Abstract
Chile is positioned in the 20th rank of water availability per capita. Nonetheless, water security levels vary across the territory. Around 70% of the national population lives in arid and semiarid regions, where a persistent drought has been experienced over the last decade. This has led to water security problems including water shortages. The water allocation and trading system in Chile is based on a water use rights (WURs) market, with limited regulatory and supervisory mechanisms, where the volume to be granted as permanent and eventual WURs is calculated from statistical analyses of historical streamflow records if available, or from empirical estimations if they are not. This computation of WURs does not consider the nonstationarity of hydrological processes nor climatic projections. This study presents the first large sample diagnosis of water allocation system in Chile under climate change scenarios. This is based on novel anthropic intervention indices (IAI), which were computed as the ratio between the total granted water volume to the water availability within 87 basins in north-central and southern Chile (30°S–42°S). The IAI were evaluated for the historical period (1979–2019) and under modeled-based climatic projections (2055–2080). According to these IAI levels, to date, there are 20 out of 87 overallocated basins, which under the assumption that no further WURs will be granted in the future, increases up to 25 basins for the 2055–2080 period. The results show that, to date most of north-central Chilean catchments already have a large anthropic intervention degree, and the increases for the future period occurs mostly in the southern region of the country (approximately 38°S), which has been considered as possible source of water for large water transfer projects (i.e., water roads). These indices and diagnosis are proposed as a tool to help policy makers to address water scarcity under climate change.
Highlights
Water projections indicate that by mid-21st century, more than half the world population will live in regions under water stress conditions, either associated to the physical lack of water supply to meet the water demand or to the inability of the water management systems to satisfy human and ecological demands for water
The indices of anthropic intervention within every catchment were calculated as the ratio between the annual surface and subsurface flow water use rights (WURs) allocated within every catchment plus the ecosystem requirements based on the ecological runoff, and the two theoretical water availability calculations here proposed
Water availability based on observed runoff and precipitation data Eighty-seven basins fulfilled the selection criteria presented in Section 3.1, where the implemented runoff models had a good performance to represent the hydrology of the catchments (NSE and R2 of the models during the calibration and validation period are around 0.8, Figure S2), as revealed by the comparison of the observed and the modeled seasonal variation of runoff in Figure 2a and b respectively
Summary
Water projections indicate that by mid-21st century, more than half the world population will live in regions under water stress conditions, either associated to the physical lack of water supply to meet the water demand (water scarcity; Van Loon et al, 2013) or to the inability of the water management systems to satisfy human and ecological demands for water (water access; UN, 2018). As population and economic development is projected to grow, the water demand is expected to increase worldwide up to 55% by 2050 (WWAP, 2014), exacerbating water scarcity in many areas of the world (Greve et al, 2018) These projections raise concerns about future global water security (Schewe et al, 2014) and the achievement of the Sustainable Development Goals (UN, 2015), most of which are strongly linked to water availability and quality (Vanham et al, 2018). Studies on hydrology have stressed the need to start planning as viewing through a “cone of uncertainty” representing the multiple unknown affecting water supply (Waage and Kaatz, 2011), as current climatic trends are no longer valid (Milly et al, 2008) In this way, advancing the understanding of the physical limits of the resource (surface and groundwater availability) and water uses (Garrick and Hall, 2014) under different possible futures (Lempert et al, 2003; Kwakkel et al, 2016) should facilitate the design of resilient water security strategies (Ericksen et al, 2011; Fazey et al, 2011)
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