According to the statistics compiled by the World Health Organization, around 800,000 people commit suicide every year. Most suicides occur in low- and middle-income countries. As an example, India has more than 130,000 suicides each year. With more than half of India's working population employed in agriculture and one third of the population living below the international poverty line, the Indian public generally believes that the suicide rates of their country has a connection to the increasing variability of agricultural income. However, there were no quantitative research and relevant data supporting this argument. According to media reports, Tamil Nadu, a state in southern India, suffered this year the worst drought in the last 140 years, triggering hundreds of suicides. Skulls and bones said to belong to the farmers who killed themselves were piled up at central New Delhi for protest.
The University of California in the US published this year an in-depth analysis of the causes of the high suicide rates in India, shedding some light on the issue. The researcher analyzed the suicide rates from 1967 to 2013 reported by India, agricultural yields and climate data. It was found that the suicide rates had doubled since 1980 and there were close relationships between the annual suicide rate, agricultural yield, and the temperature and precipitation of the growing season. The study result showed that an increase in temperature during the growing season would reduce the agricultural yield and increase the suicide rate. Similarly, a decrease in precipitation during the growing season would decrease the agricultural yield and increase the suicide rate. In contrast, variations of temperature and rainfall in non-growing seasons showed no impact on suicide rates. The study further revealed that the impacts of temperature and rainfall during the growing season could last several years. Another important finding was that there seemed to be no adaptation measures taken by India to reduce the impacts brought about by climate change. It was estimated that climate change in the last three decades had already taken a toll of more than 59,000.
The Fifth Assessment Report of the Intergovernmental Panel on Climate Change stated that climate change had an overall negative impact on global agricultural yield. As the climate continues to warm, the major agricultural yields in tropical and temperate regions will continue to decrease if there are no adaptation measures in place. The Paris climate summit agreed to keep global temperature rise below 2oC. However, based on the existing pledges made in the Paris Agreement, global temperature rise by the end of this century is likely to be around 3oC relative to pre-industrial levels. Climate change is threatening the survival of some of the vulnerable populations. While we should strengthen our emission reduction efforts to keep the temperature rise in check, we also need to be prepared for the impacts brought about by the warming climate.
Everyone has compassion on others, not to mention thousands of lives. Could we afford to procrastinate in taking actions to mitigate and adapt to climate change?
Figure 1 Climate change is threatening the survival of some of the vulnerable populations (Courtesy: Pixabay)
 World Health Organization: Suicide fact sheet
 Climate change linked to 60,000 farmer suicides in India over the last three decades, study claims
 Climate change causing suicides in India as crops fail
With a hilly terrain, Hong Kong is prone to the hazards of landslides during rainstorms, in particular for steep slopes in developed areas. Over the years, there were severe rainstorm events in Hong Kong that triggered disastrous landslides and resulted in heavy loss of lives. Apart from the notorious landslide events in 1966 and 1972[1, 2], another catastrophic incident in the early part of Hong Kong history occurred in 1925 at Po Hing Fong, a quiet and luxurious residential area in the mid-levels near Caine Road on Hong Kong Island.
At round 9 a.m. on 17 July 1925, the retaining wall of In Mi Lanewhich was beneath Caine Road collapsed after days of heavy rain. Large amount of debris ran down to Po Hing Fong and swept away seven four-storey houses from No. 12 to No. 16 (see Figures 1 and 2) with some thirty families inside, causing 75 death in this tragic event. The victims of this incident were all rich merchants and influential dignitaries, including Mr Chau Siu Ki, J.P., owner of No.12, former Chairman of the Tung Wah Group of Hospitals and a former member of the Legislative Council, and most of his family members in total 11 persons. His son, Sir Chau Tsun-nin, CBE, survived in this disaster. He was later appointed as a member of Executive Council and Legislative Council, and was knighted in 1956. For No.13-14, the owner was a descendant of Mr Chiu Yu-tin, one of the founders of Nam Pak Hong and the third Chairman of the Tung Wah Group of Hospitals. No.15 was owned by Mr Wong Pak San who was a tycoon and a former Principal Director of the Tung Wah Group of Hospitals. At the time, this was the deadliest rainstorm in the early days of Hong Kong which hit the headlines of many local newspapersand aroused major concern in the community. The event is also keeping the record of the highest mortality in a single landslide event in Hong Kong (see Table 1).
Figure 1 A rough sketch of the street map around Po Hing Fong in the 1920s.
Figure 2 Workers clearing away the debris of the collapsed retaining wall and houses at Po Hing Fong in July 1925 (photo courtesy of Mr C M Shun).
