Impacts of moisture sources on the temporal and spatial heterogeneity of monsoon precipitation isotopic altitude effects

Moisture sources affect the temporal variations of the elevation effects on the stable isotopes in monsoon precipitation. However, whether it will lead to spatial variations and form a specific spatial-temporal heterogeneity pattern remains to be explored. Based on the monthly precipitation samples collected in Ailao Mountains of East Asian monsoon region, we computed and identified five moisture source regions to facilitate its comparison to the monthly oxygen isotope composition (delta O-18) of precipitation with HYSPLIT model. We analysed the influence mechanisms of the moisture sources on the temporal and spatial heterogeneity of the elevation effect on the hydrogen and oxygen stable isotopes during dry and rainy seasons. We found that the temporal heterogeneity of the elevation effects on the precipitation O-18 depends on the proportion of the moisture sources in the dominant direction, and as the proportion increases, the elevation effect becomes more significant. The spatial heterogeneity depends on the combination complexity of the moisture sources, the simpler the combinations, the more significant the elevation effects. The results demonstrate that for precipitation delta O-18 in Ailao Mountains, the dominant of monsoon moisture sources (the ratio higher than 50%) can result in significant elevation effects, while the mixtures of multiple moisture sources and the dominant of local moisture sources will lead to no elevation effects. Future studies should pay more attention to the influence mechanism of the spatial and temporal heterogeneity of the elevation effects on a relatively larger or global scale.