Resumo

PERALTA-HERNANDEZ, A. R  e  BARBA-MARTINEZ, L. R. The risk of early and late frost behavior in central México under El Niño conditions. Atmósfera [online]. 2009, vol.22, n.1, pp.111-123. ISSN 0187-6236.

The irregular occurrence of cold temperatures (frost) in central México (~19-23° N) produces high agricultural losses each year; the greatest effect is on cold-sensitive crops, which has important socio-economic implications for the region. There is a lack of information on frost-related studies regarding the onset and duration of frosts in central México, especially in response to the El Niño (EN) phenomenon. Due to the land's irregular topography, the weather stations were grouped into 300 m range heights, resulting in five regions: I, III, and IV-VI with elevations from 875 to 2999 masl. Daily minimum temperatures (< 2 °C) from 50 weather stations and for each year from 1960 through 1998 were analyzed. The EN effect was evaluated by region comparing the frost-free period (FFP) for EN vs. neutral (N) events. Our results (although not statistically significant) show that the first frost occurs during EN years in the five regions under study; the last frost occurs in the highest regions (IV-VI) during N years. Also, during EN, the FFP is shorter than for N years, except in region VI where it was shorter during N years. The probability of frost occurrence at a 20% level was determined for stations with the shortest FFP. Regression analysis between frost periods and elevation show that frost occurrence is better correlated with elevation than with EN and N events; areas with higher elevation showed shorter FFP compared to areas with lower elevation.

Palavras-chave : Central México; early frost; late frost; El Niño; frost-free periods.

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