Impacts and Responses: A Case of Shihmen Reservoir in *

Paper prepared by

Keshav R Adhikari1, Yih-Chi Tan2, Jihn-Sung Lai3, Zueng-Sang Chen1, Yong-Jun Lin3

1Dept. of Agril. Chem., National Taiwan University (NTU), Roosevelt Rd, Sec. 4, city 106-17, Taiwan; For correspondence: [email protected] 2Dept. of Bioenviron. Systems Engg., NTU, Roosevelt Rd, Sec. 4, Taipei city 106-17, Taiwan 3Center for Climate weather and Disaster Research/Hydrotech Research Institute, NTU, Taipei City 106-17, Taiwan

* Paper prepared for oral presentation at the 2nd Int’l conference “Climate Change: Impacts and Responses.” University of Queensland, Brisbane, Australia, 08-10 July 2010.

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Climate Change Impacts and Responses: A Case of Shihmen Reservoir in Taiwan†

Abstract

Built in 1964, one of the oldest and magnificent in Taiwan, the Shihmen reservoir serves the multi-purpose of supplying fresh water (3.4 million people), irrigation (36, 500 ha), hydro-power (200 million units electricity annually), flood prevention and recreation. Scientific observations show that this reservoir is over time affected by increased frequencies of high sedimentation and overflows, due to unpredictable high rainfall and typhoons necessitating heavy repair and maintenance costs. This clearly illustrates an effect of global warming making such phenomena visible at local level (urban heat island effect, for example). A review of existing body of literature on Shihmen reservoir indicated that most previous studies focused from their own disciplinary perspectives. However, the relevant stakeholders of the reservoir including the practitioners and policy makers would be better served if such studies considered using system- approach. In this paper, we attempted to present the case by integrating salient features of both natural and human dimensions to identify potential areas that future management would find helpful to combat the effects of climate change. Utilizing the desktop information, we presented a macro-perspective of the case in hand to derive what interventions would be necessary from both private and public sectors to maintain the functioning of the reservoir. These led us to emphasize that for reduced risk of the climate change impacts and improved sustainability, all processes of decision-making and collective actions involving individual participants and the community at large, should put integrated efforts, develop robust upstream conservation regulations and adhere to the principles of an eco-friendly environment of the reservoir.

Key words: Climate change, Shihmen reservoir, eco-friendly, policy, participation

1. Introduction

Taiwan’s specific location at the juncture of Pacific, Eurasian, and Philippine Sea plates is subject to frequent earthquakes (Figure 1). Some earthquakes have caused major damage, such as the 1999 Chi–Chi Earthquake, which left 2,455 dead and 11,305 injured (Chen at al., 2006). Taiwan is also vulnerable to typhoons because it is located in the path of west Pacific typhoons. Roughly 3 or 4 typhoons strike Taiwan each year. Latest super typhoon (Morakot) occurred during August 5-10, 2009; death exceeded 700 and caused huge losses of public and private properties (Adhikari et al., 2009). Direct economic losses of Taiwan reach about 10 billion New Taiwan Dollars every year from floods due to typhoon (Hsu et al., 1995). As believed by many,

†Paper prepared for oral presentation at the 2nd Int’l conference “Climate Change: Impacts and Responses.” University of Queensland, Brisbane, Australia, 08-10 July 2010.

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recent typhoons resulting to high rainfall and greater floods over the past few years is in part the consequence of global warming. The Chi–Chi Earthquake shook the ground heavily paving the way for the following rains to easily produce a greater amount of debris flows. Similarly, Morakot typhoon produced mudflows of the extent that the whole village residing in the lap of a mountain in south Taiwan was buried under its solid mass. Although, such impacts appear to be determined largely by global or regional phenomena or processes, it is also reasonable that to a certain extent, the impacts could be accelerated or mitigated by the local policy and actions.

Figure 1: Map of Taiwan showing the island surrounded by seas and located at the interface between the Eurasian Plate and Philippines Plate.

