The dynamics of rainfall isotopic compositions (δ2H, δ18O and δ17O) from Windhoek, Namibia

The isotopic composition of rainfall is an important tracer in ecohydrology and climate studies of past and present. Most rainfall isotope studies rely on the Global Network for Isotopes in precipitation (GNIP) database which is composed almost exclusively on monthly averaged data. Therefore most studies are limited to monthly and longer timescales but relatively little is known about isotopic variability on daily time-scales and how it relates to dominate seasonal modes. Furthermore, condensation temperature and Rayleigh fractionation do not fully account for isotopic variability in some areas where meso-scale dynamics may dominate. Based on quasi continuous collection of daily rainfall from Namibia and utilizing a new hydrological tracer δ17O , we present a four year measurement of daily rainfall isotopic composition (δ2H, δ18O and δ17O) and investigate their responses to local and regional climate variations at different scales. We also use atmospheric back-trajectory modelling and associated meteorological variables to explain the variability observed in the isotopic composition of individual rain events at the study site during 2012-2016. Preliminary results show large intra-annual variations in δ2H, δ18O and δ17O across the study period and they are related to the meso-scale dynamics and multiple source moisture origins.