Water Sector Assumptions for the Shared Socioeconomic Pathways in an Integrated Modeling Framework

Abstract

The Shared Socioeconomic Pathways (SSPs) were developed without explicit assumptions for the future of the water sector; therefore, projections of future water demands based on the SSPs often lack a treatment of water technology assumptions that is consistent with the SSP storylines. This study has developed a set of qualitative and quantitative assumptions for future water sector technological advancements in the agricultural, electricity, manufacturing, and municipal sectors within the SSPs and then applied the resulting scenarios to an integrated assessment model to permit analysis of future water demand in a water‐constrained world. These scenarios are then compared to another set that excludes the adoption of water‐efficient technologies. Water demand impacts of individual SSP assumption categories are analyzed to determine scenario‐by‐scenario changes. By 2100, global annual water demands range from 3,560 to 6,600 km3. The results show that (1) technological change in the water sector can act to reduce water demand in a water limited world by up to 32% in 2100 in the SSP scenarios, (2) the most sustainable scenario produces end‐of‐century water withdrawals lower than 2010 values, (3) low‐income regions will likely be one of the largest drivers of future water demands and exhibit the greatest sensitivity to highly‐efficient water technologies, and (4) nonwater sector SSP assumptions have significant and differing impacts on demands across SSP scenarios that act to alter global water demands.

Humans drive future water scarcity changes across all Shared Socioeconomic Pathways

“…Human-dominated, water scarcity increases (H+) occur in 60% of the globe while 22% experiences decreasing scarcity due to humans (H−). Significant differences arise across SSPs as socioeconomic differences drive efficiency improvements, demand changes, and altered water dependency , Graham et al 2018. SSP1 experiences a shift from H+ to H− in a large amount of land throughout the century, leading to just 36% of the globe classified as H+ in 2100, while humans act to decrease water scarcity in 44%.…”

“…Meanwhile, much of the midwestern United States is shown to have human driven scarcity decreases in 2050 and 2100, unlike what has been shown in some previous studies . Prescribed SSP-specific improvements in water use technologies (Graham et al 2018), are likely to cause human-driven water scarcity decreases, particularly in regions where population is not expected to change dramatically in the future (Samir and Lutz 2017) while GDP growth is expected to allow for water use improvements across many SSPs . Nearly all of Africa experiences counteracting water scarcity effects as population driven increases in demand lead to increases in scarcity, while climate-driven increases in precipitation increase water supply and thus lower scarcity (supplementary figure S11).…”

“…As in figure 2(b), the robustness of the classification is again shown to decrease by the end of the century (right). This is due to differences in efficiency and the sustainability focus of the socioeconomic scenarios driving the evolution of water scarcity categories, particularly in central Eurasia and Africa where population change projections and GDP vary by SSP , Graham et al 2018. Areas of negligible changes remain the same as in figure 2(b), by definition.…”

“…The adoption of higher efficiency technologies has been shown to decrease global water demands (Graham et al 2018).…”

“…By using GCAM, this analysis can capture feedbacks between energy, land, and the human system that have previously lacked in several water scarcity studies. This analysis enables the use of a wide range of socioeconomic and climate futures that are placed under constraints to sources of freshwater, including nonrenewable groundwater, surface runoff, and desalinated seawater (Kim et al 2016, Graham et al 2018. The use of models that link energy, water, land, and climate in water scarcity assessments allows for the explicit representation of how climate-induced changes in water availability alter energy and land systems.…”