Heat wave events and the response of glaciers in the subtropical Andes

In recent decades, an increased frequency of heat waves (HWs) has been detected along the subtropical Andes (SA); however, their impact on the cryosphere has not been assessed in detail. Here we present a multi-scale assessment with the objective of quantifying the impact of HWs on Andean glaciers located in the SA. Sub-daily observations of melt at the Universidad (34°S) and Pichillancahue (39°S) glaciers show that the daily melt rate increases by approximately 25% during HW events compared to the rest of the ablation season. At the annual scale, the relationship is complex. Using seasonal HWs climatologies derived from the ERA5 reanalysis and glacial mass balances available from the World Glacier Monitoring Service (WGMS), it was determined that there is no significant relationship between the number of HW events and the annual mass balance. However, the annual mass balance of the Echaurren Norte Glacier (33°S) showed significant positive correlations (p<0.05) with the number of HW events occurring over the Pacific Ocean, during the spring and summer seasons between 1975 and 2023. Furthermore, the mass balance of the Piloto Este Glacier (33°S) also shows significant positive correlations with the number of HW events in the Pacific during spring and summer between 1979 and 2002. These correlations would indicate the importance of the higher evaporation rate during HW events, with the consequent contribution of moisture to the atmosphere, contributing to precipitation and snow accumulation on glaciers during synoptic events occurring over the Andes. The above is consistent with the fact that glaciers in the central Andes of Chile and Argentina are more sensitive to precipitation variability, as well as its relationship with the El Niño-Southern Oscillation (ENSO). While melt rates increase during HW events, the forcing  of evaporation rates during HW events over the Pacific would generate a greater impact on the annual glacier mass balance. This finding, from a glaciological perspective, calls for further investigation into the role of HW events over the oceans as drivers of evaporation and their transport and circulation mechanisms. This work is funded by the FONDECYT Iniciación Project 11240379.