A Millennium of Monsoon Failures, Droughts and Famines

By Ananda Gunatilaka
The Island Online (Sri Lanka)

The Asian Summer Monsoon (ASM) has made possible several complex civilizations to flourish over time. The monsoon domain of Asia extending from Oman to Australia affects almost 60 per cent of humanity today. Historical records have mentioned monsoon failures, droughts, famines and extreme flooding events in the past. Scientifically, the two most robust, continuous, terrestrial proxy rainfall archives are preserved in limestone cave deposits (stalagmite columns) and tree-ring growths (both of which record wet and dry phases or pluvials and droughts). Both archives require precise and very high accuracy geological dating techniques in conjunction with oxygen isotope analysis (the proxy for rainfall). During the past five years, the two archival techniques have been perfected to a degree that a yearly resolution of data is now possible with even a cross-check of dates.

Three cave proxy rainfall records from mainland Oman (Hoti), India (Danduk) and from China (the Wanxiang) have shown the past history of spatio-temporal variability of the monsoon. The Danduk record picked up periods of annually resolved, multi-decadal and centennial length episodes of reduced rainfall and drought during the past millennium, which coincided with several of India’s most devastating historical famines (e.g 879; 940-950; 1148-1159; 1344-1346 CE). The best known are two severe famines between 1350-1420, including the famous Durga Devi (1396-1409) that killed off millions of people in India. Comparing the cave proxy record with historical records, Chinese geologists constructed a record of Dynastic failures due to weakened monsoons, droughts, crop failures, famines and peasant revolts (e.g. the Tang- 850-940 CE; the late Yuan- 1350-1380 CE and Ming- 1580-1641 CE).

Decades that experienced the wettest and strongest monsoons of the past 1000 years coincided with the Northern Song Dynasty’s golden age of rich harvests, population recovery and social stability (960 – 1020 CE). This was clearly depicted in the paintings of that time. Interestingly, the demise of the Tang Dynasty and Maya Classic Periods were coeval (early 10th century) – both now related to extended drought phases, though far apart geographically. It is the amount of rainfall and its inter-regional pattern of variability, especially drought that is of importance to human populations.

Last month, the Tree-Ring Laboratory of the Lamont-Doherty Earth Observatory of Columbia University, USA (TRL-LDEO) released the Monsoon Asia Drought Atlas (MADA), which also provides an absolutely dated, annually resolved reconstruction of Asian monsoon spatio-temporal variability over the past 1000 years. MADA used tree-ring data from more than 300 sites of the forested regions of monsoon Asia to reconstruct an Index of relative drought and wetness for the region. The major finding of MADA is that historically recorded monsoon failures/excesses in the past 150 years have been exceeded in intensity and duration many times during the past millennium. The Atlas picked the Ming Dynasty Drought of 1638-1641- the worst in 500 years in northern China and its recorded final collapse in 1644; the Strange Parallels Drought (SPD 1756-1768), the East India Drought (EID 1790-1796) and the late Victorian Great Drought (VGD 1876-1878).

The EID that lasted six years coincided with one of the most severe El-Nino events of the late 18th century, which was felt worldwide and resulted in extensive civil unrest and socio-economic disaster. Its effect on India was devastating with several famines. The MADA record highlights its occurrence in the southernmost tip of India and extending to Sri Lanka, but there is no mention of it in the Sri Lankan records (or is there?). The drought is consistent with historical data for the region. The VGD also occurred during one of the most severe El-Nino events of the past 150 years. This drought was felt in much of India, Sri Lanka and Vietnam, parts of Indonesia, Thailand, Borneo and New Guinea according to MADA and is vaguely referred to in our recent historical records. Over 30 million people died across monsoon Asia from the famine (see Davis, M. 2001 –Late Victorian Holocausts, El-Nino famines and the making of the Third World. Versa, London). In the north-central region of Sri Lanka, Mannar and Mullaitivu, apparently there were no rice harvests for nine years and the coffee blight in Uva in the 1870s-1880s may have been due to this drought.

