Impact of Climate Variability on Lake Chamo Water Balance
Creators: name: Ayele, Elias Gebeyehu
Publisher: name: National Academic Digital Repository of Ethiopia
Year: 2014

description: One of the most significant potential concerns of climate variability is to understand changes in
hydrological components and subsequent change in lakes water balance. In view of this studying
the  water  balance  components  such  as  surface  water  inflow  from  gauged  and  ungauged sub
watersheds, precipitation  and evaporation  pattern of  the  natural  reservoir and  their associated
impacts vis-à-vis altering the water balance of terminal Lakes Chamo has a major concern of the
present study. It ultimately focuses on evaluating the impact of climate variability on water
balance of Lake Chamo, situated in the southern part of the Ethiopian Rift valley lakes basin
system.  Lake Chamo is the largest lake among Ethiopian Rift valley Lakes system with a total
area of 328.63Km
2
and average depth of 10.1m.
In  order  to  achieve  the  above  main  objective  of  the  study  primary  analysis  various  hydro
metrological variables of the water balance components undertaken. A conceptual hydrological 
model that could describe the underlying input-output relationship is established for the lake
catchment. Based on such established relationship net inflow to the lake surface is simulated.
Inflow to the lake surface is simulated for both historical (1995 to 2004) and future climate
scenario (2030s and 2090s) conditions obtained from regional climate model output. 
The  A1B  scenario  Regional  Climate  Model  (RCM)  organized  by  International  Water
Management  Institute  (IWMI)  is  used  for  future  climate  condition  analysis.  The  raw  A1B
scenario outputs are characterized by significant biases and hence subjected to bias correction
before  applying  the  hydrological  modeling.  The  bias  correction  for  A1B  scenario  for
precipitation, maximum and minimum temperature was done by using Linear scaling approach. 
This analysis is based on projection of two different scenarios of future time horizons: 2030s
(2031-2040) and 2090s (2091-2100). Over lake evaporation is estimated by Penman Monteith
formula, over-lake precipitation is computed by area weighing method and surface inflows are 
simulated by using HBV model. A hydrological model, HBV, was used in order to simulate the
current and future inflow to the lake. The performance of the model was assessed through
calibration and validation process and resulted R
2
from 0.64 to 0.81 during calibration and from 
0.63  to  0.77 during  validation  at  the three stations. Mean annual inflow  to  Lake  Chamo  from 
gauged and un-gauged catchment is 4391 mmyr
-1
. The estimated runoff for the period 2030s and 2090s is 4204 mmyr
-1
and 3277 mmyr
-1
respectively. The result shows the mean annual inflow is 
decreased by 4.3% and 25.4% in 2030s and 2090s respectively from the base time period.
The result revealed that the maximum and minimum temperatures increase for the two scenarios 
in future time horizons. However, precipitation decreases in all future time horizons. The A1B
scenario  reveals  the  decreasing  pattern  of  lake  water  storage  due  to  decrease  of  inflows
components such over lake precipitation and surface water inflow in all future time horizons. In
this scenario, the over-lake evaporation shows increasing pattern for all future time horizons.