forested and agricultural environments. It is also believed
that trees emit significant amount of methane, especially in
forested environment; no study to ascertain and quantify the
plant-derived methane emission exists in India. This poses a
serious constraint in making an accurate estimation of the net
ecosystem productivity and in turn the carbon sequestration
potential of the Indian forests. A large amount of vapor is
generated through the process of transpiration, but their role
in modulating the monsoon processes remains largely
unknown. Apart from insufficient observational data, there
are no significant studies for Indian region to quantify this
effect by climate modeling. Development and use of coupled
climate–carbon models could help identify the sources and
sinks of both carbon dioxide and water vapor fluxes. Inverse
models have been shown to reliably estimate the sources and
sinks of the GHGs, but insufficient observed data pose a
serious challenge to achieve the task in the Indian context.
Likewise, the role of the oceanic GHG emission on the
terrestrial carbon cycle also remains poorly constrained.
One of the important parameters is the carbon isotopic
values of certain GHGs, such as CO 2 and CH 4 , which are
known to provide valuable information about the sources,
but their use in the Indian context is almost nonexistent.
With the advent of new technology (i.e., laser-based cavity
ring-down spectroscopy), real-time in situ monitoring of
GHGs concentrations and their isotopes are possible
(Mahesh et al. 2015; Chakraborty et al. 2020). Use of outputs from such instruments would greatly enhance our
capability to characterize the GHGs source and sink patterns
on a higher temporal and regional scale.
With increasing population and rapid industrialization,
energy demand for the country is increasing at a rapid pace
resulting in more GHGs emissions. But there is no network
of observations available to monitor these emissions and to
have a better understanding of sources and sink pattern over
the country. In this context, there is an urgent need to
develop a countrywide surface GHGs concentration observational network and their fluxes at all the major ecosystems
and urban hotspots.
Other issues, such as the sensitivity of the photosynthetic
sink and the respiration-driven sources of carbon to
increased warming, relation between the CO 2 and other
green house gas fluxes with the intra-seasonal variation of
rainfall across the ecosystems, need to be investigated.
The scope of research needs to be expanded using
process-based modeling of carbon cycle to quantify the role
of different natural and anthropogenic factors. These models
do not rely on the remote-sensing data and hence can be
used to study the pre-satellite era as well as develop future
scenarios. Development of a coupled climate and GHG cycle
model constrained and validated by an extensive observational network would strengthen the effort in unraveling the
regional sources and sinks of the GHGs and develop realistic
projections of the future.
4.6 Summary
The observational records of CO 2 and CH 4 concentration are
available from a West Indian location (Sinhagad) for the last
several years. This is one of the very few flask-based measurements that is currently underway in India on a long-term
perspective.
The observation shows that the amplitude of CO 2 mixing
ratio has been increasing progressively for the past several
years. The mechanism responsible for producing such variability is not fully understood, but is likely to be linked to the
changes in vegetation and forest cover.
Reports available on Indian forest cover expansion
(contraction) are not coherent. Systematic efforts are
required to address these issues. The measurement of surface
CO 2 concentration over a wide geographical area must be
carried out on a long-term basis. Analysis of such kind of
records has been proven to be an effective means to assess
the biospheric activity.
Use of satellite-derived vegetation indices (proxy of terrestrial biosphere) indicates an increasing trend (ca. 4% per
decade) during the last two decades in India. Also, the NPP
estimates based on Dynamic Land Ecosystem Model for the
1901–2000 period show an increasing trend, from 1.2 to
1.7 PgC.yr
-1 .
The available surface GHGs concentration observations,
albeit from a limited area, indicate the role of marine processes, especially during the summer monsoon season, in
determining the seasonal pattern of CO 2 and CH 4 fluxes.
However, quantification of this process needs to be done for
a better understanding of the GHGs dynamics.
The atmosphere–biosphere exchange of CO 2 tends to be
active during summer monsoon and maximum during
post-monsoon seasons of India. However, the Kaziranga
forest in Northeast India appears to sequester maximum
carbon during the pre-monsoon season.
The net ecosystem exchange (NEE) of carbon derived
from satellite retrievals gives only a gross estimate over a
wide region. Considerable differences exist with the eddy
covariance-based in situ observations at several places.
A robust network of eddy covariance-based observations
consisting of a large number of micrometeorological tower
setup over the diverse ecosystems across the country can
lead to a better understanding of the biogeochemical cycles.
CO 2 and CH 4 projections for the Indian environment have
been made under different CMIP6 emission scenarios.
Without rapid mitigation policies, atmospheric CO 2 and CH 4
loading will continue to increase for the next several decades.
