Spatio-temporal distribution of aerosol optical depth and cloud properties over Lake Tana Basin, Upper Blue Nile River Basin, Ethiopia

Abstract

The spatio temporal variations (with respect to space and time) of some of atmospheric parameters over Lake Tana Basin, Ethiopia have been studied from 2001 to 2019 to understand their relationships among aerosol optical depth AOD) and rainfall. The origin and movement of air masses which bring aerosol particles have been studied by using the Hybrid Single Particle Lagrangian Integrated Trajectory (HYSPLIT) model. Aerosol optical depth (AOD) values were found to be maximum during the summer season (June–August), but minimum during the winter season (December–February). The annual average of AOD over the Lake Tana Basin varies from 0.21 to 0.34 during 2001–2019 while monthly and seasonal AOD values vary between 0.05 and 0.32, and 0.07 and 0.25 respectively. The HYSPLIT air mass back trajectories model indicate that air masses were traced from Eritrean Plateau, Red sea, Arabian Peninsula, Gulf of Aden and Afar depression. The negative relationship between AOD and Angstrom exponent indicates that the fine mode aerosol particles are dominate over the Tana Lake Basin. The stronger positive correlation coefficient between AOD and cloud fraction (CF) over the Gonder region (north of the Lake Tana Basin) as compared to that for Dangila region (south-west of the Lake Tana Basin; r = 0.61 and r = 0. 58 respectively), indicates the source of moisture from the Red Sea region. Nevertheless, the south-easterly increase in the spatial correlation between AOD and water vapor (WV) over the Lake Tana Basin suggests the prime source of moisture form the Western Indian Ocean. Thus, satellite derived AOD data are useful for the study of rainfall patterns.