|Rainfall extremes such as the Mumbai deluge of 2005 can become more frequent in India under the impact of climate change.|
Recent evidence of the unpredictability of the monsoon and the unusual distribution of rainfall has led to questions whether such changes are a result of global warming. Here, a dumping yard at Pallikaranai, a suburb of Chennai, which contributes its share of greenhouse gases.
THE report of the Intergovernmental Panel on Climate Change (IPCC) on the physical basis of climate change, a summary of which was released on February 2 in Paris, does not address the issues of the potential impact of global warming and the consequent changes in climate and the vulnerability of people to them in the light of the new findings contained in the report. Neither does it deal with the mitigation and adaptation measures that countries must take to minimise the adverse effects. These will be dealt with in subsequent IPCC reports, to be issued in April and May.
However, in its Third Assessment Report (TAR), issued in 2001, the IPCC provided a fairly sound scientific premise to study these aspects in sufficient quantitative detail. The Fourth Assessment (AR4) report does not alter the basic global warming scenario outlined in the TAR, and when the complete report is released later this year, it is only likely to change marginally our perspective on impact and vulnerability even in quantitative terms.
It is, therefore, pertinent to discuss the essential features of these with regard to India, a subject on which substantial scientific literature has appeared since the TAR was released. One of the direct effects of global warming is the altering of the heat budget and its regional variations in the atmosphere, the primary driver of weather systems around the world. The potential impact of warming on the monsoon in India is of serious concern, particularly with respect to agriculture, much of which is rain fed. Indeed, nearly 80 per cent of the country's water resources go to meet agricultural needs.
Recent evidence of the unpredictability of the monsoon, the unusual distribution of rainfall in space and time, the shifting patterns of precipitation, the sustained deficit rainfall and drought-like conditions in some regions and excessive rainfall in others have led experts to ask whether we are already witnessing permanent or quasi-permanent changes in monsoon behaviour as a result of global warming.
Some studies on long-term trends indicate that while there is no evidence of any change in the rainfall pattern in the gross scale of the country changes are discernible at smaller scales of space and time (Frontline, November 3, 2006). As J. Srinivasan of the Indian Institute of Science (IISc), Bangalore, who is one of the contributing authors to the AR4, has pointed out, the monsoon has so far been a stable phenomenon but the impact of climate change could be different.
More rainfall extremes
So, are we seeing the effects of global warming already? How will these apparent changes evolve well into the 21st century as long-term climate change becomes real? According to Srinivasan, simulations with climate models and observations indicate that rainfall extremes such as the Mumbai deluge of 2005 could become more frequent in India under the impact of climate change. Both 2005 and 2006 had spells of excessive rainfall that normally would have occurred once in a hundred years or so.
Using a state-of-the-art Regional Climate Model (RCM) of the British Hadley Centre for Climate Prediction and Research, called PRECIS, scientists of the Indian Institute of Tropical Meteorology (IITM), Pune, recently obtained high-resolution meteorological effects of climate change for India on the basis of the appropriate greenhouse gas (GHG) emission scenarios outlined in the TAR. The study finds a general increase in precipitation and surface air temperature (SAT) for the country as a whole for the period 2071-2100. The annual mean increase in SAT ranges from 2 to 5 °C. The warming, though monotonously widespread across the country, is more pronounced over northern India. The all-round warming seen in the mean is also reflected in the extreme temperatures, and both nights and days will get warmer in the future, notes the study. Interestingly, night temperatures are seen to be increasing at a faster rate than day temperatures.
Spatial rainfall patterns show a maximum increase over west central India and the northeastern region. Extreme precipitation is found to increase substantially over the western coast and west central India. Overall, the summer monsoon rainfall shows a 20 per cent increase over the present, and the increase is seen in all the States except Punjab, Rajasthan and Tamil Nadu, which show a slight decrease.
