by Tim Storer
Extreme weather events have major impacts on societies around the globe, and it is beneficial to have detailed climate data that show trends in extreme temperatures and precipitation. There are currently many areas with inadequate past research, such as the Arab regions in Northern Africa and the Arabian Peninsula. In order to help fill this gap, a meeting of several different climate research organizations was held so that data from all the necessary countries could be compiled. Many parts of the dry Arab region are particularly vulnerable to flooding in the case of extreme rain fall, making this an important area of study. Unlike past studies, this research did not collect data from within specific political borders, but grouped areas together based on similar climate characteristics. There were observed trends in overall warming throughout the region, as well as relationships between local temperature and multi-year climate cycles such as El Niño Southern Oscillation (ENSO) and North Atlantic Oscillation (NAO) (Donat et al. 2013).
M. Donat and others collected temperature and precipitation data from more than 100 different weather stations. Because the data came from many different countries, not all of which were able to provide data of the same level of detail, many stations were left out of the analysis and only 61 were used. Recent wars and conflicts have affected the data collection in many of the studied areas, making data compilation more difficult. In some instances, the researchers chose to exclude data from certain countries, such as Palestine and Lebanon due to gaps and inaccuracies in the records, and in some cases no data was attainable. The data were used to calculate 27 different indices for temperature and precipitation, such as the number of warm days and nights in the 90th percentile, warmest and coldest daily temperatures, and the number of consecutive days above certain thresholds for precipitation and temperature. These measures serve as indicators for different aspects weather intensity and frequency. All 27 of them were calculated for each station studied over two different time periods: 1981–2013 and 1966–2013. Because less stations have data before 1981, the longer time period has the disadvantage of having less complete data coverage of the area. In addition to calculating indices, relationships were analyzed between the data and the ENSO ad NAO. Lastly, given the complex nature of the problem, the researchers chose to weed out any inhomogeneous data rather than make adjustments.
The results show an overall warming trend in the Arab region with amplified warm extremes and smaller cold ones. The annual average of daily minimum and maximum temperatures both showed upward trends in most stations, though only some of these trends were statistically significant. These trends were stronger for the shorter time period than the longer one. The warming trends are even represented in the overall maximum yearly temperature, with many of the stations showing significant positive trends.
Rather than an amplification of both the coldest and warmest days, as seen in other parts of the globe, the data showed a decreasing number of days in the coldest 10th percentile, and an increase in the hottest 10th percentile. This means that the warmest days and the coldest days are becoming warmer. These trends are statistically significant in most of the data stations, but are relatively weak in locations at lower latitude.
As compared to temperature, there were less statistically significant trends in precipitation indices due to the high variability of rain fall in the region studied. The results also differ depending on which timeframe is used, with the longer timeframe showing a slight drying trend and the shorter one showing no trends. In the Arabian Peninsula, most stations showed decreases in the number of extremely wet days, though few were significant. Some stations in the same area also showed significant increases in the number of consecutive dry days. Researchers speculate that this is due to a lengthening of the dry season in this region.
Some stations also showed correlations between various indices and larger weather patterns, such as ENSO and NAO. In northeast Africa and in the Arabian Peninsula, the daily temperature range was generally greater in La Niña seasons. The results also show a correlation between NAO and warm temperature extremes in West Africa and the Mediterranean coastline, such that negative NAO periods corresponded to higher winter temperatures.
Unlike other parts of the globe, the temperatures in this region generally do not show amplification of both the warmest and coldest extremes, but rather a general warming trend. In order to better understand this area, further research should be done that includes adjustments for multi-year climate patterns.
Donat, M.,G., Peterson, T.C., Brunet, M. et al, 2013. Changes in extreme temperature and precipitation in the Arab region: long-term trends and variability related to ENSO and NAO. International Journal of Climatology, 34: 581–592. http://bit.ly/1yz1T9k