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-- In chaparral, evapotranspiration is often reduced by replacing deep-rooted species with shallow rooted species. -- Results of water yield studies are often reported as averages. This is misleading because this average is made up of values that seldom center on average and the 50% chance flow is often substantially less than the reported average. -- Most research is based on comparisons of yield on paired watersheds of very small size (most less than 1 miz in size nearly all less than 5 mi2 in size) with precise flow measuring gages. -- Experimental treatment regimes tend to be more extreme than conventional forest management practices to assure measurable treahnent effects. -- Persistent folklore coupled with a belief that reported averages represent commonly achievable yields have lead to the belief that low flows are augmented more and that high flows are relatively unaffected. This viewpoint is incorrect! -- Studies by Hibbert in the 1980s suggest that the increase is a uniform percentage on the hydrograph over the range of flows investigated. -- This means, for example, that if low flows increase by approximately 15% for significant treatments then it is likely that flood peaks also increase by 15%. • In most water short areas, reservoirs are operated to maximize storage and are, thus, unable to capture and store the significant yield increases associated with high runoff (flood) years. -- In Arizona, for example, Brown and Fogel (1987) found that even with the substantial number of dams in place, much of the yield increase was spilled because of reservoir operational strategies. • Extrapolating the small watershed studies to larger basins is problematic. -- Larger basins have more practical limitations and resource coordination requirements. -- The increases, while likely there, are not within our ability to detect on larger basins of 10 mi2 and larger. -- Exceptions might include insect killed forests and extensive fire and other natural events that remove substantially all the forest cover at once. • Treatments focused on water yield often result in compromising other resource values. 2. What is the science regarding water yield augmentation and what are the expected average annual yield increases by forest types? • Generally, forest harvest increases water yield and afforestation decreases water yield. Deforestation reduces the amount of precipitation intercepted by vegetation, making more water available for runoff into watercourses. • Variability and uncertainty play a large role: -- precipitation amount depends on annual and regional variations in climate