Preprints
https://doi.org/10.5194/acp-2021-40
https://doi.org/10.5194/acp-2021-40

  01 Jun 2021

01 Jun 2021

Review status: a revised version of this preprint is currently under review for the journal ACP.

Observations of Aerosol-Vapor Pressure Deficit-Evaporative Fraction coupling over India

Chandan Sarangi1,2, Tirthankar Chakraborty3,4, Sachchidanand Tripathi1,3, Mithun Krishnan1, Ross Morrison5, Jonathan Evans5, and Lina Mercado5,6 Chandan Sarangi et al.
  • 1Department of Civil engineering, Indian Institute of Technology, Kanpur, Kanpur, India
  • 2Department of Civil engineering, Indian Institute of Technology, Madras, Chennai, India
  • 3Center for Environmental Science and Engineering, Indian Institute of Technology, Kanpur
  • 4School of the Environment, Yale University
  • 5UK Centre for Ecology & Hydrology, Wallingford, UK
  • 6Department of Geography, University of Exeter, UK

Abstract. North India is a densely populated subtropical region with heavy aerosol loading, frequent heatwaves and strong atmosphere-biosphere coupling, making it ideal for studying the impacts of aerosols and temperature variation on latent heat flux (LH) and evaporative fraction (EF). Here, using in situ observations during the onset of the summer monsoon over a semi-natural grassland site in this region, we confirm that strong co-variability exists among aerosols, LH, air temperature (Tair) and vapor pressure deficit (VPD). Since the surface evapotranspiration is strongly controlled by both physical (available energy and moisture demand) and physiological (canopy and aerodynamic resistance) factors, we separately analyze our data for different combinations of aerosols and Tair/VPD changes. We find that aerosol loading and heatwave conditions both reduces SH. Further, we find that an increase in atmospheric VPD, tends to decrease the gross primary production (GPP) and thus LH, most likely as a response to stomatal closure of the dominant grasses at this location. In contrast, under heavy aerosol loading, LH is enhanced partly due to the physiological control exerted by the diffuse radiation fertilization effect (thus increasing EF). Moreover, LH and EF are positively associated with aerosol loading even under heatwave conditions, indicating a decoupling of plant’s response to VPD enhancement (stomatal closure) in presence of high aerosol conditions. With heat-stress, VPD and aerosols expected to increase in future India, our results warrant in-depth analysis of aerosol-plant-temperature-EF continuum and its impact on Indian monsoon dynamics and crop vulnerability.

Chandan Sarangi et al.

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on acp-2021-40', Anonymous Referee #1, 23 Jun 2021
  • RC2: 'Comment on acp-2021-40: Finding on relation ET-VPD-AOD is very interesting, but demands more analysis', Anonymous Referee #2, 29 Jul 2021

Chandan Sarangi et al.

Chandan Sarangi et al.

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Short summary
Generally, transpiration fluxes by vegetation are reduced under heat stress to conserve water. However, in-situ observations over North India shows that, the strength of the inverse association between transpiration and atmospheric vapor pressure deficit is seen to be weakening in presence of heavy aerosol loading. This finding not only implicates the significant role of aerosols on modifying the evaporative fraction, but also warrant in-depth analysis of aerosol-plant-temperature-EF continuum.
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