulnerabilities" (SREX Report:293). Other smaller scale infrastructure damage can also become a danger and often a source of frustration/anger for the population (NDTV: Mumbai Potholes & Crumbling Infrastructure). 

Widespread contamination of water sources also occurs due to flooding. For example - the 1998 floods in Dhaka, Bangladesh, were associated with high numbers suffering from diarrhoea, especially those that did not have access to tap-water (Hashizume et al., 2008). Other water-borne diseases such as dermatosis, cardiovascular disease and gastrointestinal disease can result from pollution 'in-wash' into water sources through flooding (AR4). Additionally, Fritze et al. (2008) studied the effects of mental illness resulting from extreme events such as flooding. Often overshadowed by the physical impacts, such afflictions as PTSD, anxiety and depression are common (SREX Report). Effects are often long lasting, with those affected suffering from various disorders or even resorting to drug/alcohol abuse (Fritze et al., 2008).    

Figure 2 - Adapted groundwater resources (Taylor et al., 2012)

There are of course silver linings (pun intended). The most obvious of which is the potential for bumper crop years but that is for another post. Population growth coupled with increased demand will stress groundwater resources. The Indo-Gangetic Plain is a major regional water source (Figure 2) for Northern India and will benefit from the increased precipitation (Taylor et al., 2012), benefiting the economies in the area which all have a high dependence on agriculture in terms of GDP (World Bank). There are also other more unexpected benefits as a consequence of the monsoon rains (BBC: High Wire Fishing). Thus, the future of the monsoon may benefit the region in some ways, but the focus must be on adaptation/mitigation to the impacts that heavy precipitation events will bring...if this is not achieved the costs may far outweigh the benefits.  

Next up is drought.

Bada Din...Shub Naya Baras!

A Christmas tale from the land of the South Asian monsoon...

A part of the British Empire until 1947, some relics of that time remain in India today. Though predominantly dominated by Hinduism (80.5%) and Islam (13.4%), there are also 2.3% of the population practising Christianity. That doesn't seem a lot but with a population of over a billion, it equates to over 24 million people (Census India, 2011). Christmas, known as Bada Din ("Big Day"), is celebrated in much the same fashion as the UK, but some elements have a twist..."Servants are given baksheesh (money tips) by their employers, lemons (a symbol of esteem) are offered with the hope that they will give long life and prosperity, the populations of the plains form Christmas trees from straw, twigs and mud and adorn them with candles, the aboriginal Bhils have all-night caroling sessions for the whole of Christmas week, in other areas homes may be decorated with mango leaves, and in the south diyas (lit oil lamps) are placed on rooftops and walls" (Crump, 2013). 

Christmas spirit in Mumbai (Times of India)

So to you all...Shub Naya Baras ("Merry Christmas")!

Geoengineering the Goldilocks monsoon

A tangent, albeit an interesting one...

Geoengineering - possible saviour for the Earth or one-way street to disaster induced by mankind's arrogance? It is a matter of opinion either way, but for the first time geoengineering was acknowledged in the IPCC AR5 Summary For Policymakers as a possible course of action. More recently an article dubbed Transforming Earth appeared in the New Scientist, noting that the location and planetary geoengineering methods that will have to take place, can now be identified (Figure 1 - click to enlarge). This got me thinking...how might geoengineering affect the South Asian monsoon? 

Figure 1 - Various proposed geoengineering projects and 
their locations around the globe (New Scientist)

Geoengineering is generally split into two camps (Desmogblog) - solar radiation management and carbon dioxide removal. The Enhanced Weathering centred in India in Figure 1 is an example of CO₂ removal. It's based on the idea of crushing minerals such as Olivine into a powder and applying it to the land surface, creating a larger surface area for chemical weathering to occur and thus increasing the draw-down of CO₂. Potential impacts are changing the river/surface water alkalinity and this could have an impact upon one of the foundations of South Asia - agriculture. Dependent upon the materials used, enhanced weathering could lead to better water efficiency of crops and more productive soils (Hartmann et al., 2013 - great study if you are interested in the detail).

Possibly more well known is stratospheric aerosol injection to manage solar irradiance and 'dim' the Earth by reflecting more shortwave radiation back into space (Figure 2). This is one of three possibilities, alongside albedo enhancement of marine stratocumulus clouds and sunshades in space, that Lenton and Vaughan (2009) have identified as having the potential to bring the climate closer to pre-industrial levels. You might remember from an earlier post that the major monsoon driver is the moisture flux from ocean to land driven by temperature gradients - any change in the amount of solar radiation reaching the surface could impact upon this. Tilmes et al. (2013) modelled the effects of stratospheric aerosol injection and noted that global average precipitation decreased by 4.5%. The impacts also appeared much more pronounced during months of heavy monsoonal rains, leading to precipitation reductions of 7% in North America, 6% in East Asia and South America, 5% in South Africa and 2% in India. 

