Impact of Climate Change on Water Security in China

Transcription

1 Impacts and Adaptation Article ID: (2009) Suppl Impact of Climate Change on Water Security in China Zhang Jianyun 1, 2, Wang Guoqing 1, 2, Yang Yang 1, 3, He Ruimin 1, 2, Liu Jiufu 1, 2 1 Research Center for Climate Change, Ministry of Water Resources, Nanjing , China; 2 Nanjing Hydraulic Research Institute, Nanjing , China; 3 Hydrology Bureau, Ministry of Water Resources, Beijing , China Abstract: Global warming has become an important environmental issue, and water is the resource most directly affected by climate change. Global warming will alter the amount and spatial distribution of available water resources by accelerating the atmospheric circulation and the hydrological cycle. Moreover, global warming would likely lead to more severe water shortages, deterioration of aquatic systems and more floods disasters. In this paper, the possible impacts of global warming on water security with respect to flood control, water supply, aquatic environment, and water conservancy engineering, are discussed. Key words: climate change; water security; impact Introduction Water is subject to the atmospheric and hydrological circulation systems, which are directly affected by climate change. It is generally believed that global climate change will result in significant increases in temperature, sea level and the frequency of extreme weather/climate events [1J2]. Climate-related studies began in the late 1970s with the launch of programs by the WMO (World Meteorological Organization), UNEP (United Nations Environment Programme) and IAHS (International Association of Hydrological Sciences), such as WCIP (World Climate Impact Program), and GEWEX (Global Energy and Water Cycle Experiment). These programs have resulted in great advances in the study of climate change, water resources, floods, and droughts. For example, Schwarz [3] analyzed hydrological regimes in northeast USA and appraised the effects of climate change on water supply. Furthermore, Karl et al. [4] conducted a preliminary assessment of the future regime of water resources in USA based on the output of GCMs and concluded that the annual runoff and floods in the northwest Pacific region would increase under future climatic change scenarios, and the impact of future climate change on water resources would be larger in low flow regions than in high flow regions. However, due to the limitation of data and technology, as well as the complexity of current climate issues, very few studies have been conducted to evaluate the effects of climate change on aquatic ecological systems and aquatic engineering. China has a large population with a low level of economic development and a vulnerable ecological environment, therefore is quite vulnerable to climate change. Due to its specific climate condition and geographical location, China suffered from many floods and droughts in the past. In the 1990s, the average annual loss associated with floods accounted for approximately 62% of the total losses of natural disasters, which was equivalent to about 1.55% of GDP for that period [5]. In addition, China is currently undergoing rapid economic development and increasing human activities; therefore, water-related issues such as deterioration of water quality, over-exploitation of ground water, and soil erosion have become severer. Global warming would likely accelerate future atmospheric and hydrological cycles, thus changing the spatio-temporal distribution of water resources. Therefore, climate change could exacerbate the water shortages that currently exist in China, as well as the deterioration of the aquatic ecological environment that is Received: March 10, 2009 Corresponding author: Zhang Jianyun, jyzhang@mwr.gov.cn 2009 Editorial Office of 34

2 occurring. It is also likely that climate change will lead to an increase in the frequency and intensity of extreme events in China such as serious floods and large-scale droughts. Hence, climate change has potential to directly threaten the water security of China. Therefore, the potential effects of climate change on flood control, water supply, aquatic ecological environments, and hydraulic engineering projects were analyzed in this study. 1 Flood control China has long been prone to floods and droughts. Floods usually bring about vast losses of life and property due to their rapid development and unpredictable nature. Accordingly, flood control is persistently a concern in China. The trend of historical flood disasters in China has demonstrated that flood control is still a major concern. Indeed, since the 1990s, many major rivers in China have flooded. Specifically, in 1991 the Yangtze River and Huaihe River flooded, while the southern Haihe River flooded in 1996, the Yangtze River, Songhua River and Minjiang River flooded in 1998, the Huaihe River, Weihe River and Hanjiang River flooded in 2003, and the Huaihe River and Hanjiang River flooded in In addition, the largest whole basin flood since 1954 occurred in the Huaihe River basin in The increasing number of high intensity rainstorms has also struck Chongqing, Nanjing, Jinan, as well as other large cities since the 1990s. Indeed, China s national annual flood loss during 1990J2005 exceeded 110 billion RMB, accounting for 1%J2% of GDP in the same period. The following issues have led to inadequate flood control in China. 