"Beijing Central Axis: A Building Ensemble Exhibiting the Ideal Order of the Chinese Capital" has been inscribed on the United Nations Educational, Scientific and Cultural Organization (UNESCO) World Heritage List, becoming China's 59th World Heritage Site. It was announced at the 46th session of the World Heritage Committee in New Delhi, India, on July 27.

The Central Axis in Beijing consists of former imperial palaces and gardens, sacrificial structures, and ceremonial and public buildings. Their combination has together been a testimony to the evolution of Beijing and showcases evidence of the imperial dynastic system and urban planning traditions of China. Actually, according to World Heritage Convention of UNESCO, the Chinese tradition and wisdom embodied in Beijing Central Axis has made important contributions to the history of urban planning worldwide.

Beijing Central Axis Source: website of UNESCO

Beijing Central Axis converges the most monumental national monuments, ceremonial buildings and landmark buildings in Chinese history since the 13th century, which bears unique witness to the Chinese civilization. How does climate affect the evolution of Beijing Central Axis? And how can we better preserve this ancient World heritage site?

The historic Beijing Central Axis, located in the center of the ancient city of Beijing, running through its north and south, was constructed in the 13th century, spanning over the Yuan Dynasty, Ming Dynasty, Qing Dynasty and modern and contemporary times, to the present.

There are numerous meteorological elements behind it.

Over the past 10 decades, the temperature and precipitation in Beijing area have undergone pronounced changes, which have also exerted a profound impact on Beijing Central Axis and its surrounding landscape.

Since the 20th century, the temperature in Beijing has shown a rising trend on the whole. The temperature has increased by 2.24℃ over the past 100 years.

During this period, the average annual precipitation of Beijing registers 588.6 mm, which shows a downward trend before 2020 and an upward trend after 2020.

As rising temperatures lengthen the seasons and warm climate, plant communities around Beijing Central Axis show a lusher scene, but at the same time, some less heat-resistant plants are also confronted with survival challenges. This change in vegetation cover not only enriches the landscape with layers and colors, but also affects the ecosystem and its balance.

In addition, the high temperature also poses a threat to ancient building materials, especially wood and masonry structures which are more vulnerable to damage amid high temperature and call for meticulous maintenance.

There are many meteorological factors influencing the protection of cultural relics and ancient buildings along Beijing Central Axis, such as heavy rain, lightning, hail, low temperature, freezing and etc. Among them, flood hazards, especially rainstorm and flooding, are one of the most frequent and grave natural disasters confronting Beijing, and their threat to ancient buildings is particularly marked.

The Palace Museum is equipped with a scientific and sophisticated drainage system, including three parts of roof, ground and underground. The roof design follows the characteristics of high ridge and steep slope, which not only makes the building more majestic and imposing, but more importantly, enables the rain to flow away quickly.

The Palace Museum Source: Qianku website

Shunning the impact and erosion of water, ancient buildings also face the direct damage caused by lightning. Due to the characteristics of material, structure and location, the fire accident rate of ancient buildings after lightning strikes is quite high.

Fortunately, many important ancient buildings on the central axis of Beijing have taken advanced lightning protection measures. Currently, the main method of lightning protection is to install lightning protection devices, including direct lightning protection devices and inductive lightning protection devices.

What is more, in the urban planning and construction management process of Beijing, the "resilient city" construction program has been incorporated, in a bid to enhance the city's resilience to natural disasters and climate change.

Editor: LIU Shuqiao