Background: The aim of this study was to determine trends in the airborne pollen concentration and pollination period for the principal sources of pollen in Badajoz (southwest Spain) over 15 years of monitoring (1994-2008).

Methods: Airborne pollen was monitored by continuous sampling with a Hirst volumetric sampler. Pollen trends were investigated by linear regression and correlation analysis using mean annual and monthly pollen concentrations. The aerobiological results were compared with meteorological data (temperature and rainfall).

Results: During the study period, the mean total annual rainfall was 66.2 mm lower than normal and the mean annual temperature 0.8°C higher than normal. No temporal trend was found for total airborne pollen concentration, but differences were observed for monthly data, namely, an increase in January, February, and May and a decrease in March and June. For the different pollen types studied, there was a general trend toward increased values in the month with the highest values, and this trend seemed to be related to temperature. The beginning of the main pollen season occurred later, and the end occurred sooner; therefore, the main pollen season seems to be shorter.

Conclusions: Our data reflect trends in the response of plants to changing rainfall stress patterns in Mediterranean countries, and these trends seem to be different from those of temperate countries. Nonetheless, a longer study period will be required to confirm these
preliminary conclusions.

Key words: Aerobiology. Airborne pollen trends. Climate change. Pollen.