India’s Climate Change Concerns and the Need for Better Climate Models
By: Prof. R.R. Kelkar
India is a vast country with a billion-plus
population and it has a variety of climates and topographical features. It depends
on the monsoons for meeting all its water needs, with its major rivers either originating
from the Himalayas or fed by the monsoon rains. Indian agriculture is critically
linked to weather and climate. India has faced severe droughts, widespread floods
and devastating tropical cyclones. The threat of climate change induced by global
warming therefore looms large over India in a real sense. Although this problem
has global dimensions, there are certain challenges that are specific to India.
It would also like to ensure that the mitigation actions do not themselves become
a stumbling block in the path of sustainable development.
India has reason to be concerned about the likely impacts of climate change on at
least six major fronts:
Many investigations have addressed the above concerns using global climate models.
Since India is a country of sub-continental dimensions and phenomena like the Indian
monsoon are a major component of the global atmospheric circulation system, it is
not illogical to use global models for this purpose and many significant results
have indeed been obtained about likely climate change over India. However, it has
to be accepted that global models have a coarse resolution of 250 to 500 km and
the results cannot bring out the finer features such as orography-induced rainfall.
Moreover, monsoon processes show up quite differently in different climate models.
In fact, several global models have not even been able to capture the basic climatology
of the Indian monsoon on either spatial or temporal scales or both. This casts a
shadow of doubt on the projected anomalies of temperature and rainfall when the
mean values are themselves uncertain. Paradoxically, many models indicate a weakening
of the monsoon circulation but an intensification of the rainfall and an extension
of the monsoon season. The projected increase in monsoon precipitation has a wide
difference across models, ranging from 3 to 17 %.
- Change in the amount and distribution pattern of monsoon rainfall, which is India’s only source of water
- Effect of temperature rise and change in the rainfall pattern on agricultural production and its impact on food security
- Possible increase in the frequency and intensity of tropical cyclones over the Bay of Bengal and Arabian Sea, which cause heavy losses of life and property in the coastal regions
- Threat of sea level rise to India’s 7,500 km long coastline including the Andaman, Nicobar and Lakshadweep islands
- Retreat of Himalayan glaciers and its effect on the Indian rivers which originate in the Himalayas
- The possible effect on the health of the population arising from the growth of vector-borne diseases due to rising temperatures
The only regional model used in climate change assessments over India is the Hadley
Centre’s high-resolution (50 km) regional climate model, PRECIS (Providing Regional
Climates for Impact Studies). The results that have become available as recently
as in August 2011 are again not free from uncertainty. They provide more of a qualitative
direction than a quantitative estimate, and the experiments need to be repeated
with multiple emission scenarios and multiple models. The indications are that the
summer monsoon precipitation over India may be 9 to 16% more in the 2080s compared
to the 1970s, but the rainfall may in fact decrease over some regions of the country.
Also, the rainfall distribution in terms of the number of rainy days in the monsoon
season is likely to change.
The results of the climate model runs, both global and regional, have to be viewed
against the observed fact that the all-India summer monsoon mean rainfall has not
show any statistical trend whatever over since at least 1875. Today, when even seasonal
scale monsoon predictions are difficult to make and often go wrong, like in 2009,
making climate scale monsoon predictions over the next 50 or 100 years remains a
formidable challenge. There are only a few global models that can be trusted with
this job and there is no single climate model currently available nationally or
internationally that can be truly relied upon from all angles pertaining to the
monsoon for purposes of policy making.
Agriculture: There have many investigations into the likely effects of climate
change on Indian agriculture. However, many of them have considered only baseline
shifts in temperature and rainfall, while it is well-known that Indian agriculture
is extremely sensitive to the timing of wet and dry spells, heat and cold waves,
etc. The incidence of crop pests and diseases is a major weather-dependent imponderable
and it can very adversely impact the crop yields. Simplistic models often give rise
to alarmist results and what are required are very robust models that would incorporate
the diverse inputs that determine crop production.
Tropical cyclones: Tropical cyclones over the Bay of Bengal and the Arabian
Sea are much fewer in number than those in the Pacific and Atlantic basins, but
they have been responsible for comparatively much heavier losses of life and property
in the countries of the south Asian region. One of the pre-conditions for the formation
of a tropical cyclone over the ocean is that the sea surface temperature (SST) should
be 26.5 °C or higher. Tropical storms therefore tend to form only over certain ocean
basins of the world and in certain preferred seasons where and when there is a possibility
of this condition being satisfied in the first place. The primary effect of global
warming, logically speaking, would be to cause the climatological SST isotherm of
26.5 °C to spread out and so favour the formation of tropical cyclones over a larger
oceanic area than at present. However, it should be remembered here that a warm
ocean is just one of the many pre-conditions for the formation of a tropical cyclone,
and not the only one. Further, it is not only the number of tropical storms that
is important, but also the peak intensity that they reach, and the length and orientation
of the tracks that they follow. Hence, statistical correlations between global warming
and the frequency of occurrence of tropical storms cannot be derived or viewed in
isolation without due regard to these other aspects.
