Reinterpretation of Relations Between Vegetation Removal and Water Yield

While the relation between vegetation clearance and increasing streamflow appears to be strong for data aggregated among geographic regions, results are equivocal in local areas. Earlier data are re-analyzed to consider the role of hydroclimatology. While vegetation clearance increases absolute streamflow, the proportional change is not significant. Residuals of regressions of absolute and proportional change in streamflow on vegetation clearance are related to precipitation, with positive and negative slopes, respectively. A few outliers with high responses are important in creating a pattern, and hydroclimatology is a better predictor of change in streamflow than is vegetation clearance for aggregate data. With data disaggregated in five classes of precipitation, significant regressions are found only in one class. No significant relations are found for selected regional data sets. Regional hydroclimatology affects responses at both global and local scales. The aggregate result, influenced by outliers, cannot be used to guide water resources management at particular locations.