Abstract:
For basin-wide water balance studies, understanding the sources of precipitation and their relative contributions is essential. In Ethiopia some previous studies attempted to examine the relationship between the isotopic composition of precipitation and the transport route of atmospheric water vapor. However, the significance of isotopes in tracing water vapor source was not studied for this region. Numerical water vapor tracers (HYSPLIT model), and physical water vapor tracers (isotopes) are among the methods used in the current study to realize the main objective of this study by identifying the source of atmospheric moisture for Abaya-Chamo basin. The potential locations of atmospheric moisture sources and the direction of the air mass causing precipitation before reaching Abaya-Chamo basin were investigated through HYSPLIT with Graphical User Interfaces and 1◦ × 1◦ climatic data set generated by GDAS which is used as an input to the HYSPLIT model from the NOAA ARL archive. Secondary data of Oxygen and hydrogen stable isotopes in precipitation collected from GNIP station and Iso GSM models from 2018 to 2020 in Abaya-Chamo basin, South Ethiopia, were presented in this paper to validate HYSPLIT model. Results of back trajectory cluster analysis imply that the potential moisture source for the study area during Belg seasons were the anticyclone from the Arabian High which is located in Arabian and Mediterranean Sea. And also the Indian Ocean owing to Mascarene highs carried by the equatorial easterlies contributes moisture. Furthermore, during Kiremt, the Mascarene highs which is located in South Indian Ocean, the St Helena high which is centred in the subtropical southern Atlantic Ocean and the Continental source: Air masses that originated from Congo basin were the potential moisture source region for the study areas. Seasonal variations of the isotopic composition imply that the multiple moisture sources bringing precipitation into the study area. The Belg season rainfalls are the enriched compared to the Kiremt rains. During this time, oceanic moisture reaches the area from the northern Indian Ocean. However the Kiremt rainfalls waters are relatively depleted in δ18O and they have higher d-excess. This generally agrees with the results of model analysis on backward trajectories. And this study recommends a further investigation using event-based observations for further validation of HYPLIT model.
