Modeling the contributions of oceanic moisture to summer precipitation in eastern China using 18O

Abstract

Ocean-continent interaction is an important component of the global climate systems and influences hydrological cycles at regional and local scales. Oceanic moisture (OM) advection and terrestrial evapotranspiration (ET) are two main sources of precipitation in eastern China. The objectives of this study are to quantify the contribution of the OM to precipitation and to better understanding the water cycle processes in the region. Summer months when the East Asian monsoon is strongest are studied, and a two-component mixing model using 18O as a tracer is applied to apportion the spatiotemporal contributions of OM. The Gaussian first-order approximation is employed to assess the uncertainty of the estimates. In the entire study area, OM predominates summer precipitation, with ET playing a supplemental role. The contributions of OM to precipitation decrease from June to August in Central China and Northern China. For example, in Central China the proportional contributions of OM are 94% in June, 92% in July and 81% in August. Spatially, the OM contributions decrease along the transport route from south to northeast. The 95% confidence intervals of the estimated contributions range from ±0.07 to ±0.38, with the standard errors between 0.03 and 0.17 for all months and sub-regions. The relative uncertainty contributions of each source to the total uncertainty follow the order of precipitating vapor > advection > ET. The large variances of δ18O in precipitable water vapor account for the most uncertainty of the proportional estimates.