Figure 2 - Stratospheric Aerosol Injection to cool the Earth by enhanced
reflection of shortwave radiation back to space (Carnegie Institution)

Bala et al.. (2008) looked into the impact of geoengineering on the water cycle and they cite a study demonstrating the effects of the Mt Pinatubo eruption in 1991. Although short-term, the sulphate released into the stratosphere led to a substantial reduction in precipitation and run-off decreased to a record low, something that would hugely impact South Asia agriculture accounts for 21% of India's GDP (World Bank). Robock (2012) notes that any small scale tests of stratospheric aerosols would be hard to detect from interannual variability and so a full-scale implementation would be needed to fully investigate the impacts, which sounds rather risky to me!   

Like many geoengineering 'solutions', the effects of any efforts, even regional, are likely to have global effects - especially with stratospheric aerosol injections. It is largely down to the nations with wealth to implement geoengineering, but a history of colonialism may make parts of the world distrustful of the admirability of the wealthier nations intentions. Furthermore, once started the impacts of stopping could be worse in the long run as this blog shows. Worryingly, a recent news article notes that geoengineering trials that do not involve material input into the oceans, whilst widely believed to be illegal, are perfectly legal according to the language of environmental treaties. This begs the question of when and how mankind goes about geoengineering - if done in the wrong manner, the consequences upon a sensitive system such as the South Asian monsoon could be huge. 

Next up...precipitation

The Himalayan Tsunami

Figure 1: Headlines regarding the June 2013 flooding event (hover to show -- source)

The flash floods in Uttarakhand in mid-June 2013...evidence of anthropogenic influence? Uttarakhand, north-west India, is home to some of the highest mountains in the world e.g. Nanda Devi (25,646 feet [7,817 metres]) and is drained by numerous rivers of the Ganges system (Encyclopaedia Britannica). It made the headlines around the globe this year (Figure 1) due to devastating flash floods, that affected the region in mid-June. Heavy pre-monsoon snowfall during March-May led to increased meltwater in June; Two unusually intense weather systems combined (BBC) to produce prolonged heavy rainfall in June, further enhancing snow melt, and raising river levels higher still (The Hindu). Water accumulated in a glacial lake which eventually was breached (GLOF), causing the flash flood and widespread devastation (BBC - Video 1; BBC - Video 2).

Flash floods, typically coinciding with the summer monsoon, are the most common weather-driven natural disaster in this area, causing more fatalities in Uttarakhand than anywhere else in India (Panda, 2010). Panda (2010) also notes that flash floods have enjoyed a long history in Uttarakhand. This begs the question - where does anthropogenic influence fit into this equation?      

 Video 1                                                     Video 2

"Warming of the climate system is unequivocal, and since the 1950s, many of the observed changes are unprecedented over decades to millennia" (AR5 Summary For Policymakers). Goswami et al. (2006) project an increase in intense precipitation events in a warming climate. Additionally, the rate of glacial retreat (majority of the world's glaciers are in retreat) and snow cover reduction, has increased through time (AR5 Summary For Policymakers). Combined or in isolation, these will increase the risk of flash floods (Guardian).          

The point at which an event becomes a disaster often highlights mankind as the culprit. As I alluded to in Land-use & the monsoon, space is at a premium in India where ~72% of the population are rural (World Bank) often living in 'at risk' areas. It is with 'high confidence' that settlement patterns e.g. mountain settlements, have influenced the observed trends in exposure and vulnerability to extreme events (SREX Summary Report). It is often inadequate land management, such as construction or deforestation, that both put people at risk and create antecedent conditions that exacerbate climate effects (SREX Summary Report). 

It remains very difficult to attribute individual extreme events to anthropogenic influence, especially those localised events like flash floods driven by cloud bursting (SREX Report). Were the 2013 floods evidence of anthropogenic influence? Arguably yes. Furthermore, anthropogenic influence on other potential drivers of flash floods is apparent and as such, headlines such as these could become more frequent in the future. 

Next up...effects of extreme precipitation...bring your umbrella

The capricious monsoon?