88
S. Chakraborty et al.
that trees emit significant amount of methane, especially in
forested environment; no study to ascertain and quantify the
plant-derived methane emission exists in India. This poses a
serious constraint in making an accurate estimation of the net
ecosystem productivity and in turn the carbon sequestration
potential of the Indian forests. A large amount of vapor is
generated through the process of transpiration, but their role
in modulating the monsoon processes remains largely
unknown. Apart from insufficient observational data, there
are no significant studies for Indian region to quantify this
effect by climate modeling. Development and use of coupled
climate–carbon models could help identify the sources and
sinks of both carbon dioxide and water vapor fluxes. Inverse
models have been shown to reliably estimate the sources and
sinks of the GHGs, but insufficient observed data pose a
serious challenge to achieve the task in the Indian context.
Likewise, the role of the oceanic GHG emission on the
terrestrial carbon cycle also remains poorly constrained.
One of the important parameters is the carbon isotopic
values of certain GHGs, such as CO 2 and CH 4 , which are
known to provide valuable information about the sources,
but their use in the Indian context is almost nonexistent.
With the advent of new technology (i.e., laser-based cavity
ring-down spectroscopy), real-time in situ monitoring of
GHGs concentrations and their isotopes are possible
(Mahesh et al. 2015; Chakraborty et al. 2020). Use of outputs from such instruments would greatly enhance our
capability to characterize the GHGs source and sink patterns
on a higher temporal and regional scale.
With increasing population and rapid industrialization,
energy demand for the country is increasing at a rapid pace
resulting in more GHGs emissions. But there is no network
of observations available to monitor these emissions and to
have a better understanding of sources and sink pattern over
the country. In this context, there is an urgent need to
develop a countrywide surface GHGs concentration observational network and their fluxes at all the major ecosystems
and urban hotspots.
Other issues, such as the sensitivity of the photosynthetic
sink and the respiration-driven sources of carbon to
increased warming, relation between the CO 2 and other
green house gas fluxes with the intra-seasonal variation of
rainfall across the ecosystems, need to be investigated.
The scope of research needs to be expanded using
process-based modeling of carbon cycle to quantify the role
of different natural and anthropogenic factors. These models
do not rely on the remote-sensing data and hence can be
used to study the pre-satellite era as well as develop future
scenarios. Development of a coupled climate and GHG cycle
model constrained and validated by an extensive observational network would strengthen the effort in unraveling the
regional sources and sinks of the GHGs and develop realistic
projections of the future.
4.6 Summary
The observational records of CO 2 and CH 4 concentration are
available from a West Indian location (Sinhagad) for the last
several years. This is one of the very few flask-based measurements that is currently underway in India on a long-term
perspective.
The observation shows that the amplitude of CO 2 mixing
ratio has been increasing progressively for the past several
years. The mechanism responsible for producing such variability is not fully understood, but is likely to be linked to the
changes in vegetation and forest cover.
Reports available on Indian forest cover expansion
(contraction) are not coherent. Systematic efforts are
required to address these issues. The measurement of surface
CO 2 concentration over a wide geographical area must be
carried out on a long-term basis. Analysis of such kind of
records has been proven to be an effective means to assess
the biospheric activity.
Use of satellite-derived vegetation indices (proxy of terrestrial biosphere) indicates an increasing trend (ca. 4% per
decade) during the last two decades in India. Also, the NPP
estimates based on Dynamic Land Ecosystem Model for the
1901–2000 period show an increasing trend, from 1.2 to
1.7 PgC.yr
-1 .
The available surface GHGs concentration observations,
albeit from a limited area, indicate the role of marine processes, especially during the summer monsoon season, in
determining the seasonal pattern of CO 2 and CH 4 fluxes.
However, quantification of this process needs to be done for
a better understanding of the GHGs dynamics.
The atmosphere–biosphere exchange of CO 2 tends to be
active during summer monsoon and maximum during
post-monsoon seasons of India. However, the Kaziranga
forest in Northeast India appears to sequester maximum
carbon during the pre-monsoon season.
The net ecosystem exchange (NEE) of carbon derived
from satellite retrievals gives only a gross estimate over a
wide region. Considerable differences exist with the eddy
covariance-based in situ observations at several places.
A robust network of eddy covariance-based observations
consisting of a large number of micrometeorological tower
setup over the diverse ecosystems across the country can
lead to a better understanding of the biogeochemical cycles.
CO 2 and CH 4 projections for the Indian environment have
been made under different CMIP6 emission scenarios.
Without rapid mitigation policies, atmospheric CO 2 and CH 4
loading will continue to increase for the next several decades.
88
S. Chakraborty et al.