可用水量不確定下之水權配置制度的比較利益分析

Analysis of Comparative Advantages of Water Rights Allocation under Uncertainty over Water Supply

本文比較分析優先權制與比例分享制對水資源之社會效益的差別，結果顯示，在不考慮可用水量不確定的情況下，優先權制在缺水時期，將對水資源的社會效益產生相當大的損失，而施行比例分享制、調整水權費、或允許水權交易，皆可望顯著提升水資源的效益並減少缺水的損失。此外，本文進一步考慮可用水量的不確定性而提出一個水權人的決策模型，用以模擬分析我國北、中、南、東各區水權人對優先權制與比例分享制的偏好。分析結果顯示：凡缺水機率愈高的地區（南部與中部），農業用水人愈偏好優先權制，而工業用水人則愈偏好分享制，因此，無論實施優先權制或比例分享制，都不免造成農、工用水人之閉的利益衝突。反之，在雨量豐沛的地區（如東部），農、工用水人都偏好優先權制，因此實施優先權制會是一個理想的選擇。此外，風險趨避態度（或風險規避係數）與水權人的確定性當量密切相關，無論在何種水權制度下，各標的水權人的確定性當量皆會隨風險趨避度的增加而下降，表示越風險趨避的用水人，其確定性當量愈低。不過，水權人在兩種配水制度下的利差，則無如此明確的關聯。

This paper starts with a comparative analysis of the welfare effects of various water rights allocation systems, including the priority rule, capacity-sharing approach, water rights fee, and water rights trading. The results indicate that, the priority rule is less favorable when uncertainty over water supply does not exist. Nevertheless, the situation could be changed when uncertainty is taken into account. Empirical results based on a certainty equivalent maximization model reveal that priority rule may be more favorable in the areas where probability of water shortage is low. In the areas with greater probability, however, preference over the allocation systems differs between agricultural users and industrial users such that the former prefer the priority rule and the later the capacity-sharing approach. In all cases, the certainty equivalent of water users decreases with risk attitude.