Daily temperature extremes over Egypt: spatial patterns, temporal trends, and driving forces
Spatial and temporal changes of daily temperature extremes are investigated over Egypt using a standard set of 23 indices. Our analysis uses a database consisting of complete, high quality and homogenous daily maximum and minimum air temperature records at 40 stations, spanning the period from 1983 to 2015. The trends were assessed using a least squares regression model, and its significance was determined by means of the modified Mann-Kendall test (p < .05). Results demonstrate that the frequency, intensity, and persistence of warm extremes increased significantly over the study period, with a clear spatial gradient from southeast to northwest. The strongest warming was more evident in coastal areas along the Red Sea and the Sinai Peninsula. In contrast, changes in cold extremes were mostly non-significant, with a divergence in the trends (i.e. positive and negative). Changes in variability indices such as the diurnal temperature range (DTR) were more consistent with those of warm extremes than with cold extremes. Our results also demonstrate that maximum air temperature witnessed stronger warming than minimum air temperature, leading to a dramatic increase in DTR, especially in the last decade. This study also points at the possible physical mechanisms responsible for the detectable changes in temperature extremes using sea level pressure and geopotential field data. Results indicate that anomalous warm events over Egypt are directly related to easterly winds that bring warm and dry air from the Arabian Peninsula and the Iranian Plateau, accompanied by strong ridges over the eastern Mediterranean and an intensification of the Asian monsoon lows. On the other hand, the occurrence of anomalous cold events can be linked to the east-west pressure gradient between the North Atlantic Highs and the Siberian and Persian Troughs, which enhances a northerly and northwesterly cold advection from Northern Europe to Egypt. This situation is also combined with a subsidence of cooler air from the mid to low troposphere. Overall, the observed changes in warm extremes could have profound ecological, hydrological and socioeconomic impacts, especially for crop production, water resources management and energy consumption. As such, improving the insight and understanding of such changes is of considerable importance to provide guidance to policymakers and stakeholders to develop more appropriate adaptation strategies.