15-year variability of desert dust optical depth on global and regional scales

Abstract. This study aims to investigate the global, regional and seasonal temporal dust changes as well as the effect of dust particles on total aerosol loading, using the MIDAS fine resolution dataset. MIDAS delivers dust optical depth (DOD) at fine spatial resolution (0.1° × 0.1°) spanning from 2003 to 2017. Within this study period, the dust burden has been increased across Central Sahara (up to 0.023 yr−1) and Arabian Peninsula (up to 0.024 yr−1). Both regions observed their highest seasonal trends in summer (up to 0.031 yr−1). On the other side, declining DOD trends are encountered in Western (down to −0.015 yr−1) and Eastern (down to −0.023 yr−1) Sahara, Bodele Depression (down to −0.021 yr−1), Thar (down to −0.017 yr−1) and Gobi (down to −0.011 yr−1) Deserts and Mediterranean Basin (down to −0.009 yr−1). At spring, the most negative seasonal trends are recorded in Bodele Depression (down to −0.038 yr−1) and Gobi Desert (down to −0.023 yr−1) whereas in West (down to −0.028 yr−1) and East Sahara (down to −0.020 yr−1), and Thar Desert (down to −0.047 yr−1) at summer. Over western and eastern sector of Mediterranean Basin, the most negative seasonal trends are computed at summer (down to −0.010 yr−1) and spring (down to −0.006 yr−1), respectively. The effect of DOD to the total aerosol optical depth (AOD) changes is determined calculating the DOD to AOD ratio. Over Sahara Desert the median ratio values range from 0.83 to 0.95 whereas in other dust affected areas (Arabian Peninsula, South Mediterranean, Thar and Gobi Deserts) is recorded approximately around 0.6. In addition, a comprehensive analysis of the factors effecting the sign, the magnitude and the statistical significance of the calculated trends is conducted. Firstly, the implications between the implementation of geometric mean instead of arithmetic mean to trend calculations are discussed revealing that the arithmetic-based trends tend to overestimate compared with the geometric-based trends both over land and ocean. Secondly, an analysis interpreting the differences in trend calculations under different spatial resolutions (fine and coarse) and time intervals is conducted, which sounds a critical aspect when satellite-based measurements are utilized.