Hydrological impacts of afforestation in the semiarid Patagonia a modelling approach

Afforestation has been widely encouraged with different goals, including as a strategy to tackle global warming. However, the side‐effects of this land‐use transformation have been in many cases underestimated. Particularly, the hydrological impacts may become relevant in (semi)arid regions where water is a key element. In this work, we evaluated the hydrological effects triggered by afforestation with ponderosa pine in the semiarid Argentine Patagonia that is currently a focus of afforestation programs. For this purpose, we used complementary approaches that included hydrological modelling (DINAQUA model), satellite image analysis, and soil wetness data. All analyses provided convergent results into hydrological effects of afforestation. The modelling results showed that afforestation significantly increased transpiration in relation to native grass shrub steppe. In the steppe in degraded condition, transpiration accounted for only 10% (40 mm year−1) of total water flux, whereas in adult pine plantations, it accounted for up to 73% (277 mm year−1). Deep drainage was also severely affected by afforestation as it decreased from 182 mm year−1 in the steppe to zero in adult plantations, according to model simulations. Estimates from Landsat images also showed that evapotranspiration was higher in plantations compared with the steppe. Soil wetness data also revealed significantly drier soils in plantations. Our results indicate that pine plantations in the semiarid Patagonia evaporate all rainfall inputs, resulting in zero deep drainage and groundwater recharge. If the afforested area in the region increases, downstream meadow ecosystems, which are hotspots of primary productivity, may be negatively impacted.