As shown in Figure 3, the weather in Hong Kong was unsettled with occasional heavy showers from 14 to 16 July 1925 with a total of about 140 mm of rainfall recorded at the Observatory during the period. The weather deteriorated further with torrential rain in the early morning on 17 July and by 9 a.m., more than 240 mm of rainfall had fallen at the Observatory since midnight. Overall, the total rainfall during the period of 14 - 17 July at the Observatory was around 404 mm. While there was no rainfall station near the site at Po Hing Fong, the total rainfall recorded at the Botanic Garden from 14 to 17 July 1925 was about 436 mm (17.17 inches) according to reports by the Botanical and Forestry Department at the time, suggesting that the rainfall amount over Hong Kong Island during the period was likely to be comparable or slightly higher than that recorded at the Observatory in Tsim Sha Tsui.
Figure 3 Hourly rainfall recorded at the Hong Kong Observatory from 14 to 17 July 1925
Looking back at the weather charts, a tropical cyclone made landfall to the east of Hong Kong near Shantou on the night of 14 July and tracked northwards, weakening over eastern China in the next couple of days (Figure 4). The southwest monsoon affecting the coastal area of Guangdong strengthened in the wake of the landfalling tropical cyclone and brought unsettled weather to Hong Kong on 14-17 July (Figures 5 to 7). The Hong Kong Observatory hoisted the local storm signal No. 5 (meaning at the time Gale winds expected to affect Hong Kong from the west) between 4:10 a.m. on 14 July and 10:00 a.m. on 15 July. Coincidently, this was very similar to the main cause behind the historical rainstorm event that occurred just over a year later in 1926 after another tropical cyclone made landfall near Shantou. However, it sounds a bit strange that, according to the track of the tropical cyclones at the time, both storms continued to tracking north after making landfall to the east of Hong Kong, but they still caused heavy rain in Hong Kong. This may not be in line with our general understanding that the heavy rain in Hong Kong induced by the strengthening of the southwest monsoon usually occurs when a tropical cyclone moves west to the north of Hong Kong (at 115oE or its west) after making landfall to the northeast of Hong Kong. Did these two tropical cyclones which brought disastrous rainstorms to Hong Kong come closer to the north of Hong Kong than what were depicted in the historical records of the Observatory? It may be a subject of further research.
Figure 4 Track of the tropical cyclone from 9 to 16 July 1925 that affected the landslide at Po Hing Fong.
Figure 5 Weather chart at 1400 H on 14 July 1925.
Figure 6 Weather chart at 0600 H on 17 July 1925.
Figure 7 Hourly mean wind speed and direction recorded at the Hong Kong Observatory on 14-17 July 1925. The wind speeds were calculated from data recorded by the Beckley anemometer at HKO Headquarters in 1900 and the conversion factors from HKO Technical Note No. 66.
During the inquest in the Coroner's court, Mr Charles William Jeffries, the then Acting Director of the Hong Kong Observatory, analyzed the rainfall records in June and July, and indicated that while the rainfall of this event was not unprecedented, it was also not common. A similar quantity had only been recorded on three occasions previously in 1885, 1891 and 1892. There would not be much difference between the rainfall at Po Hing Fong and the Hong Kong Observatory on that day. Summarizing the evidence and statements from the expert witnesses and the engineers of the Public Works Department, the collapse of the retaining wall was mainly attributed to inadequate safety margin of the retaining wall, deficiency in drainage system and judgment error in the retaining wall inspection in 1923. The court also offered the following recommendations for improvement:
Later on the Legislative Council passed in its meeting on 24 September 1925 a funding of HKD 241,750 for the repair of the rainstorm damages. In the Legislative Council meeting on 22 October 1925, the Government committed to conduct systematic inspection of retaining walls in different districts. As the Government was not obligated to use public funds to maintain private retaining walls, they will inform the owners of the retaining walls with problems to carry out the repair work . Canadian geologist, Dr William Lawrence Uglow, arrived at Hong Kong to conduct a comprehensive geological survey on 6 November 1925 and submitted a study report on 21 April 1926. He pointed out that the weathered granite can be very vulnerable and the retaining wall of Po Hing Fong was a typical example of this. While the report mainly focused on the feasibility of developing underground water resources, it could be considered as a response by the Government to the recommendation of establishing the committee of experts.
