Historical intensity and predictive uncertainty of extreme maximum temperatures in south-central Chile: An integrated approach using the HSobs and IGpred indices

Abstract

This study proposes an integrated approach for characterising extreme maximum temperatures through two complementary indicators: the observed summer extreme heat-load index (H^S_obs) and the predictive geometric index (I^G_pred). The former summarises the historical intensity of absolute maximum temperatures recorded in December, January, February, and March during 2000–2026. Its exponential weighting assigns progressively more importance to the most intense thermal events. The latter quantifies the relative width of the 2026–2030 prediction bands within a common thermal domain, thereby providing a dimensionless measure for comparing predictive uncertainty among locations. The method is applied to Temuco, Los Ángeles, Chillán, Talca, Curicó, Santiago Quinta Normal, and Santiago Pudahuel. The joint representation (I^G_pred, H^S_obs) contrasts the historical burden of extreme heat with the width of future predictive uncertainty. Los Ángeles exhibits the greatest historical heat load, whereas Temuco combines a relatively low load with the widest prediction band. Chillán and Talca occupy intermediate positions, confirming that thermal intensity and predictive uncertainty describe distinct, non-equivalent dimensions of climate behaviour. The proposed indices provide a comparative agroclimatological tool; however, H^S_obs is a relative climate indicator rather than a direct measure of physiological damage, which would require system-specific experimental calibration.