In this paper, an attempt has been made to present the concept of climate change affecting the performance of Shihmen Reservoir of Taiwan aimed at deriving some policy implications for sustainability and beneficial uses of the reservoir. The paper is divided into 7 distinct but interrelated sections: The concept of climate change related to the reservoir, heat island effect, the reservoir environment, changes in effective water storage capacity of the reservoir, rehabilitation of the reservoir, and strengths and weaknesses with the reservoir related government policy, and conclusions.

2. Climate change and theoretical underpinning

Over time, the climate change has been more contentious subject among scientists. Despite a strive for the true science, recent literature shows that both consensus and skeptics prevail in the scientific world and the debate continues spanning around whether the climate change is a fact or just an anomaly (noise in the environmental data). Amidst these debates, some fundamental points are agreed by all that increasing greenhouse gas (GGs) concentrations tend to warm the planet (Intergovernmental Panel on Climate Change, IPCC, 2007). The most abundant GGs are water vapour, carbon di-oxide (CO2), atmospheric methane, nitrous oxide (N2O), ozone, and

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chlorofluro-carbon (CFCs). The two sides of the greenhouse effect are that: without it, the Earth would not be warm enough for humans to live, but if the effect becomes stronger, it could make the Earth warmer than usual. Even a little extra warming may cause problems for humans, plants, and animals.

In computer-based models, rising concentrations of these gases produce an increase in the average surface temperature of the Earth. Rising temperatures may, in turn, produce chain effects such as faster melting of ice, , changes in precipitation patterns, and storm severity commonly referred to as "climate change." Greater rise in temperatures and CO2 concentrations on the Earth atmosphere in more recent times are primarily attributed to the human causes of industrial revolution, burning of fossil fuels, deforestation, agricultural practices (mainly low- land rice), and the urbanization with increased uses of home appliances such as air-conditioning facilities, and so on.

Assessments by IPCC suggest that the Earth’s climate has warmed between 1.1° and 1.6°F over the past century and that human activity affecting the atmosphere is "very likely" an important driving factor. However, it is a fact that local and seasonal variations are much larger than the globally averages. In the case of Taiwan, transformation of the subsistence economy into the industrial economy in the last 50 years brought the nation to the status of one of the three Asian Tiger Economies. However, it did not happen without significant policy changes in land and water resource development and uses. After industrial development and urbanization, it seems plausible that Taiwan also exhibits a heat island effect. In one way or the other, this effect works in combination with other drivers of climate change contributing to the changed weather pattern in the island which may also affect the performance of local natural resources including the water bodies or reservoirs located in the surrounding natural landscapes. Does then heat island effect constitute an element of the climate change?

3. Heat island effect in Taiwan

Describing the urban heat island phenomena, Akbari (2005) characterizes urban areas as having higher air temperatures than their rural surroundings as a result of gradual surface modifications that include replacing the natural vegetation with buildings and roads. As urban areas develop, changes occur in their landscape. Buildings, roads, and other infrastructure replace open land and vegetation. Surfaces that were once permeable and moist become impermeable and dry (except in deserts). These changes cause urban regions to become warmer than their rural surroundings, conceptually forming an "island" of higher temperatures in the physical landscape.

Taiwan is relatively a small island (36000 km2) and presents a case of heat island effect primarily due to rapid industrialization and associated increases in urban population density (602 people/km2) (Lin et al., 2005). Research evidences show that this has caused the diurnal temperature increases by about 1.1oC since 1950, which is about twice the corresponding values over the major continents. Owing to rapid economic growth and living standards, energy consumption increased up to about 20 times in the last 4 decades in Taiwan. The big cities in western plains such as Taipei, , Chiyai, and cities have suffered from a regional scale heat-island effect (Lin and Tsai, 2005) and it is clearly visible on the remote

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sensing images (Liu et al., 2002). The impact was measured by making pairwise comparison where about 88% of the urban-rural pairs exhibited negative urban-heat island values during the daytime due to the impact of denser urban developments. Records show that annual and daily temperature fluctuations have also increased in Taiwan (Hsu and Chen, 2002) and these changes are also associated with the seasonality.

