Australia is a large, comparatively dry, and sparsely inhabited continent, almost as large as the 48 contiguous U.S. states. Australia, the only continent that consists of a single nation, is also the only inhabited continent which is isolated from all others (total coastline exceeds 22,000 miles). Average elevation is about 985 feet, which makes it the flattest continent on earth. This is among the prime reasons for sparse annual rainfall--16.5 inches, which is less than two-thirds the world average (26 inches). Further, the rain falls mainly on coastal regions: forty percent of the surface gets less than 10 inches per year, and annual evaporation exceeds annual rainfall on about three quarters of the land. Overall runoff is less than half that of the Mississippi basin; Australia has no navigable rivers of any commercial significance.
In general, the country is warmer than the U.S. (the northern one-third is in the Tropics, the rest in the Temperate Zone). Temperature extremes are much less pronounced. Sydney's average daytime temperature in the coldest month (July) is 59°F; in the warmest month (January), 81°F.