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Large-scale water quality modeling
Hot spots and causes of water pollution
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Outline
• The modeling framework
• Model results for Africa
– Progress since October 2013
• Hot spots of water pollution
– Fecal Coliform bacteria  Risk to human health
– BOD  Threat to inland fishery
• Causes of water pollution
– Main sectors contributing to pollution
• Conclusions & preliminary findings
• Next steps
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Modeling framework
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spatial: 5’
temporal: monthly
results: monthly
spatial: 5’
temporal: daily
results: daily/monthly
WaterGAP3
Hydrology Model
discharge, runoff,
flow velocity
consumptive
water use
WorldQual
Water Quality
Model
return flow
spatial: 5‘ temporal: daily results: daily/monthly/yearly
WaterGAP3
Water Use Models
agriculture
domestic
manufacturing
electricity
production
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Progress since October 2013
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point sources
urban
surface
runoff
manufacturing
(wastewater)
diffuse sources
domestic
(urban)
domestic
(rural)
– sewage
– sewage
– hanging
latrines
agriculture
– septic tanks (organic
– pit latrines fertilizer)
domestic
– inadequate
sanitation
agriculture
(industrial
fertilizer)
“scattered settlements”
Data from Joint Monitoring Programme; country files (1980-2011)
natural
background
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Connectivity & treatment
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Loadings: Fecal coliform bacteria
2010
Human and animal input
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Dilution capacity
Climate normal period
(1971-2000)
Example:
Modeled FC concentration at Mhlatuze River, South Africa
January to December 2010
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FC in-stream concentration
February 2010
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Comparison: FC in-stream concentration
February 2010
August 2010
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Sensitivity analysis: Assuming 100% connectivity…
February 2010
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…but no improvement of treatment levels
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BOD loadings in 2010
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Total BOD loads in 2010
~ 8.5 million tons
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BOD in-stream concentration
February 2010
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August 2010
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Uncertainty of model assumptions
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High: assuming 7.5% of washed-off
manure contributes to BOD load
Low: assuming 3% of washed-off
manure contributes to BOD load
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Sensitivity analysis for BOD: “low rate“ assumption
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Total BOD loads in 2010
~ 5 million tons
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Hot spots of BOD for “low rate“ assumption
February 2010
August 2010
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Model validation
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High: assuming 7.5% of washed-off
manure contributes to BOD load
Low: assuming 3% of washed-off
manure contributes to BOD load
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Cause of water pollution: sources of BOD loads
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Transboundary river basin scale
Example:
Total BOD loads in the Nile river basin
contributing loads per country [%]
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Conclusions
First time:
 Synthesize information about population, sanitation and
connectivity and make spatially explicit for all of Africa
 Compute loads of organic pollution and bacterial
contamination for each river basin in Africa (grid cell
basis)
 Geographic comparison of BOD and fecal coliform
loadings in Africa
 Calculation of BOD and coliform levels for all rivers in
Africa
 Estimation of hot spot water pollution areas in Africa
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Preliminary findings
 Hot spot areas: 17% of population living at big rivers with
bacterial contamination >1000cfu/100ml in Africa
 Hot spot areas: Dilution capacity + magnitude of loadings
 Magnitude of BOD loading uncertain (manure runoff)
 Most important source of BOD: manure runoff; least
important: urban surface runoff
 Source profile of BOD loadings vary greatly between countries
(e.g. Somalia: manure runoff; Egypt: urban domestic)
 Total BOD loads steadily increased in Africa between 1990 and
2010 (increasing population, livestock, connectivity)
 High potential to provide policy-relevant overview of water
quality issues for Africa and other regions
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Next steps
 Further improvement of estimates for Africa
– getting regional feedback
 Extension of estimates to Asia and Latin America
 Extension of estimates to include:
– other water quality parameters (total dissolved solids, total N,
total P, water temperature)
– lakes
 Apply water quality guidelines as thresholds
 Merger of model-driven & data-driven analyses: threats
to human health & inland fisheries (food security) and
policy responses
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