1) Incomplete flood control systems, especially along major rivers. 2) Prominent issues regarding the stabilization of reservoirs. For example, approximately 37% of the constructed reservoirs in China are currently not well stabilized. 3) Weak nonstructural measures. Specifically, the current ability to provide early warnings, to forecast and manage floods and to provide emergency response needs improvement. 4) The rapid social economic development that China has recently experienced has enhanced the damage loss associated with floods; however, imperfect flood insurance acts and flood control laws have made decision-making and disaster mitigation more difficult. Climate change will also create a need to focus on the following three aspects of flood control. (1) The frequency and intensity of extreme events, such as high intensity rainstorms, have increased in response to global warming. Trenberth [6] suggested that an increase in surface temperature would lead to an increase in the evaporation of land surface and the moisture holding capacity of air, thus resulting in an increase in atmospheric moisture. The increased surface evaporation will aggravate drought disaster in some areas while leading to increased precipitation and flooding in other areas. In addition, climate change will lead to significant warming in the lower atmosphere, likely bring about increased frequencies of high temperatures, heat waves, and droughts, and enlarged areas affected by drought disasters. Strong rainstorms are usually generated by interactions between cold and warm air masses; therefore, increased warming of the lower atmosphere will increase instability of the atmosphere. As a result, increased amounts of warm air will likely flow upward, resulting in an increase in extreme weather events. Simulated results for China indicate that heavy rainfall events and rainy days will increase remarkably in most areas of southern China in response to global warming, especially in Fujian Province, the west part of Jiangxi Province, and parts of Guizhou Province, Sichuan Province and Yunnan Province of Southwest China. In addition, simulations also indicate that coastal areas of China will suffer from more frequent, and much stronger typhoons, while the area affected by droughts in northern China will also likely increase. Liu et al. [7] evaluated the historical records of storm floods in China and found the follows: a) Since the 1990s, the intensities of rainfall events of short duration recorded or obtained in flood survey in China have approached to and reached the world s records. For example, the intensity of 1300 mm in 6J7 h (surveyed value) in a rainfall event at Kuanping in Shaanxi Province in July of 1998 exceeded the previous world record; while the rainfall of mm was recorded in 24 h at Arli Mountain in Taiwan in 1996, which was close to the world record. Furthermore, the maximum rainfall intensity over Mainland China ( mm within 24 h) was recorded at Xifu Farm in Guangdong Province in August 2007 [8]. b) Decadal variations in rainstorms have shown different rising or declining trends in different areas of China. For example, the decadal maximum rainfall events of long duration in northern China and southern China both occurred in the 1960s; however, the secondary maximum process rainfall occurred in northern China in the 1950s while in southern China in the 1990s. c) Since the 1990s, floods of entire basins have occurred frequently, and rainstorm-induced geological hazards have increased. Such as the Chongqing district suffered from a severe drought/heat wave with a 100-year 35

3 Zhang Jianyun et al.: Impact of Climate Change on Water Security in China return period in 2006, and encountered a rainstorm with a 100-year return period in 2007, resulting in ten thousand tons of debris flowing into the urban area of the city and 42 deaths. Recent studies have also indicated that global warming will lead to an annual increase in rainfall in China over the next 50 years. Specifically, the annual nationwide rainfall is expected to increase by an average of 2%J3% by 2020, and 5%J7% by 2050, with the southeast coastal areas experiencing the greatest increases. This increased average precipitation will likely lead to increased frequency and magnitude of regional torrential rain [2]. (2) Recently, the number of strong typhoons affecting China has increased significantly, and as a result, the economic losses associated with typhoons have also increased. Strong typhoon or super strong typhoon has been becoming one of the severest natural disaster sources, especially since 2000, the number of China landfall typhoons, as well as its intensity, have markedly increased. But the relationship between increase in number of typhoons and climate change is still not clear, which needs to be studied in further. (3) Since the 1950s, the sea level rising rate near China s coastal line is about 1.4J3.2 mm/a. Based on projected data, global warming will lead to an average increase in sea level of 12J50 cm by 2050, while the water levels near the Zhujiang River Delta, Yangtze River Delta and Yellow River Delta will increase by 9J107 cm [2]. Increased sea levels will likely lead to an increased threat of floods in coastal areas that could be further aggravated by storm surges. 