Capricious – adjective – changing according to no discernible rules; unpredictable: a capricious climate (Oxford English Dictionary)...or in other words, the South Asian monsoon...or is it? 

Several observational datasets exhibit a reduction in South Asian monsoonal rainfall since the 1950s, with this drying tendency particularly evident over central India (Annamalai et al., 2013). Although this drying trend could be attributable to the factors discussed in GHGs, Aerosols & Cookfires and Land-use & the monsoon, another cause in the form of anthropogenically driven SST warming has been proposed (Annamalai et al., 2013). This will be the focus of today's post and I'll be focussing on a couple of studies along the way...

Figure 1 - Running mean (31 year), using two datasets over June-
September (JJAS) or July-August (JA) (Annamalai et al., 2013) 

Annamalai et al. (2013) show a succession of ~30 year wet and dry periods that can be seen throughout the 20th century (Figure 1), and as such suggest that South Asia should have entered a wet phase in ~1990 -this has not been the case. They point towards the western Pacific SST warming, as the culprit for the reduced South Asian monsoon rainfall (this effect can be seen here - NOAA). They also note that despite Indian Ocean SST rising, sea level pressure (SLP) has increased, decreasing the monsoonal circulation and thus evaporative potential. The western Pacific exhibits low SLP and increased rainfall, and Annamalai et al. (2013) suggest that this will incite a Rossby wave that forces descending air westwards, drying South Asia. Additionally they note the eastward shifting trend of ENSO, which could further explain the pattern of reduced rainfall over the South Asian monsoon region. Turner and Annamalai (2012) note that by the end of the 21st century the South Asian summer monsoon will experience more rainfall, and as such Annamalai et al. (2013) propose that the monsoon is currently in a transient phase. 

El Niño–Southern Oscillation (ENSO) is entwined with the South Asian monsoon. The ENSO-monsoon relationship generally brings drought conditions during El Niño and flood conditions during La Niña; for example recent moderate El Niño events in 2002 and 2004 led to All India Rainfall (AIR) deficit of 19% and 13% respectively (Annamalai et al., 2007). Krishnamurthy and Krishnamurthy (2013) studied the Pacific Decadal Oscillation (PDO) and suggested that potentially it could influence ENSO (Figure 2) through:

Figure 2 - Scatter plot showing Niño 3.4 index vs PDO index. The col-
ours relate to the IMR (Indian Monsoon Rainfall) index. Higher 
IMR=higher rainfall (Krishnamurthy & Krishnamurthy, 2013)   

• Warm phase PDO + El Niño = Enhanced drought as they complement each other.
• Warm phase PDO + La Niña = No strong signature as they counteract each other.
• Cold phase PDO + El Niño = No strong signature as they counteract each other.
• Cold phase PDO + La Niña = Enhanced flooding as they complement each other.   

Krishnamurthy and Krishnamurthy (2013) also separated ENSO from PDO and found that the effects of ENSO cover the whole of India, whilst in isolation the effects of PDO are confined to north of 18°N. They propose that ENSO/PDO affect the monsoon through the Walker and Hadley Circulation, whereby low SLP anomalies in the North Pacific during winter, create an SST footprint in the subtropics that persists through to the following summer (Vimont et al., 2001). This causes the eastward propagation of the ascending limb of the Walker Cell, due to the enhanced westerly trade winds. A descending and ascending limb of the Walker Cell will then form over the Maritime Continent and equatorial Indian Ocean respectively. The Hadley Cell linked to the Indian Ocean, will thus ascend much further south in the Indian Ocean, rain out and then descend upon India causing a rainfall deficit (Krishnamurthy and Krishnamurthy, 2013). Annamalai et al. (2007) note that rather than being related to climate change, much of ENSO appears to be spontaneous. However, there may be predictability of the mean monsoon and its interannual variability due to the slowly varying boundary conditions associated with ENSO (Annamalai et al., 2007). 

The effect of the oceans on the variability of the South Asian monsoon is clear from the evidence, and with no sign of anthropogenic emissions slowing, their influence upon the South Asian monsoon looks set to grow. Over the last few posts we've looked through the effects of aerosols, land-use and now the ocean, and hopefully you can now appreciate the difficulty in (a) identifying the cause for change in the monsoon, (b) attributing that change to anthropogenic influence and (c) creating models to form accurate projections. Further complicating this task are other variables interacting on intraseasonal and interseasonal time-scales; factors such as Madden-Julian Oscillation, Indian Ocean Dipole and Tropical Biennial Oscillation. Despite this, there are green shoots regarding projection but for now the monsoon remains somewhat of a mystery, albeit a little less capricious than before.  

