在地下水水權交易制度下之用水決策與取水許可證之價格分析

Water Use and Price Dynamics of Water Right Permit under Groundwater Trading System

本文是國內首篇考慮水權人對水權交易價格具有完全預期能力，探討水權交易制度|與水權人整合性用水需求行為下，政府如何透過水權交易制度管理地下水資源的有效使用，以達成環境目標之文章。本文研究結果發現如下：（1）在水權人整合性用水的最適決策下，地下水與地面水具有替代之關係，且由於水權人考量地面水使用回流及地下水的影子價值，有增加地面水使用之誘因，因此具有節約地下水使用的效果；（2）在水權人對水權交易價格具有完全預期的考量下，政府若能寬鬆核發水權分配量，以引導水權交易價格下降，將可以促使水權人更節約地下水使用；（3）若水權量能夠儲存，則地下水資源的開採率將不滿足Hoteling's法則，水權人若為儲蓄者（或需求者），水權交易價格的成長率將高於市場利率，表示地下水資源的開採率將過高，產生地下水資源利用的「泡沫現象」；反之，水權人若為預借者，水權交易價格成長率將低於市場利率，表示地下水資源的耗竭率較低，有利環境目標的達成。

We explored the water right owner's decision under a ground water right trading system by establishing an intertemporal model that takes into account several important factors such as banking and borrowing, integrated use of surface water and ground water, etc. It differs from the conventional model in such a way that the authorities manage groundwater through operation of policy instruments, such as water right fees, rather than the maximum safety yield. The result indicated that the firm has more incentive to reduce groundwater use under the trading system. Should the authorities be able to allocate initially more water right permits to the users so that market price of water right permit is low enough, users will demand less for groundwater. When banking is allowed in the trading system, it happens that the growth rate of permit price does not follow Hotelling's rule. If the water user is a savor, the growth rate of permit price will be greater than rate of return earned from holding any other assets, implying that the pumping of groundwater have a "bubble effect". In contrast, if the water user is a borrower, the growth rate of permit price will be smaller than rate of return earned from holding any other assets, implying that the groundwater use tends to be more conservative.