by Tim Storer
Climate change is an enormously complex subject, but thankfully copious temperature and precipitation data exist from around the globe that allow for detailed analyses of global and local patterns. In many parts of the globe, increasing trends in weather intensity have been observed, and the most recent data analysis of Caribbean weather reaffirms increased weather intensity throughout the last fifty years (Stephenson et al. 2013). There have been strong rising trends in surface temperatures at several land weather stations throughout the region, but much weaker trends in precipitation than those related to temperature. Still, there were trends of increased average yearly and daily rainfall. The Caribbean region is especially noteworthy because of its high potential for damage related to climate change and high intensity weather events.
With the data compiled from 51 weather stations around the Caribbean, and with some knowledge of past studies, researchers divided the region into six clusters to group areas with similar rainfall patterns. Researchers used RClimDex software to analyze trends in several indices: total annual precipitation, average rainfall per rainy day, the number of consecutive dry/wet days, days above certain thresholds (10mm, 20mm, and 50mm), annual maximum precipitation, and the number of days in the 95th percentile. Temperature data were collected from the same stations, and a similar set of indices was studied: annual min/max temperature, annual mean temperature range during a day, the number of days in the 90th hottest and coldest percentiles, and the yearly minimum and maximum temperatures. Because the Caribbean region consists largely of developing countries, there have been difficulties in the past with missing and/or erroneous data associated with poor funding, but researchers took many measures to minimize these concerns. One way of dealing with this was to simultaneously study two time periods: 1961–2010 and 1986–2010. The purpose of introducing a shorter timeframe was that it allowed the inclusion of more weather sites that lacked old data.
Very few statistically significant results came from the precipitation analysis, and researchers postulate that this is due to the higher variability of precipitation in general. The only significant results with a high degree of confidence were a 2.05% increase in the number of 95th percentile wet days and a 0.59mm increase in average wet day rainfall, both in the 1986–2010 timeframe.
Almost all temperature indices showed significant changes in both time periods studied. Because almost all figures were significant, the results from the shorter timeframe (with more stations) are discussed in detail. In recent decades, there have been many more especially warm days. This is shown by sizeable changes in the percentage of day-time peak temperatures in the 90th percentile (5.97%) and night-time peaks in the 90th percentile (6.49%). There were also increases in the average daily minimum and maximum temperatures of 0.22°C and 0.12°C. Overall warming trends were also shown with increasing trends in yearly minimum and maximum temperatures, at both day and night. In addition to overall warming, temperature has generally begun to fluctuate less within a single day. This is especially true of the 90th percentile days, where there was a decline in daily temperature range of 0.08%. Researchers also acknowledge that many of these indices showed strong relationships with broader weather cycles, such as the Atlantic Multidecadal Oscillation (AMO). Further studies on the effects of AMO on Caribbean climate would help to analyze data more efficiently and single-out effects that are from long-term climate change.
Stephenson, T.S., Vincent, L.A., Allen, T. et al, 2013. Changes in extreme temperature and precipitation in the Caribbean region 1961–2010. Int. J. Climatol. doi:10.1002/joc.3889 Full paper at: http://onlinelibrary.wiley.com/doi/10.1002/joc.3889/full