Resumen

MATIAS RAMIREZ, Lucía G. et al. Analysis of the main causes of the floods on September 2003, in the south of the state of Guanajuato, Mexico. Invest. Geog [online]. 2007, n.64, pp.7-25. ISSN 2448-7279.

The intense rainfalls happened on September 2003, caused that in the basin of the Lerma, several rivers increased their level, also, Allende and Solis dams reached their maximum capacity. This generated severe floods in 17 of the 46 municipalities in the south of the state of Guanajuato. The affected population was estimated in more than 18 000 inhabitants and six deceases. The economic losses were estimated to be more than 900 million pesos and the agricultural sector underwent the most serious effects. The purpose of this paper is to review the main causes of the floods of 2003. The analysis consisted on identifying the systems of weather that produced extraordinary rains for the continuity and persistence. It is carried out a space distribution of the precipitation, the calculation of the period of return (Tr) and the frequency to study the behavior of the storms of that season and other similar. The above-mentioned is supplemented with the construction and hydrographs interpretation of one of the main rivers, with historical registrations and previous studies of the morphological characteristics of the region. The floods that happened in the south of the state are due to extraordinary rains generated by the singular interaction of three systems of weather. The most severe storm reached 98 mm of intensity whose Tr was considered in 50 years, the values accumulated during 14 days were of more than 300 mm, the runoff daily means oscillated between the 180 and 200 m3/seg. It was found that most of the towns affected by the 2003 event had presented important floods in previous events with minor intensity rainfalls; by example, 50 to 70 mm, accumulated of 250 mm and expenses of 170 to 210 m3/seg. The morphology and the changes of land use also favor these phenomena.

Palabras llave : Hidrometeorological phenomena; Intense rainfalls; floods; Lerma river basin; state of Guanajuato.