Heavy science over...next up...the effects!        

Land-use & the monsoon

The monsoon circulation is primarily driven by large scale pressure gradients, created by the thermal disparity between the ocean and the land (Clift and Plumb, 2008:17). The South Asian monsoon should therefore be classified as a coupled atmosphere-ocean-land phenomena, with the land as influential as the ocean (Yasunari, 2007). Douglas et al. (2006) note that most studies have focussed on the larger scale dynamics of the monsoon, and as such relatively few studies have investigated the potential effects of regional land-use. With 18% of the world's population on just 2.4% of the global land surface, and the projection that India will become the world's most populous country by 2050 followed closely by China, the pressures on the environment are intensifying and any effect upon the South Asian monsoon could be increasing (Ray, 2011).

Although much of India had experienced deforestation and been transformed into agricultural land by 1700, significant agricultural expansion into the north-west around the Himalayan foothills began in 1940. Further intensification coincided with the significant change in farming practices, including the increased use of groundwater irrigation, with the Green Revolution of the 1960s (Roy et al., 2007). Douglas et al. (2006) looked at the influence of agricultural irrigation on evapotranspiration (vapour flux) and surface radiative balance and concluded that these can affect the local convection and rainfall. Furthermore, it was suggested that vapour flux and rainfall changes can influence monsoon and global circulations through teleconnections, if the components cover a large enough area. 

Figure 1 - GA analysis showing strong and negative
trends in rainfall (Niyogi et al., 2010)

Niyogi et al. (2010) employed an Empirical Orthogonal Function (EOF) approach to explore climatic trends within the South Asian monsoon region. They found that there been significant increases in summer rainfall over east India and reductions over north and north-west India over the last five decades. Interestingly two north-western states most affected by an intensification of irrigated agriculture since the 1960s, Punjab and Haryana, have experienced significant reductions in surface sensible heat flux leading to a reduction in rainfall (Douglas et al., 2006). Niyogi et al. (2010) performed additional Genetic Algorithm (GA) analysis, the use of which ties spatial patterns to strong temporal trends, which confirmed the same result (Figure 1). This trend has been linked to an increase in soil moisture and vegetation changes, both of which can effect the radiation balance, causing regional surface cooling (Niyogi et al., 2010) along with changing regional convection (Douglas et al., 2006). 

The culprit for the increase in soil moisture is the increased use of groundwater irrigation; the area utilised for paddy cultivation tripled during 1960-1990, with much of it occurring in the premonsoon season (up to 4 weeks earlier than in the past) due to the diminishing reliance on monsoon rains to kick-start the growing season. Bringing the growing season forward increases the normalized differential vegetation index at a crucial stage of monsoon circulation evolution. Through increased albedo, the intensity of the negative pressure anomaly can reduce and thus weaken the pressure gradient, influencing rainfall amount and distribution (Niyogi et al., 2010). Other factors such as urbanization could also influence the precipitation, however Kaufmann et al. (2007) demonstrate this effect reduces rainfall, but not during the summer monsoon as the mechanism overwhelms local urban effects. Arguably it is the intensification of agriculture and the associated surface feedbacks where the evidence is most compelling. Indeed, Douglas et al. (2006) suggest that monsoonal rainfall variability is regulated by antecedent land surface conditions. 

Due to the complexities of the South Asian monsoon system and the relatively youthful nature of this area of study, it is difficult to definitively attribute the changes in the monsoon to land-use change, although there is compelling evidence of its influence. Arguably, it is the role of land-use changes in exacerbating monsoonal effects, as opposed to their effect of upon the monsoon itself, that are of greatest importance. With the population increasing rapidly and the country getting no bigger, the proportion of the population living in 'at risk' areas may increase, and as a result the extent of our influence could become evermore significant. 

IPCC...A Swift Update

To understand both the current and projected changes of the South Asian monsoon and put them into context, it is helpful to get to grips with the whole picture. 

For those haven't found the time to trawl through the IPCC AR5 Summary For Policymakers, let alone all 2216 pages of the Full Report for the Working Group 1 contribution, the IPCC released a summary video a few days ago. Enjoy... 

GHGs, Aerosols & Cookfires

In "What's the story?" we explored the basic science of anthropogenic influence upon the South Asian monsoon, but the devil is very much in the detail, and so I'll be delving into the many whys and hows over the next few posts. So without much further ado...

