Rainfall that is relatively evenly distributed throughout the year may not cause a great deal of reef mortality. However, a short period of intense rain during an extreme low tide can be devastating. The proportion of annual rainfall for the period December to March is progressively lower when one travels south. In the north, 80 percent of the region's annual precipitation can fall during this period. Whereas in the south, at the [M011 / Tropic of Capricorn], there may only be a 60 percent contribution. Therefore, the northern reef, where coral communities are closer to shore, are more vulnerable to death from exposure to rain or the sediment runoff from the adjacent mainland.
The most lethal combination of conditions for a reef community would be a location close to a river outlet in an area of little vegetation cover that experienced intense rain over an extended period during an abnormally low tide. Not only would water [G 26 / salinity] be reduced to intolerable levels, sediment discharge from the river would provide a knockout blow.
