The role of continental evapotranspiration on water vapour isotopic variability in the troposphere

ABSTRACT

Rainforests play an important role in hydrological and carbon cycles, both at regional and global scales. They pump large quantities of moisture from the soil to the atmosphere and are major rainfall hotspots of the world. Satellite-observed stable water isotope ratios have played an essential role in determining sources of moisture in the atmosphere. Satellites provide information about the processes involving vapour transport in different zones of the world, identifying sources of rainfall and distinguishing moisture transport in monsoonal systems. This paper focuses on major rainforests of the world (Southern Amazon, Congo and Northeast India) to understand the role of continental evapotranspiration in influencing tropospheric water vapour. We have used satellite measurements of ¹H²H¹⁶O/¹H₂¹⁶O from Atmospheric InfraRed Sounder (AIRS), evapotranspiration (ET), solar-induced fluorescence (SIF), precipitation (P), atmospheric reanalysis-derived moisture flux convergence (MFC) and wind to discern the role of ET in influencing water vapour isotopes. A global map of the correlation between δ²H_v and ET-P flux indicates that densely vegetated regions in the tropics show the highest positive correlation (r > 0.5). Using mixing models and observations of specific humidity and isotopic ratio over these forested regions, we discern the source of moisture in pre-wet and wet seasons.

KEYWORDS:

• AIRS
• Evapotranspiration
• hydrogen-2
• hydrological cycle
• isotope hydrology
• rainforests
• TES
• troposphere
• water vapour

Acknowledgements

This work was carried out under the SARITA programme of the Land Hydrology Division, Space Applications Centre (ISRO). The authors thank Mr. N.M. Desai, Director-SAC for his valuable guidance and support. They also thank Dr. Robert Herman and Dr. John Worden, JPL-NASA for sharing AIRS data used in this study. They sincerely acknowledge precipitation data from Global Satellite Mapping of Precipitation (GSMaP) provided by JAXA Global Rainfall Watch. The authors acknowledge NASA Langley Research Centre Atmospheric Science Data Centre for the TES dataset. They thankfully acknowledge ECMWF for ERA5 Reanalysis data and IAEA/WMO for the GNIP dataset used in this study. They also thank NTSG for providing MODIS ET datasets.

Disclosure statement

No potential conflict of interest was reported by the author(s).