Abstract:
Study region: The volcano-tectonic lakes basin of Abaya-Chamo is part of the Main Ethiopian Rift
system and exhibits large variations in geomorphology, physiography and climate between the
rift floor and the plateau.
Study focus: Despite the importance of streamflow for water resources management and planning
in the basin, many of the rivers there are ungauged. To make quantitative estimates of streamflow
for spatially resolved water availability in such a highly heterogeneous environment,
therefore, requires numerical modeling. This study is the first to quantify the surface and shallow
groundwater resources in Abaya-Chamo, and to validate the physically fully distributed hydrologic
model WetSpass under highly data-limited conditions, in a complex two-lake environment.
New hydrological insights: Simulated total river flow and estimated baseflow were verified at 15
gauging stations, with a good agreement. The WetSpass model is shown to be suitable for such a
complex setting with a correlation coefficient of 0.95 and 0.97 for total flow and baseflow respectively
at a statistically significant level (p-value<0.05). The simulated annual water budget
reveals that 74.6% of the 22.1 billion lit/yr in total precipitation in the basin is lost through
evapotranspiration, 15.7% through surface runoff, and only 9.7% recharges the groundwater
system. The simulations also revealed the surface runoff and groundwater recharge are the most
sensitive to soil textural class, while evapotranspiration depends more strongly on land use.
