台灣颱風災害之影響評估──以蔬菜供需為例

Assessing Damage by Typhoon in Taiwan—an Example of Vegetable Demand and Supply

台灣每年幾乎皆會遭受颱風侵襲，為評估颱風災害所造成的影響，我們利用颱風所挾帶的豪雨對蔬菜供給產生的負面衝擊，及颱風來臨前因民眾對未來蔬菜價格上漲預期對蔬菜需求的外生改變，做為認定需求及供給函數之工具變數，並進一步估計蔬菜需求及供給函數。我們的實證結果顯示台北第一市場葉菜類之需求彈性估計值介於−0.30至−0.31之間，而台北第二市場則介於−0.35至−0.36之間，不過此兩市場之供給曲線在極短期下皆幾為垂直線。另外，結果亦顯示大豪雨造成蔬菜價格上漲，而其影響程度呈現先遞增再遞減的趨勢，且影響時間持續約四週。所以平均在大豪雨過後四週內，以台北第一市場為例，葉菜類消費者剩餘將減少4,873萬元，生產者收益增加3,157萬元，而整體社會福利損失則為1,717萬元。然而此處生產者收益增加部分並非全由農民所獲得，其中部分收益將為中間商及進口商所獲。

Taiwan has been hard hit by typhoons every year. In order to assess the damage caused by typhoon on the agriculture sector, we use leafy vegetable as an example. Particularly, we use the heavy rain fall which comes along with a typhoon as a negative shock on leafy vegetable production to identify the demand on the vegetable. Before the arrival of a typhoon, consumers usually expect that the future leafy vegetable price will rise. Thus, the information with regard to the arrival of a typhoon is used a positive shock on demand to identify the supply of leafy vegetable. Our empirical results show that the elasticity of demand on leafy vegetables is ranged from -0.30 to -0.31 in the first Taipei market and from -0.35to -0.36 in the second Taipei market, while the supply is nearly a vertical line. The possible reason may be that the supply is fixed and inelastic in very short run. Besides, the impact of heavy rain on the price of leafy vegetable increases at beginning and falls after the second week and lasts around four weeks long. As the result, over the four-week period the consumer surplus decreases 48.73 million NT dollars and producer surplus increases 31.57 million NT dollars in the first Taipei market. The welfare loss after the heavy rain fall is 17.17 million NT dollars, but note that the increase in producer surplus is not completely acquired by farmers. Instead, middlemen and vegetable importers gain part of the surplus.