Science in brief

Cool roofs in China mitigate heat waves
In a new study of Guangzhou, researchers from the US's Lawrence Berkeley National Laboratory (Berkeley Lab) working with Chinese scientists found that white roofs can significantly mitigate the effect of heat waves.

The researchers simulated conditions from six of the strongest historical heat waves over the last decade, and compared them to 25 typical summer weeks between 2004 and 2008.

For the purposes of the study, they made all the roofs in the city as reflective as an aged white roof. While it is unlikely that will ever occur, it was necessary to have a statistically significant signal. Using a regional climate model combined with an urban model that allowed researchers to adjust roof reflectance, they found that the average urban midday temperature was lowered by 1.2 deg C during heat waves, or 50% than the 0.8 deg C reduction for typical summer conditions.

Reflective roofs, also called cool roofs, save energy by keeping buildings cooler, thus reducing the need for air conditioning. Hot surfaces such as dark roofs that warm the outside air contribute to the urban heat island effect. Previous Berkeley Lab research in China found that cool roofs could substantially reducing energy use and greenhouse gas emissions in climate zones with hot summers.

In addition to reducing city temperatures more during a heat wave, the researchers also found that cool roofs can decrease the intensity of the urban heat island effect more during extreme conditions. "Looking at the average difference in temperature between every grid cell in the city and the adjacent rural area, cool roofs had a more dramatic effect during heat waves," researcher Dev Millstein said.

US produces new fuel for space missions
The first US production in nearly 30 years of a specialised fuel to power future deep space missions has been completed by researchers at the US Department of Energy's (DOE) Oak Ridge National Laboratory (ORNL) in Tennessee.

The production of 50 g of plutonium-238 - roughly the mass of a golf ball - marks the first demonstration in the US since the Savannah River Plant in South Carolina ceased production in the late 1980s.

Radioisotope power systems convert heat from the natural radioactive decay of the isotope plutonium-238 into electricity. These systems have been used to power the exploration of the solar system and beyond, from the Viking missions on Mars, to the Voyager spacecraft entering interplanetary space, and most recently powering the Curiosity Mars Rover and the New Horizons spacecraft sailing past Pluto.

The currently available radioisotope power system is called the "Multi-Mission Radioisotope Thermoelectric Generator" (MMRTG). Essentially a nuclear battery, an MMRTG can provide about 110 W of electrical power to a spacecraft and its science instruments at the beginning of a mission. On some missions, such as NASA's Curiosity Mars rover, the excess heat from the MMRTG can also be used to keep spacecraft systems warm in cold environments.

The next NASA mission planning to use an MMRTG is the Mars 2020 rover. Fabrication of the fuel pellets for the Mars 2020 MMRTG, using the existing US supply of plutonium dioxide, is already underway.

Long view needed for climate change assessment
Most ocean data sets are far too short for the accurate detection of trends resulting from global climate change, according to research published in the journal Global Change Biology.

This study, by scientists at the UK's National Oceanography Centre (NOC), will help to make decisions about where, and for how long, we should monitor the ocean in order to spot climate trends in ocean biology.

Around 15 years of continuous data is sufficient to detect changes in the ocean that are a direct response to increases in atmospheric CO2, such as sea surface temperature and ocean acidity. However, changes that are less directly related to increasing CO2 levels are harder to pick out from the noise of natural variability. These include populations of tiny marine plants, known as phytoplankton, which are the base of the marine food web and help the ocean absorb CO2 from the atmosphere.

Lead author Dr Stephanie Henson estimates the natural variability in phytoplankton populations is so great that spotting any trends relating to climate change will require 30-40 years of continuous data. This is a problem, as currently the longest available continuous global data set is 20 years.

A brief history of the Gap Rock Lighthouse
By Ir Dr S W POON, Dr Y DENG, Ir K Y MA, Ir K F MAN and T W TSIN

The lighthouse on Gap Rock Island was amongst the earliest similar projects in Hong Kong(1,2). It was opened in 1892 and thereafter administered by the Hong Kong Government until 1950. Despite its heyday being over, the lighthouse is a unique type of built heritage whose enlightening history deserves to be retold.

In 1875 and 1876, the first three lighthouses in Hong Kong were opened at Cape D' Aguilar, Green Island and Cape Collinson(1,2). Proposals to build lighthouses on Gap Rock Island and Waglan Island were also put forward, but no agreement was reached between the Imperial Qing Dynasty and Great Britain since these two places belong to China(3). As early as 1872, the cost of constructing a lighthouse on Gap Rock was estimated at 㾶,000 by Henderson, chief engineer of the Chinese Lighthouse Department(3). In March 1886, Captain J P Maclear, RN of HMS. Flying Fish, made it known that an outside lighthouse would be needed particularly for vessels coming from the south. Thus, the proposal to erect a lighthouse on Gap Rock Island was re-opened(3).

A number of proposals were made by Hong Kong's colonial government, but all were turned down by the Imperial Qing Government until May 1888. The British Foreign Minister in Peking was informed that the Chinese Foreign Office had authorised the construction of the Lighthouse with a different arrangement. The Chinese Foreign Office instructed that the Imperial Chinese Maritime Customs be in charge of the construction of the lighthouse and its implementation be delegated to Kowloon Customs for its implementation. The colonial government was employed by Kowloon Customs as the agent for constructing and maintaining the lighthouse. The Imperial Qing Government would pay HK$7,500 for the construction and an annual maintenance fee of HK$750. The sovereignty of Gap Rock Island would still be vested with China and the land should be used for the sole purpose of the lighthouse(3,4,5).

