Abstract: In this paper,the 110-year history of the estimated global runoff volumes was reviewed.The land slope and aridity index were taken as the independent variables,the method of Ordinary Least Squares (OLS) regression was employed to estimate the runoff coefficients in typical regions,and the empirical formula of runoff coefficient was used to calculate the runoff volumes in China.Based on the empirical formula and high-resolution precipitation grid data,the Grid and Spatial Analysis module in Geographic Information System (GIS) was applied to calculate the high resolution spatial distribution fields of global water resources.Main calculated results were that the total runoff volume in the world (excluding the Antarctic Continent) was 47 884 km³,the average runoff depth was 359 mm,and the average runoff coefficient was 0.462;the runoff depth in Africa was 230 mm,the runoff coefficient was 0.345,and both were the lowest in the 6 continents; the runoff depth in South America was 770 mm,the runoff coefficient was 0.507,and both were the highest;the runoff depth in Asia was 313 mm,which was lower than the average in the world,and the runoff coefficient was 0.495,which was higher than the average in the world.The results were compared with the relevant literatures.This study emphasized the importance of groundwater runoff and groundwater increment in arid and semiarid regions,and the estimated runoff depths in these regions were increased significantly.The calculated runoff volumes in Africa and Australia were 6 944 km³ and 3 026 km³ respectively,which were obviously higher than the average of 24 estimations between 1973 and 2014 in literatures.Moreover,the authors also calculated the runoff patterns of all the 31 interior drainage areas in detail in the world.The total area of the interior drainage areas in the world was 28.47 ×10⁶ km²,the total runoff volume was 1 663 km³,the average runoff depth was 58.4 mm,and the average runoff coefficient was 0.252.The runoff depth in the interior drainage areas in Oceania was 35 mm,the runoff coefficient was 0.129,and both were the lowest in the world.Case studies in the interior drainage areas showed that the runoff depth fields calculated by the empirical formula were in accordance with the actual runoff distribution patterns in Africa,Oceania and 4 regions in Asia,including the Nura River in Kazakhstan,Hexi Corridor and west Inner Mongolia Plateau in China,southeast Mongolia and China’s central and eastern Inner Mongolia Plateau,and the interior drainage areas in Arabian Peninsula.The theoretical hypothesis was confirmed for the interior drainage subregions,and the higher the spatial resolution was,the larger the calculated runoff value would be.Main conclusions of this study are as follows: the spatial resolution of this study was 0.166 7 degrees,and it was 3 times of the major resolutions used in the runoff calculation;the runoff volumes were calculated from the high spatial resolution runoff fields in this study,including the runoff volumes in interior drainage basins and the runoff volumes consumed in the exorheic drainage basins before flow inflowed into the oceans;the differences between the runoff volumes in this study and the actually measured runoff volumes at the debouchures to the oceans or inland lakes should be the interruptive consumption of the evaporation from natural water surface and wetlands,the net water consumption of agricultural irrigation,and the net dissipation of artificial water usage in urban and industrial regions in watershed;the groundwater runoff and the increment of groundwater and of soil available water are the main forms of runoff in arid and semiarid climate zones.In available literatures,the underestimation of water resources was mainly the ignored evaporation from natural waters and wetlands as well as the net dissipation of artificial water usage.

Key words: global, water resources, empirical formula, runoff coefficient, spatial distribution field, high resolution, geographic information system