2 Security of water supply Although the total amount of water resources for China is approximately 2800 billion m 3, the amount per capita is only about 2185 m 3, which is less than 25% of the world average. Furthermore, water resources are spatially and temporally unevenly distributed, therefore the water resource has become one of the important factors which constrain the socio-economic development of China. Water supply security involves drinking water supply, agricultural water supply, and ecological water security. Currently, 40% of the population of China lives in the areas of water shortage. Huang-huai-hai plain and the inland of northwest China account for 35% of the areas currently experiencing water shortage. Accordingly, the security of drinking water in these areas is a prominent problem. A survey conducted by the Health Ministry in 1984 revealed that only 66% of the rural residents of China had access to clean drinking water. Currently, 34% of rural residents still do not have access to clean drinking water. In addition, an investigation conducted by the Ministry of Water Resources found that there are still over 300 million people in China suffering from unsafe water supplies due to problems associated with water sources and water quality. The annual water deficit for China is approximately 40 billion m 3 in a normal year. As a result, more than 400 cities out of the 668 medium-sized cities of China are experiencing water shortage, 108 of which are experiencing severe water shortage, and 160 million individuals living in urban areas are affected by water shortage. The water shortage has led to the overexploitation of groundwater. There were 56 areas of groundwater overexploitation in the 1980s; the number of areas had increased to 164 by the end of the 1990s, the total area was 180 thousand km 2, and the total accumulated amount of overexploitation was 100 billion m 3. This excessive exploitation of groundwater has caused a series of secondary ecological and social problems, such as land subsidence, seawater intrusion and groundwater pollution. Global warming leads to increased demand for agricultural irrigation water. Climate change may affect the potential evaporation during the crop growing season, which could lead to reduced soil moisture and increased demand for agricultural irrigation water. For example, the annual amount of irrigation water used in Huang-huai-hai Plain will increase by 66%J84% if there is a 20% decrease in annual rainfall. Agricultural droughts are characteristic of wide range and heavy economic losses. Since the 1990s, the annual drought-affected area in China has increased to acres, causing a reduction of kg in grain productivity, or approximately 5% of the total grain productivity. On average, the annual drought-induced economic loss is approximately RMB, which accounts for 2%J3% of the GDP of China [2]. Reduced precipitation is one of the key factors which exacerbated the contradiction between water supply and demand. Although the annual rainfall increased slightly from 1991 to 2000, it has generally decreased at a rate of 2.9 mm/10a over the past 50 years [2]. The annual rainfall in South China (the Pearl River basin), East China (the Huaihe River basin, the lower and middle reaches of the Yangtze River, etc.), and the western part of China (west of 103 E) has increased, especially in South China and East China it has increased generally at a rate of 5J40 mm/10a, with a large increase rate of 120 mm/10a in some parts of the areas. However, the annual rainfall in central China including 36

4 North China, the southeast part of Northeast China, Shaanxi Province, Sichuan Province, and the southern part of Gansu Province has decreased [8]. As a result, the distribution pattern in which southern China was generally characterized by a wet climate and northern China by a dry climate has been aggravated to some extent under the global warming. These changes have resulted in exacerbation of the discrepancy between water supply and demand in northern China. The observed discharges of six large rivers in China, i.e. the Haihe River, Huaihe River, Yellow River, Songhua River, Yangtze River and Pearl River, especially of the Haihe River and Yellow River have generally decreased over the last 50 years. Indeed, since the 1980s the recorded discharge from the Haihe River has reduced by 40%J70% in comparison with that before. However, due to extreme flood events in recent years, the recorded discharges