Geography and topography
Gap Rock, a tiny island of about 12,000 sq m, is situated at the southwestern extremity of Dangan Islands (SW Lema) and Jiapeng Islands (H Kypong), and is about 50 km away from the southwest of Hong Kong. The island consists of two main portions. The southern portion, a strip of about 30 m by 120 m, lies in the northwest and southeast direction and rises 29 m above the mean sea level. The northern portion is approximately circular in shape and measures 85 m in diameter at its base. The top is a flat area, 30 m by 25 m, and is 23 m above the mean sea level6. The grassless rocky island was so named because of the existence of a gap between these two portions. The name in Chinese (F) literally means "the tail of the mosquito" and describes the tiny size of the Island.

Construction works covering the light tower, the European and the Chinese Quarters as well as a house for condensing apparatus commenced in 1889(7). The buildings were made of brickwork and clad with dressed granite blocks (Figure 2). During a visit in May 2015, severe concrete spallings with exposure of rusted iron rods at some concrete flat roofs were noticed by the authors.

The light tower (9 m in height) is flanked by the European Quarters measuring 11.5 m long, 5.5 m wide and 9 m tall. It contains a basement with storage space and a water tank, surmounted by two floors for the accommodation of the keepers. A short passage connects the European Quarters with the building (13.3 m (L), 6.3 m (W), 6.7 m (H)) where the Chinese assistant keepers and the telegraph clerk were accommodated. The lantern containing a revolving light of the first order and the level of the focal plane of the light was 43 m above the mean sea level and would be visible at a distance of about 32 km in clear weather(7).

Surveyor General S Brown attempted to reduce the in-situ works because the rough seas would prevent the construction materials from being landed during winter. Tsang Keng was appointed as the contractor, J R Mudie the engineer, and Donald Fraser the foreman. A ship titled Fame was employed from the Whampoa Dock of Hong Kong to transport all the construction materials to the island in the summer, so that erection work could be carried out in the winter(7). On 1 September 1890, the foundation stone laying ceremony was held by Acting Governor Sir Francis Fleming. All officials including the Surveyor General and the Harbour Master went to the site on board the Fame(7,8). With a total cost of HK$192,008.38(7), the works were completed in early 1892 and the light was exhibited on April 17.

The lighthouse had an extra function in providing weather information to the Hong Kong Observatory. A direct cable costing HK$87,253.33 was laid to ensure effective communication(7). In 1895, guns were mounted to replace the fog signalling apparatus and a magazine was also constructed(7).

Repair and maintenance
In 1893, all the glass windows of the lighthouse were damaged by a severe typhoon(6). Director of Public Works, F A Cooper, had doubts about the safety of the lighthouse. A consultant, who was summoned from Britain, suggested rebuilding the lighthouse on the north part of the island(9). The idea was dropped due to extremely high construction costs. In 1906, one of the biggest typhoons in history attacked Hong Kong, once again breaking the glasses of the lantern and damaging the lens prisms. The two derricks were disabled and partly washed away, and the cable was broken(7). Repairs and replacements were made accordingly.

Post Second World War
The wreckage of and damages to the lighthouse, as noted from the visit, suggest the island was subjected to heavy bombardment and intense gunfire during fighting around the lighthouse during the wars in the 1930s and 1940s. The island eventually came under the control of the People's Republic of China in 1950(10). In July 1986, a solar cell system was installed for the light and the cook house was converted into a heliport by Heyuan Engineering Company(10). All window openings have been blocked and the water tank has been exposed after the upper parts of the building collapsed (Figure 2). The lighthouse continues its service based on an automated system. In 2011, it was declared a heritage by the Zhuhai Municipal Government(10).

The Gap Rock Lighthouse, standing on China's soil throughout its 120 years of existence, was the product of the first-ever joint venture project between the Imperial Qing Dynasty and Great Britain. It was initiated by Hong Kong's colonial government in the late 17th Century, yet partly funded by the Imperial Qing Government for both construction and maintenance costs. The lighthouse was constructed by a Hong Kong contractor and maintained thereafter by Hong Kong's colonial government until 1950. Typhoon damage to the lighthouse and other installations on the island were frequent. The idea of reconstructing the lighthouse was raised but abandoned due to the high cost. Despite the destruction during wartime, the lighthouse has operated on an automated system since the mid-1980s. The history of this rare piece of built heritage shows the collaboration between different regimes well beyond the project level.

1. "Hong Kong Lighthouses", Leisure and Cultural Services Department, HKSAR Government, 2014.
2. Ha, L and Waters, D: "Hong Kong's Lighthouses and the Men Who Manned them", Journal of the Royal Asiatic Society, Hong Kong Branch, Vol 41 (2001), pp 281-320.
3. Correspondence respecting a proposed lighthouse on Gap Rock or its vicinity - presented to the Legislative Council by Command of His Excellency the Officer Administering the Government, on 17 September, 1886.
4. Hong Kong Government Administrative Report No 10 of 1888 - Correspondence respecting a proposed lighthouse on Gap Rock.
5. Sir John Walsham to Governor William Des Voeux, dated 22 May 1888; and Governor William Des Voeux to Colonial Office dated 7 July 1888, Hong Kong Government Administrative Report No 18 of 1888.
6. Gibbs, L: "The Gap Rock - Some Early History", The Hong Kong Naturalist, Vol 1, No 3, August 1930, pp 124-128.
7. Annual Reports of Public Works Department, Hong Kong Government.
8. Hong Kong Daily Press, 2 September 1890.
9. Coode, Son & Matthews report dated 10 January 1895.
10. Information from internet.

About the authors: Ir Dr S W Poon is an adjunct professor of the University of Hong Kong's Department of Real Estate & Construction. Dr Y Deng is an adjunct assistant professor while Ir K Y Ma, Ir K F Man and T W Tsin are adjunct associate professors of the same department.

Figure 1: The lighthouse on Gap Rock Island

Figure 2: Exposed water tank, brickwork and granite cladding

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