Impacts of land cover and land use changes on stream flow:

A case from the Nile Basin

BySimon Mutie, Hussein Gadain, and Guleid Artan

Background

• Since 1960’s LULC changes have been a threat to life in the Nile Basin;

• High population increases has led to changes in land tenure systems resulting in deforestation expansion and intensification of agriculture;

• These changes in land cover have caused changes in the water balance of the basin.

Problem Statement

• Population growth rate 7.5%,• High population = changes in land

tenure systems,• Deforestation and intensification of

agriculture and overstocking,• Reduction of perennial natural

vegetation,• Rise in bare and agricultural lands.• Modifications of land cover and soils

affect runoff hence water availability,• High sedimentation and water quality

concerns.

Deforestation-Mau

Wheat-Narok

Flooding-Nzoia

Study Area

Upper Nile Basin

Economic Importance of the basins

• Both basins originate from the indigenous and exotic greater Mau, Mt. Elgon and Cherangany forests.

• Large-scale/cash crop plantation– Tea, sugarcane, rice, wheat and high value

horticultural crops. Small-scale mixed farming also practised

• Pastoralists with the nomadic Maasai community in Mara River basin.

• Mara basin houses the Serena-Mara-Serengeti wildlife sanctuary declared the seventh wonder in the world

• Swamps (Yala & Mosirori) which support a lot of biodiversity.

Major Ecosystem Threats

• Widespread encroachment and deforestation of the Mau forest tower, Mt Elgon Forest

• Rapid population growth and immigration into the basins.

• Expansion and intensification of agriculture• Conversion and rehabilitation of basin wetlands

for agricultural production e.g. Yala swamp

Source: Nation media

Deforestation-Mau

Rice Growing-Yala swamp

Overstocking-MaraMosirori Swamp

Overall objective

To determine the effects of land use & land cover changes on the river

flow in the two basins

Source: USGS

Pixel Resolution

MSS – 79 * 56 m

TM and ETM – 28.5 * 28.5 m

Data and Methods

• LANDSAT images for the dry season (MSS and TM/ETM, for the years 1973, 1986 and the 2000 respectively)

• Image processing and classification; GPS used for surveys to collect ground-truth data on vegetation and land use/cover

False Color composite of bands 2,3&4 – 1986 data

LULC Mapping

Land cover type1973

(km2)1986

(km2)2000

(km2)

Change (1973-

2000)(km2)

Change (%)

Forests 1008 893 689 -319 -32

Tea/Open forests 621 1073 1948 +1327 +214

Agricultural land 826 1617 2504 +1678 +203

Shrubland 5361 5105 3546 -1815 -34

Grassland 2465 1621 1345 -1120 -45

Savannah 3163 2867 2354 -809 -26

Wetlands 286 604 1394 +1108 +387

Water Bodies 104 54 55 -49 -47

LULC ChangesLULC ChangesMara River Basin

Nzoia River Basin

Nzoia River Basin

No.

Land Use Land Cover Type

1973 (km2)

1986(km2)

2000(km2)

Change(1973-2000)

(km2

Change (%)

1 Forests 2,842 1,680 1517 -1325 -47

2 Shrubland 6,228 942 1215 -5013 -75

3Agricultural Land

3,152 9,486 9167 6015 96

4 Wetland 86 114 135 49 48

5Built up areas

373 515 690 317 83

6Water Bodies

89 33 46 -43 49

Geo-spatial SFM System Diagram

Preprocessing

MAP

MAE

Basin

Linkage

Routing Parameters

Soil Parameters

Stream Flow Model

Water Balance

Lumped Routing

Dist. Routing

Streamflow

Data

Rain

Evap

Soil

LU/LC

DEM

Obsv. S.Flow Data

Effects of Land use change on

stream flow

– Earlier than normal peaks– Higher peaks– Change in evaporation process– Soil erosion and sedimentation– produced streamflow at rainfall

magnitudes that did not generate any streamflow with the 1973 dataset.

– Changes are slight in Nzoia

Basin Item 1973 2000

Mara Peak flow (m3/s) 827.0 877.9 m3/s

 Time to Peak

(days) 158th Julian day 154th Julian day

NzoiaPeak flow (m3/s)

 546.3 553.4 m3/s  

 Time to Peak

(days) 126th Julian day 125th Julian day

Conclusions• There has been decline of natural vegetation in the two basins and

a rise in land covers due to anthropogenic influences in the basin.• The changes have caused higher and earlier occurrence of flood

peaks.• Increase in agriculture coupled with poor farming practices in the

two basins has led to high sediment loads deposited on the river mouths.

• In Mara basin, sediment deposition at river mouth has caused backwater flow which has increased the wetland submerging farms.

• In Nzoia basin, deposition at lower river stages is raising the river channel, hence water topping the flood dykes every season

Potentialities/Limitations RS

Limitations• Data Availability• Cost• High cost analysing

Potentialities• Descision making and planning