This problem is adapted from environmental hydrology, 3rd edition, by andy ward (crc press). the table on the last page (from the same source) provides information on the world water balance by continent. 've also 6. created an excel file with these data that you will be much easier to use to do the calculations, assuming that you know how to use excel. if you don't know how to use excel, this is a great time to learn some basic skills- you will be using excel frequently this semester. a. determine the evaporation rates on all continents as a percentage of the precipitation that falls on that continent. determine the surface water runoff rates in all continents as a percentage of the precipitation that falls on that continent. b. c. why do you think these percentages are so different for south american and africa?