Calama is a city and commune in the Atacama Desert in northern Chile. It is the capital of El Loa Province, part of the Antofagasta Region. Calama is one of the driest cities in the world with average annual precipitation of just 5 mm (0.20 in). The River Loa, Chile's longest, flows through the city. Calama has a population of 147,886 (2012 census).