Thailand, Cambodia and Sri Lanka connections

The annually resolved MADA dendro-hydroclimatic record shows that there were persistent weak monsoons and extended decadal droughts in tropical South and Southeast Asia over the past 500-700 years. In the mid-late 14th and early 15th centuries, especially the long period from 1351-1368 CE that was coeval with severe decade long droughts alternating with strong monsoons and floods instigated the collapse of the Khmer civilization in Angkor (Cambodia). The droughts devastated the complicated water supply, management and distribution networks and agricultural base of Angkor, the largest medieval city of the time with upwards of 500,000 people, while flood episodes in turn destroyed the water control infrastructure. Droughts and floods at interdecadal scales are characteristic of the Asian monsoon.

From Sri Lanka’s point of view, it is imperative to mention two references to famines in the late 14th and early 15th century (Gampola Period?) from palm-leaf scrolls in Thailand, where it is mentioned that a contingent of priests from Chiang Mai, Thailand who came here in the early 1400s on a long pilgrimage were forced to return due to a severe drought/famine in Sri Lanka (but where?). This event, as far as is known went unrecorded (?) in our chronicles. The very disappointed priests lamented that they had to turn back as there was "mai mee khao gin" – there


A Millennium of Monsoon Failures was no rice to eat! The references to Sri Lanka are in Thai and from Phitsanulok in Thailand (Wyatt and Wichienkeeo, 1998- The Chiang Mai Chronicles and R.P. Thera, 1967- Jinakalamali Prakor). These droughts were recorded in the state chronicles of the Chao Praya Basin, which mention that the droughts extended west to India and Sri Lanka (see Buckley, B.M. et. al, 2010, Proc. Nat. Acad. Sc., Vol. 107(15): 6748-6752; Cook, E. et. al., 2010., Science, Vol. 328: 486-489).

The year 1403 is recorded by TRL as the most severe in the dendro-record (visit of monks?). Also, six of the twenty wettest years alternated with drought years during the latest 14th and early 15th centuries when the hydraulic infrastructure at Angkor was damaged by flood episodes, just after agricultural productivity was devastated by the preceding decadal droughts. The geological record of the floods is still preserved in the abandoned canal networks of Angkor. Despite over a century of research at Angkor, the ultimate causes of its collapse remained uncertain. The dearth of textual records after the 13th century hindered historical research. This has now been resolved by the detailed hydro-climatic record compiled from tree-ring data.

It was not that repeated droughts and floods were the ultimate cause of civilizational demise. The empire was already under severe pressure from wars, population expansions and social and political upheavals and perhaps even a shift from the Hindu faith, which bestowed unquestioned "godly" powers on the uncompromising rulers (Devaraja), to acceptance of Buddhism due to its more tolerant and democratic outlook that gradually diminished the authority of the weakened rulers. It went into ruin after about five centuries. The hydraulic city had the seeds of its own destruction with a constant battle with droughts and floods. It was a society totally dependent on the annual monsoonal flooding of its lowlands, which supported an extensive rice based agriculture-irrigation infrastructure. It just could not cope with the pressures on its infrastructure and the bureaucracy failed. Decadal droughts alternating with severe floods just pushed it over the edge and never recovered.

Despite the vicissitudes, quite amazingly, the Rajarata hydraulic civilization survived for over a thousand years – far more resilient than any known. It was even resuscitated after more than 600 years of abandonment and its basic infrastructure still functions today. Sri Lanka too had droughts and floods as has been recorded in the chronicles. However, the textual content and detail is very poor. For over 600 years (from 619-628 CE to 1237-1270 CE) there are no references to famines (droughts) when most of monsoon Asia experienced floods/droughts. There is no evidence whatsoever that Rajarata demise had climatic connotations before collapse. However, like in Angkor, it could have been pushed over the edge when the regimes were already weakened in succession by various other pressures and moved out to the southwest for a variety of reasons.

The Danduk cave record shows at least fifteen regional droughts between 1000-1500 CE. The two worst decadal droughts were in the late 14th and early 15th centuries that were also picked up by the dendro-records in the Columbia study quite independently. The references in the Thai records to a major drought in Sri Lanka in the early 1400s were mentioned earlier (same time as the Durgadevi drought in India and decadal droughts in Angkor?). A drought of similar magnitude and extent today with billions more people are unimaginable!

