Analysis of Precipitation Variability in the Kulfo River Watershed: Insights from Wavelet Analysis and Back-Trajectory Approaches

Analysis of precipitation time series is a fundamental undertaking in meteorology and hydrology. The heavy precipitation scenario of the Kulfo River watershed is studied using wavelet analysis and the advanced atmospheric transport model. Daily rainfall data for the 1991-2020 study periods are collected from the office of the Ethiopian Meteorology Institute. Meteorological fields on a three-dimensional grid at 1o x 1o spatial resolution and daily temporal resolution are also obtained from the Global Data Assimilation System (GDAS). Wavelet analysis of the daily precipitation processed with the lag-1 coefficient reveals some high power recurred once every 38 to 60 days with greater than 95% confidence for red noise. The analysis also identified inter-annual periodicity in the periods 2002 - 2005 and 2017 - 2019. Back trajectory analysis for 3-day periods up to the heavy precipitation day during the main and short rain seasons indicates the Indian Ocean and Gulf of Eden source; trajectories crossed the southern and eastern African escarpment to arrive at the Kulfo watershed. Atmospheric flows associated with the Western Indian monsoon redirected by the low-level Somali winds and Arabian ridge are responsible for the moisture supply. The spatial distribution of relative humidity (RH) during heavy precipitation events ranges from 50% to 88%. The findings indicated that the time-localization of the wavelet power spectrum yields valuable hydrological information and the back-trajectory approaches provide useful characterization of air mass sources and pathways. Keywords:  Back trajectory; Extreme Precipitation Events; Kulfo Watershed; Power Spectrum