蘭陽平原的建成環境改變對夏季弱綜觀降雨型態影響之研究

Abstract

在過去已有許多大氣模式類與統計類的文獻指出在全球各大都市中，如亞特蘭大、北京、臺北，都市化導致地表建物增加的過程，已顯著影響當地的降雨型態。從大氣方程推導的角度，可以預估不同的都市熱島程度，會帶來不同的熱對流條件，進而讓降雨型態有所差異，該結果已在多篇數值模式的研究中得到證實。透過臺灣近二十年來的衛星影像分析，發現除了在各大都會區外，鄉村地區同樣面臨了建物面積的急遽增加。以宜蘭地區為例，蘭陽平原各處皆發生建物擴張的情況，多數建物為散佈在蘭陽平原中的農舍。該種建物增加型態，並非如同大型都會區的集中式都市擴張，而是分散式地增加於平原中，這與過往文獻主要討論的都市擴張有所不同。因此，本研究針對蘭陽平原近二十多年來的改變，以弱綜觀事件為目標，討論建物以分散式增加的情況下，對當地的降雨型態帶來變化。分析結果指出蘭陽平原的建物有逐年增加的趨勢，造成當地熱島效應增強。而整體熱環境的改變，更使當地的降雨型態產生變化。不僅增加弱綜觀事件的發生機會，也增加弱綜觀事件對於當地降水的影響程度。同時，也讓當地更容易出現極端的弱綜觀事件。可以得知在臺灣鄉村地區，建物分散式地擴張型態，同樣造成降雨型態發生改變。

In the past, there have been many atmospheric models and statistical studies showing that the increase of buildings resulted from urbanization has significantly affected the rainfall patterns in major metropolitan areas around the world, such as Atlanta, Beijing, and Taipei. From the perspective of atmospheric equation, it can be predicted that different level of urban heat islands will bring about different thermal convective conditions, which will lead to different rainfall patterns, and this result has been confirmed by a number of numerical model studies. Analysis of satellite images in Taiwan over the past two decades reveals that, in addition to metropolitan areas, rural areas are also facing a rapid increase in building area. In Yilan, for example, building expansion has occurred everywhere in the Lan-Yang Plain, and most of the buildings are in form of farmhouses. Instead of centralized urban sprawl as in the case of large metropolitan areas, this type of building increase is dispersed in the whole plain, which is different from the urban sprawl that has been discussed in the literature in the past. Therefore, this study focuses on the changes in the Lan-Yang Plain over the past two decades, and discusses the changes in rainfall patterns under the scenario of decentralized building growth under weak synoptic condition . The analysis results show that there is an increasing trend of building construction in Lan-Yang Plain, which leads to the enhancement of the urban heat island effect. This also leads to changes in local rainfall pattern. Not only increases the chance of occurrence of weak synoptic events, but also increases the impact of weak synoptic events on local precipitation. At the same time, it also makes the ground more susceptible to the occurrence of extreme rainfalls. It can be seen that in the rural areas of Taiwan, the dispersed expansion of buildings also causes changes in rainfall patterns.