Regional or local climate is generally much more variable than the global because variations in one region are usually compensated by opposite variations elsewhere. Therefore, emphasizing on the importance of regional/local scale phenomena, Kukla et al. (1986) and Liu et al. (2002) documented that a proportion of the 0.5oC global warming seen over the last century for the Earth surface maybe directly related to urbanization influences. From a long-term study in Japan, Ichinose (2001) also pointed out that urbanization has weakened the daytime penetration of sea wind around big cities resulting in regional warming. It might also mean that stronger the urban heat island effect and taller the buildings, greater the deflection of the sea winds which in turn would cover a larger aerial extent in the adjacent suburb or rural landscapes. If the wind is carrying heavy load of water vapors, it is then expected that adjacent suburb or rural landscapes would receive greater storms affecting the development infra-structures such as dams, roads, power lines, erosion/landslides and so on. Based on Taipei Airplane Weather Center, Lin (2003) observed about 86% probability of a typhoon that would bring over 240 mm of rainfall to northern Taiwan if average sea surface temperature (SST) rises to 28.5oC in the nearby Pacific Ocean. The increased SST increases evaporation on sea surface and raised water vapors after hitting the surfaces of cooler temperatures would then result in a landfall. These discussions support that heat island effect can trigger the changes in weather patterns in the adjoining peri- urrban or rural areas. The following section briefly presents the physical environment and water uses of Shihmen reservoir.

4. The reservoir environment

About 52 km southwest from Taipei City, the Shihmen Reservoir is located midstream of Dahan River (catchment area, 763 km2) in northern Taiwan's Taoyuan County. The source of water originates in north of the Tapachien Mountain (Tapachienshan). Mountains with elevation above 1000 m are situated at the southeastern corner of the catchment. The major slope of the catchment faces to the northwest direction (Lo, 1994). After 8 years of construction work at a cost of US$ 85 million, the reservoir came to operation first in 1964. The reservoir is 16.5 km long and covers an area of 8 km2. It has six water gates, a power generation plant, the Shihmen Dam, and a circular walkway (Figure 2). The reservoir is approximately 133 meters high.

Since August 1, 2004, the government opened the scenic area of this reservoir to the visitors for free of charge. The catchment area has 37 km2 of cropland, and 708 km2 of forestland. The farmers only grow mono-crops such as tea, rice, oranges and bamboo in the lowland, and fruit trees (pear, plum, and peach), bamboo and pine trees in higher elevations. The reservoir has contributed greatly to the northern part of Taiwan through agricultural improvement, industrial development, enhancement of the people’s standard of living, increased employment, prevention of flood and drought and also remained a top favorite for local tourists.

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Figure 2: Photo showing (i) spillway, powerhouse and entire catchment area of Shihmen Reservoir.

Multiple uses of water from 1963 to 2001 (values 53 to 92 shown on the X-axis are Chinese Years) is shown in Figure 3. This figure shows that year to year inflow varied greatly, and water supply to domestic purpose and energy production increased steadily at the cost of water previously used for crop production (irrigation).

Electric power Irrigation Inflow Water supply 25000

20000

15000 Ton 5

10 10000

5000

0 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 Year Figure 3: Four major water uses of Shihmen reservoir (Lee and Su, 2004)

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The average annual rainfall ranges between 1500 and 2500 mm in this area. Heavy rain is concentrated during summer months. Winter months are also not very dry. The average annual temperature is about 20°C. July is the hottest month with temperature exceeding 27°C, however spikes of noon temperatures as high as 40°C this July 2010 were also observed in Taipei city not very far from the reservoir. With this background, the following section presents briefly, the temporal changes in water storage capacity of the reservoir.

5. Trend of effective water storage capacity of the reservoir

In Taiwan, typhoon is necessary because natural water bodies such as reservoirs, ponds and rivers are recharged with typhoon rainfall, lush green forest vegetation maintained and natural ecosystem revived annually. Therefore, light and medium typhoons mostly serve as a boon because they bring gentle rain and not the disaster. Contrarily, heavy typhoons are more like a curse to the nation due to their catastrophic nature and the whole nation needs to divert costly resources to the emergency preparedness. The historic trend shows that the sustainability of the Shihmen reservoir is threatened by the impacts of series of heavy typhoons of the past bringing sediment deposits of massive scales (Table 1). The sediment depositions from the recent typhoons are much higher than the design annual deposition rate (Table 1). Similarly, design gross storage capacity of the reservoir in early 1960s was about 3.16 X l03 m3 (Lo, 1994). According to the IPCC Working Group II Fourth Assessment Report (2007) the frequency of heavy rain increases in the middle or at low latitudes of Taiwan and this reservoir area occurs within these latitude boundaries reported by IPCC. Since Taiwan is in this zone, extreme hydrological events are likely to become more frequent phenomena in Taiwan’s future.

