Water Supply

Water Supply Sector

Purpose and Perspective

The Water Supply sector calculates the average yearly supply of water from renewable sources. The water supply sector does not consider seasonal variations of water supply and only represents dam capacity as a year-to-year smoothing factor in water supply. The Water Supply sources are structured based on FAO’s Aquastat classification. Based on water supply and withdrawal, Raskin’s water resources vulnerability index is also calculated. The Water Supply sector also calculates access to improved water sources and sanitation based on public and private investment.

Model Structure and Major Assumptions

  • Sources of water supply are structurally based on FAO (2015) [1]

  • The water resources vulnerability index is calculated based on Raskin et al. (1997) [2]

  • Unit cost of improved water source is based on WHO (2012) [3]

  • Unit cost of sanitation facilities is based on WHO (2012) [4]

Exogenous Input Variables

  • Average yearly precipitation - Units: Mm/Year

  • Cross border inflow - Units: Cm/Year

  • Dams capacity - Units: Cm

  • Fraction of rain not adding to surface or ground water resources - Units: Dmnl

  • Indicated proportion of sanitation expenditure for urban areas - Units: Dmnl

  • Indicated proportion of water and sanitation expenditure for improved water source - Units: Dmnl

  • Indicated proportion of water expenditure for urban areas - Units: Dmnl

  • Proportion of population living in urban areas - Units: Dmnl

Initialization Variables

  • Initial access to improved sanitation facility[area] - Units: Dmnl

  • Initial access to improved water source[area] - Units: Dmnl

  • Initial average access to improved water sources and sanitation facility - Units: Dmnl

  • Initial cross border outflow - Units: Cm/Year

  • Initial fraction of increase in water withdrawal from cross border outflows - Units: Dmnl

  • Initial proportion of population with access to private water and sanitation infrastructure - Units: Dmnl

Modeling Details

The oscillations in the flows of renewable water resources are smoothed by dam capacity: the smoothing time depends on dam capacity. Part of the water from precipitation and cross border inflow is accumulated in dams: dams work therefore as buffers for oscillations in supply. The larger the dam capacity, the stronger the buffer effect.

Concerning the water resources scarcity index, a country is considered water scarce if annual withdrawals are between 20 and 40% of annual supply, and severely water scarce if withdrawals exceed 40% [5]. We also include Falkenmark’s (1989) [6] water scarcity threshold, as a benchmark for water availability to affect access.

Footnotes and References

[1] FAO (2015). AQUASTAT database. Rome: Food and Agriculture Organization of the United Nations.

[2] Raskin, P., Gleick, P., Kirshen, P., Pontius, G., & Strzepek, K. (1997). Water Futures: Assessment of Long-range Patterns and Prospects. Stockholm, Sweden: Stockholm Environment Institute.

[3] WHO (2012). Global costs and benefits of drinking-water supply and sanitation interventions to reach the MDG target and universal coverage. Geneva: World Health Organization.

[4] WHO (2012). Global costs and benefits of drinking-water supply and sanitation interventions to reach the MDG target and universal coverage. Geneva: World Health Organization.

[5] Raskin, P., Gleick, P., Kirshen, P., Pontius, G., & Strzepek, K. (1997). Water Futures: Assessment of Long-range Patterns and Prospects. Stockholm, Sweden: Stockholm Environment Institute.

[6] Falkenmark, M. (1989). The massive water scarcity threatening Africa-why isn’t it being addressed. Ambio 18(2): 112-118.