Caracterización de la Pequeña Edad de Hielo en el México central a través de fuentes documentales

Abstract

Comparing instrumental climatic sources with proxy data, in order to review existing climatic models and to acknowledge climatic variability in time and space, is widely recognized nowadays. In Mexico the study of past climate along the last 500 hundred years, has mostly been conducted through the analysis of instrumental sources. Studies that have 1877 as time limit, when the first continuous records started to be taken in Mexico City. For the study of climate along the last centuries, documentary sources have proved their accuracy, if compared to physical and biological data, usually modified by human activity. Tree ring information is among biological sources also useful for recent centuries, but in Mexico it is still necessary to have a better regional coverage. The Little Ice Age (lia) was defined back in the 1930s through information gathered in North America and Western Europe, but much is still unknown about the climatic behavior of lower latitudes in the Northern Hemisphere and the Southern one during lia.The reconstruction of past climates, through documentary sources started under scientific principles, only until the mid 20th century and it was a task conducted mostly by British and French authors. Emmanuel Le Roy Ladurie, recognized French historian, was the first to reveal to the world in the early 1960s, the documentary source that has resulted more precise for climatic reconstruction within the Hispanic cultural realm: the record of the rogation ceremonies. But it was not until the 1990s, when Spanish researchers like Mariano Barriendos, Javier Martín-Vide or Fernando S. Rodrigo, published and disseminated outside Spain, the climatic data obtained at City Councils and Cathedrals throughout the Iberian peninsula. In Mexico this kind of work started to be achieved by 2001. Rogation ceremonies are a reliable source of ancient climatic variability, because of its public and institutional origin, and their homogeneous information and precise dating.Central Mexico is where most of this sort of research has been conducted in Latin America. The information obtained comes from the City council’s and Cathedral archives of the following cities: Mexico City, Puebla, Morelia and Guadalajara (also from Durango in Northwestern Mexico trying to acknowledge climatic patterns in a larger area). With the information obtained, the characteristics and intensity of the Maunder and Dalton minimums in solar spots, coldest spells of LIA, have been acknowledge for Central Mexico. According to Lonnie Thompson and colleagues after their research at the Quelccaya glacier, they were able to define a humid lia (ca. 1500-1720) and a dry lia (ca. 1720-1880) for Western South America: the climatic data obtained through the consulting of Rogation ceremonies records recognizes the same pattern for Central Mexico.The minimum Maunder (M.m.) has been proposed to occur worldwide between 1645 and 1715, the data obtained at Mexican City councils and Cathedrals suggest a later beginning (ca. 1660-1680) and hazardous years between 1680 and 1720. The late minimum is more humid than the Dalton minimum (D.m.) in Central Mexico. During M.m., 18 years show excess rainfall, while only 8 years were recorded under such circumstances between 1730 and 1830. Droughts are also less frequent during M.m. and they were usually ended by intense rainfall seasons. The D.m. is usually considered warmer than the M.m. around the planet, however in Central Mexico, the first one is much colder, since nearly 50% of all the frosting sever enough to be registered by City or Cathedral councils took place between 1780 and 1820.Rogation ceremony records have also shown regional differences within Central Mexico, during the D.m. the Western part of this area shows a more humid pattern during its first stage, but after 1800, the Eastern part shows more rainfall than the Western one. Furthermore, rogation ceremony records, because of their precise dating, can show us if rainy seasons were late, if falls and winters were very dry and can even prove the intensity and duration of canículas (mid rain season dry periods common in Mexico, Central America and the Caribbean), warm and dry spells that can compromise summer time food production, specially maize harvesting.