Figure 1 - Aerosol-Cloud Interactions in (a) clean
 air and (b) polluted air (IPCC AR5:Chapter 7)

The concentration of Carbon Dioxide (CO_₂) has increased since ~1850 (Keeling Curve) and along with other greenhouse gases (GHGs) has driven surface warming and intensification of rainfall associated with the South Asian summer monsoon (Ueda et al., 2006). This relationship is not as simple as it seems due to aerosols, predominantly sulphate and black carbon borne from the continued industrialization of South Asia (Turner and Annamalai, 2012). Aerosols interact with the climate in two main ways; interaction with clouds (Figure 1) and interaction with sunlight (Figure 2). The total radiative forcing effect of aerosols is calculated to be -0.35 (-0.85 to +0.15) W m⁻² (IPCC AR5) and Ramanathan et al (2005) have suggested that aerosols may have masked up to 50% of surface warming from the increasing levels of GHGs. Accounting for up to 60% of black carbon emissions in Asia (UNEP, 2012) through the burning of biomass, the humble cookfire has stepped into the limelight and has recently undergone a technological make-over (BBC video). The reduction of black carbon emissions has been dubbed a saviour of glaciers (which will appear in a later post) in addition to saving lives (Ramanathan, 2013).

Figure 2 - Aerosol-Radiation Interactions. The left panels are
instantaneous & the right, overall effects (IPCC AR5:Chapter 7) 

The effects of aerosols upon the monsoon are hotly debated (Turner and Annamalai, 2012) with many opposing voices. Turner and Annamalai. (2012) suggest solar radiation could be limited by both the direct scattering effect of aerosols and by their increasing the albedo of clouds. A potential result of this is a reduction of the meridional temperature gradient, leading to a lower increase in rainfall than is expected. Ramanathan et al (2005) projected a decrease in Indian Ocean SSTs due to reduced solar radiation, resulting in decreased evaporation and thus rainfall; however Annamalai et al. (2012) note that SST over the Indo-Pacific warm pool have risen, enhancing moisture content, and making reduction in rainfall unlikely. Ueda et al. (2006) calculate the overall effect as increased monsoonal precipitation, due in the most part to the enhanced moisture transport, despite the influence of aerosols. Indeed, many coupled ocean-atmosphere models simulate this result with increases in GHG concentrations (AR5). 

Furthermore there is a suggestion that increased SSTs (Annamalai et al., 2012) along with aerosols (Bollasina et al., 2011) could cause geographic redistribution of monsoon rainfall, most notably a drying of Central India (Krishnamurphy et al., 2009 in AR5). Bollasina et al. (2011) demonstrated that along with the effect upon rainfall, aerosols have driven a weakening of monsoonal circulation. Further effects of aerosols include an increase of cloud burn-off due to increased cloud lifetime and potential aerosol driven tropospheric warming (Koch and Genio, 2010), though increases of cloud cover in some areas and an increase of extreme precipitation events (Goswami et al., 2006) suggest this effect is not a main driver. Levermann et al. (2009) noted that the South Asian monsoon has two stable states; a 'wet' state and a 'dry' state. It is the moisture-advection feedback that predominantly drives the monsoon circulation, and as such a change in radiative forcing that weakens the pressure gradient (Whats, Whys, Wheres & Hows), could prompt an abrupt transition from the current monsoon regime to one characterized by reduced precipitation. On the other hand, the effects of aerosols are somewhat constrained by those of increasing GHGs, meaning a switch in monsoon regime during the 21st century and beyond is unlikely (AR5). 

CMIP models simulate the annual precipitation and temperature cycles quite well for South Asia, but although they are improving (Sperber et al., 2012 in AR5), they are still not brilliant at simulating rainfall variability on regional and local-scales (Turner and Annamalai, 2012). One cause for this uncertainty within the models is driven by the gaps in our knowledge regarding the effects of aerosols, particularly regarding aerosol-cloud interactions, and this is a major stumbling block to our understanding the monsoon. Finding the point at which GHGs overcome the effects of aerosols will also further our understanding of the monsoon, and thus our ability to model it (Turner and Annamalai, 2012). Mankind has been running an unintentional experiment on one of the largest hydrological systems on the planet and so, if having read this you have more questions than when you started, you have likely understood the point of this post...uncertainty reigns for now.  

Procrastination on a global scale...

