A Re-Evaluation of the Average Annual Global Water Balance

Legates and Mather (1992) used the Thornthwaite/Mather water balance and mean monthly air temperature and precipitation data on a 0.5° of latitude by 0.5° of longitude grid to refine spatial estimates of annual evapotranspiration and runoff on a global scale. Because Legates and Mather used the Thornthwaite potential evapotranspiration equation, they were unable to apply bias-adjustments to their precipitation estimates because, as Legates and Mather discovered, the Thornthwaite equation implicitly accounts for gage measurement biases by underestimating potential evapotranspiration. Here, we re-evaluate the results of Legates and Mather using bias-adjusted precipitation estimates and an alternative method of estimating potential evapotranspiration (i.e., the Hamon, 1963, method). These new results are compared with those from previous studies and are considered to be an improvement over the Legates and Mather values, as they are based on bias-adjusted precipitation estimates.