What are SSPs?
The Shared Socioeconomic Pathways (SSPs) are five reference narratives of how society, demographics, economics, technology and the environment might develop during the 21st century. Each storyline is accompanied by quantitative projections, including population, urbanisation, human development and economic development.
In WaterPath, SSP projections provide consistent future inputs for scenario analysis with the GloWPa model. The WaterPath project input data includes SSP data for population, human development, GDP per capita, sanitation, wastewater treatment and livestock. They currently include years: 2025 (baseline), 2030, 2050 and 2100.
The SSP descriptions below are taken from O'Neill et al., 2017 and the driver notes describe the rough trends observed in WaterPath data.
SSP1: Sustainability — Taking the Green Road
The world shifts gradually, but pervasively, toward a more sustainable path, emphasizing more inclusive development that respects perceived environmental boundaries. Management of the global commons slowly improves, educational and health investments accelerate the demographic transition, and the emphasis on economic growth shifts toward a broader emphasis on human well-being. Driven by an increasing commitment to achieving development goals, inequality is reduced both across and within countries. Consumption is oriented toward low material growth and lower resource and energy intensity (O'Neill et al., 2017).
Population: Growth slows, while urbanisation and human development increase strongly.
Sanitation: Unimproved sanitation and open defecation decrease rapidly as latrines, septic tanks and sewers expand.
Wastewater treatment: Treatment coverage and the share of advanced treatment increase rapidly.
Livestock population: Growth in animal numbers is restrained by lower-resource consumption patterns.
Production systems: Efficient, better-managed production increases and extensive grazing pressure decreases.
Exposure pathways: Rising GDP per capita increases access to drinking-water treatment and reduces exposure.
SSP2: Middle of the Road
The world follows a path in which social, economic, and technological trends do not shift markedly from historical patterns. Development and income growth proceeds unevenly, with some countries making relatively good progress while others fall short of expectations. Global and national institutions work toward but make slow progress in achieving sustainable development goals. Environmental systems experience degradation, although there are some improvements and overall the intensity of resource and energy use declines. Global population growth is moderate and levels off in the second half of the century. Income inequality persists or improves only slowly and challenges to reducing vulnerability to societal and environmental changes remain (O'Neill et al., 2017).
Population: Population, urbanisation and human development continue to increase at moderate rates.
Sanitation: Unimproved sanitation decreases gradually as improved technologies expand unevenly.
Wastewater treatment: Treatment coverage and treatment levels increase moderately.
Livestock population: Animal numbers increase moderately along historical trends.
Production systems: Intensive production expands gradually, while extensive systems remain important.
Exposure pathways: Rising GDP per capita gradually expands drinking-water treatment and reduces exposure.
SSP3: Regional Rivalry — A Rocky Road
A resurgent nationalism, concerns about competitiveness and security, and regional conflicts push countries to increasingly focus on domestic or, at most, regional issues. Policies shift over time to become increasingly oriented toward national and regional security issues. Countries focus on achieving energy and food security goals within their own regions at the expense of broader-based development. Investments in education and technological development decline. Economic development is slow, consumption is material-intensive, and inequalities persist or worsen over time. Population growth is low in industrialized and high in developing countries. A low international priority for addressing environmental concerns leads to strong environmental degradation in some regions (O'Neill et al., 2017).
Population: Population grows strongly, while urbanisation and human development increase slowly.
Sanitation: Unimproved sanitation and open defecation decline slowly and remain widespread.
Wastewater treatment: Treatment coverage grows slowly, with little expansion of advanced treatment.
Livestock population: Animal numbers increase strongly as population grows and productivity improves slowly.
Production systems: Extensive systems remain dominant and intensification progresses slowly.
Exposure pathways: Slow GDP-per-capita growth limits drinking-water treatment and keeps exposure high.