from the middle and lower reaches of the Yangtze River and the upper reaches of the Huaihe River and Nenjiang River have increased slightly (Table 1) [9]. Climate change has already changed the amount of water available in China as well as its distribution. For example, North China was continuously dry in the 1980s, and the average annual precipitation in the Jingjin district, the Hailuan River basin, and the Shandong Peninsula during this period has decreased by 10%J15%. The average annual discharge from the Hailuan River basin was only m 3 in 1980J1989, 46.2% less than the discharge in 1956J1979. Since the 1990s, the drought area of North China has extended to the southwest. The average annual Table 1 Discharges for large rivers in China River basin Station site Average annual discharge/(m 3 /s) 1955J J J2005 Changes in discharge since the 1980s/ % Compared with Compared with 1955J J1980 Yichang J0.5 J0.8 Yangtze River Hankou Datong Tangnaihai J1.6 J3.2 Yellow River Huayuankou J21.4 J33.0 Lijin J40.5 J55.5 Huaihe River Wangjiaba Wujiadu J J4.8 Guantai J65.4 J77.9 Shixiali J64.2 J76.6 Haihe River Xiangshuipu J45.5 J61.2 Xiahui J22.4 J40.1 Zhangjiafen J45.6 J62.2 Tieling J21.9 J30.9 Songliao River Jiangqiao Haerbin J1.3 J2.5 Pearl River and Minjiang River Wuzhou Shijiao J1.2 J0.5 J2.2 J0.9 Zhuqi J0.9 J0.9 37

5 Zhang Jianyun et al.: Impact of Climate Change on Water Security in China precipitation over 1990J1998 in the upper and middle reaches of the Yellow River, including Shaannxi, Gansu and Ningxia, as well as in the Hanjiang River basin, the upper reaches of the Huaihe River, and the Sichuan Basin have reduced by 5%J10% when compared with the normal level; and correspondingly the recorded annual discharge at Lijin station of the Yellow River was 32% less than the multi-year average discharge [10]. Moreover, the water availability has decreased significantly due to persistent droughts in areas of northern China experiencing water shortage, the reduction in flow of the Yellow River, Huaihe River, Haihe River and Hanjiang River, human activitiesinduced water pollution, and excessive extraction of groundwater. In addition, higher temperatures have resulted in increased water consumption, thus increasing the discrepancy between water supply and demand in northern China. Reduced discharge occurred as the joint effect of human activity, climate change and socio-economic development; however, climate change played an important role in the reduction of river discharge. Indeed, some studies have shown that climate change might be responsible for 35%J40% of the reduction in runoff that has occurred in the middle reaches of the Yellow River [11]. China s Second Assessment Report for National Water Resources, which was based on the data from 1956J2000, demonstrated that total amount of water resources in China was still m 3, but the regional distribution has changed from 18% to 16% in northern China, and 82% to 84% in southern China. The output from the RCM-PRECIS of the Hadley Center (UK) under the SRES A2 and B2 scenarios was used to study the water vulnerability and contradiction between water supply and demand in a national key scientific research project of the 10th Five-Year Plan [12]. The study indicates that future climate change will have a significant effect on water resources in China. Specifically, the results of this study indicated that: 1) in the next 50J100 years, the average annual discharge from rivers in northern China, especially in Ningxia and Gansu Province, will decrease significantly, while the discharge will likely increase in southern China, especially in Hubei Province and Hunan Province. Therefore, climate change will likely increase the possibility of flood disasters in southern China and drought disasters in northern China. 2) Water shortage in northern China from 2050J2100 will be exacerbated, especially in Ningxia and Gansu Province, which will result in an increase in per capita water deficit. 3) Water resources in the Haihe River and Luanhe River basins are most vulnerable to climate change, and the second most vulnerable basins are the Huaihe River and Yellow River basins. Due to the dry climate, the load capacities of water resources in all inland river basins are also vulnerable to climate change. 3 Security of aquatic ecological systems Due to a dry climate and water shortage, ecological issues such as flow running dry, river channels shrinkage, soil desertification, excessive groundwater extraction, and reductions in the area of wetlands have increased. In addition, rapid socio-economic development has led to increased levels of river water pollution. A survey of soil erosion at the end of the 1990s revealed that the area of soil erosion was approximately km 2, accounting for approximately 37% of the total area of China, and approximately tons of soil was lost in each year. Moreover, the area of human activities-induced soil erosion was approximately km 2 each year. The soil erosion has led to large amounts of deposition in river channels, lakes, and