Day-night differences in δ18O and d-excess of convective rainfall in the inland tropics of Brazil

Abstract

The tropical central-southern part of Brazil (CSB) is characterized by strong convective systems that bring generous water supply for agro-industrial activities but also pose flood risks for large cities. Here, we present high-frequency (5-10 minutes) rainfall isotopic compositions to better understand those systems. In total, 260 intra-event samples representing 18 rainfall events were collected during the period 2019-2021. In summer, convective rainfall activity modulates regional and local isotopic characteristics, revealing a novel perspective on day-night contrast in δ18O and d-excess values. During the daytime, enhanced sub-cloud effects are related to high δ18O and low d-excess, while at night-time, continuous regional rainout results in more depleted δ18O and high d-excess values. Our results offer a new framework of key drivers controlling the isotopic variability of rainfall across the tropics.