The palaeoclimate archives of monsoon Asia is a very active field of research today. The big gap is between Sri Lanka and Thailand (mostly ocean). However, the continental archives are being added to and refined. The LDEO-dendrochronology survey here was interrupted twice by the civil conflict and the 2004 tsunami event and good analytical material was not found. If the survey restarts and obtains good tree-ring dates, then new interpretations to our climate and social history are possible just as in the cases above.

Early chroniclers recorded only historical events that mattered in state affairs. Droughts and floods were not. It was more important to record alms-giving to priests and mass reciting of pirith to pray for rains. Unlike in India or China, the detail and textual content is lacking when describing famines. This author believes that droughts, famines and floods were as frequent in ancient Sri Lanka as in the rest of Asia and that the chroniclers were indifferent to natural disasters and did not bother to record them. They were only periodically recurring extreme events (as in Angkor) and in the natural order of things. Else, how come major droughts were "missed" here, but were recorded in Thailand and elsewhere? With smaller populations in Sri Lanka, the effects of a disaster may not have been very dramatic unlike in India or China where millions perished at a time. Perhaps our historians will enlighten us on these aspects!

* The author is a retired Professor of Geology

Climate a Factor in Demise of Angkor: Study

By Im Sothearith, VOA Khmer
Original report from Washington
07 April 2010

A decades-long drought interspersed with intense monsoons in the 14th and 15th centuries may have contributed to the fall of the Angkorean civilization, a new US research study suggests.

Brendan Buckley, a researcher at Columbia University, and his colleagues studied tree rings in the region, putting together a high-resolution record of periods of drought and moisture, and while it is not clear what exact role climate played in the fall of the empire, Buckley told VOA Khmer climate certainly played a part.

“We wanted to be careful not to make it sound like we were saying correlation equals causation,” Buckley said. “I mean there is plenty of evidence in our record, or in other records, where you know that drought doesn’t always lead to collapse, but what it does do if you have sustained drought is it certainly puts a stresser on societies when other factors are stressing them.”

The Angkorean empire had suffered a gradual decline in regional power and had not been maintaining its water systems for about a century, Buckley said.

But by studying tree rings, which can be a clear indicator of precipitation, Buckley and his team found a large drought in the middle of the 1300s that lasted nearly three decades. That was followed by a severe wet period, followed again by sharp drought in the early 1400s.

The opposing pressure of these weather patterns may have helped damage the empire’s infrastructure. The collapse of the empire coincided with this period.

Nearly all Angkorean archeology has been done with what is available above ground, on visually spectacular sites like the temples of Bayon or Angkor Wat, Buckley said, but no one has yet gone into the forest and looked underground. Another interesting question would be to look at the links between drought and disease outbreaks, he said.

The fall of Angkor is still the subject of much debate among researchers—including whether it collapsed at all or simply saw a slow migration of its people due to war, internal conflict or a change in religion.

Until now, climate change has not been widely discussed as a factor, but Cambodian historians and archaeologists told VOA Khmer the idea has at least some merit.

“When there is sustained flooding or drought, it affects the economy,” said Son Soubert, a member of Cambodia’s Constitutional Council and an archaeologist. “As you may know in Jewish history, in the Bible, during that time there was drought in Egypt, which negatively affected many people, especially Jewish. The climate may have affected Khmer society in that period. It’s important because it can also help explain the causes of the demise of Angkor. There was conclusion before that war was the only cause.”

To some researchers, war and conflict remain the main suspects in the empire’s fall.

“The major factor is the human factor,” said Michel Tranet, a Cambodian archaeologist who has worked extensively on Khmer temples and antiquities. “What I mean here is the cruelty of war.”

“Whenever there were wars between the Khmer and Siamese, Siamese troops were stronger and destroyed our nation, our heart, our soul and our great national structures, during which our great Angkor was abolished,” he said.

A religious shift, from Hindu to Buddhist, was another factor, he said, as was internal conflict between royal family members. He called climate change a small tree in a large forest.

“When we had internal conflicts, we were weak, and other nations attacked us, broke us apart,” he said.

