Global sinusoidal seasonality in precipitation isotopes

Abstract

Abstract. Quantifying seasonal variations in precipitation δ2H and δ18O is important for many stable isotope applications, including inferring plant water sources and streamflow ages. Here we present global maps that concisely quantify the seasonality of stable isotope ratios in precipitation. We fit sine curves defined by amplitude, phase and offset parameters to quantify annual precipitation isotope cycles at 653 meteorological stations on all seven continents. At most of these stations, including in tropical and subtropical regions, sine curves can adequately represent the seasonal cycles in precipitation isotopes. Additionally, the amplitude, phase, and offset parameters of these sine curves correlate with site climatic and geographic characteristics. Multiple linear regression models based on these site characteristics can map global precipitation isotope amplitudes, phases, and offsets. We then adjusted the regression-based maps for residual spatial variations that were not captured by the regression models. We make these gridded global maps of precipitation δ2H and δ18O cycles publicly available. We also make tabulated site data and fitted sine curve parameters available to support the development of regionally calibrated models, which will generally be more accurate than our global model for regionally specific studies.