This fire season has been one of the worst in Australia’s history, with at least 15 people killed, hundreds of homes destroyed and millions of acres burned. And summer is far from over.

This week, thousands of residents and vacationers in southeastern Australia were forced to evacuate to shorelines as bush fires encircled communities and razed scores of buildings. Military ships and aircraft were deployed on Wednesday to deliver water, food and fuel to towns cut off by the fires.

The hot, dry conditions that have fueled the fires are nothing new in Australia. Here’s why this fire season has been so calamitous.