Long-term changes in seasonal temperature extremes over Saudi Arabia during 1981-2010

Long-term changes in seasonal temperature extremes based on daily data across Saudi Arabia for the period 1981-2010 are analysed by assessing the trends for the four conventional seasons. Surface observations of daily maximum and minimum temperatures from high-quality datasets at 27 stations are used as the input. The trend throughout each season is then derived by employing Sen's slope estimator to four extreme value indices, four relative indices and three mean value indices. Warming trends for extreme value indices are observed for the majority of stations, particularly significant (at 95% level) in spring and summer seasons, however, mixed increase/decrease trends are found for the cold temperature extremes in autumn and winter seasons. Relative indices show significant warming trends for the majority of stations in all seasons; however, strong warming (above 5 days decade(-1)) is witnessed in the spring, summer and autumn seasons. The rapid rise (fall) of the number of warm (cool) days compared to warm (cool) nights is observed in the winter, summer and autumn (winter and spring) seasons. Warming of cool/warm nights is insignificant for the majority of stations in winter. The national average of mean value index diurnal temperature range shows an increasing trend for all seasons; however, its mixed increase/decrease trends are observed for the majority of stations in summer and autumn seasons. Time series analysis reveals that irrespective of seasons, warming is clearly visible in Saudi Arabia after 1997. Variations of warming for different regions across the country are also noticed.