Hydrological response to land use scenarios under climate change. Adaptation measures for an agricultural basin: Rapel river basin in central Chile.

Faced to reduced future water availability, associated with climate change variability and population growth, it becomes important to study the hydrological response under various modifications of crop patterns currently present in an agricultural basin in Chile. The focus of this research is to improve the future water resources management knowing the behavior of the hydrological cycle under meteorological forcings during the historical period 1985 to 2015.

We selected the Rapel River basin, in Central Chile, with a relevant agricultural activity and high water consumption in the study area.

VIC (Variable Infiltration Capacity) hydrological model, was calibrated considering base land use and historical records determined with the product CR2Met (www.cr2.cl/datos-productos-grillados/) for a grid with cells of 5 km by 5 km. For the near future (2030-2060) we proposed agricultural land use scenarios, considering a set of 40 crops that are representative of the area. The variation of the future forcings was considered according to the climate change scenario RCP 8.5 for four Global Climate Models (CCSM4, CSIRO, IPSAL, and MIROC).

Results show the variation in evapotranspiration demand and runoff, according to crop class and geographical ubication. An important variation of both flows is revealed, which is mainly related to the class of crop.  For this reason, the selection of crops determines a specific hydrological response, so the study of the change in land use is crucial. Based on the hydrologic response of each class of crop over the basin,  crop arrays were obtained and patterns are recommended for future scenarios. The arrays consider the optimal location of the crop, which reduces evapotranspiration demand and increases runoff. Also, changes in the percentage of the cultivated area of each crop class are recommended.