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CR 10:201-215 (1998)
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Abstract
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Principal components-based regionalization of precipitation regimes across the southwest United States and northern Mexico, with an application to monsoon precipitation variability
Andrew C. Comrie1,*, Erik C. Glenn2
1University of Arizona, Department of Geography and Regional Development, Tucson, Arizona 85721, USA
2University of Arizona, Office of Arid Lands Studies, 1955 E Sixth St, Tucson, Arizona 85719, USA
*E-mail: comrie@climate.geog.arizona.edu
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ABSTRACT: We determine precipitation regions for the United States-Mexico border region based on seasonality and variability of monthly precipitation at 309 stations for the period 1961 to 1990. Using a correlation matrix of input data to avoid the effect
of elevation on precipitation, we apply principal components analysis with oblique rotation to regionalize this large, climatologically complex study area. We examine the applicability of the method, 2 techniques for defining region boundaries, the
various defined regions themselves, and the effects of transforming input data and changing obliquity of component rotation. We obtain 9 consistent and largely contiguous regions from each of the analyses, including regions for the North American monsoon,
the low deserts, the California Mediterranean regime, and for summer precipitation regimes adjoining the Gulf of Mexico. The derived regions and associated boundaries make physical sense in terms of the driving atmospheric processes, and they are robust
to transformed input data and changes in rotation procedures. The central border regions are remarkably consistent across analyses, with small changes to peripheral regions. We also identify 4 monsoon sub-regions, and we illustrate the applicability of
the regionalization via an analysis of relationships between monsoon precipitation variability and 500 mb pressure heights. Significantly different 500 mb circulation patterns are associated with wet and dry monsoon seasons in each of the sub-regions, and
it appears that shifts in 500 mb circulation relative to the geographic position of each sub-region influence seasonal precipitation variability, directly or indirectly. There are important differences between some sub-regions, but in general wet
monsoons are associated with northward meridional bulging of the subtropical anticyclone over the continental monsoon areas, while dry monsoons are associated with zonal stretching of the subtropical anticyclone over adjacent oceans with slightly higher
pressure-heights. Overall, the study provides a clear regionalization of the precipitation climatology for the southwest United States and northern Mexico, and shows its utility for studies of climate variability.
KEY WORDS: Climate regionalization · Precipitation · Southwest United States · Northern Mexico · Principal components analysis · Monsoon variability
Full text in pdf format
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Published in CR Vol.
10, No. 3
(1998) on December 10
ISSN: 0936-577X.
Copyright © Inter-Research, Oldendorf/Luhe, 1998
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