Changes in heat waves in Chile

This research aims to examine changes in heat waves (HWs) over Chile from 1961 to 2016 using daily maximum (TX) and minimum temperature (TN) data recorded at 13 weather stations. Based on three HW-definitions and five aspects for each definition some 15 indices were calculated and analyzed for the extended summer period (November-March). The three definitions of the HWs employed in this study were based on: (1) the TX exceeding the 90th percentile for at least three consecutive days, (2) the TN exceeding the 90th percentile for at least three consecutive days, and (3) the positive values of excess heat factor (EHF) maintaining for at least three consecutive days. The five aspects calculated for each of the definitions provided information related to the frequency, duration, and intensity of HWs. Trends (be them increasing or decreasing), magnitude (change per decade) and statistical significance (p < 0.05) were identified using the ordinary least square method and the t-test. Therefore, in terms of HW aspects, the results of the HWs climate regime analysis showed that the most extreme region of Chile is the Atacama Desert, followed by the Santiago metropolitan area. Change analysis revealed that Chile experienced increasing trends in most of the HW data sets. Thus, the frequency of trend types of all HW indices time series showed an increasing trend of 79%. About 24% of the time series showed statistically significant increasing trends. Decreasing trends were found in about 20% of the analyzed data, less than 1% of which being statistically significant. Stationary trends were detected in only 2% of the series. The highest frequency of statistically significant increasing trends was found in the HWs identified based on TX, followed by those computed based on EHF. Regarding their aspects, the number of events had the highest frequency of significant increasing trends. In terms of spatial distribution, the most important changes were found in central Chile.