- Lower rainfall and an increase in temperature would generate a 32.1% decrease in the flow of the Cauquenes river basin for the period 2037-2050.
- The drop would be more significant if, together with climate change, a future scenario with plantations of exotic species is considered, reaching up to 46.2%. In contrast, if it is reforested with native species, it would be only 23.3%
By Mauricio Galleguillos1,2, Fernando Gimeno1,2, Cristóbal Puelma1,2, Mauricio Zambrano-Bigiarini2,3, Antonio Lara2,4,5 and Maisa Rojas2,5,6
The mega-drought and the increase in temperatures have caused various impacts on the water cycle of central Chile, such as greater evaporation from its bodies of water, increased evapotranspiration of crops and natural vegetation, and accelerated melting of snow, and a significant decrease in the flows, changes that could be even more severe in the near future.
Along with the effects of climate, the land cover also plays a vital role in water availability. Different studies have determined that soil with exotic plantations would tend to decrease the water resource, contrary to what would happen in soil with native vegetation.
Thus, a recent investigation published in the Journal of Hydrology carried out an analysis of the changes that there would be in the water availability of the Cauquenes river basin, Maule Region, under the following conditions: 1. Scenarios with different land cover taking into account the present climate (2006-2018), 2. availability of water with the current land cover, but considering the climate change projections  for the years 2037-2050, and 3. a combination of the different land cover and the projection of climate change.
The scenarios with the different land covers are:
(a) with the current cover;
(b) based on current Chilean forest policy, which seeks to afforest half a million hectares by 2035;
(c) an extreme scenario, in which exotic forest plantations replace all native scrublands;
(d) a scenario with the current land cover, but with a hypothetical strategy for adaptation to climate change in the management of plantations;
(e) a scenario where forest plantations move from the headwaters of the basin to the lower parts, being replaced by native scrub;
(f) one of massive restoration where native forests and shrubs entirely replace exotic forest plantations.
In the present climate, under the current forest policy and the extreme scenarios, the flow would decrease between 2.5 and 17.3%, accentuated in June (4.5 and 31.8%). On the other hand, the flow could increase by 2.3% in the replacement scenario. In contrast, it could increase by 10.9% in the massive restoration scenario, with a more significant increase in December of 15.2%. Meanwhile, no changes in flow were detected in the adaptive strategy scenario.
Under a condition of future climate change, annual precipitation would decrease by 15%, and the temperature would increase by 0.95 ° C. This generates a drier condition in the Cauquenes river basin, decreasing its flow by 32.1%. These results refer to the median of 24 climate models assembly. However, when analyzing the extreme simulations, significant variability is identified in the projections, with a range that oscillates between an increase in the flow of 8% and a decrease of up to -62% in most unfavorable simulations.
Finally, in the third condition, which combines the scenarios with different land covers with climate change, a negative synergy occurs when the plantation area increases, causing a decrease in flow by 46.2% under the extreme scenario. However, under the restoration scenario with native vegetation, its decrease could be only 23.3%. As in the previous condition, a similar range of variability is reported when the projections of the more and less favorable climate change models are analyzed.
With this, the study confirms that there would be a general decrease in water availability if the remaining native vegetation is replaced by exotic forest plantations, even more so if the climate change variable is added. This is because the plantations generate more real evapotranspiration and less percolation to sustain their active growth. In this sense, the study also reports a possible low resilience of pines to drier conditions than native vegetation, which could compromise their productivity and carbon sequestration capacity, affecting the commitments of the State of Chile in its targets for reduction cope with climate change.
Therefore, the land cover and its impact on the water availability of the flows should be an essential component when establishing any public policy regarding the future forestry model for Chile. That is why it is recommended to seek strategies for planning the territory in harmony with nature to achieve the Sustainable Development Goals proposed by the United Nations and thus guarantee a better future for future generations.
1 Departamento de Ciencias Ambientales y Recursos Naturales Renovables, Universidad de Chile; 2 Centro de Ciencia del Clima y la Resiliencia (CR)2; 3 Departamento de Ingeniería Civil, Universidad de La Frontera; 4 Instituto de Conservación, Biodiversidad y Territorio, Universidad Austral de Chile; 5 Fundación Centro de los Bosques Nativos; 6 Departamento de Geofísica, U. de Chile.
 For the second condition, the climatic scenario called RCP 8.5 was used, which follows the current trend of CO2 emissions. This is one of the four scenarios posed by the IPCC.
Galleguillos, M., Gimeno, F., Puelma, C., Zambrano.Bigiarini, M., Lara, A. & Rojas, M. (2021) Disentangling the effect of future land use strategies and climate change on streamflow in a Mediterranean catchment dominated by tree plantations. Journal of Hydrology, 595, 126047.