Procrastinate - verb - delay or postpone action; put off doing something: the temptation will be to procrastinate until the power struggle plays itself out. 
Origin: Late 16th century: From Latin procrastinat - 'deferred till the morning', from the verb procrastinare, from pro 'forward' and crastinus 'belonging to tomorrow' (Oxford English Dictionary)

...At the start of this blog I did mention that I liked the odd tangent or two, but I failed to tell you that these tangents are often the result of procrastination, as perfectly demonstrated above. This blog is largely focussed upon the South Asian monsoon, but it is impossible whilst researching not to be distracted by all of the other sub-systems within the global monsoon system. I've pulled together some key points from the AR5 for monsoons around the globe. As always feel free to ask if you have any burning questions...enjoy! 

NB: Click the 'YouTube Logo' on the bottom right of the video to see it in all its HD glory!

Video References: Image accessed here. Music - Am I Not Human? - Two Steps From Hell (accessed Nov 2013) 

Aside from the monsoon...

A quick aside...I came across this today and although unrelated to the monsoon, I thought it worthy of an appearance here...

Sea level rise - a pressing concern resulting from climate change, and now a visual reality thanks to an interactive map from the National Geographic...take a look! 

Rising Seas - Interactive: If All The Ice Melted

What's the story?

We've seen the IPCC Headlines for the global picture but what's going on with the South Asian monsoon, and more importantly why? But first a bit of science...

Figure 1 - (IPCC AR5: Chapter 12)

Much of the monsoon response is explained by basic climate dynamics - global precipitation and global temperature exhibit a fairly linear relationship (IPCC AR5; Figure 1). This is very much governed by the Clausius Clapeyron relation, whereby the water-holding capacity of the air is increased by ~8% per °C increase in temperature, but is somewhat limited by the changes in the net radiative cooling rate with the troposphere (AR5). Furthermore, the gradual increase of CO₂ over time will cause an increase in both temperature and water vapour, and thus increase precipitation (Held and Soden, 2006 in AR5).

With regards to the South Asian monsoon, the tropical Indian Ocean SSTs (sea surface temperature) are projected to rise and the temperature of the land to rise further still (aided by the shear amount of land in the northern hemisphere), creating a larger temperature gradient. This leads to increased evaporation and enhanced moisture flux from the ocean to the land, increasing precipitation (Liepert and Previdi, 2012) despite the circulation of the South Asian monsoon weakening. Chung and Ramanathan (2006) have linked this weakening to a trend whereby the SSTs of the equatorial Indian Ocean have warmed but those of the northern Indian Ocean have not. This is evidenced with reduction in the meridional SST gradient, causing the monsoon circulation to weaken, and leading to a re-distribution of rainfall within the South Asian monsoon. Figure 2 from the IPCC report summarises what is going on rather nicely and makes linkages between factors more visible.

Figure 2 - (a) and (b) are fairly self explanatory but (c) is the water vapour flux convergence in the lower troposphere and (d) is the convergence of winds in the lower troposphere. RCP 2.6 = dark blue line, RCP 4.5 = light blue line, RCP 6.0 = orange line and RCP 8.5 = red line (IPCC AR5: Chapter 14). 

Another major change to the South Asian monsoon is the increase of extreme rainfall events and the decrease of weaker events (Goswami et al., 2006), and CMIP5 models also suggest an earlier onset and later retreat leading to a lengthening on the monsoon (AR5). Hopefully this has given you an insight into the basic science behind the anthropogenic influence upon the South Asian monsoon. Over the next few posts I'll be exploring the drivers in more detail and their manifestations... 

Monsoon fashion bonanza...

STEP RIGHT UP….STEP RIGHT UP….DON’T BE SHY!! Monsoon fashion must-haves thanks to Vogue India…

Brighten up your monsoon with some banana earrings from Prada or a pair of colourful flip flops. How about a Morinne cotton-twill cape from Diane Von Furstenburg and put down that drab black umbrella…try a nautical stripe bow umbrella from Accessorize! Don’t bother with a dress – you’ll just get muddy! Instead buy these CK shorts and why not throw in some crazy printed wellington boots by Burberry?! For the full experience feel free to find out more here…

Whilst researching for this week’s edition of the blog I stumbled upon this. For those of you who have ever met me you are probably aware of this already, but for those that haven’t, my idea of fashion stretches as far as what was (a) clean, and (b) closest to me at the time I was getting ready. Therefore finding this article amongst the doom and gloom of the many impacts of the South Asian monsoon offered some light relief I thought I ought to share. Unfortunately gentlemen, I'm yet to find any monsoon fashion advice for you, but to the women, you're welcome...

Pictures accessed here

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?