reservoirs. River water pollution has aggravated greatly since the 1980s. In 1980, the annual amount of sewage released was approximately m 3. During the 2002J2006, the discharged industry waste has significantly increased, and the total discharged sewage in 2006 was approximately 2 times more in Additionally, the river reaches where water quality was below Class III standards in 1980 accounted for only 13% of the total river length in China, but this increased to 41% in Currently, approximately rural residents have problems associated with their drinking water, among them individual have drinking water problems associated with poor water quality. The impact of global warming on the aquatic ecological environment will likely lead to the following problems: 1) Reduction in wetland area. Due to the effects of climate change and human activities, rivers in northern China frequently ran dry, lake area has shrunk, and the storage of water in reservoirs has decreased significantly. As a result, the function of wetlands has deteriorated [13]. Indeed, the number of natural lakes with an area larger than 1 km 2 declined from 2800 in 1950 to 2350 in1980, which corresponded to 11% reduction in the area of lakes. 2) Coastal ecological issues caused by an increase in sea level. Increased sea level will affect the ecological system in coastal wetlands and result in sea water intrusion. Salt water intrusion will not only interfere with the supply of freshwater in the estuary region, but also cause soil salinization in coastal areas. As a result, a freshwater 38

6 replenishment project has been implemented in the Pearl River to prevent seawater intrusion. 3) Due to global warming and rapid socio-economic development, the contradiction between water supply and demand will be exacerbated, and groundwater exploitation as a complementary measure will increase. It is likely that excessive groundwater extraction will lead to unexpected ecological problems. 4) Increases in high-intensity rainstorms will aggravate soil erosion in central China, western China and Southwest China; decreased precipitation and increased temperature and evaporation will accelerate soil desertification in Northwest China; changes in the frozen soil belt in response to climate change in Northeast China and the Qinghai-Tibet plateau will likely alter the distribution and type of vegetation, which will also likely lead to increased soil desertification and erosion [14]. 5) Changes in precipitation and runoff will directly affect water quality, especially in the northern areas of China, if there is no strong and effective protection measures, water quality will deteriorate further. 4 Hydraulic engineering security Many hydraulic engineering projects of large scale have been completed or are currently underway in China. For example, the South-North Water Transfer Project (SNWTP) connects the Yangtze River, Yellow River, Huaihe River and Haihe River to optimize the allocation of water resources from different sources in northern and southern China. The project consists of a large number of large node structures and wide-spread small structures. The middle route of the SNWTP is composed of more than 1000 concrete structures, including channels, inverted siphons, aqueducts, culverts, bridges, pumping stations, cross buildings and distribution structures. Most of these structures are thin-walled and subject to complex forms of stress. As a result, destruction of one such structure by an extreme weather event could have serious impacts on the entire project. Therefore, the SNWTP is particularly sensitive and vulnerable to climate change. Climate change is likely to have a negative impact on hydraulic engineering projects. For example, a reduction in river discharge will lead to increased salinity and conductivity of water body. In addition, climate change has resulted in increases in sulfur dioxide and other acidic gases in the atmosphere; and approximately 30% areas of China are now affected by acid rain. In southeast coastal areas, increases in the sea level and frequent sea tides with increased levels of salinity could aggravate erosion damage to concrete structures of hydraulic projects. Significant increases in the intensity and frequency of extreme weather events, such as droughts, cold waves, and freezing could also have a direct effect on hydraulic engineering projects. For example, a long-lasting drought or a decline in annual average air moisture could lead to greater number of cracks appearing in hydraulic concrete materials and structures in humid areas. Similarly, extended cold waves could have adverse effects on hydraulic mass and thin-walled structures. For instance, in the beginning of 2008, southern China encountered the lowest temperatures recorded to date, and sleet and freezing destroyed many structures. Based on incomplete public reports regarding the cold waves, the direct economic loss for the water industry in Hunan, Guizhou, Sichuan, Guangxi, and Hubei provinces and Chongqing city was RMB, approximately accounting for 5.3% of the total loss reported by the Civil Administration Department in Large-scale water conservation projects are the primary structural measures being conducted to optimize the use and allocation of water resources in China. Generally, the period required for hydraulic engineering construction projects is quite long; therefore, hydraulic engineering structures in the construction and operation periods should be designed to resist the effects of various extreme climates. Accordingly, it is necessary to develop effective measures that ensure the safety of hydraulic engineering projects providing flood control and water supply. 