Standardized Precipitation Index Zones for México

Abstract

"Precipitation zone systems exist for México based on seasonality, quantity of precipitation, climates andgeographical divisions, but none are convenient for the study of the relation of precipitation with phenomenasuch as El Niño. An empirical set of seven exclusively Mexican and six shared zones was derived from threeseries of Standardized Precipitation Index (SPI) images, from 1940 through 1989: a whole-year series (SPI-12)of 582 monthly images, a six month series (SPI-6) of 50 images for winter months (November through April),and a six-month series (SPI-6) of 50 images for summer months (May through October). By examination ofprincipal component and unsupervised classification images, it was found that all three series had similarzones. A set of basic training fields chosen from the principal component images was used to classify all threeseries. The resulting thirteen zones, presented in this article, were found to be approximately similar, varying principally at zone edges. A set of simple zones defined by just a few vertices can be used for practicaloperations. In general the SPI zones are homogeneous, with almost no mixture of zones and few outliers ofone zone in the area of others. They are compared with a previously published map of climatic regions.Potential applications for SPI zones are discussed."