Isotopic content in high mountain karst aquifers as a proxy for climate change impact in Mediterranean zones: The Port del Comte karst aquifer (SE Pyrenees, Catalonia, Spain).

The objective of this work is to characterize the impact of climate change in the karst aquifer of the Port del Comte Massif (PCM). Six regional climate models (RCMs) from CLYM'PY Project are used to analyse the magnitude and trends of changes on precipitation and temperature (RCP4.5 and RCP8.5 scenarios) and how these changes propagate through the hydrogeological system as groundwater resources availability and the associated water isotopic content. The study uses the RCMs climate change forcings as input data to a combination of (1) a semi-distributed hydrological model for simulating the hydrodynamical response of the aquifer, and (2) a lumped parameter model for simulating the isotopic content in groundwater at the outlet of the aquifer. A mean decrease of 2.6% and 1.9% in yearly precipitation and a mean increase of 1.9 and 3.1 °C in average temperature is expected in PCM at the end of the 21st century in the RCP4.5 and RCP8.5 scenarios, respectively. This climate signal entering the hydrogeological system results in a mean decrease in recharge of 3.9% and 0.5% from rainfall and of 59.3% and 76.1% from snowmelt, and a decrease of 7.6% and 4.5% in total system discharge, but also generates an isotopic enrichment in groundwater discharge (δ18OGW) of 0.50‰ and 0.84‰, respectively. Moreover, from a long-term (2010-2100) perspective, the mean trend in δ18OGW is 0.7‰/100 yr and 1.2‰/100 yr for RCP4.5 and RCP8.5, respectively, resulting in easily measurable annual lapse rates with the current analytical methods.