Likewise, Ros Chantrabot, a Khmer historian and vice president of the Royal Academy of Cambodia, told VOA Khmer by phone that climate was a small contributing factor.

The invasions between neighboring regions were a main factor, starting with the expansion of Genghis Khan’s Mongol empire into China, he said. This pushed groups of ethnic Thais and Vietnamese into today’s Burma and the northern Khmer empire, leading to Angkor’s ultimate demise.

Drought could have destroyed ancient city

2009/09/23
AP

A PROLONGED and intense drought may have contributed to the demise of Cambodia’s great ancient city Angkor, an American researcher said .

Brendan M Buckley said bands on tree rings that he and his colleagues have examined show that Southeast Asia was hit by a severe drought from 1415 until 1439.

That would coincide with the time period during which many archeologists believe Angkor collapsed. From the city of famed temples, Angkorian kings ruled over most of Southeast Asia between the ninth and 14th centuries.

During that time, they oversaw construction of architectural stone marvels, including Angkor Wat, regarded as a marvel of religious architecture and designated as a World Heritage Site by Unesco.

“Given all the stress the Khmer civilisation was under due to political reasons and so forth, a drought of the magnitude we see in our records should have played a significant role in causing its demise,” said Buckley, a research scientist at Columbia University’s Tree-Ring Laboratory in New York. Scientists have a historical record of droughts with the thickness of a tree’s rings. Since trees grow more during wet periods, the rings will grow thicker at those times. Trees grow less in dry times, so those rings will be thinner.

While the 1431 invasion from Siam – now Thailand – has long been regarded as a major cause of Angkor’s fall, archaeologists working at the sprawling temple site have long suspected that ecological factors played a role. The Greater Angkor Project is run by the University of Sydney in collaboration with the French archaeological group Ecole Francaise d’Extreme Orient and Apsara, the body responsible for the management of the Angkor World Heritage Park. The project concluded in 2007 that ancient Angkor had become unwieldy and that efforts to expand rice production to support a population of one million had led to vast deforestation, top-soil degradation and erosion.

Last year, the group went further to show that the deforestation resulted in flooding and huge amounts of sediment clogging the network of canals that was at the heart of the city’s vital water management system.

Dan Penny, a University of Sydney researcher who is a director at the Greater Angkor Project, said the new findings on drought will help researchers gain a greater understanding of why Angkor collapsed.

“Angkor was a civilisation obsessed with managing water. It was an agrarian society,” Penny said. “It’s hard to imagine that a society like that could have shrugged off 20 or 30 years of drought.”

However, Penny said it was likely that the drought was more of a contributing factor to the kingdom’s demise than a driving force. Not only was it forced to contend with the impacts of deforestation, but also attacks from the Siamese and the Cham of southern Vietnam.

“We have these droughts occurring on top of pre-existing pressures,” Penny said.

“Climate change was an accelerant,” he said. “It’s like pouring petrol on a fire. It makes social and economic pressures that may have been endurable disastrous.”

Climate change helped Angkor's decline: scientist

July 1, 2009
ABC Radio Australia

Cambodia's Angkor temple complex was the heart of the mighty Khmer empire and the ruins are one of the most popular attractions in Southeast Asia.

Angkor Wat, the centerpiece of the Angkor complex, was built in the 9th Century and was surrounded by huge reservoirs and canals - believed to be partly Hindu symbols and partly an irrigation system. So why did the pre-industrial city apparently collapse in the late 16th Century? That's a question that's fascinated historians and archeaologists for decades.

Presenter: Sen Lam
Speakers: Professor Roland Fletcher, archaeologist at the University of Sydney and co-director of the Greater Angkor Project

Click here to listen to the audio program in English (Windows Media)

FLETCHER: Well, it was actually the largest low density pre-industrial city on earth. It covers nearly 1,000 square kilometres, but that's all spread out, something like modern Los Angeles. So it was really enormous and it had somewhere in the order of at the top end 750,000 people in it, so it was pretty spectacular.

LAM: Indeed, water as you've heard was a key factor to Angkor's success, but how did it shape Angkor's downfall?

