Study of trend and fluctuations of global solar radiation over Egypt

Climatological spatiotemporal variability of global solar radiation (GSR) and its trend analysis, fluctuations and abrupt changes based on seven sites (Cairo, Arish, Barrani, Matrouh, Aswan, Asyut, Kharga) in Egypt were studied during the period 1985–2018. Fifth-generation dataset of European Center for Medium-Range Weather Forecasts (ECMWF) reanalysis of the global climate and weather for the past 4 to 7 decades (ERA5) data after validation with available observed GSR data has been used. Monthly, seasonal and annual GSR values have marked variations. The results revealed that the highest values of coefficient of variation occurred at stations in winter, while the lowest values occurred in summer. Moreover, in winter and spring, all stations presented a positive Mann-Kendell (MK) trend and almost all stations in annual except Aswan, Asyut and Kharga, whereas in autumn, all station presented a negative MK trend, summer in all stations except Barrani and Cairo. The fluctuations in the annual GSR were investigated using the cumulative sum charts (CUSUM) method, where all stations have alternating trend between negative and positive CUSUM along period.