WATER SCARCITY !!! OR WATER AWARENESS...??

As water scarcity problems grow in many Indian cities, civil society groups have been advocating rooftop rainwater harvesting for achieving water security. They use it as a way to stop public investments on large infrastructure projects that are necessary for dealing with urban water scarcity. Their perspectives about managing urban floods are even poorer. The implications of extreme hydrologic variability for the effectiveness of water management choices we make for cities that experience floods and droughts have hardly been appreciated by them. This chapter analyzes how the antagonistic view of some activists toward large water infrastructure projects, their obsession with “rainwater harvesting” as an approach for ensuring water security, and their increasing influence on the civil society at large weaken the institutional capability to evolve long-term strategies to deal with floods and droughts, using the case of Chennai city floods. The chapter also examines the effectiveness of rooftop rainwater harvesting, especially the quantity and quality aspects of water collected through rooftops, and the technical feasibility and economic viability of roof water harvesting for mitigating droughts and controlling floods.

Water scarcity arises in situations where there is insufficient water to simultaneously support both human and ecosystem water needs (White, 2014). Most often this arises as a result of a basic lack of water (i.e., physical water scarcity), but it may also result from a lack of suitable infrastructure to provide access to what might otherwise be considered ample available water resources, which is referred to as economic water scarcity. Physical water scarcity may occur as a result of both natural phenomena (e.g., aridity, drought) as well as from human influences (e.g., desertification, water storage; Pereira et al., 2009; White, 2014), although these influences are often coupled. For example, the process of desertification often commences as a result of water overuse during periods of temporary drought; droughts are more common in arid regions (McMahon et al., 1992). A key distinction between these various processes is in degree of permanency and reversibility. In the case of drought and water overuse, for example, the impacts may be temporary; however, those arising from aridity and desertification are more likely to be irreversible (Water, 2006). As Pereira et al. (2009) point out, this distinction is often confused when discussing water scarcity and its impacts, but it may be important in understanding both impacts and mitigation options. 

Regardless of the cause, water scarcity impacts both human populations and natural ecosystems on all continents (Fig. 6.1). For example, recent estimates suggest approximately 4 billion people live under conditions of water scarcity for at least one month each year, with roughly 0.5 billion people exposed to severe water scarcity all year round (Mekonnen and Hoekstra, 2016). These figures nearly double previous estimates, in part by considering the flows required to remain in rivers to sustain flow-dependent ecosystems, as well as the goods and services they provide for people. In most, though not all regions, climate change is forecast to exacerbate water scarcity even further (Gosling and Arnell, 2016). These assessments highlight the massive global impacts of water scarcity on human livelihoods and on natural systems, and many global programs such as those of the United Nations focus on improved human access to water within a more sustainable ecosystem footprint. From a global perspective, less attention has in the past been given to the environmental impacts associated with water scarcity (Mekonnen and Hoekstra, 2016), although environmental flow needs are now being incorporated into assessments of water scarcity at both global and catchment scales (Liu et al., 2016; Mekonnen and Hoekstra, 2016).

Here, we focus on physical water scarcity, which causes greater impacts to ecological systems than economic water scarcity. We begin by outlining the natural and human drivers of physical water scarcity and the hydrologic impacts arising in water-scarce regions. We consider primarily the impacts of water scarcity on low flows, although infrastructure such as water storages may also have an impact on high flows in water-scarce regions (Rolls and Bond, 2017). Next, we identify the physical stressors associated with those hydrologic impacts, and the exposure pathways and mechanisms by which these physical changes affect aquatic ecosystems. Using illustrative case study examples, we then summarize key ecological responses to those physical changes and consider how interactions with other stressors can modify (and often amplify) water scarcity impacts. Central among these interactions is that between hydrologic alteration and land use in the surrounding catchment. Finally, we consider options for mitigating or reversing the effects of water scarcity and identify priority areas for future research.

WAYFORWARD : 

To strengthen water security against this backdrop of increasing demand, water scarcity, growing uncertainty, greater extremes, and fragmentation challenges, clients will need to invest in institutional strengthening, information management, and (natural and man-made) infrastructure development. Institutional tools such as legal and regulatory frameworks, water pricing, and incentives are needed to better allocate, regulate, and conserve water resources. Information systems are needed for resource monitoring, decision making under uncertainty, systems analyses, and hydro-meteorological forecast and warning. Investments in innovative technologies for enhancing productivity, conserving and protecting resources, recycling storm water and wastewater, and developing non-conventional water sources should be explored in addition to seeking opportunities for enhanced water storage, including aquifer recharge and recovery. Ensuring the rapid dissemination and appropriate adaptation or application of these advances will be a key to strengthening global water security.