Meteorological records have been kept for barely a century. In respect of earlier times, there is sporadic rainfall data, tax records show how good crops were and harbours recorded sea levels. The remaining signs of past climate are only the rates of tree growth, or the stalagmite precipitation in caves.
Siyang Li, Ke Ding, Aijun Ding, Lejun He, Xin Huang, Quansheng Ge, Congbin Fu, from Nanjing University and the Collaborative Innovative Centre for Climate Change, Nanjing, and the Chinese Academy of Science, Beijing, write in the American Association for the Advancement of Science journal, Science Advances, of the design of rooftops in China, down the ages, as another indicator of changes in snowfall. Apart from being one more instrument in the climate scientist’s toolbox, it could bring the spotlight on architecture as a means to tackle the climate challenge we face today.
Climate, while shaping the geology of regions, has also influenced the growth of human settlements and cities. Indeed, climate change has affected commerce and industry, and led to the downfall of dynasties. The current study in Science Advances, the authors say, is the first enquiry into how architecture proves to be a record of the climate in parts of Central and Eastern China.
“…although meteorological factors are widely considered in modern architecture design, it remains unclear whether and how ancient people adapted to climate change from the perspective of architecture design, particularly on a millennium time scale,” the paper says. The study, however, reveals “a positive trend in roof slope of traditional buildings,” and “demonstrates climate change adaptation in traditional Chinese architecture, driven by fluctuations in extreme snowfall events over the past thousand years.”
The authors consider remains of structures in the northern part of Central and Eastern China. Across the period from the second part of the Tang dynasty (618-905 CE) to the middle of the Qing dynasty (1644-1912), or about a thousand years, the region, which is full of traditional Chinese culture, provides a time-series of abundant instances for study, the paper says. The region is a semi-humid area and the climate is sensitively affected by several factors, which include the summer and winter monsoons, the cold-dry air from the North-west and warm-wet air from the South-east. As a result, conditions in the region respond sharply to climatic fluctuations, which would bring out emphatically the effects of climate change on social life, and hence on architecture, the paper says.
The sloping and curved roofs, a distinctive feature of traditional Chinese architecture, are based on underlying traditions of the beam structure used in construction. Hence, although there would be differences according to social hierarchy and aesthetics, the basic form would be maintained. And so, they are, in China, the paper says, since prehistoric times to the present. Despite this constant basic form, however, there have been significant modifications from time to time, and those, the paper says, are revealing of particular aspects of the periods.
The paper explains that the sloping structure has to do with the function of roofs to protect the dwelling from snow. The cost of the structure depends both on the load of snow the roof must bear, and the material used in building a steep slope. Roofs that face lighter snowfall can make do with a shallow slope, but if there is heavy snowfall, the snow needs to slide off before it builds up. The slope hence needs to be steeper. As a steeper slope costs more, it would be provided only where snowfall is expected to be heavy. Figure one shows two forms of the roof, one where the height to span ratio, or HSR, is low and the other with a steeper slope.
The intensity of snowfall during the period between 950 and 1750 CE was estimated using a combination of data and statistical methods. One step in the estimation was to use the available, current data to estimate the relationship between snowfall levels and variation from the mean temperature, at the relevant spots in China. And, as the topography of the region has not changed, it is considered that the relationship in past centuries would be the same as at present.
Next, the temperature data for the past period was accessed from a published study based on historical data and statistical analysis. The data is of plant and animal cycles affected by cold/warm events, and analysis links the data with available temperature information, to project temperatures where other data is not available. Such projections, which have been cross verified, are fine-grained and show variations across periods as narrow as 10-30 years. By combining that information with the current relationship between temperature and snowfall, it has been possible to arrive at the ancient snowfall intensity with the same 10-30-year resolution.
That done, the data of snowfall over the centuries was compared with the roof slope of some 200 remains of structures in the region of the study. And it was found that the HSR, or the measure of how steep the slope of the roof was, clearly increased or fell, in step with the rise and fall of the intensity of snowfall.
Figure two shows the rise and fall of steepness of the slope, and the rise and fall of the difference in temperature from the mean, over the period from 950 to 1750 CE. And we can see that both measures vary in the same way. In cold periods, the paper says, “Roofs became steeper (1100-1200 CE and 1300-1750 CE, which corresponds to the “Little Ice Age”), whereas, in warm periods, the roof pitch descended notably (1200-1300 CE, which corresponds to the “Medieval Warm Period” in Europe).” The paper points out that the roof slope lags the snowfall by 30 years, as it takes some time for construction methods to adapt to changes in severity of the winter.
“The responses of roof modification to the climatic fluctuations indicate an intelligent long-term adaptive behaviour of the ancient Chinese. They adjusted their buildings for a more stable and suitable roof formation when faced with various weather extremes caused by climate change,” the paper says. The data we have of roof architecture is more exact than the estimates of temperature that we have made. The exact HSR information can hence be used to refine the quality of temperature data, and in turn, sources of that data.
The study underlines the need, the paper says, for architects to consider the rapid climate change and frequency of extreme events that we now face. Designs hence need to be both sustainable as well as future-proof, as we may not have 30-year margins to adapt to.
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