Abstract
The importance of mountains as “natural water towers” has been quantified by comparing water budgets in upstream (mountain) and downstream (lowland) areas, but their importance for tap water supplies has not been assessed. Here, we propose an isoscape approach to estimate the mean recharge elevation of tap water sources (rivers, reservoirs, springs, and wells) and apply it to a region in central Japan as a case study. Errors in the estimation of mean recharge elevation were estimated at 90–140 m. Results show that mean recharge elevations for about 90% of sources in the region are at 1000 m above sea level or higher. A little over half of the land area is above that elevation, while 98% of the population lives below it. These findings indicate that tap water disproportionally depends on recharge in mountains and is disproportionately supplied to lowland residents. Higher locations of spring water sources and longer (vertical) distances of groundwater flow for well water sources make the recharge-to-popula...
Highlights
Mountains are important recharge areas for freshwater resources, including those used by people living at lower elevations
Findings on recharge-to-population disproportionality (RPD), which is derived from mean recharge elevation (MRE) estimation, could raise awareness among people living in lowland cities of how much they depend on mountains for their water supply
If we calibrate distributed runoff models or groundwater flow models taking MRE into account, recharge areas for each tap water source can be mapped with higher reliability
Summary
Mountains are important recharge areas for freshwater resources, including those used by people living at lower elevations. They are often likened to water towers (Liniger et al 1998; Messerli et al 2004; Viviroli et al 2007). Mountains’ role in the recharging and supply of water resources has been investigated by analyses of water budgets for mountains, downstream lowlands, and drainage basins. Viviroli et al (2007) suggested a new typology of mountain areas as natural water towers based on water budgets and human water needs, showing that .50% of the areas have an essential or supportive role in water supply to downstream areas The mountain contribution to river discharge is even greater, in some cases exceeding 95%, in arid and semiarid regions (Viviroli and Weingartner 2004). Viviroli et al (2007) suggested a new typology of mountain areas as natural water towers based on water budgets and human water needs, showing that .50% of the areas have an essential or supportive role in water supply to downstream areas
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