Table 1: Typhoon events bringing sediment deposition > 5000 m3 in Shihmen reservoir. Year Typhoon event Annual Annual deposition / deposition design annual* deposition （*103 M3） *103 M3） 2007 KROSA, WIPHA 9,620 12.0 2004 AERE, MINDULLE 27,840 34.8 1996 HERB, GLORIA, CAM 8,670 10.8 1972 BETTY 5,230 6.54 1970 OLGA, WILDA 5,030 6.29 1963 GLORIA 19,470 24.3 *: Design annual deposition = 80*103 m3 Source: Northern Region Water Resources Office, Water resources Agency, Ministry of Economic Affairs (http://www.wranb.gov.tw/ct.asp?xItem=2573&ctNode=703&mp=5)

Two major typhoon events of the recent past, viz., AERE, MINDULLE and KROSA, WIPHA appeared to be the most destructive in terms of reducing the effective water storage capacity of the reservoirs drastically from 237 X 103 m3 in 2004 to 210 X 103 m3 in 2007 (Figure 4). Conversely, the ‘U’ shaped little curves (Figure 4) for the time before 2004 also indicated that repair and maintenance activities particularly the dredging of sediments improved the storage and supplying capacity of the reservoir. It became feasible mainly because the earlier damages

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were not as heavy as the recent ones. Question then turns to why effective storage capacity of the reservoir did not improve after the typhoon AERE, MINDULLE in 2004.

3 3 10 m Effective Storage 250,000 245,000 240,000 AERE, MINDULLE of 2004 235,000 230,000

225,000 Effective Storage 220,000 KROSA, WIPHA of 2007 215,000 210,000 205,000 1958 1968 1978 1988 1998 2008

Figure 4: Changes in the effective storage capacity of the reservoir from 1963.5-2008.12 Source: Northern Region Water Resources Office, Water resources Agency, Ministry of Economic Affairs (http://www.wranb.gov.tw/ct.asp?xItem=2573&ctNode=703&mp=5)

It was briefly stated in the preceding section that the Chi–Chi Earthquake of 1999 shook the ground heavily. As a result, large numbers of gullies were formed upstream catchment as evidenced by the satellite images after the earthquake. The loosened fragile mass was then easily washed into the reservoir by series of rains and big typhoons (AERE, MINDULLE and KROSA, WIPHA) that followed. One hundred year-long rainfall recorded at the station showed that average annual rainfall increased from < 3000 mm to as high as 4000 mm in these years in the North of Taiwan from where the Shihmen reservoir is not that far (Figure 5). It appears that such consistent increase in annual rainfall in this area is in part related to patterns of interactions among atmospheric circulations, land uses and ocean/sea surfaces and temperature variations over time. Going back to the question of reduced effective storage capacity of reservoir, it was clear that a huge amount of sediment deposits spreading over the entire catchment area far exceeded the short term dredging capacity of the reservoir management authority. This coupled by the faulty land-use practices (not detailed in this paper) in the upstream such as growing of fruit trees, and date palm trees, both accelerating erosion in the hill slopes appear to have magnified the severity of problem (personal communications with technical staff in Water Resource Agency of Taiwan Government). These two, were seen the visible principle reasons, explaining why effective storage of the reservoir did not improve much in the short term. However, major rehabilitation work is an on-going government effort which would probably take longer and therefore full restoration of effective water storage in the short-term could not be realized in comparison with the magnitude of the damage.