Although the rainstorm in 1926 set a historical rainfall record, it was relatively less deadly than that of 1925. As such, the proposed amendment of the Building Ordinances was not submitted to the Legislative Council until 1935. The amendment was then passed with a number of new measures including regulations on the construction of foundations, restricting the maximum height of a retaining wall to 25 metres, at least one weep hole of not less than 75 millimetres in diameter for every three square metres, installing a hydrophobic layer at the back of each retaining wall, accompanying the design with a stress diagram, and increasing the fine to 500 dollars for any offence against the Building Ordinances.
The Po Hing Fong disaster in 1925 is still a record keeper of the highest death toll in a single landslide event in Hong Kong. Although the rainstorm did not set a new rainfall record, the disastrous landslide occurred due to inadequate safety margin of the retaining wall, deficiency in drainage system and judgment error of the retaining wall inspection. Given the concerned retaining wall was designed over a century ago (referring to the completion time) and the relatively primitive geotechnical engineering knowledge at the time when compared with the present day, the below par safety margin of the retaining wall was only a post-event assessment and not totally the fault of the then engineers. Accidents and disasters are usually the result of a combination of factors rather than a single one. Coincidentally, the accumulated rainfall of the rainstorm on 18 June 1972 was also not extreme enough to break any historical record, but the induced landslides resulted in the highest mortality in the history of Hong Kong. Since the Government established the Geotechnical Engineering Office (GEO) in 1977, the upgrading and maintenance work of man-made slopes had improved significantly with a noticeable decrease in the number of landslide fatalities (Figure 8). This truly demonstrates that the Government has been working in the right direction for slope safety and landslide prevention.
Against the background of climate change, extreme weather events including heavy rain are expected to become more frequent, posing a great challenge to the safety of natural slopes. With a view to preparing Hong Kong for the climate change challenges, we have to learn from the historical lessons to improve prevention measures and make a concerted effort to better the slope safety and maintenance work. Moreover, we should promote public awareness and enhance the resilience of the community against the risk of natural terrain landslides in Hong Kong.
Figure 8 Landslide fatalities in Hong Kong (Data source : GEO)
T. C. Lee, K.Y. Ma* and C.M. Shun
(* Mr K.Y. Ma is a retired government engineer and also an enthusiast in the history of engineering in Hong Kong. He is currently Adjunct Associate Professor at the Department of Real Estate and Construction, University of Hong Kong)
 T. Y. Chen, 1969 : The severe rainstorms in Hong Kong during June 1966, Supplement to Meteorological Results 1966, Royal Observatory, Hong Kong
 T. T. Cheng and Martin C. Yerg, Jr, 1979 : The severe rainfall occasion, 16-18 1972, Royal Observatory Technical Note No. 51.
 In Mi Lane is no longer exist nowadays
 Report of the Director of Public Works for the year 1925 http://sunzi.lib.hku.hk/hkgro/view/a1925/576.pdf
 South China Morning Post and 華僑日報 on 18 July 1925; the China Mail, and Hong Kong Daily Press on 20 July 1925
 Ho Pui-yin, 2003: "Weathering the Storm: Hong Kong Observatory and Social Development", Hong Kong University Press, 364 pp
 Unforgettable Incidents @ Kwun Tong, https://mmis.hkpl.gov.hk/kt_03
 Yang, T. L., S. Mackey and E. Cumine, Final Report of the Commission of Inquiry into the Rainstorm Disasters 1972, GEO Report No. 229
 Report on the Botanical and Forestry Department for the Year 1925, Appendix N to Hong Kong Administrative Report for 1925. http://sunzi.lib.hku.hk/hkgro/view/a1925/573.pdf
 The Phenomenal Rainstorm in 1926 http://www.hko.gov.hk/blog/en/archives/00000135.htm
 Lam, H.K., 1975: The August rainstorms of 1969 and 1972 in Hong Kong. Hong Kong Observatory Technical Note No. 40
 W.C. Poon, HKO Technical Note No. 66, 1982: Tropical cyclone causing persistent gales at the Royal Observatory 1884-1957 and at Waglan Island 1953-1980
 Hong Kong Daily Press, the China Mail and Hong Kong Telegraph on 25 July 1925
 Hong Kong Telegraph on 5 September 1925
 Report of Hong Kong Legislative Council Meeting on 24 September 1925
 Report of Hong Kong Legislative Council Meeting on 22 October 1925
 WL Uglow, Geology and Mineral Resources of the Colony of Hong Kong, 1926
 Hong Kong Government Gazette, No. 300, 12 April 1935
 There were three consecutive days with daily rainfall exceeding 200 millimetres on 16-18 July 1972, unprecedented in the record of the Hong Kong Observatory
 GEO, 2016 : Natural Terrain Landslide Hazards in Hong Kong http://www.cedd.gov.hk/eng/publications/geo/naturalterrain.html
 Telegram from the Governor of Hong Kong to the Secretary of State on 30 May 1957, reporting the damages of the rainstorm on 22 May 1957
Hong Kong is a densely populated coastal city with complex topography and large variations in the extent of urbanization. Weather data from various automatic weather stations of Hong Kong reveal that there are significant temperature variations over different parts of the territory. In some cases, there could also be noticeable temperature differences between stations within the same region (e.g. urban area) due to the influence of weather condition and surrounding environment.
