Trends in seasonal precipitation extremes and associated temperatures along continental Chile

Abstract

We characterize trends in maximum seasonal daily precipitation (seasonal Rx1day), and minimum (Tn), and maximum (Tx) daily temperatures during days with precipitation over continental Chile for the period 1970–2017, using surface stations and the AgERA5 gridded product derived from the ERA5 reanalysis dataset. We also examine seasonal trends of Sea Surface Temperature (SST), Precipitable Water (PW), Convective Available Potential Energy (CAPE), Eddy Kinetic Energy (EKE), Atmospheric Rivers (ARs) frequency, and upper air observations to seek for possible mechanisms that explain precipitation trends. Our results show an increase in precipitation extremes during fall in Northern Chile (15–30°S) and during fall and winter in Austral Chile, and mostly negative trends in Central Chile, where a few locations with positive trends are found along the coast. Although warming trends prevail for Tn (< 0.5°C/dec), cooling trends are observed in Tx during seasonal Rx1day events for almost all seasons. The highest values in Tn trends are obtained on the western slopes of the Andes. We also explore temperature scaling in surface stations, finding strong positive super Clausius Clapeyron with Tn, especially during the fall. Sounding observations in five stations across Chile, suggest warming trends at 23.5°, 33°S and 53°S, with a stabilization effect by enhanced warming in the upper troposphere, while presenting cooling trends in Puerto Montt (41.5°S). Seasonal trends in PW reveal moistening along southern-Peru and Northern-Chile during spring and summer. Positive trends in CAPE are observed over 35–40°S (austral summer and fall) and the northern altiplano (autumn). SST analyses reveal strong cooling around 30°S in winter, which may explain the negative trends in seasonal Rx1day in central Chile. A warming spot on the northern Peruvian coast during fall may be responsible for humidification in front of Northern Chile, particularly during summer and fall. Positive EKE trends are detected south of 40°S, being stronger and reaching almost all of the coast during spring. ARs frequency unveils negative trends up to -5 days/dec during summer, and positive trends of 1 day/dec in 40°- 50°S coastal regions during spring. More generally, the results presented here shed light on the main large-scale processes driving recent trends in precipitation extremes across continental Chile.