Characteristics of Hydrogen and Oxygen Isotopes and Water Vapor Sources in Atmospheric Precipitation in Subtropical Monsoon Islands

Abstract

<p>Globally, more than 600 million inhabitants are living in thousands of islands where communities rely on rainwater, shallow groundwater and springs to meet the needs of drinking and economic development. However, the knowledge of the water cycle is still limited in the small islands. Fieldworks were conducted from Oct. 2018 to the end of 2019 to study the seasonal and spatial changes of isotope compositions of rainwater in the Wanshan Island (area = 8.07km<sup>2</sup>), Zhuhai, Guangdong, China. The results show that the hydrogen and oxygen isotopes in the island precipitation are enriched in the dry season and depleted in the rainy season because of the seasonal changes of the vapor sources and migration paths simulated by the HYSPLIT model. Compared with GMWL, LMWL (δD = 8.077δ<sup>18</sup>O + 15.202) has almost the same slope and a higher intercept (R<sup>2</sup> = 0.976), which is the same as the local meteoric water line Line of Taiwan, Hong Kong, and other islands in the subtropical monsoon region. The d-excess value on the island was low in the summer season and high in the winter season, ranging from 10.49‰ to 17.06‰, which provides more details for changes in moisture sources. Also, hydrogen and oxygen isotopes in the island have a negative correlation with month precipitation, elevation, and distance from the sea. Our results are significant for the understanding of the hydrological processes of small islands in the tropical and subtropical climate.</p>