Development of an integrated agricultural economic and hydrological/ water quality model in Lake Biwa Watershed

本研究旨在建立一个综合农业经济和水文/水质模型，以分析农业环境政策对耕作方式的影响以及由于耕作方式变化而导致的水环境变化。我们评估了滋贺县为减轻农业环境负担而推行的政策对琵琶湖流域水质的影响。通过对滋贺县农户的问卷调查，揭示了农户采用环境友好耕作方式的影响因素及其对环境友好耕作面积分配比例的决定。此外，构建了MIKE模型来估计琵琶湖小流域采用环保耕作方式对磷负荷的影响。根据该模型，如果取消对环境友好型农业的补贴，磷肥负荷将增加几个百分点。

This study aimed to develop an integrated agricultural economic and hydrological/ water quality model to analyze the effects of agri-environmental policies on farming practices and the change in water environment due to the changes in farming practices. We evaluated how the policy which Shiga Prefecture is promoting in order to reduce environmental burdens from agriculture affected the water quality in Lake Biwa Watershed. We conducted a questionnaire survey to farm households in Shiga Prefecture and revealed factors affecting farmers' adoption of environmentally friendly farming and their decision on the ratio of area allocated for environmentally friendly farming. In addition, MIKE model was constructed to estimate the change in phosphate loadings due to the adoption of environmentally friendly farming in a subwatershed of Lake Biwa. According to the model, if the payment for environmentally friendly farming were abolished, the phosphate loading would increase several percent.