Changes in Aridity across Mexico in the Second Half of the Twentieth Century

Six regions in Mexico, with typical interannual changes in the aridity index, have been defined by the 1951-2001 meteorological dataset. Peak months of rainfall differwithin the regions. Most of the land in the Mexican terrain has had a slow aridization since the early 1980s. The decline in the aridity index in the early 1950s and late 1990s was caused by droughts in the area. The distinctive features of the aridization ofMexican dry lands are characterized by steady and extensive droughts during 1948-57, 1960-65, and 1994-2003 in the second half of the twentieth century. During the drought of 1951-57 substantial aridization in most of the dry lands was observed, including the Sierra Madre Occidental, Sierra Madre Oriental, andMexican Altiplano. Aridization of dry lands during the drought in 1960-65 affected mostly the southern part of the Mexican Altiplano, the Sierra Madre del Sur, and the Yucatán Peninsula. For the drought in the 1990s, one special feature of the aridization was its propagation primarily beyond the Mexican Altiplano. Increased aridization of dry lands caused by long-term droughts during the last decade of the twentieth century did not result in a sizeable shift of the southern boundary of the dry lands. The only exception is the southern boundary (aridity index = 5 0.75) in the state of Sinaloa. In this area, the boundary moved southward and aridization intensified. The results obtained here can be used in studies of possible anthropogenic impact on the drought of the twentieth century's last decade in Mexico, which includes changes in land use.