|
E. Linacre and B. Geerts |
9/'99 |
A comparison of the annual and spatial average rainfall onto various continents, with the river discharge into the oceans from the respective continents, and the mean rate of evaporation, shows that the three variables are related. South America is the wettest and has the largest river flow and evaporation (Table 1). Australia, with the lowest rainfall, discharges the least in consequence. Antarctica is an exception: it is very dry, and very little snow sublimates. Most water leaves this continent as ice. With the exception of Antarctica, evaporation is seen to be more uniform across the world than the rainfall.
|
region |
precipitation: mm/a |
discharge mm/a |
ratio: percent |
evaporation mm/a |
|
Antarctica |
110 |
100 |
94 |
10 |
|
Australia |
440 |
40 |
9 |
400 |
|
Asia |
650 |
240 |
37 |
410 |
|
Africa |
740 |
110 |
15 |
630 |
|
Europe |
820 |
230 |
28 |
590 |
|
North America |
800 |
330 |
41 |
470 |
|
South America |
1600 |
700 |
44 |
900 |
|
global mean (land) |
730 |
300 |
41 |
430 |
|
oceans |
1140 |
-120 |
11 |
1260 |
Table 1. Approximate amount of annual precipitation, river discharge (the total annual discharge into the oceans divided by area of the continent), the fraction of precipitation that reaches the oceans, and the difference between precipitation and discharge (i.e. evaporation or sublimation). The negative 'discharge' for the oceans is the total river/glacier inflow, divided by the area of the oceans. The numbers are rounded to the nearest 10 mm/a.
Reference
(1) Australian Bureau of Meteorology undated. 'Australia; climate of our continent', cat. no. 476164.