Abstract
Abstract. The effectiveness of population policy in reducing the combined impacts of population change and climate change on water resources is explored. One no-policy scenario and two scenarios with population policy assumptions are employed in combination with water availability under the SRES scenarios A1b, B1 and A2 for the impact analysis. The population data used are from the World Bank. The river discharges per grid of horizontal resolution 0.5° are obtained from the Total Runoff Integrating Pathways (TRIP) of the University of Tokyo, Japan. Unlike the population scenarios utilized in the SRES emission scenarios and the newest representative concentration pathways, the scenarios employed in this research are based, even after 2050, on country-level rather than regional-level growth assumptions. Our analysis implies that the heterogeneous pattern of population changes across the world is the dominant driver of water stress, irrespective of future greenhouse gas emissions, with highest impacts occurring in the already water-stressed low latitudes. In 2100, Africa, Middle East and parts of Asia are under extreme water stress under all scenarios. The sensitivity analysis reveals that a small reduction in populations over the region could relieve a large number of people from high water stress, while a further increase in population from the assumed levels (SC1) might not increase the number of people under high water stress considerably. Most of the population increase towards 2100 occurs in the already water-stressed lower latitudes. Therefore, population reduction policies are recommended for this region as a method of adaptation to the future water stress conditions. Population reduction policies will facilitate more control over their future development pathways, even if these countries were not able to contribute significantly to greenhouse gas (GHG) emission cuts due to economic constraints. However, for the European region, the population living in water-stressed regions is almost 20 times lower than that in the lower latitudes. For countries with high population momentum, the population policy scenario with fertility-reduction assumptions gained a maximum of 6.1 times the water availability in Niger and 5.3 times that in Uganda compared with the no-policy scenario. Most of these countries are in sub-Saharan Africa. These countries represent 24.5% of the global population in the no-policy scenario, and the scenario with fertility-reduction assumptions reduces it to 8.7% by 2100. This scenario is also effective in reducing the area under extreme water stress in these countries. However, the policy scenario with assumptions of population stabilization at the replacement fertility rate increases the water stress in high-latitude countries. Nevertheless, the impact is low due to the high per capita water availability in the region. This research is expected to widen the understanding of the combined impacts of climate change in the future and of the strategies needed to enhance the space for adaptation.
Highlights
The global population projections utilized in the new representative concentration pathways (RCPs) and other emissions scenarios (IPCC, 2000, EMF22 cited in Van Vuuren et al, 2010; Riahi et al, 2011) have uniform regional growth assumptions after the year 2050 (Arnell, 2004; Van Vuuren et al, 2010; Riahi et al, 2011)
Two other population scenarios evaluated the strength of the fertility-reduction policy (SC2) and its combination with population stabilization with replacement fertility (SC3) to reduce future impacts on water resources
For countries with high water stress, the climate change effects are far outpaced by the population change effects
Summary
Global water resource assessments project grim futures, with increased water stress in many parts of the world (Vorosmarty et al, 2000; Arnell, 2004; Arnell et al, 2011; Murray et al, 2012). Arnell (2004) projects 36.5–57.2 % of Published by Copernicus Publications on behalf of the European Geosciences Union.N. The global population projections utilized in the new representative concentration pathways (RCPs) and other emissions scenarios (IPCC, 2000, EMF22 cited in Van Vuuren et al, 2010; Riahi et al, 2011) have uniform regional growth assumptions after the year 2050 (Arnell, 2004; Van Vuuren et al, 2010; Riahi et al, 2011) Their use in climate impact assessments (Arnell, 2004; Shen et al, 2008; Arnell et al, 2011; Murray et al, 2012) masks vulnerabilities as a result of population growth below the regional scale. A sensitivity analysis is carried out in order to understand the relative influence of the climate and population drivers of water stress
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