Thesis final presentation-Abay

Climate Change Impacts on Water Resources

in the Lake Tana Basin in Ethiopia

Abaye Getahun Abebe

Supervisor:

Professor M.McClain

Mentor:

Dr. Shreedhar Maskey

Delft, April 2016

Examination Committee:

Professor M.McClain

Dr. Shreedhar Maskey

Dr. Patricia Trambauer

Contents

Introduction

• Study Area

Objectives

Materials and methods

Result and Discussion

Conclusion and Recommendation

2

Introduction

Tana Basin

Catchment area: 15,054km2

Altitude range: 1788-4109 masl

Annual precipitation: 964-2000mm

Origin of Blue Nile river

Lake Tana

3

Study Area

Introduction

4

Scope of

studies

Abdo et al.

(2009)

Setegn et al.

(2011)

Taye et al.

(2011)

Thesis

Hydrological

model HBV SWATVHM

NAM SWAT

Climate model

HadCM3

ccma_cgcm3.1,

cnrm_cm3,

csiro_mk3.0,

csiro_mk3.5,

gfdl_cm2.0,

ipsl_cm4,

mpi_echam5,

mri_cgcm2.3.2a

ipsl_cm4,

miroc3.2,

cnrm_cm3,

mri_cgcm2.3.

2.a

cnrm_cm3

miroc3.2

Scenarios &

scenario

periods

B2, A2(2020s, 2050s,

2080s)

B1, A1B, A2 (2050s, 2090s)

B1, A1B(2050s)

A1B, A2(2055s, 2090s)

Contribution

of major

subbasins

Gilgel Abay(11% of Tana

basin)

Gilgel Abay Lake outlet

Gilgel Abay,

Gummera,

Ribb, Megetch,

Lake outlet

Focus of

impact

analysis

Hydrology of

Gilgel Abay

Hydroclimatolo

gy of Gilgel

Abay

Hydrologic

al extremes

at lake

outlet

Water resource

availability at 4

major subbasin

outlets and WB

of Lake

v

Previous studies:Either 1 sub-catchment of

Tana basin or lumped

hydrological processes for

the entire basin area. Due to

high climatic variability

within the basin, impact of

climate change may not be

similar throughout the basin. j

v

Objectives

Main objective:

To analyse climate change impacts on hydrology and water

resources of Tana basin using process based hydrological model

Specific objectives:

To analyse the past and future climatic variable changes in

precipitation and temperature

To analyse climate change impacts on water resources in the Tana

basin

To study the variations in climate change impacts at different sub-

basins of Lake Tana

5

Materials and Methods

Data

Hydrometerological data

• Precipitation

• Temperature (max. and min.)

• Discharge

Spatial data

• DEM (90m)

• Soil and Land use map

GCM output data

• Precipitation and Temperature outputs of GCMs(http://globalweather.tamu.edu/cmip)

6

http://globalweather.tamu.edu/cmip


GCM output data:

Downscaled to: 0.50 x 0.50

BCSD downscaling

Temporal resolution: daily

7


GCM outputs of base period Vs observed data (1980-2000)

8

• CCCMA_CGCM3.1

• CNRM_CM3

• GFDL_CM2

• GFDL_CM2.1

• MIROC3.2

• CNRM_CM3

• MIROC3.2

GCM models


Software used: SWAT2012

Model setup

• 11 Sub-basins• 84 HRUs• Lake Tana as a

reservoir

Methods used inSWAT model:

9


Hydrological model results

10

Monthly flow at Gilgel Abay

Calibration Validation

ENS R2 PBIAS ENS R2 PBIAS

0.88 0.89 7.09 0.93 0.96 -16.34

SWAT model underestimated high

flows in years (1991, 1993 & 1996) and

overestimated peak flows in years

(2003 & 2005) which could be in part

due to:

high rainfall events that operate at

time scales smaller than the SWAT

model time step that was set daily

less data quality



11

Monthly flow at Gummera



0.87 0.89 10.57 0.86 0.86 -5.27

Model systematically

underestimated peak flows:

might be due to its poorly

gauged nature of

precipitation

High PET would be due to

high temperature associated

in the area



12



0.68 0.72 -19.51 0.78 0.83 12.11

Monthly flow at Megetch

In Megetch and Ribb catchments;

percolation to deep aquifer is a

part of the water yield component.