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6000 annual rainfall 5500 linear regression 5000

4500

) 4000

3500

3000 Rainfall (mm

2500

2000

1500

1000 1903 1906 1909 1912 1915 1918 1921 1924 1927 1930 1933 1936 1939 1942 1947 1950 1953 1956 1959 1962 1965 1968 1971 1974 1977 1980 1983 1986 1989 1992 1995 1998 2001 2004 2007 Ye ar

Figure 5: Average annual rainfall (mm depth) for 1903 to 2007 in Keelung rain gauge station of Taiwan. Data source: Central Weather Bureau (CWB), Government of Taiwan.

The above discussions led to the point that impact of global or regional climate change could be related to local resources conditions and the levels of impacts could be mitigated by the local policy or actions governing the use of natural resources (e.g., land-use practices in the reservoir upstream) which in turn would affect the resource performances. In this case, sedimentation problem would not have occurred of this scale provided the upstream areas were kept intact by some means of controlling the human encroachment, creating some kind of buffer zone (which has not yet been developed), selecting fast growing and deep rooted plant and under story species, and providing attractive alternative arrangements to those living on the resources within the catchment boundaries in the upstream. It is then important to understand what kinds of rehabilitation efforts are being undertaken by the competent authorities in order to restore and maintain water levels in the reservoir.

6. Rehabilitation program of the reservoir

In order to improve the functioning of the reservoir, the following rehabilitation programs and activities have been launched:

Compensation policy in place: Water allocation to irrigation sector is of the least priority. The user farmers who could not acquire water for irrigating paddy fields, Council of Agriculture, Executive Yuan developed a policy to offer them a compensation of about 46,000-73,100 NTD/ha depending on the stage of rice cultivation (such as seeding). On an average, every hectare of paddy field can save about 15.5-18.9*103 m3 of water in each growing season. For the paddy field, it is common to grow two crops per year. This compensation applies to only one crop season in a year since the 2nd paddy field is rarely affected.

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Due to the torrential rain brought by typhoons during 2001-2005, the sediment was washed into the Shihmen reservoir and raised the turbidity of raw water to 80,000-120,000 NTU (normally 30-50 NTU). Due to reduced input of water into the reservoir, government suspended water supply to about 29% of the irrigated rice area in 2002. In 2004, this kind of incident induced the 18-day water shortage in Taoyuan area, and the economic loss of this event was calculated to be about 4.92 billion NTD. The number of affected households for drinking water supply amounted to 770,000.The damaged power plant suffered loss of annual revenue of 0.57 billion NTD during the period of repair.

In the mean time, an alternative water supply arrangement was being made to the disadvantaged. For example, a plan was made to construct a new dam upstream of the Shihmen reservoir but it was later cancelled because estimated construction time (roughly 20 yr) was too long and the inconvenience it may impose when building the new dam. Building an upstream new dam can affect the normal operation of Shihmen Reservoir.

The major rehabilitation, control and supervisory works: In 2006 and 2007, two phases of mitigation plan of Shihmen reservoir and its upstream catchment were launched with a total estimated cost of 25 billion NTD (special budget). This budget came into effect after promulgating eight articles on January 27, 2006 under Presidential Decree Hua-Zong-Yi-Yi-Zi- 09500012581; effective for a period of six years from the date of promulgation in order to improve water supply to safeguard the water use rights of the residents (http://shihmen.wra.gov.tw/lp.asp?CtNode=6533&CtUnit=1274&BaseDSD=7).

Phase I of the plan is for 2006-2009 and Phase II for 2009-2011. The plan includes the upstream watersheds, reservoir, and improvements of downstream water treatment plant. z Upstream catchment area conservation, restoration, and regulation (cost allocation is 8.855 billion NTD) 1. Land use management 2. Land use, environment, and disaster prevention monitoring project 3. Catchment conservation and restoration plan 4. Promotion of environmental education z Reservoir storage area emergency water supply engineering projects and reservoir improvements (11.195 billion NTD) 1. Surface water pumping capacity of 960,000 tons/day 2. Emergency repair of power plant and the outlet of the river channel 3. Three new permanent intakes for 1,400,000 tons/day 4. Improvement of the afterbay, auxillary storage pool, and artificial lake at floodplains 5. Debris barriers for blocking the debris 6. Dredge through hydraulic (PRO, sluiceways, spillways, silt suction…etc.) and mechanical (grab hopper, on-land excavation, divers, cable cars, conveyor belts, tunnels, barges…etc.) means 7. Provide incentives for reuse and recycle of dredged material for construction works. Prioritize the use of domestic gravel and sand as light aggregates. 8. Sediment ejection through tunnels bypassing the storage area z Major pipelines improvement downstream and water supply stabilization (4.95 billion NTD)

