Streamflow variability and its linkage to ENSO events in the Ethiopian Rift Valley Lakes Basin
Study Region: The Ethiopian Rift Valley Lakes basin is found in the main Ethiopian Rift Valley
system.
Study Focus: Understanding the hydrological impact of El Nino-Southern ˜ Oscillation (ENSO) is of a
paramount importance for society since it substantially affects the environmental and socioeconomic conditions. The relation between ENSO indicators (SOI, MEI and Nino3.4) ˜ and
streamflow magnitude was statistically evaluated with partial correlation, cross correlation,
extreme streamflow indices and streamflow deficits to provide empirical evidence on how ENSO
phases (La Nina ˜ and El Nino) ˜ affect streamflow variability. Trends of streamflow and ENSO indicators were tested using the non-parametric Mann-Kendall test.
New Hydrological Insights for the Region: Our findings indicate that the partial correlation between
the catchment area and ENSO effect on streamflow were not statistically significant at p < 0.05
after removing the south-north gradient. The direction of the ENSO effect is spatially inconsistent
since El Nino ˜ (La Nina) ˜ causes positive deviation in some catchments and negative deviation for
other catchments. Though statistically insignificant, reduced flow is detected for many catchments during El Nino ˜ years. For most catchment, the extreme high flow has a larger magnitude
during La Nina ˜ than El Nino ˜ whereas the extreme low flow has a larger magnitude during El Nino ˜
than La Nina ˜ years. Overall, the relationship between ENSO and streamflow of the study area is
found spatially inconsistent and statistically insignificant for most catchments.
system.
Study Focus: Understanding the hydrological impact of El Nino-Southern ˜ Oscillation (ENSO) is of a
paramount importance for society since it substantially affects the environmental and socioeconomic conditions. The relation between ENSO indicators (SOI, MEI and Nino3.4) ˜ and
streamflow magnitude was statistically evaluated with partial correlation, cross correlation,
extreme streamflow indices and streamflow deficits to provide empirical evidence on how ENSO
phases (La Nina ˜ and El Nino) ˜ affect streamflow variability. Trends of streamflow and ENSO indicators were tested using the non-parametric Mann-Kendall test.
New Hydrological Insights for the Region: Our findings indicate that the partial correlation between
the catchment area and ENSO effect on streamflow were not statistically significant at p < 0.05
after removing the south-north gradient. The direction of the ENSO effect is spatially inconsistent
since El Nino ˜ (La Nina) ˜ causes positive deviation in some catchments and negative deviation for
other catchments. Though statistically insignificant, reduced flow is detected for many catchments during El Nino ˜ years. For most catchment, the extreme high flow has a larger magnitude
during La Nina ˜ than El Nino ˜ whereas the extreme low flow has a larger magnitude during El Nino ˜
than La Nina ˜ years. Overall, the relationship between ENSO and streamflow of the study area is
found spatially inconsistent and statistically insignificant for most catchments.