Water vapor δD dynamics over China derived from SCIAMACHY satellite measurements

This study investigates water vapor isotopic patterns and controls over China using high-quality water vapor δD data retrieved from the Scanning Imaging Absorption Spectrometer for Atmospheric Chartography (SCIAMACHY) observations. The results show that water vapor δD values on both annual and seasonal time-scales broadly exhibit a continental effect, with values largely decreasing northwestward from coastal lowlands to high-elevation mountainous regions. However, region-specific analysis reveals spatially distinct patterns of water vapor δD between seasons. In the monsoon domain (e.g., China south of 35°N), depletion in D in the summer and fall seasons is closely tied to monsoon moisture sources (the Indian and Pacific oceans) and subsequent amount effect, but higher δD values in winter and spring are a result of isotopically-enriched continental-sourced moisture proceeded by less rainout. In contrast, farther inland in China (non-monsoon domain), moisture is derived overwhelmingly from the dry continental air masses and local evaporation, and δD values are largely controlled by the temperature effect, exhibiting a seasonality with isotopically enriched summer and depleted winter/spring. The observation that the spatial pattern of water vapor δD is the opposite to that of precipitation δD in the summer season also suggests that partial evaporation of falling raindrops is a key driver of water vapor isotope in the non-monsoon domain. This study highlights the importance of non-Rayleigh factors in governing water vapor isotope, and provides constraints on precipitation isotope interpretation and modern isotope hydrological processes over China.