Interannual Variability of Daily Extreme Precipitation Events in the State of São Paulo, Brazil

Brant Liebmann Climate Diagnostics Center, University of Colorado, Boulder, Colorado

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Charles Jones Institute for Computational Earth System Science, University of California, Santa Barbara, Santa Barbara, California

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Leila M. V. de Carvalho Department of Atmospheric Sciences, University of São Paulo, São Paulo, Brazil

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Abstract

The climatology and interannual variability of heavy, or “extreme,” precipitation events are studied, using station data from the state of São Paulo, Brazil. An extreme event is defined at each station when daily rainfall exceeds a certain percent of its seasonal or annual mean. It is found that these events occur mainly from November to March and that there is a distinct interannual variation in their number. The count of extreme events is not well correlated with mean precipitation. The relationship between extreme events and activity in the South Atlantic convergence zone (which, when active, is associated with increased precipitation) is therefore not obvious. From October to March, the interannual count of extreme events in the entire state is correlated positively with SST anomalies in the equatorial Pacific from near the date line to the west coast of South America. The interannual count at stations near the Atlantic coast from November to February is correlated positively with SST anomalies in the Atlantic Ocean near the latitude of São Paulo. In both cases the relationship between SST and mean precipitation is weak. The associations are confirmed with composites and rank correlations. The relationships described are apparent in the period 1976–77 to 1994–95. There is no correspondence evident between extreme events and SST if data beginning in 1948 are included in the analysis.

Corresponding author address: Brant Liebmann, NOAA–CIRES Climate Diagnostics Center, R/CDC1, 325 Broadway, Boulder, CO 80305-3328.

Email: bl@cdc.noaa.gov

Abstract

The climatology and interannual variability of heavy, or “extreme,” precipitation events are studied, using station data from the state of São Paulo, Brazil. An extreme event is defined at each station when daily rainfall exceeds a certain percent of its seasonal or annual mean. It is found that these events occur mainly from November to March and that there is a distinct interannual variation in their number. The count of extreme events is not well correlated with mean precipitation. The relationship between extreme events and activity in the South Atlantic convergence zone (which, when active, is associated with increased precipitation) is therefore not obvious. From October to March, the interannual count of extreme events in the entire state is correlated positively with SST anomalies in the equatorial Pacific from near the date line to the west coast of South America. The interannual count at stations near the Atlantic coast from November to February is correlated positively with SST anomalies in the Atlantic Ocean near the latitude of São Paulo. In both cases the relationship between SST and mean precipitation is weak. The associations are confirmed with composites and rank correlations. The relationships described are apparent in the period 1976–77 to 1994–95. There is no correspondence evident between extreme events and SST if data beginning in 1948 are included in the analysis.

Corresponding author address: Brant Liebmann, NOAA–CIRES Climate Diagnostics Center, R/CDC1, 325 Broadway, Boulder, CO 80305-3328.

Email: bl@cdc.noaa.gov

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