The number of cyclonic storms over the north Indian Ocean constitutes a small statistical
sample, the number of severe cyclonic storms is still smaller and the instances
of storms developing into supercyclones are just a few. Further, the number of landfalling
systems varies widely across different sectors of the Indian coastline making some
states more cyclone-prone than others. Therefore, it is difficult to draw robust
conclusions from a statistical analysis of historical data and derive periodicities
or trends. Although there is some evidence of an increasing trend, it cannot be
extrapolated simplistically into the future. A lot of modelling effort is required
to be put in, including factors such as projections of the sea surface temperature
so that more credible and realistic conclusions can be drawn.
Sea level rise: The sea level at a given place is influenced by several local
factors such as coastal ocean temperature, salinity, wind, atmospheric pressure
and ocean currents. The sea level is also affected by the changes in coastal geometry
resulting from sedimentation, coastal erosion, storm surges and the action of waves.
Tide gauge observations are available for some Indian coastal stations since the
mid-nineteenth century and they have shown that mean sea level along the east coast
of India is higher than that along the west coast. Sea level trends derived from
historical tide gauge records are sensitive to the choice of stations and the data
period analyzed but there is no evidence of a monotonic rising trend at any of them.
The prime advantage of satellite altimetry over tide
gauge measurements is that satellite-derived sea level data are available across
the oceans and not just on the coast. Satellite measurements have shown that over
the Arabian Sea and the Bay of Bengal, sea level rise in recent years has been negligibly
small and the sea level has in fact exhibited a fall in some parts.
Different sectors of the long Indian coastline have different physiographic and
environmental characteristics. Problems such as erosion, flooding, subsidence, salinization
and deterioration of local ecosystems like mangroves already prevail in the coastal
regions. Anthropogenic factors also play a role in the deterioration of the environment
of the coastal zone. There is, however, a growing tendency to attribute all sea
level rise observed anywhere on the coast entirely to global warming, which needs
to be curbed and a balanced view taken considering other possible reasons as well.
Himalayan glaciers: The Himalayas, including the Karakoram range, constitute
the largest glacier system in the world outside of Antarctica and Greenland. Scientific
observations of Himalayan glaciers were started about a hundred years ago. The snout
of the Gangotri glacier in Uttarakhand was mapped in detail way back in 1935 and
it had shown signs of retreat even at that time. After the 1970s remote sensing
satellites have made it possible to carry out glacier mass balance investigations
on a large spatial scale. The retreat of glaciers has assumed great importance in
recent years as it is being projected as an indicator of the current global warming.
In the case of Himalayan glaciers, however, the issue is also of great practical
concern as India’s three major river systems, Ganga, Yamuna and Brahmaputra have
their origins in the Himalayas.
Observational evidence indicates that the Himalayan glaciers have been exhibiting
a continuous secular retreat since the earliest recording began in the mid-nineteenth
century, and the retreat in the recent years in not unusual. Another interesting
and important point is that not all of the Himalayan glaciers have been retreating.
Making high quality and reliable measurements of glacier
retreat at remote and inaccessible locations in the Himalayas is difficult but is
greatly desirable. Otherwise one can very easily arrive at wrong and threatening
conclusions. In fact many studies have shown that it is premature at
the present time to say with certainty that the retreat of the Himalayas glaciers
is attributable to the current global warming. Glaciers are known to be influenced
by several geophysical features and local climate fluctuations and it is particularly
difficult to correlate individual snout movements to large scale global warming.
Vector-borne diseases: The PRECIS model has been
used recently for malaria incidence investigations and updated results under the
A1B scenario have now become available for many parts of India. By the 2030s, compared
to the 1980s, the Himalayan region and northeastern states of India are likely to
be adversely affected by an increase in the transmission window, while the effect
may be minimum over the Western Ghats and even beneficial over the east coast. Here
again, such results have to be considered with due care and caution, since the incidence
and spread of malaria is governed not just by temperature and humidity but by several
other socioeconomic factors not related to climate such as urbanization, population
migration, health infrastructure and intervention practices. For proper preparedness
planning, there is a great need to construct comprehensive models which can envisage
how these factors will evolve over time, with global warming being one of the inputs
and not the only one.