氣候風險分析－以台灣近百年氣溫變化為例

Abstract

風險管理可使一個經濟單位經由科學客觀之分析，對所面臨之不確定危險進行損害之轉移或降低。近年來，在財務金融相關領域中開始利用風險值（Value at Risk, VaR）作為衡量市場風險之工具，由於風險值以簡便操作且易於理解的數字型態出現，很快便受到歡迎。 台灣之氣象觀測已累積超過百年以上之長期資料，故本研究擬以台灣近百年來之氣溫觀測資料作為測試標的，嘗試利用風險值作為衡量指標進行觀察分析。 研究結果顯示，台灣百年來的氣溫變化趨勢為升溫，而年均溫有時會掩蓋當年度氣候高低溫反常的現象。測站百年來的升溫幅度以年均最低溫的上升幅度最為明顯，都會區測站因都市熱島效應的影響，升溫現象較為顯著。 依據迴歸結果，年平均氣溫升溫速度約在1∼1.5℃/100年間，年均最高溫升溫速度在0.5℃/100年左右，年均最低溫升溫速度在2℃/100年以上。 由VaR與CVaR的計算得知極端炎熱及極端寒冷的天氣出現的可能性越來越大。經過月均溫平減前後之VaR變化趨勢雖不相同，但不論以平減前或平減後之風險值來判斷，台灣北部的氣候風險均屬較大。 以新穎的風險管理工具進行氣溫變化之分析判斷，可顯示出不同的議題焦點，值得持續關注。

Risk management is helpful for an economic unit to transfer or decrease the danger caused from uncertainty by impersonal scientific analysis. Recently, it is popular to use VaR (Value at Risk) to calculate the market risk as a result of its simplicity and numerical type. It is exceed 100 years in meteorological observation of Taiwan. This study adopts the VaR method to air temperature data of Taiwan, and would like to find the tendency of climate risk during the past century. The results are shown that the air temperature of Taiwan is increasing over this hun-dred years, especially in mean minimum temperature. The slopes of regression are about 1∼1.5℃/100 years for mean temperature, 0.5℃/100 years for mean maximum temperature, and 2℃/100 years for mean minimum temperature. Both VaR and CVaR indicate the day of extreme hot or cold appears more often in recent years. Monthly mean temperature is used as a deflator to adjust the seasonal effect of air temperature, and northern part of Taiwan is the most climate-risky area before and after the adjustment. To apply VaR method for climate risk is a novel approach and the results are really interesting.