在可完全執行下之最適水權費費率的訂定

Optimal Pricing of Water Rights for Efficient Use

本文考慮水權人對地面水與地下水整合使用之需求行為，建立一個社會規劃模型，藉以訂定以社會淨效益最大化為目標的水權費費率，並分析其比較靜態與比較動態的特性。結果顯示最適費率應因時而異、因地而異、因水權量而異，因用水標的而異、因水源而異；這些原則適足以說明當前開徵水資源費之諸多國家的作法。分析結果亦顯示，地下水水權費費率應隨時間而遞減，地面水費率則反是，而地下水之邊際損害成本大於地面水之邊際損害成本為地下水費率大於地面水費率之充分條件，但非為必要條件；二者在長期下均將趨於收斂。本文同時明白劃分了最適水權費費率與水資源之影子價格的差異，在短期下，前者可能大於、等於或小於後者，但在長期穩定均衡狀態下，地下水之最適水權費費率仍應大於其影子價格。 Among the various options to enhance efficient use of water resources, the levy on water rights tops them all in terms of the economic, social and political concerns, and had received nation-wide support in Taiwan. This is not only because the levy was already authorized by the Water Act long time ago (yet never in practice since then), but because the collection of water-rights fee represents an immediate and acute conflict between the government and water rights owners. This paper identifies a number of reasons to explain why water resource is not used as efficiently as it could be. Based on a dynamic optimization model, a socially optimal pricing scheme of water rights is proposed to enhance efficiency of water use. To make the pricing scheme theoretically sound, several important factors are taken into account, including integrated use of surface water and ground water, alternative incentive instruments, government budget constraint, and restrictions on hydraulic head to prevent ecosystem from catastrophe or to assure sustainability. The results indicate that the optimal levy might be different from the conventional shadow price of water resources. A comparative static analysis is presented to show how the optimal levy should be adjusted in response to changes in water-rights allocation and geographic parameters such as hydraulic head, etc. A comparative dynamic analysis is also presented to describe the time path of the optimal levy on the water rights of ground water as well as surface water.