Holiday special: The Basilica cistern

Istanbul is an intriguing city that thrives at the interface: between east and west, Islam and Christianity, antiquity and modernity.  It is a city of monuments spanning two millennia, including the Hagia Sophia which was constructed and reconstructed while Istanbul was the capital of the Byzantium Empire, and the Topkapi Palace and Blue Mosque which were constructed later during the Ottoman Empire.

One of the city’s most unusual attractions, however, is situated deep underground: a cavernous enclosure known as the Basilica Cistern. Constructed in the sixth Century by emperor Justinian I, it was designed as one of several important stores of water to nourish the half-million inhabitants of the city, and supply the city’s countless public baths, gardens and fountains. Supported by 336 columns of Ionic and Corinthian style sourced from various corners of the empire, it has a total area of 9800 m2 and a storage volume of 80,000 m3.

Basilica_cistern

The cistern is just one element of a much more complex water distribution network. It was designed to draw water from ancient springs scattered throughout Thrace, and convey it to the city via a complex network spanning more than 250 km and comprising more than 30 aqueducts, kilometers of underground tunnels and above-ground canals, approximately 70 cisterns and (possibly) some dams further upstream. It is described as one of the ancient world’s greatest achievements of hydraulic engineering, surpassing the infrastructure of ancient Rome in both scale and complexity. Importantly, it not only provided an essential resource during peacetime, but also had a military purpose to protect the city during sieges, with parts of the network running parallel to the city’s defense walls and with the total constructed storage capacity within the walls adding up to close to a million cubic metres.

With its scale and importance, it is staggering that at some point in its history the cistern was lost, only to be re-discovered in the mid-sixteenth century by the French scholar Pierre Gilles who observed that the inhabitants were drawing water from wells underground, not knowing from whence the water came. It was then recommissioned and used by the Ottoman Empire to supply water to the Topkapi palace, and is now used as a museum as well as a venue for occasional concerts due to its remarkable acoustics.

Basilica_cistern_tearsWhen walking around the cistern today it is hard not to feel awed by its grandeur, and the no-doubt considerable cost of its construction. On one of the columns, carvings of teardrops can be seen covering its eight metre height, which are said to represent the hundreds of slaves who died during the cistern’s construction. We also came across two statues of Medusa, one placed upside down and the other on its side, so that those looking at her would not be turned to stone. The purpose of these statues is unknown, but one of the rumours is that she was placed there to protect large structures in special locations. The fact that the cistern is still intact one and a half millennia after its construction suggests that she has been extremely successful in executing her role.

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Climate change back in the spotlight

Few of you would have missed the news that the Intergovernmental Panel on Climate Change has released its latest Assessment Report. Only the Summary for Policy Makers has been released thus far, with the unedited version of the remainder of the report due for release on Monday.

The findings are largely unsurprising and are consistent with the last assessment report published in 2007. This latest version strengthens its statement of confidence about the Continue reading

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Thinking outside of the bell curve

Statistical distributions do not usually generate widespread public enthusiasm. Sure, some people spend hours admiring the shape-shifting forms of the beta distribution or the unflappable positivity of the exponential distribution; the limitless potential of the Gumbel distribution or the black-or-white certainty of the Bernoulli distribution. But those people usually reside at the extreme reaches of the societal bell curve.

Until now. The financial crisis has been blamed on numerous factors: inflated house prices, greedy bankers and weak regulation of Wall Street, but a commentator recently Continue reading

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Changes to the temporal distribution of Australian rainfall

The question of how rainfall intensity will change with global warming is an important one, and confidence is building within the scientific community that rainfall extremes will on average become more intense and/or more frequent as global temperatures increase. While this may be true on average, however, what is perhaps less well appreciated is that there are different types of weather systems that produce rainfall, and that these might change in different ways and sometimes even in opposing directions as the climate warms. This substantially complicates efforts to provide robust projections of likely changes to Continue reading

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Calculating the probability of compound events: a risky proposition

The following is a guest post from Dr Michael Leonard, a research associate at the University of Adelaide.

Hurricane Sandy in late October 2012 was widely noted to involve the alignment of a tropical storm with an extra tropical storm, and a cold air mass moving from the northwest helped push the storm onshore in the vicinity of New Jersey. The manner in which all these factors combined to produce the flood impact was strongly emphasized in the media discussions following the event, and here the term ‘compound event’ (following Continue reading

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How good are climate models at simulating sub-daily rainfall patterns?

Climate models are one of our most important tools to help us understand likely changes to extreme rainfall under a warmer climate. These models are complex

Timing of daily minimum rainfall throughout southeast Australia. The colours inside circles represent diurnal cycle of observed rainfall, and remainder of figure shows diurnal cycle from the WRF model.

mathematical representations of the world’s climate system, and simulate the circulation of the earth’s atmosphere and oceans. They are closely related to the numerical weather prediction models which are used to develop weather predictions, except that they are run over longer timescales (often decades at a time) and therefore need to be run at coarser resolutions. Continue reading

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An increase in the intensity of extreme rainfall?

One of the most alarming projections associated with human-induced climate change is the potential for an increase in the intensity and frequency of rainfall extremes. But how much do we really understand about the likely changes to extreme rainfall patterns over the coming decades? Continue reading

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2011: A busy year for global extremes

By all accounts, 2011 was a busy year for climate extremes. Readers from Australia will no doubt remember the year starting with extremely heavy rainfall drenching much of the state of Queensland, followed by the catastrophic flash floods in Toowoomba in the middle of January, the Brisbane floods only a few days later, and cyclone Yasi devastating northern Queensland in early February. Taking a more global perspective, it can be seen in the figure below that this was only one of many major climate disasters which occurred that year, with other notable extremes in Thailand, the Continue reading

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A warm summer in the Arctic

It is around this time every year that I start obsessively checking the National Snow and Ice Data Centre (NSIDC) website to look at the latest measurements of Arctic sea ice. I have no idea why I do this – I’m not an expert on ice, I have never been to the Arctic, and I certainly don’t like the cold. But there is something awe-inspiring about the dramatic changes taking place in this region, and I cannot help being struck by the idea that humans may play a dominant role in transforming this most hostile of environments. What is more, this year is already breaking the record for the lowest observed sea ice extent, and Continue reading

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Why blog about hydrology?

The hydrological cycle has fascinated humanity for millennia, with a diversity of ancient civilisations known to manipulate river systems for agricultural purposes, and adapt – although not always successfully – to periodic floods and droughts. It was not until seventieth century, however, that hydrology (literally, the study of water) was born as a quantitative science, with some of the first ‘hydrologists’ taking measurements of both rainfall and river flows in catchments in France, and showing that the former was sufficient to cause the latter. Since that time, continued research and developments in Continue reading

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