The Southern Highlands give the impression of verdant bounty, and the average rainfall (700 mill/p.a.) is higher than further inland, the region has always suffered from the extremes of the harsh Australian environment. The earliest settlers found out from the aborigines that the rivers alternated between flood and drought. The greenness of the countryside soon may change to olive drab during drought - some of which may last years (El Nino or not). The countryside in summer is always dryer as higher temeratures cause increased evaporation.
Although there seems to be more rivers and creeks than other parts of the countryside, these do not always run. Most water is in fact subterranean - like much of Australia. That is why creeks sometimes seem to rise out of nowhere, and water seems to flow from out of the escarpments even when there is no rain. The many dams on farms indicate the need for conserving water.
Being on the Great Dividing Range the Highlands receives heavier precipitation on the escarpments - those to the east contain sub-tropical rainforests - and the run-off to the Wollondilly River in the west, the Nepean to the north, and the Shoalhaven to the south feeds into the water supplies for Sydney and the South Coast.
The Highlands has a land area almost as big as the city of Sydney, so it is not surprising it contains many micro-climates. The local weather stations are at Bowral and Moss Vale and conditions there can often be different to the prevailing winds, rainfall and temperature just 5 to 10 kilometres away. However, it gives a general overview of local conditions. Precipitation is always heavier north of Mittagong and to the east around Robertson and Fitzroy Falls. The air temperature and wind chill factor can vary throughout the Highlands on any given day.
Europeans, by and large, made pretty good colonists in other parts of the globe: they were able to adjust to very different climates and survive. However, they still retained deep subconscious links with the cool climate of their homeland and wherever they were, the English - come the first heat of summer - headed for the hills. The Highlands was a popular destination in summer up to the mid 20th century with its four distinct seasons, clearly heralded not only by changes in the climate, but by the changes in the many European trees, shrubs and flowers widely planted throughout the district.
Summer is cooler than the coast with average temperatures from 15 to the mid 20s Celsius - up to 10 degrees cooler. Spring and Autumn are markedly cooler. Winter temperatures are typically in the teens down to freezing and heavy frosts are common, and from time to time it snows.
Part of the attraction of the Highlands are its seasonal changes - which has made it a popular destination for visitors year round since the 19th century.