Evolution of heatwaves in Chile since 1980

Heatwaves (HWs) are highly dangerous threats to human and ecosystem health, as well as to many economic sectors around the world. In the present work focused on Chile, we use a high-resolution (similar to 5 km) gridded product (CR2Met v2.0) to evaluate the spatiotemporal distribution and trends of HWs. We analyze daily maximum temperatures (Tx) from late austral spring to early autumn (November to March) to evaluate the HWs behavior during 1980-2020, using three criteria: i) three consecutive days with Tx > 30 degrees C, ii) three consecutive days with Tx > 90th percentile (P90), and iii) three consecutive days with Tx > 95th percentile (P95). We validated our results using HWs statistics based on eighteen official meteorological stations; this procedure revealed a coherence with gridded data mainly over the Central Valley and the Andes. Using the P90 threshold, we found upward trends across the Andes between 20 degrees and 36 degrees S (>1 events per decade), and in the Central Valley between 34 degrees - 43 degrees S (>0.75 events per decade). In addition, using the P90 and P95 thresholds, HWs exhibit upward trends (>1 and 0.5 events per decade, respectively) throughout most of Chile, including Andes and Patagonia. Moreover, using all thresholds, we found an increase in HW frequency during the 2011-2020 megadrought period (ranging from 1 to 4 HWs events/decade) in comparison to the previous period (1980-2010). Meteorological factors such as an increase in the frequency of Puelche (Fohn-like) winds are proposed as an amplifying mechanism of HWs in South-Central Chile.