I. Introduction
II. The Hydrological Role of Forests
2.1 General evidence
2.2 Thai evidence
III. The Mae Taeng Watershed and Downstream Water Users
3.1 The Mae Taeng Watershed
3.2 Downstream users - Mae Taeng Irrigation Project
3.3 Downstream users - Chiang Mai City
IV. Has Water Yield Changed Over Time?
4.1 Results for Ban Muang Kud
4.2 Results of Ban Sop Kai
4.3 Results for Mae Taeng weir
V. Do Climatological Factors Explain the Reduction in Water Yield?
VI. Do Land-Use Changes Explain the Reduction in Water Yield?
VII. What are the Downstream Impacts of the Reduction in Water Yield?
7.1 Impacts on irrigated, dry-season agriculture
7.2 Costs of reduced stream flow
VIII. What Should be Done About Reduced Water Yield?
References