SSP4: Inequality — A Road Divided
Highly unequal investments in human capital, combined with increasing disparities in economic opportunity and political power, lead to increasing inequalities and stratification both across and within countries. Over time, a gap widens between an internationally-connected society that contributes to knowledge- and capital-intensive sectors of the global economy, and a fragmented collection of lower-income, poorly educated societies that work in a labor intensive, low-tech economy. Social cohesion degrades and conflict and unrest become increasingly common. Technology development is high in the high-tech economy and sectors. The globally connected energy sector diversifies, with investments in both carbon-intensive fuels like coal and unconventional oil, but also low-carbon energy sources. Environmental policies focus on local issues around middle and high income areas (O'Neill et al., 2017).
Population: Population grows mainly in poorer regions; urbanisation and human development diverge sharply.
Sanitation: Improved sanitation expands for wealthier groups but changes slowly for poorer populations.
Wastewater treatment: Coverage becomes more unequal, with advanced treatment concentrated in wealthier settings.
Livestock population: Animal-number changes diverge between high-productivity markets and lower-productivity regions.
Production systems: Intensive systems expand in connected markets, while extensive systems persist elsewhere.
Exposure pathways: Unequal GDP growth widens differences in drinking-water treatment and exposure.
SSP5: Fossil-fueled Development — Taking the Highway
Highly unequal investments in human capital, combined with increasing disparities in economic opportunity and political power, lead to increasing inequalities and stratification both across and within countries. Over time, a gap widens between an internationally-connected society that contributes to knowledge- and capital-intensive sectors of the global economy, and a fragmented collection of lower-income, poorly educated societies that work in a labor intensive, low-tech economy. Social cohesion degrades and conflict and unrest become increasingly common. Technology development is high in the high-tech economy and sectors. The globally connected energy sector diversifies, with investments in both carbon-intensive fuels like coal and unconventional oil, but also low-carbon energy sources. Environmental policies focus on local issues around middle and high income areas (O'Neill et al., 2017).
Population: Growth slows, while urbanisation and human development increase rapidly.
Sanitation: Unimproved sanitation decreases rapidly as septic tanks and sewer connections expand.
Wastewater treatment: Treatment coverage and advanced treatment increase strongly.
Livestock population: Demand for animal products and intensive production increase, raising animal numbers for several species.
Production systems: Intensive production expands strongly and the extensive share decreases.
Exposure pathways: Rapid GDP-per-capita growth expands drinking-water treatment and reduces exposure.
WaterPath SSP data
The driver mapping follows the estimated values in each WaterPath data source:
| WaterPath driver | Source dataset | Relevant variables |
|---|---|---|
| Population | world_population and hdi |
Population, urbanisation, fraction under five and Human Development Index |
| Sanitation | jmp_household_surveys |
Sanitation technology fractions |
| Wastewater treatment | treatment_fractions |
Primary, secondary, tertiary and quaternary treatment fractions |
| Livestock population | livestock_projections |
Animal heads by species |
| Production systems | livestock_projections |
Intensive, extensive, grazing and other production fractions |
| Exposure pathways | gdp |
GDP per capita used to scale drinking-water treatment maps |
References
- O'Neill, B. C., Kriegler, E., Ebi, K. L., Kemp-Benedict, E., Riahi, K., Rothman, D. S., van Ruijven, B. J., van Vuuren, D. P., Birkmann, J., Kok, K., Levy, M., & Solecki, W. (2017). The roads ahead: Narratives for shared socioeconomic pathways describing world futures in the 21st century. Global Environmental Change, 42, 169–180. https://doi.org/10.1016/j.gloenvcha.2015.01.004
- van Puijenbroek, P. J. T. M., Beusen, A. H. W., & Bouwman, A. F. (2019). Global nitrogen and phosphorus in urban waste water based on the shared socio-economic pathways. Journal of Environmental Management, 231, 446–456. https://doi.org/10.1016/j.jenvman.2018.10.048
- Strokal, M., Kumar, R., Bak, M. P., Jones, E. R., Beusen, A. H. W., Flörke, M., … Micella, I. (2025). Advancing water quality model intercomparisons under global change: perspectives from the new ISIMIP water quality sector. Environmental Research: Water, 1(3), 035002. doi:10.1088/3033-4942/adf571
- WaterPath project input data (2025): https://github.com/WaterPath-Project/waterpath-data
