|Abstract: ||摘要:目前極大多數學者都同意，人為因素是造成地球暖化的主要原因。如果地球暖化已經是不可避免的事，那麼面對它所可外帶給地球的後果做一客觀的、科學的評估，然後再提出可能的對應之道是學科學的人所應該做的事。至於未來要採取什麼政策、措施來減低它的衝擊，則是政治上的事。本計劃的主要目的是希望能比照外國學者，利用科學的方法、提出數據，藉以評估氣候變遷對臺灣海岸地區的影響。限於筆者個人能力，目前僅將目標侷限於臺灣現有的海岸防護措施。 可以簡單地把氣候變遷的影響分成長期和短期的兩種。前者是緩慢的，一般人無法立刻察覺的，而科學家非常擔憂的現象，如極地的冰融化、空氣及海水的溫度上昇，以及全球的海平面上昇等等。後者則是一般民眾可以感受到的劇烈天氣、天然災害的增多。2002年8月造成歐洲捷克、奧地利、德國等8個國家淹水的百年大洪水﹔2005年8月淹沒80%紐奧良市，最大風速一度達到280 km/h的颶風『卡崔娜』(Hurricane Katrina)﹔2009年八月在四天半內為嘉義縣阿里山帶來2855毫米降雨的中度颱風『莫拉克』(Morakot)﹔以及今年七月開始，持續近四、五個月的泰國大洪水等等，似乎都證實了這個推論。不管從長、短期的那一個角度來說，海岸都是可能受到地球暖化影響最大的地區。台灣四面環海，雖然不致像某些太平洋島國一樣，會有整個島被海水淹沒的危險，然而隨著溫室效應的日益嚴重，沿海地區的土地也一樣可能會被海水大量侵蝕﹔人們的生命、財產遭受損失也會日益嚴重。 台灣西部沿海地區大都設置了海岸防禦工程。同時，還有幾個大商港及數以百計的漁港。一般來說，海事工程大都是要耗費龐大的金額的。它們預期的壽命通常都是在三、五十年以上。大多數的學者都相信，到這個(廿一)世紀末，海平面可能會上昇。如果再加上考慮其它劇烈天氣的可能影響，這些海事工程是否能承受這些衝擊，維持當初設置它們的功能，是極需考慮的嚴肅課題。 一般在設計、評估時，對海岸防禦工程可能遭遇的自然條件，如最大風速、最高波浪等等，用的是所謂『極值統計模式』推估未來五十、一○○年可能會發生的機率。這種模式的一個基本假設，就是所謂的『平穩性』(stationarity)。這也就是說，(至少)它們的一階和二階矩都不會隨著時間(有太大的)變化。但是，如果學者有關全球暖化的預測–温度及海平面上昇、降水强度增加、熱帶氣旋發生機率變多等等–是正確的話，那麼幾乎所有的自然現象都會變成不合乎『平穩性』的假設。在這種情況下，用一般的極值統計模式來推估工程上可能遭遇的『最糟情況』就變得有點不切實際。同時，對工程來說也可能會危害到它們的功能與壽命。一個比較合理的作法就是用『隨時間變化的極值統計模式』來模擬自然現象。 如果說，從自然現象的紀錄中可以找到它們的統計值都在(循著某種線性或非線性的『趨勢』)變的話，那麼，把這些『極值統計模式』的參數改寫成時間的函數，一方面能更貼切地描述這個現象，另一方面對所謂『極值』可能出現機率的估算也會比較可靠。 從這個想法出發，筆者這些年來收集了『中央氣象局』全省各海象測站的波浪紀錄及若干時間較長氣象站的風速紀錄，希望從裡面找到若干「隨時間變化」的證據，以便能建立一(數)個模式，未來可以用在對台灣的海岸地區以及海事工程可能遭受的衝擊的評估上面。|
abstract:Nowadays, the majority of the scientific world agrees that anthropogenic emissions are the main cause of global warming. If and when global warming is inevitable, then it is the responsibility of the scientists to make objective estimates of the possible effects. The politicians will be responsible to make the right policies and measures to mitigate the (possible) disastrous consequences. The main objective of this project is to evaluate, based of scientific studies, future possible impacts of climate change on the coasts of Taiwan. Due, however, to limitations of the man power, only existing coastal defenses of our coasts will be considered at present. The words ‘climate’ and ‘weather’ differ in that, the former denotes long term effects, whereas the latter is a daily event. Climate may or may not change slowly and gradually, not discernable in short terms. Changes in the Arctic temperatures and melting and shrinkage of the glaciers are examples that worry the scientific worlds. Whether these are due to long-term cycle of the nature itself, or (partly or mainly) due to anthropogenic effect is still in dispute. However, as mentioned before, it is believed by the majority of the scientists that the latter is responsible for global worming. Anyone, on the other side, who experiences or witnesses the extreme weather events in recent years will not argue that their catastrophic and disastrous results. There seems to have a trend of extreme weathers increasing since the last decade of the 20th century. Extreme events, such as heavy precipitations/floods, wildfires, heat waves, draughts, and tropical cyclones/typhoons are reported almost every year. The 100-year flood of August 2002, which flown over eight European countries such as Czech Republic, Austria, Germany, has killed dozens of people, meanwhile dispossessing thousands, the estimated damage is several billions of Euros; Hurricane Katrina, with its peak strength of 280 km/h maximum sustained wind speed, flooded 80% of the city of New Orleans in late August 2005; as well as typhoon Morakot in 2009, with its record-breaking amount of 2855 mm precipitation in four and half days (August 5, 20:00 ~ August 10, 08:00) measured at Ali mountain metrological station. And more recently, the 2011 flood of Thailand where heavy rain and flooding started in July, and continued into December this year, should also be mentioned. All these seem to testify the predicted emerging threats caused by (anthropogenic) climate change. Taiwan, as an island surrounded by sea water, might not be like Tuvalu to consider relocation plans, but as sea level rises, and extreme weather increases possibly in the next 50 years, the lost of lives and properties in the coastal areas might just increase to the extent beyond imagination. The majority of the western coastal areas of Taiwan have sea defense constructions. Furthermore, there are several major ports as well as numerous fishing harbours. It is well known that the costs of coastal/ocean engineering constructions are enormous, and they are designed to have a life time of 30 to 50 years or more. It is a common engineering practice to use extreme value theory (statistics) to estimate worst possible maximum/minimum that a construction might to encounter in its lifetime. Usually, the parameters of these extreme value theories have fixed values. When, however, the climate is changing, as predicted and evidenced by researchers, it seems questionable whether estimates based on these “stationary” theorems should still be valid. A seemingly more reasonable way to consider the “worst-case scenarios” is to use so-called “time-dependent” parameters for these extreme value models. The main objective of this project is to try to build up a criterion for the assessment of coastal structures around Taiwan. In carrying out this, we will proceed in three steps: a) In the first place, we will use possible conditions derived from extreme value theorems; b) In the second step, effects due to global warming will be considered. The possible conditions will be borrowed from other researchers such as KLIMU (Schuchardt & Schirmer, 2005); c) In the third step, we will try to derive extreme value models with time dependent parameters using wave and wind records from Central Weather Bureau. The predicted T-year quantiles are then used for the possible conditions.