Notwithstanding the limitations of global climate models (GCMs) in capturing the finer details of spatial and temporal variations, an earlier study based on an atmosphere-ocean-coupled GCM by Murari Lal of the Indian Institute of Technology Delhi and Japanese scientists found that by the 2080s winter rainfall might experience a 5 to 25 per cent decline even as monsoon rainfall shows a 10-15 per cent increase.
The Himalayas as seen from Gulmarg in Kashmir. Gangotri, one of the largest glaciers in the Himalayas, has been receding at an alarming rate in recent years, influencing the stream run-off of Himalayan rivers.
The changes in the precipitation pattern will impact significantly the water resource situation in the subcontinent, point out R.K. Mall of the Central Ground Water Board and others writing in Current Science. A fall in winter precipitation implies greater water stress during a lean summer monsoon season. Secondly, intense rain occurring during the summer monsoon months will mean that much of the monsoon rain would be lost as direct run-off, leading to lower groundwater recharging potential. Groundwater is the chief source of water to meet the domestic needs of over 80 per cent of the rural and 50 per cent of the urban populations and also meets the needs of about 50 per cent of irrigated agriculture.
According to a study of 12 river basins of the country by A.K. Gosain of IIT Delhi and others, under a global warming scenario, there is a general reduction in the overall quantity of the available run-off. The Luni basin with its westward flowing rivers, Kutch and Saurashtra, which constitute about one-fourth of the area of Gujarat and 60 per cent of the area of Rajasthan will face situations of acute water scarcity.
River basins of the Mahi, the Pennar, the Sabarmati and the Tapi will also face water shortage conditions. The Cauvery, the Ganga, the Narmada and the Krishna will experience seasonal or regular water-stressed conditions. The basins of the Godavari, the Brahmani and the Mahanadi will not have water shortages but will frequently face severe flood situations.
Glaciers melting faster
Meltwater from the Himalayan glaciers and snowmelt from the Himalayan snow cover feed important rivers of northern India such as the Ganga and the Brahmaputra. There is enough evidence around the world of accentuated melting of glaciers because of global warming in the last century, and the Himalayan glaciers, too, have been found to be retreating rapidly. Gangotri, one of the largest glaciers in the Himalayas, has been receding at an alarming rate in recent years (Frontline, April 13, 2001), influencing the stream run-off of Himalayan rivers.
Anil Kulkarni of the Indian Space Research Organisation's Space Applications Centre (SAC) in Ahmedabad and other scientists investigated the glacial retreat of 466 glaciers in the Chenab, the Parbati and the Baspa basins using data from the Indian Remote Sensing satellite and field expeditions and comparing them with the 1962 topographic surveys by the Survey of India. The study has shown an overall 21 per cent reduction in the glacier surface area. The process of deglaciation also led to the fragmentation of the larger glaciers. The mean area of glacial extent also declined from 1 sq km to 0.32 sq km during 1962-2004.
Glacial thickness being directly proportional to the areal extent, large glaciers (which have thicknesses between 150 and 600 metres) would respond to climate change much more slowly (15 to 60 years) than small (less than 1 sq km) glaciers (4 to 11 years). So smaller glaciers and ice fields get more prominently affected by global warming. This is already evident in the Himalayan region. The study found that smaller glaciers have deglaciated by almost 38 per cent in this 40-year period. As the world gets into an even warmer phase in the present century, the process of deglaciation and fragmentation will have a profound impact on the water resources in the Himalayan region and the Gangetic plains.
The same group of scientists also investigated the process of snow accumulation and ablation, which is highly sensitive to climatic changes, in the Beas and the Baspa basins, using remote-sensing data. Melting of snow cover in summer is an important source of water for many Himalayan rivers, and an increase in atmospheric temperature accentuates the melting of snow cover. From a study of winter run-off - which is only on account of snowmelt - the scientists found that accumulation during winter declined between the late 1990s and the turn of the century. Also, the snow accumulation pattern had changed significantly.
