The Annual Water Balance

Abstract

The average annual one-dimensional water balance is expressed for natural surfaces in terms of physically-significant dimensionless parameters. This provides the basis for dynamic similarity of the water balance and for an improved understanding of climate-soil-vegetation coupling. A sensitivity analysis points out the critical importance of the potential rate of evapotranspiration in defining water balance variations due to changes in other climate and soil parameters. A first-order analysis of the average annual water balance gives an equation for the annual water balance that can be used to estimate the cumulative distribution functions (cdf) of the components of the annual water balance in terms of the cdf of the annual precipitation and of observable parameters of the physical system. This provides a rational basis for assessing the risk due to physical changes in the land surface and for estimating the recurrence interval of such water balance components as basin yield.