Although the annual average precipitation is slightly lower than 1,000 mm,[11] the rainy period, which usually lasts just two months a year, is unstable. Sometimes precipitation halts for one year or more, often causing regional droughts. Sustained occurrences of below average water availability can happen in all areas of the country as a consequence of abnormally low precipitation rates and high evaporation rates; but it is in the Northeast where they happen with greater frequency.[12] The zona da mata, which runs along the Northeastern coast and in which major cities are located.