**3.2 Future scenarios**

*Resources of Water*

**2.2 Water balance**

**2.3 Predictive models**

century (the most pessimistic).

**3.1 Regional differences in water availability**

population density is less than 20 people km<sup>−</sup><sup>2</sup>

).

contrast to the Metropolitan Region (462 people km<sup>−</sup><sup>2</sup>

**3. Results**

total amount of water expressed in km3

The water balance by region at an annual scale was estimated considering precipitation as the main input and evapotranspiration as the main output of the system, i.e. a positive surplus means precipitation > evapotranspiration and a negative surplus evapotranspiration > precipitation. These data were obtained from Fick and Hijmans [2] for the period 1970–2000 that is considered as the reference period to study changes in climatic variables. Evapotranspiration was determined by using the Turc method [9]. The total land surface of each one of the 16 regions (used to estimate the

total amount of available water per person) was sourced by Chilean official statistics. Since Ñuble Region (XVI) was officially created in September 2018, its values have been considered within the region of Bio-Bio in which Ñuble was previously included.

The predictive models utilized in this work were proposed by the

Intergovernmental Panel on Climate Change (IPCC) in 2013 [10]. Within those global models used in the fifth stage of the inter-comparison of coupled models, we have chosen the predictions given by the model MIROC5 for 2050 because it has been successfully tested in neighbor countries such as Peru [11]. We have considered two scenarios: (a) RCP 4.5 that assumes an increasing trend in the concentration of greenhouse gases (GHG) until 2040 (the most optimistic) and (b) RCP 8.5 that assumes an increasing trend in GHG concentration for the whole twenty-first

**Figure 2** shows the mean values (1970–2000) of water surplus per person for each one of the Chilean regions. The lowest values have been recorded in the Metropolitan Region (due to its high population density) and the desert regions of Antofagasta y Tarapacá. Contrariwise, the highest values were observed in Aysén, Magallanes, and Los Lagos. The regions of the north of Chile show relatively low values of annual water comparing inputs by rainfall and losses by evapotranspiration. Of particular interest are the central regions of the country where, on the one hand, the dominant climate is Mediterranean (naturally erratic) and, on the other hand, the pressure for water resources is particularly higher (the Metropolitan region of Santiago is inhabited by more than 7 million people, for instance). In fact, the highest spatial variability was observed in the central regions of the country where, regardless people and their activities, they show a significant contrast in natural water surplus. These differences start to be visible in the Region of Valparaíso (V) where climatic conditions change to Mediterranean and evapotranspiration is significantly reduced. The five northern regions of Chile (Arica and Parinacota, Tarapacá, Antofagasta, Atacama, and Coquimbo) are scarce in precipi-

but their needs in water keep in consonance with other regions because their

), and their evapotranspiration is also high (>600 mm y<sup>−</sup><sup>1</sup>

),

in the best of the cases. These values

) and Valparaíso Region

) and their population (used to quantify the

**12**

tation (<250 mm y<sup>−</sup><sup>1</sup>

(111 people km<sup>−</sup><sup>2</sup>

The (optimistic and pessimistic) predictions considered in this research returned similar values for 2050. It means the effects of climate change will be particularly remarkable in the central regions of Chile, characterized by their Mediterranean climate type and their high population densities. Both scenarios foresee the highest decrease in annual precipitation (**Figure 3A**) and increase in evapotranspiration (**Figure 3B**). Regarding water surplus they forecast annual losses of about 1000 mm y<sup>−</sup><sup>1</sup> in many regions of the country (**Figure 3C**). These losses are particularly worrying in the centre where most of Chilean people are now living.

The existing differences between both scenarios (optimistic vs. pessimistic) are not significantly different between them. For instance, the most optimistic foresees a reduction of 936 mm y<sup>−</sup><sup>1</sup> in precipitation and the pessimistic one of 1052 mm y<sup>−</sup><sup>1</sup> . Regarding water surplus, both scenarios forecast losses around 1000 mm y<sup>−</sup><sup>1</sup> (optimistic, 968 mm y<sup>−</sup><sup>1</sup> , vs. pessimistic, 1094 mm y<sup>−</sup><sup>1</sup> ) regardless of the number of people and the water consumption of their agricultural activities. In the south of the country, the model returns predictions of an increase in precipitation much higher than the foreseen increase in evapotranspiration. It means much more available water will be in the south, and perhaps it can suppose migrations from the north and central of the country to these regions. Regarding the desert regions of the north of Chile, the future situation will be presumably similar than the current one. So, no significant effects on local population are expected.

**Figure 3.**

*Differences between the averaged values of the period 1970–2000 and those foreseen by the predictive models for 2050.*
