Impacts of land cover and land use changes on stream flow: A case from the Nile Basin
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Transcript of Impacts of land cover and land use changes on stream flow: A case from the Nile Basin
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