Winter crops in the Delhi region (India) absorb as much CO2 as is released by neighbouring urban emissions: New observations of CO2 uptake by commercial airliner-based measurements

　The CONTRAIL project has been conducted in collaboration with Japan Airlines (JAL), JAMCO Corporation and the JAL foundation. JAL’s aircraft regularly carry a Continuous CO₂ Measuring Equipment (CME), which measures atmospheric CO₂ concentrations continuously from take-off to touch down along the flight track. From millions of CO₂ data collected worldwide, a recent study analysed 787 vertical profiles taken over Delhi, India from 2006 to 2014.

　Northern India (the Indo-Gangetic Plain) is a region of intense agriculture. Double cropping, typically rice in summer and wheat in winter, is the major agricultural practice. The seasonal variation of CO₂ concentrations over Delhi shows a clear deviation from that typically observed at background stations in similar latitudes (outside India); while CO₂ increases gradually over the winter at other background stations, CO₂ over Delhi stays almost constant for the period. Decreases in CO₂ toward the ground were found frequently in the vertical profiles in the season. These phenomena actually coincide with the growing season of winter crops (mainly wheat). An analysis of vertical profiles for relative depletion and enhancement of CO₂ in the atmospheric boundary layer indicated that the CO₂ uptake by winter crops exceeds in magnitude the urban CO₂ emissions from Delhi.

　This study demonstrates the significant role of agricultural practices in India’s carbon budget and highlights the relatively overlooked importance of agriculture in the global carbon cycle. The CME measurements by the CONTRAIL commercial airliner provide high-frequency CO₂ data over regions under-sampled by the current world atmospheric monitoring networks, like northern India in this study. The CONTRAIL datasets will complement measurements at other observational platforms and will be of increasing help to constrain local to regional CO₂ fluxes by being incorporated into atmospheric transport models.

CONTRAIL
URL: http://www.cger.nies.go.jp/contrail/
(Language: English)

Umezawa, T., Y. Niwa, Y. Sawa, T. Machida and H. Matsueda (2016), Winter crop CO2 uptake inferred from CONTRAIL measurements over Delhi, India, Geophys. Res. Lett. doi: 10.1002/2016GL070939.

This study was funded by the Global Environmental Research Coordination System and by the Environment Research and Technology Development Fund (2-1401) from the Ministry of the Environment Japan.

Taku Umezawa,
Research Associate, Office for Atmospheric and Oceanic Monitoring
Center for Global Environmental Studies
National Institute for Environmental Studies, Japan
Tel: +81-29-850-2525, E-mail: umezawa.taku (add “@nies.go.jp”)

Toshinobu Machida,
Head, Office for Atmospheric and Oceanic Monitoring
Center for Global Environmental Studies
National Institute for Environmental Studies, Japan
Tel: +81-29-850-2525, E-mail: tmachida (add “@nies.go.jp”)