**3. Conclusions**

In water management, a lack of knowledge about the natural water source contribution variability in different periods of the year exists, which is critical at any time when it is necessary to maintain the water balance between supply and demand in a certain territory. Within the large basins, there is still a great complexity for the determination of water sources in high elevation areas. This is also a challenge for small basins, where water systems can be even more fragile. The difficulty lies in the fact that in high-altitude areas with different water sources, there are variations in the contribution proportion from each kind of water source, along each season of the year. Among them, we can count the presence of glaciers, snow, total precipitation, wetlands, groundwater, and permafrost, where all can contribute to the runoff and recharge aquifers in territories located in lower areas within the basin. As could be observed in this chapter, using chemical tracing through natural tracers represents a reliable way to distinguish and quantify the different water sources input in a river.

Society is the main target of any water basin analysis, and, based on it, territorial prospecting can make important contributions in the estimation of impacts and in the mitigation infrastructure design. In this context, this chapter focuses on the determination of water sources in high-altitude areas using natural tracers, which can be very useful for the communities that inhabit the basins in mountain areas. The spatial and temporal distribution data of the water supply's main components is fundamental for the hydrological resource use and distribution planning among the basin's different social actors. These tools could be relevant to water supply projections and water demand regulations when analyzing the water source bail in upper basin areas, as a consequence of precipitation reduction and temperature increase in high elevations, which, for example, has resulted in a generalized retreat of the glaciers along the Central Andes [8, 20–22]. It is estimated that these glaciers' fronts and areas' negative variations are largely due to the rise of the 0°C isotherm in the region [23]. Also, when some corporations deny any specific water source contribution relevance, these tools can provide a good exploration analysis to determine their water contribution.

Recently, between 2010 and 2015, the Andes region between 29° and 35°S experienced the longest drought in the instrumental record [3]. This extraordinary event has occurred in the warmest decade of the last 100 years and apparently has no analogies in the last millennium, according to paleoclimatic reconstructions of this area [3]. The long-term climate projections also do not present an encouraging picture for this region of the Andes, since they indicate a tendency to warming and a greater recurrence of droughts in the coming decades [1, 3, 24].

In view of the worrying future perspective that is coming for this region (and others) in terms of its reduction of strategic water resources, it is vital to know in detail the behavior of the different water sources associated with climate variability. In this chapter we have shown the different contribution along time and space from different water sources, which can be key information for the development of reservoir infrastructure and water distribution networks, generation of water supply, and distribution models for different uses, in addition to other adaptation plans aimed at specific sectors of the population.

**3. Conclusions**

input in a river.

In water management, a lack of knowledge about the natural water source contribution variability in different periods of the year exists, which is critical at any time when it is necessary to maintain the water balance between supply and demand in a certain territory. Within the large basins, there is still a great complexity for the determination of water sources in high elevation areas. This is also a challenge for small basins, where water systems can be even more fragile. The difficulty lies in the fact that in high-altitude areas with different water sources, there are variations in the contribution proportion from each kind of water source, along each season of the year. Among them, we can count the presence of glaciers, snow, total precipitation, wetlands, groundwater, and permafrost, where all can contribute to the runoff and recharge aquifers in territories located in lower areas within the basin. As could be observed in this chapter, using chemical tracing through natural tracers represents a reliable way to distinguish and quantify the different water sources

**Water source Glacier Groundwater Rock glacier Other Total** Water source contribution (%) 9 56 34 1 100

sources that contribute to the Cuevas River in February (Source: [4]).

44 Achievements and Challenges of Integrated River Basin Management

**Figure 10.** Scatter plot showing the isotopic and average electrical conductivity (EC) compositions for the different water

**Table 1.** Percentage contribution from different water sources to the Cuevas River along February 2014 (source: [4]).

Society is the main target of any water basin analysis, and, based on it, territorial prospecting can make important contributions in the estimation of impacts and in the mitigation infrastructure design. In this context, this chapter focuses on the determination of water sources in high-altitude areas using natural tracers, which can be very useful for the communities that The use of ionic and isotopic tools, together with traditional hydrological and climatic data, can allow the creation of new information and early warning systems to reduce the risk of droughts and floods, among other applications that will modernize the way we guide decision-making in complex climate dynamic mountain basins. Besides this, extending these tools to other areas of the landscape, such as the foothills, lowlands, and valleys, will be useful to recognize and quantify changes in isotopic signatures in space and time. The knowledge of this water information can be considered analogous to the knowledge of the circulatory system in living organisms, because it is vital to diagnose the functioning and health of the ecosystems that feed on this resource in different basin zones. This information will favor the different water source feature identification from the feeding areas within the basin to the areas where it is used by each inhabitant of the territory.

In summary, the development of new geographic and temporal information systems using chemical and isotopic tools is of fundamental importance for water distribution, flood, and drought damping infrastructure planning scenarios. Interconnected to other environmental parameters, it will serve as a basis to establish development strategies and provide information for decision-making in areas that depend on mountain hydrology and its complex network of water sources that supply the territory.