5 Conclusions and discussion Climate change has recently drawn a great deal of public interests as an important global environmental issue. China is prone to many natural disasters, such as floods and droughts. Additionally, it is currently undergoing rapid socio-economic develop-ment, which has exacerbated ecological problems and environmental issues. Climate change has already threatened the water security of China. Under global warming, the intensity of floods and droughts in China has increased, while the discharge from six large rivers has generally declined, especially from the Haihe River and Liaohe River. Increased sea levels are also threatening the coastal flood defense system and altering the ecological environment in estuarine systems through sea water intrusion. Furthermore, future increased temperature and drought will likely affect the durability of hydraulic engineering projects designed to address these issues. It is important to note that the 39

7 Zhang Jianyun et al.: Impact of Climate Change on Water Security in China aforementioned changes in floods, river discharge, and natural disasters resulted not only from climate change, but also from the combined effects of many factors including anthropogenic activities. It is expected that climate change characterized by increased temperatures will continue. Therefore, it is essential to pay attention to the issues of water security under global warming, to enhance scientific assessment, mitigation and adaptation of water security to climate change, and to provide scientific supports for China s water security guarantee. Acknowledgement The paper is financially supported by National Nonprofit Research Programme on Water (No ). References [1] [2] [3] [4] [5] IPCC. Climate Change 2007: Impacts, Adaptation, and Vulnerability. Contributions of Working Group II to the Forth Assessment Report of the Intergovernmental Panel on Climate Change. Cambridge, UK and New York, USA: Cambridge University Press, 2007 Compilation Commission of National Assessment Report of Climate Change. National Assessment Report for Climate Change. Beijing: Science and Technology Press, 2007 (in Chinese) Schwarz H E. Climate Change and Water Supply: How Sensitive Is the Northeast? Washington DC: National Academy of Science, 1977 Karl T R, Reibsame W. The impact of decadal fluctuations in mean precipitation and temperature on runoff: a sensitivity study over the United States. Climatic Change, 1989, 15 (3): 423J447 Office of State Flood Control and Drought Relief Headquarters, The Ministry of Water Resources of the People s Republic of China. The Bulletin for Flood and Drought Disasters in China in Beijing: Water [6] [7] [8] [9] [10] [11] [12] [13] [14] Conservancy and Hydropower Press of China, 2007 (in Chinese) Trenberth K E. Atmosphere moisture residence times and cycling: implications for rainfall rates with climate change. Climatic Change, 1998, 39: 667J694 Liu Jiufu, Zhang Jianyun, Guan Tiesheng. Variations in extreme values of rainstorms and floods in China in 20th Century. China Water Resources (2): 35J37 (in Chinese) Wang Shaowu, Dong Guangrong. The Characteristics of Environment and Its Evolution in Western China. Beijing: Science and Technology Press, 2002 (in Chinese) Zhang Jianyun, Zhang Silong, Wang Jinxing, et al. Study on runoff trends of the six larger basins in China over the past 50 years. Advances in Water Science, 2007, 18 (2): 230J 234 (in Chinese) Liu Changming, Chen Zhikai. Current Situation and Trends of Demand and Supply of China Water Resources. Beijing: Water Conservancy and Hydropower Press of China, 2001 (in Chinese) Zhang Jianyun, Wang Guoqing. Impact of Climate Change on Hydrology and Water Resources. Beijing: Science Press, 2007 (in Chinese) Hydrology Bureau of the Ministry of Water Resources of China. Overall Evaluation of Impacts of Climate Change on National Freshwater Resources and Its Thresholds, in the National Key Scientific and Technological Project in the Tenth Five-Year Plan (2001-BA611B-02-04). Beijing: Hydrology Bureau of the Ministry of Water Resources of China, 2003 (in Chinese) Jin Huijun, Li Shuxun, Wang Shaoling, et al. Impacts of climatic change on permafrost and cold regions environments in China. Acta Geographica Sinica, 2000, 55 (2): 161J173 (in Chinese) Qin Dahe. Comprehensive Assessment Report for Environment Evolution in Western China. Beijing: Science and Technology Press, 2002 (in Chinese) 40