Changing mechanism of global water scarcity events: Impacts of socioeconomic changes and inter-annual hydro-climatic variability

Highlights

• We execute a scenario analysis to assess the mechanism of global water scarcity.

• We quantify over-/underestimates in water scarcity if studied under fixed conditions.

• Hydro-climatic and socioeconomic conditions interact, influencing scarcity events.

• Hydro-climatic variability accounts for >79% of the yearly change in water scarcity.

• Socioeconomic changes become the most important driving force only after 6–10 years.

Abstract

Changes in available fresh water resources, together with changes in water use, force our society to adapt continuously to water scarcity conditions. Although several studies assess the role of long-term climate change and socioeconomic developments on global water scarcity, the impact of inter-annual climate variability is less understood and often neglected. This paper presents a global scale water scarcity assessment that accounts for both temporal changes in socioeconomic conditions and hydro-climatic variability over the period 1960–2000. We thereby visualized for the first time possible over- and underestimations that may have been made in previous water scarcity assessments due to the use long-term means in their analyses. Subsequently, we quantified the relative contribution of hydro-climatic variability and socioeconomic developments on changing water scarcity conditions. We found that hydro-climatic variability and socioeconomic changes interact and that they can strengthen or attenuate each other, both regionally and at the global scale. In general, hydro-climatic variability can be held responsible for the largest share (>79%) of the yearly changes in global water scarcity, whilst only after six to ten years, socioeconomic developments become the largest driver of change. Moreover, our results showed that the growth in the relative contribution of socioeconomic developments to changing water scarcity conditions stabilizes towards 2000 and that the impacts of hydro-climatic variability remain significantly important. The findings presented in this paper could be of use for water managers and policy makers coping with water scarcity issues since correct information both on the current situation and regarding the relative contribution of different mechanisms shaping future conditions is key to successful adaptation and risk reduction.

Introduction

Globally, water scarcity and its societal consequences is recognized as one of the most important global risks, both in terms of likelihood and impact (Howell, 2013). Governments and institutions managing water resources have to adapt constantly to regional water scarcity conditions, which are driven by climate change, climate variability, and changing socioeconomic conditions. Over the past decades, changing hydro-climatic and socioeconomic conditions increased regional and global water scarcity problems (Kummu et al., 2010, Vorosmarty et al., 2000, Wada et al., 2011a, Wada et al., 2011b). Future climate change, projected population growth, and the continuing increase in water demand, are expected to aggravate these water scarcity conditions world-wide (Alcamo et al., 2007, Haddeland et al., 2014, Kiguchi et al., 2015, Lehner et al., 2006, Prudhomme et al., 2014, Schewe et al., 2014, Sperna Weiland et al., 2012, Stahl, 2001, Van Vliet et al., 2013, Wada et al., 2011a).

Whilst most research on water scarcity has focused on the role of long term changes in hydro-climatic and socioeconomic conditions, the role of inter-annual hydro-climatic variability has received less attention. This is problematic, since variability has been identified as a key theme for water scarcity assessments (e.g. Mason and Calow, 2012), and changes in variability may be more important than changes in average conditions when examining extreme events, such as flood and droughts, in a changing climate (Adger et al., 2005, Hall and Borgomeo, 2013, IPCC, 2012, Katz and Brown, 1992, Mason and Calow, 2012, Smit and Pilifosova, 2003). Omitting the climate-driven inter-annual variability in water resources availability (i.e. hydro-climatic variability) can mean that areas that only sporadically experience water scarcity are overlooked. On the other hand, those areas that are identified as ‘water scarce’ based on hydro-climatic mean conditions, in reality do not experience water scarcity every year (Kummu et al., 2014, Mason and Calow, 2012). Likewise, studies using such multi-year averages, either with respect to hydro-climatic or socioeconomic conditions, might misinterpret the relative contribution of these driving forces on changing water scarcity conditions towards the future (Hulme et al., 1999, Kummu et al., 2014, McPhaden et al., 2006, Murphy et al., 2010, Seneviratne et al., 2012, Vera et al., 2010). Moreover, earlier research showed that the adaptive capacity of people to gradually changing means is relatively high, whereas adapting to yearly variations and extremes poses more difficulties (Smit and Pilifosova, 2003). This holds especially for those regions that lack a minimum level of hydraulic infrastructure for water storage and redistribution (Grey and Sadoff, 2007, Hall and Borgomeo, 2013). A thorough understanding of the present-day contribution of inter-annual variability is essential to model future interactions between different driving forces and their impacts on future water scarcity conditions, and is therefore a prerequisite for successful adaptation (Adger et al., 2005, Hall and Borgomeo, 2013, Mason and Calow, 2012, Smit and Pilifosova, 2003).

To address the considerations discussed above, we present in this contribution a global scale water scarcity assessment that accounts for both temporal changes in socioeconomic conditions and hydro-climatic variability. A first effort to estimate the effects of hydro-climatic variability on water scarcity conditions at the global scale was made by Kummu et al. (2014). In this study, however, an assumption of fixed socioeconomic conditions was used, which may have led to an over- or underestimations of water scarcity conditions at the global and regional scale. Using a scenario analysis, we visualize here the size of these potential over- and underestimations. In addition, we quantify the relative impacts of these driving forces on changes in water scarcity, using a calculation method that takes into account their inter-action effects and thereby avoids the risk of over- or underestimations as specified above. We conclude with a discussion on the implications of our results for water management and policy, for example in designing adaptation strategies.