6-8%: Megetch

13-17%: Ribb



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Into Lake:• Precipitation over the lake (49%)

• River inflows to the lake (51%)

Out from Lake:• Evaporation over lake surface (45%)

• River outflows from the lake (55%)

Result and DiscussionProjected change in climate

Climate change analysis (Scenarios: A1B & A2; Projected period: 2046-2064 &

2081-2100; base period:1980-2000)

Precipitation: monthly, seasonal and annual time horizons

14

Gilgel Abay

Mean daily precipitation is projected to increase towards to the beginning of dry

season from October to December


15

Gilgel Abay

Increase

upto 14%

Increase

upto 51%


16

Gummera

Both GCM models project precipitation in 2055s and 2090s higher than

the base period from October to December


17

Gummera

Increase

upto 10%

Increase

upto 58%


18

Megetch


19

Megetch

Increase

upto 13%

Increase

upto 52%


Temperature

20

A1B Scenario Both GCM models

show Tmax & Tmin

for future periods

∆Tmax ( 0.1 to 4.1 oC)

∆Tmin (1.6 to 5.2 oC)

A2 Scenario

∆Tmax ( 0.3 to 5.2 oC)

∆Tmin (1.3 to 6.9 oC)

Change in Tmin is

higher than change

in Tmax


Projected precipitation in our study increases towards to the end of

rainy season for the case of Gilgel Abay subbasin which is in lined with

Abdo et al.(2009). The mean annual projected precipitation in the Tana

Basin ranges from -1% to 58% which signifies the finding of Kim et

al.(2009) indicated that the climate likely become wetter in the mid of

the century.

The projected temperature change in our study increases upto 6.9oC in

Tana basin during 2090s. Previous studies made by Abdo et al. (2009)

and Setegn et al.(2011) have obtained the increase upto 5.8oC in the

end of the century. Hence, the Tana Basin is likely become warmer

due to climate change in the future.

21

Result and DiscussionClimate Change impact on water resources

Actual evapotranspiration

22

Change in AET

increases under both

scenarios in 2055s

and 2090s:

• Increased in

projected P & T

Change in AET in

Megetch, Gummera

and Ribb is higher

than Gilgel Abay

under both scenarios

Result and DiscussionClimate change impact on water resources

Catchment runoff

23

Annual runoff changes in the major subbasins of Tana ranges from -13% to 135%

under both scenarios and projection periods

Outputs given by MIROC3.2 model results higher than CNRM_CM3 in all catchments


Catchment runoff

The annual runoff changes in Gilgel Abay, Gummera, and Ribb are

increased in the scenario periods. This is supported by Taye et al (2011)

obtained that the annual runoff increases upto 79% at outlet of Tana

basin in the middle the century. Besides, Abdo et al (2009) argues the

runoff in the Gilgel Abay catchment increases in the future.

The studies made by Conway (2005), Kim et al.(2009) and Beyene et

al.(2010) reported the increase of streamflow in Blue Nile due to

climate change that are relevant for Tana basin.

24


Lake Tana water balance

25

Percentage of change from the base period

CNRM_CM3 MIROC3.2

Scenarios 2055s 2090s 2055s 2090s

Inflow to the lakeA1B 22 11 38 35

A2 3 9 66 93

precipitationA1B 5 2 15 27

A2 -3 2 35 51Evaporation from lake surface

A1B 1 1 2 2

A2 2 11 2 2

The projected water balance components of the lake are increased under both

emission scenarios

Projected precipitation and inflow to the lake given by MIROC3.2 model is

comparably higher than CNRM_CM3 model

Projected change in evaporation is almost similar under both scenarios except

in 2090s under A2 scenario from CNRM_CM3 model. This would be due to

higher projected temperature in 2090s from this model & probable increase

of the surface area of the lake that lead to increase evaporation.

Conclusion and RecommendationConclusion

Projected precipitation and runoff increased in the basin for scenario

periods

Water resources availability could be improved

Increasing of precipitation towards to the beginning of the dry season

from October to December

Negative impact on harvesting activities

Precipitation on Lake and river inflows to the lake increases during

scenario periods in 2055s and 2090s

Increased water level of the lake could result flooding in the flood plains

around the lake Tana

Recommendation

Using more GCM models in the impact investigation would be better so

that uncertainty due to climate models will be improved

Using Latest RCPs Climate scenarios might be expected to provide

more certain projections (Knutti and Sedláček, 2013). So it would be

better to use RCPs26

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Documents

Thesis final presentation-Abay