Main causes of spatial temperature variations
Among the weather stations in Hong Kong, the Hong Kong Observatory Headquarters (HKOHq) at the heart of Tsimshatsui is one of the World Meteorological Organization stations in Asia with over a century of continuous observations of essential surface meteorological observations. With the advent of the automatic weather station network since 1980s, local climate statistics at enhanced temporal and spatial resolution have also been compiled over the past several decades. Figures 1(a) and 1(b) show respectively the spatial variations of average maximum temperature in summer (June - August) and average minimum temperature of different stations in winter (December - February) in the years 2010-2015. The observed spatial temperature variations can be attributed to three main factors, namely geographic location, site environment, and weather condition (see table in the Appendix). The combined effect of these factors will contribute to the day-to-day or seasonal changes in spatial temperature patterns over Hong Kong.
Figure 1(a) Spatial variation of the average maximum temperature at different stations in summer (June - August) for 2010-2015. Stations on high ground are in green.
Figure 1(b) Spatial variation of the average minimum temperature at different stations in winter (December - February) for 2010-2015. Stations on high ground are in green.
Some interesting cases for illustration
High temperatures on 24-27 June 2016
Under the dominance of the subtropical ridge, the weather was generally fine and very hot in Hong Kong with the maximum temperature at HKOHq topping 35oC on 24-27 June. Located roughly at the centre of the urban area in Kowloon with significant on-going urbanization effect, HKOHq experienced a long-term decreasing trend in wind speed. With very little wind to speak of and under prolonged sunshine during the day, HKOHq reported very high daytime temperatures over this period. Meanwhile, there were also isolated showers each day affecting the northern part of the New Territories and parts of Sai Kung and Hong Kong Island that suppressed daytime temperature rise elsewhere. As a result of site environment, geographic exposure and local weather conditions, the maximum temperatures at HKOHq ended up higher than many stations in the territory (the situation on 25 June as an example shown in Figure 2).
Figure 2 Daily maximum temperature at different stations and daily rainfall distribution in Hong Kong on 25 June 2016. Stations on high ground are in green.
Clear and cold morning on 18 December 2010
Under the influence of a continental airstream over southern China, local weather was mainly fine on 17 December. Light wind condition and clear sky at night enhanced the radiation cooling effect in Ta Kwu Ling, bringing the temperature all the way down to a minimum of 0.2oC in the early morning on 18 December 2010. In the urban area, shielded by the urbanization effect, the night time cooling rate was much slower and the minimum temperature at HKOHq was 10.7oC, more than 10 degrees higher than that of Ta Kwu Ling (Figure 3).
Figure 3 Schematic showing variation of daily minimum temperatures across the territory from urban to rural areas on 18 December 2010.
Consistency in temperature observation amid changes
Hong Kong is a high-density city with a constant need for new development. HKOHq and other weather stations, either in rural or urban areas, will unavoidably experience a varying degree of changes in their surrounding environment over time (e.g. land use, building development, vegetation coverage, etc.). The temperature at HKOHq has been serving as one of the key references for Hong Kong since 1884. The setting up of more weather stations over different parts of Hong Kong, including those within the urban area itself, has added more spatial information for reference in recent years. Analyses of the temperatures of HKOHq and other urban stations nearby suggest that the year-to-year and seasonal variations of these urban stations, as well as their overall trends, are generally in line with each other despite the observed spatial differences in geographic location and site environment. Long-term weather observations from these stations, in particular data at HKOHq that are more than a century long, document the climate variations in Hong Kong through time due to global climate change impact as well as local urbanization effect, thereby providing an invaluable source of climate information not only for Hong Kong but also for the world.
T.C. Lee, K.W. Li and Y.H. Lau
 秋風夜雨 (Chinese only)
 Why is my home colder?
 The Higher the Place, the Stronger the Wind?
 What is gravity wind?
 Warm nights
 Example: Exposure of Kai Tak Wind Station