Future Transboundary Water Stress and Its Drivers Under Climate Change: A Global Study

Abstract

Various transboundary river basins are facing increased pressure on water resources in near future. However, little is known ab out the future drivers globally, namely, changes in natural local runoff and natural inflows from upstream parts of a basin, as well as local and upstream water consumption. Here we use an ensemble of four global hydrological models forced by five global climate models and the latest greenhouse‐gas concentration (RCP) and socioeconomic pathway (SSP) scenarios to assess the impact of these drivers on transboundary water stress in the past and future. Our results show that population under water stress is expected to increase by 50% under a low population growth and emissions scenario (SSP1‐RCP2.6) and double under a high population growth and emission scenario (SSP3‐RCP6.0), compared to the year 2010. As changes in water availability have a smaller effect when water is not yet scarce, changes in water stress globally are dominated by local water consumption—managing local demand is thus necessary in order to avoid future stress. Focusing then on the role of upstream changes, we identified upstream availability (i.e., less natural runoff or increased water consumption) as the dominant driver of changes in net water availability in most downstream areas. Moreover, an increased number of people will be living in areas dependent on upstream originating water in 2050. International water treaties and management will therefore have an increasingly crucial role in these hot spot regions to ensure fair management of transboundary water resources.

Future global urban water scarcity and potential solutions

“…Based on the approach used by McDonald et al 2 and Munia et al 50 , we quantified the contribution of socioeconomic factors (i.e., water demand and urban population) and climatic factors (i.e., water availability) to the changes in global urban water scarcity from 2016 to 2050. To assess the contribution of socioeconomic factors ( ), we calculated global urban water scarcity in 2050 while varying demand and population and holding catchment runoff constant ( ).…”

A Review of Water Stress and Water Footprint Accounting

“…However, current water quality stress evaluation seldom considers environmental flow requirements [48,78,80,81]. Even though there are more than 200 methods to estimate environmental flow requirements, which can be classified into hydrological methods; hydraulic rating methods; habitat simulation methods; and holistic methods (combination of hydrological, hydraulics, ecological, and social sciences) [130], it is still common to just use a certain percentage of total water resources as a proxy [8,17,19,74,[130][131][132], because calculating environmental flow requirements for a catchment is always an elaborate task [22]. However, there are huge uncertainties in these estimates [17] and they cannot easily be transferred to different geographic contexts.…”

Watershed science: Linking hydrological science with sustainable management of river basins

“…When substantial modifications need to be made to the water management plan, a new water-management cycle begins (He et al, 2000;NRC, 2004;Engle et al, 2011;USACE, 2012;WWAP, 2006WWAP, , 2017WWAP, , 2019Zipper et al, 2020). Munia et al (2020) report that changes in upstream water availability influences downstream net water availability. Reduced water availability for downstream users due to increasing demand by upstream users can be managed through negotiations between upstream and downstream users.…”

“…Reduced water availability for downstream users due to increasing demand by upstream users can be managed through negotiations between upstream and downstream users. However, changes in the upstream availability caused by climate change (e.g., droughts and floods) requires adaptation strategies beyond local water management (Munia et al, 2020).…”