Although annual rainfall averages between 500 and 800 millimeters over most of the sertão and 1300 millimeters on the northern coast of Fortaleza, it is confined to a short rainy season. This season extends from January to April in the west, but in the eastern Sertão it generally occurs from March to June. However, rainfall is extremely erratic and in some years the rains are minimal, leading to catastrophic drought. The duration of droughts has increased over the last 36 years, with the 2012–2016 drought being the longest drought in the region's history. Because of this vulnerability to the climate, Sertão is also known as a “polygon of drought.” Due to global warming, more frequent, more severe and longer droughts are estimated to hit the region over the next 90 years. Despite the increasing severity of the droughts, Brazil has become increasingly able to mitigate the negative social impacts associated with drought.