Identification and explanation of continental differences in the variability of anneal runoff

Continental differences in the variability of annual runoff were investigat ed using an expanded and improved database to that used in previous work. A statistical analysis of the data, divided by continent and Koppen climate type, revealed that continental differences exist in the variability of ann ual runoff. The variability of annual runoff far temperate Australia, arid southern Africa and possibly temperate southern Africa were noted to be gen erally higher than that of other continents with data in the same climate t ype. A statistical analysis of annual precipitation by continent and Koppen climate type revealed that differences in the variability of annual precip itation could account for some but not all the observed differences in the variability of annual runoff. A literature review of potential causes of co ntinental differences in evapotranspiration resulted in the hypothesis that the significantly higher variability of annual runoff in temperate Austral ia and possibly temperate southern Africa may be due to the distribution of evergreen and deciduous vegetation. The process model Macaque was used to test this hypothesis. The model results indicate that the variability of an nual runoff may be between 1 and 99% higher for catchments covered in everg reen vegetation as opposed to deciduous vegetation, depending on mean annua l precipitation and the seasonality of precipitation. It is suggested that the observed continental differences in the variability of annual runoff ar e largely caused by continental differences in the variability of annual pr ecipitation and in temperate regions the distribution of evergreen and deci duous vegetation in conjunction with the distribution of mean annual precip itation and precipitation seasonality. (C) 2001 Elsevier Science B.V. All r ights reserved.