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1. Increase the treatment capacity to 60,000 m3/day of Dai-nan water treatment plant 2. Increase the treatment capacity by 500,000 m3/day of Shi-men water treatment plant 3. Increase the treatment capacity to 140,000 m3/day of Shi-men water treatment plant 4. Project for water supply from Tahan River to Taoyuan area (including connection between the Northern and the Southern Taoyuan) 5. The two-way water supply between the Taoyuan County and

Seven public sectors, viz., Council of Indigenous People, Ministry of Interior, Ministry of Transportation and Communication, Council of Agriculture, Water Resource Agency of Ministry of Economy Affairs, Taiwan Water Corporation, and the local governments are responsible for restoration of the upstream catchment area. Obviously, much of the restoration would depend on their coordinated efforts.

The work is supervised by the task force committee of mitigation plan of Shihmen reservoir and its upstream catchment which consists of representatives of related authorities (such as just mentioned above) and experts, duty governors, and related private sectors( such as Taiwan Water Corporation). The rehabilitation work including compensations to water users is totally funded by the Central Government of Taiwan.

7. Strengths and weaknesses with the reservoir related government policy

Major strengths: 1. Infrastructures which can largely reduce possibility of failures of the water supply system. 2. The system is highly integrated and can support each others’ needs. Weaknesses: 1. Short term strategy, the reduced storage is hard to recover. 2. The upstream watershed management is limited because it doesn’t include strong codes for land use, attractive alternative arrangements for local residents is lacking in the existing reservoir conservation policy and regulations. 3. Different sectors of the plan have different authorities instead of an inter-agency authority although a task force committee is formed. Suggestions: 1. Development of a national spatial plan is necessary to help planners to be able to easily locate the best suited and alternative locations for sustainable reservoir development. 2. Reforestation to increase the stability of slope land and demarcating a buffer-zone to reduce human encroachment. 3. Raise the price of the water which is cheaper compared to other countries’ to reduce the daily volume of water per capita and to increase water use efficiency (WUE). 4. Increase WUE by reusing and recycling of gray water. 5. For agriculture purpose, lower water quality of water can be used instead. 6. Given the upstream check dams are fulfilled and capacity of the reservoir downstream is greatly reduced, there is high possibility that heavy typhoons in near future may easily break the dam of the reservoir. The authority should therefore be prepared for protecting the infrastructures and water supply against the worst scenarios. 7. Adhere to the principles of developing an eco-friendly environment of the reservoir.

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8. Conclusions

In this paper, we present the temporal changes in effective water storage capacity of Shihmen water reservoir of Taiwan in relation to impacts of climate change and government responses involving major rehabilitation task of the reservoir. Although immediate reason for reduced storage capacity of the reservoir was primarily attributed to the increased sedimentation in more recent times, we recognize that elements of climate change would have triggered for such new records in this region. Although global climate change may continue to be a subject of huge debate, research evidences show that heat island effect raising urban temperature and rainfall patterns appear stronger in Taiwan affecting the sustainability of Shihmen reservoir. The literature review work observed that while government policy instruments are set to reservoir restoration, we emphasize on the need to invest enough to protect upstream land-uses by involving local stakeholders living in the area to help develop an eco-friendly environment of the reservoir. Integrating physical repair work with social aspect of the reservoir is a must for a robust upstream conservation plans and outcomes needed to cushion the reservoir capacity against the unprecedented high rainfall and sedimentation in the future.

Acknowledgements

The authors appreciate Mr. Yo-ta Chen –a scientific staff working for the Water Resource Agency under Ministry of Economic Affairs in Taipei, for furnishing some of the very important information to this paper.

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