FLETCHER: Well, the key things to bear in mind is that as you would well know, people in South East Asia have to manage a massive monsoon and then a long dry season and the great water system some of whom canals are about 40 kilometres long appears to have been the mechanism for holding water and using it as reserve in case monsoons were bad.

LAM: Right, and so this is matter of managing the rainfall and the vast amounts, the copious amounts of water that's falling down.

FLETCHER: That's right, to control flooding and to deliver water.

LAM: Mmm, so it wasn't the case of the city growing too fast and outgrowing its infrastructure?

FLETCHER: Well, it's probably more that it built too massive an infrastructure, rather as we're tending to do today, it built an infrastructure that you could not move. The West Baray for instance, has 20 million cubic metres of dirt in its banks. This is massive engineering and between [the years] 1350 and about 1500, the whole region is hit by a very unstable climate period, where there are droughts and severe monsoons all mixed up with each other, in other words, the degree of difference between the years greatly increased.

LAM: So, even all those centuries ago, climate change played a role as well?

FLETCHER: Oh climate change has been occurring all the time. The planetary temperature goes up and down on a very long cycle, quite normally. The period of Angkor, for instance, coincides with what's called the Medieval Warm phase, from about the 9th Century through to about the 15th, 16th Century. And then we got into what's called the Little Ice Age, which is a cold period that ran up to about the 18th Century.

LAM: Professor Fletcher, are there lessons there in Angkor for modern cities?

FLETCHER: Well, I would suspect there are in the sense that what you see in Angkor is a landscape that has been completely cleared of forests in order to grow a dominant crop, so basically a focus on a simplification of the landscape and removing the tree cover and on the other hand, the dependency on very big infrastructure for managing daily life. So, for instance, if you have really heavy monsoons that these canals and systems weren't designed to deal with, you would get severe damage to the structures and we actually find that there is a dam up in the north that's been torn away and the big southern canals of Angkor are full of sand, which suggest very severe flooding.

LAM: You mentioned the forest cover. I understand that some of the trees were studied. What did they show?

FLETCHER: Well, it's the trees in Vietnam, not in Angkor, but in northern Vietnam that actually provide the climate sequence. Trees as you know grow annually and some trees enable you to see how much water was available in a given year. So in a very dry year, you'd get a very thin tree ring growth and in a very wet year, you'd get a big ring and that's what we've used in the work of Brendan Buckley from Colombia to identify the change in the climate and then my colleague, Dan Penny, who is a paleo-environmentalist, has been looking at the changing conditions inside Angkor, looking at the pollen particularly and algae.

LAM: And just briefly Professor, how useful is it for us in modern times to get to the heart of what happened in Angkor?

FLETCHER: Well, I think the thing to bear in mind is the situation is not absolutely equivalent and one reason being that we know a great deal more in the modern world and we have a great deal more capacity available to us to deal with situations. But when you consider that Angkor was a giant low density city, that had cleared its regional landscape of its natural vegetation cover, was dependent upon massive infrastructure and hit by climate change. It does sound a little topical, it does sound a little like the modern world.

Cambodia relics vulnerable to further ruin

Dougald O'Reilly; in the trench, an archaeologist from the University of Sydney, collects soil samples during excavation of an Angkorian hydraulic site in Siem Reap province, Cambodia, on Wednesday Jan. 23, 2008. An international research group is now trying to dig up answers to the question about Angkorian hydraulic network as par of its quest to shed more light on the puzzles left since the demise of the Angkor city centuries ago. (AP Photo/Heng Sinith)
A Cambodian worker collects soil samples during an excavation of an Angkorian hydraulic reservoir in Siem Reap province, Cambodia, on Wednesday Jan. 23, 2008. An international research group is now trying to dig up answers to the question about the Angkorian hydraulic network as part of its quest to shed more light on the puzzles left since the demise of the Angkor city centuries ago. (AP Photo/Heng Sinith)

February 22, 2008
By Ker Munthit

SIEM REAP, Cambodia (AP) - By destroying vast tracts of forest to enlarge their farmland, inhabit- ants of the wondrous city of Angkor ignited the fuse to an ecological time bomb that spelled doom for what was once the world's largest urban area.

