Secular changes of east‐coast rainfall regimes

The mean rainfall along the east coasts of North America and Australia is shown to have decreased abruptly at the end of the 19th century, in conformity with results for the tropics obtained in an earlier paper. A simultaneous decrease of the rainfall in the semi‐arid western parts of New South Wales also conforms to conditions in other dry regions such as Arabia. In terms of seasons, the change appears to have been largest in autumn and summer for North America and in autumn and spring for Australia. Reasons for this are discussed. A sudden decrease of rainfall at the end of the last century may have occurred also in East Asia and on the east coast of South Africa though it was much less pronounced than in Australia and North America. In South America the amplitude of the change was large, but did not extend far south of the Equator. Dynamic causes and possible implications for research into long‐range forecasting are discussed in a concluding section.