Abstract
Global warming and abrupt seasonal changes are the current challenging issues across the globe. This study investigated the trends in average temperature and precipitation on monthly basis for the designated stations of Najd and Hejaz regions of Saudi Arabia, namely Qassim, Riyadh, Tabuk, Medina, Mecca, Al-Baha, Hail and Jizan. Two non-parametric techniques are used for this purpose. In the first stage, the Mann-Kendall test is applied to determine the trends and in the later stage, the Sen's slope test is utilized to determine the extent of the trends. The Mann-Kendall test with a 5% significance level was applied to the 30-year data of eight selected stations from 1985 to 2014. The analysis showed increasing trends only in mean monthly temperature at all eight stations throughout the year, whereas Tabuk and Riyad showed increasing trends, while Medina, Qassim and Hail exhibited decreasing trends in precipitation in four different months of the year. The trend in precipitation at Mecca, Al-Baha and Jizan was insignificant throughout the year. From the results of Sen's Slope test, it was concluded that the trend pattern is associated with the intensity of trend values. It was also found that temperature is rising in three of the four seasons on an annual basis during the study period. From the results, longer summer and shorter winter are expected in the future due to rising temperature. It can also be inferred that the increasing temperature will increase the evaporation from the sea causing a humid environment which can result in a heavy downpour in the near future especially in coastal areas. The rising temperature and changing pattern of precipitation may increase uncertainty in developing strategies for water resources management.