So theorize archaeologists engaged in groundbreaking research into the ancient civilization of Angkor.

They are warning that history could repeat itself through reckless, headlong pursuit of dollars from tourists flocking to see Angkor's fabled monuments.

"It's just a weird cycle. It seems like Angkor is self-repeating itself," said Mitch Hendrickson, who recently led an excavation as part of research into Angkor as a human settlement.

Conservationists have long expressed concerns about the state of the monuments, especially the stress from the tourist invasion. They also say the uncontrolled pumping of underground water to meet rising demand of hotels, guesthouses and residents in the adjoining town of Siem Reap might be destabilizing the earth beneath the centuries-old temples so much that they might sink and collapse.

"There's just so much building going on without any concern about the long term. Things are moving so fast in Siem Reap today that it's going to chew itself up very quickly and become unsustainable," said Mr. Hendrickson, an archaeologist from the University of Sydney in Australia.

From their city, Angkorian kings ruled over most of Southeast Asia during their pinnacle between the ninth and 14th centuries, overseeing the stone constructions, including Angkor Wat, regarded as a marvel of religious architecture.

Although the 1431 invasion from what is now Thailand has long been regarded as a major cause of Angkor's fall, archaeologists from the Australian university's Greater Angkor Project suspect earlier ecological forces led to the city's demise.

Their findings supported a theory put forward in the early 1950s by Bernard-Philippe Groslier, a French archaeologist, that the collapse of Angkor resulted from exploitation of the environment.

Angkor's inhabitants started rice farming from the low-lying area near the Tonle Sap lake, just south of the town of Siem Reap, said Roland Fletcher, another archaeologist with the project.

They gradually cut down natural forest to extend their farmland to the slope of Kulen mountain, 50 miles to the north, said Mr. Fletcher, who led 10 archaeologists to excavate various sites near the Angkor complex.

Flooding ensued, and huge amounts of sediment and sand washed into canals, probably choking the vital water-management system.

Using NASA's airborne imaging radar data, the project has conducted numerous aerial and ground surveys across nearly 1,200 square miles, which revealed that the city — with about 1 million inhabitants — was far larger than previously thought.

It covered about 385 square miles and featured a sophisticated hydraulic system that proved too vast to manage.

Angkor was "a huge, low-density, dispersed urban complex" comparable to Los Angeles and "by far the most extensive preindustrial city on the planet," Mr. Fletcher said.

Its water network included an artificial canal used for diverting water from a natural river about 15½ miles north of Angkor, and two mammoth, man-made reservoirs known as the East and West Barays.

"They probably didn't necessarily need any of this extra water ... because just a rain-fed rice agriculture is quite sufficient to feed a very substantial population," said Damian Evans, a project member.

One theory, he said, is that the Angkorian kings built the water system just "to demonstrate their power and their authority to rule."

He said only excavations and soil analysis could yield more clues.

"It's a process of going to those sites on the ground and looking for finer detailed information like the profiles of the canals underneath the ground and the types of sediment that lie within those canals," he said.

Armed with a printed digital map of the Angkor area, Mr. Evans and Mr. Fletcher toured an excavation site at the West Baray where archaeologists dug trenches to seek traces of an ancient channel through the bank. They were trying to determine whether the channel really existed and could have served both as water inlet and outlet.

The reservoir is walled by four banks — now covered with jungle — each 40 feet high, 110 yards wide and about 12 miles in length. It can store up to 1.8 billion cubic feet of water.

Mr. Fletcher called it "the single largest artifact and piece of engineering in the preindustrial world."

"All of this work is aimed at understanding how the water-management system of Angkor functioned ... and how it stopped working," he said, adding that forest clearance is "the current key piece of information" about the ecological peril that caused Angkor to tumble.

Although past environmental problems were associated with deforestation, they also underline the menace the tourism boom is posing to the temples, the researchers said.

"The same types of things which we knew were problems of Angkor are essentially being repeated in our modern-day context in the Angkor area — things like unsustainable use of water, massive overdevelopment without any consideration of the long-term effects," Mr. Evans said. "There's definitely lessons to be learned from what happened here before."