一個考量外部性的補貼政策與政府現行治水政策之成效比較–以彰化縣大城鄉為例

Evaluation of the effectiveness of a subsidy policy with externality consideration and the Flood Control Program in the Da-cheng County

本研究以大城鄉的蜆養殖業為例，提出一個以地下水使用之外部性影響作為補貼優先依據的政策，來管制地下水使用，進而解決因超抽地下水所導致的地層下陷與淹水問題，我們模擬當政府以補貼來減緩地下水使用時，其所需的支出，以及這項管制在減緩地層下陷後，於未來所能避免的淹水損害。若將本研究的補貼支出及避免掉之淹水損害與政府目前正在當地推行的「易淹水地區水患治理計畫」進行比較可發現，本研究設定之各種地層下陷管制情境所能獲得的益本比值，皆較政府的治理計畫為高，在某些特定的管制設定下，經保守估計的益本比值更可達1.15，此隱含政府若能由源頭來解決水患問題，則能將資源作更有效率的使用。

Using Da-cheng Township as an example, this research proposes a subsidy policy that based on the severity of externality from groundwater extraction to mitigate the land subsidence and flood problems associated with the overuse of groundwater by calm farmers in Taiwan.We simulate the required total subsidy expense and the monetary value of avoided flood damages fromalleviating the land subsidence and find that the benefit-cost ratios from our proposed subsidy regulation are all higher than that from the Flood Control Program in the Flood Prone Areas currently adopted by the government. Under certain regulation scenario suggested in our study, the ratio can be as high as 1.15. This implies that if the government wants to use the limited budget more efficiently, it should solve the flood problem from its very beginning.