Likewise, they found that the winter run-off had increased by as much as 75 per cent between 1966 and 1995. If additional areas start melting in the middle of winter - this is already happening even at high altitudes - less snow will be available for the summertime stream run-off that feeds the rivers, the scientists point out. The reduced sizes of many permanent snow and ice fields have already led to water scarcity in villages in Himachal Pradesh. Though the period of study is too small to make any definitive statement about the long-term impact of warming on snow accumulation and ablation, the trend would seem ominous.
Cyclones & storm surges
An important effect of global warming on meteorological conditions is an increase in sea surface temperature (SST) in the oceans around the subcontinent. The resulting greater convective activity will lead to an increase in the intensity or wind speed of cyclones that form in them, particularly the Bay of Bengal where over 80 per cent of the cyclones originate. Higher wind speeds will also result in bigger storm surges. The rise in sea level owing to this regional meteorological cause will have a compounding effect on the global rise in sea level caused by the melting of ice and glaciers from higher latitudes and volume expansion due to the warming of ocean waters. The recent IPCC report has projected a global mean sea-level rise of 0.59 m by the end of the 21st century. This, in fact, may be conservative, according to other estimates.
On the basis of simulations of the occurrence of cyclones in the Bay of Bengal for the period 2041-2060 using an RCM of the Hadley Centre with emission scenarios of the IPCC, A.S. Unnikrishnan of the National Institute of Oceanography, Goa, and others have shown that in a global warming scenario, while the frequency does not show any discernible long-term trend, the number of intense cyclones in the post-monsoon period increases. Combining this result with a storm surge model, they have concluded that storm surge heights will be far greater under warmer conditions. The increased surge heights are over and above the mean sea level, which itself rises under the impact of warming.
A parched paddy field in Tezpur village of Assam's Sonitpur district. Low rainfall and hotter-than-usual weather in Assam and other northeastern States last year have had their impact on farm productivity.
The risk of cyclone-related disasters is thus far greater in a warmer subcontinent. The vulnerability of the population on the 7,000-km Indian coastline is huge considering the fact that a quarter of India's population lives within 50 km of the coastline and this includes some major cities as well. The mean sea level rise itself, in the absence of protection, can inundate a large swath of predominantly agricultural land on the coast, and the surviving coastline faces the threat of extreme storm surges. India, in fact, is one of the 27 countries the United Nations Environment Programme (UNEP) has identified as most vulnerable to sea level rise.
The impact of climate change on crop productivity and food security of the country will also be severe. According to Sushil Kumar of the National Centre for Plant Genome Research (NCPGR) in New Delhi, given that 60 per cent of land is already under cultivation, the adverse effects of climate change are impossible to mitigate by adding area under agriculture.
Food security issues
Crop productivity, he says, must be stabilised against climate change by adopting measures to cope with the higher temperatures and the highly skewed patterns of water availability. These include better water management and the use of new agriculture technologies in a region-specific manner and, more importantly, evolving new cropping patterns and developing crop varieties that have tolerance to higher temperatures and water stress and rice varieties that can be cultivated aerobically with irrigation instead of rain-fed standing water.
Given the imminent deficit in rainfall in the Indo-Gangetic plains, he has recommended that conventional rice cultivation be reduced in this region and increased in the northwestern and central-western regions where rainfall is expected to increase. "To keep the western parts of the Indo-Gangetic plains as a major food-producing region, despite the adverse effects of climate change, is the major challenge for agricultural research," Sushil Kumar wrote in Current Science.
Changes in plant phenology, or timing of lifecycle events in the species such as leaf-formation, flowering, leaf-fall, fruit development, seed dispersal and germination, may be one of the earliest observed responses to rapid climate change, point out Monika Koul Moza and A.K. Bhatnagar of the University of Delhi. These changes are the result of the plants adapting to long-prevailing climatic patterns, they say. An increase in the atmospheric concentration of carbon dioxide (CO2) and higher temperatures could have potentially serious consequences for both plant and animal species that depend on periodically available resources in the ecosystems of the country, they warn.
A related study of the impact of climate change on forest types by N.H. Ravindranath of the IISc and others says that by the mid-2080s around 70 per cent of the forest grids in India are likely to experience a shift in forest types. This study also used an RCM of the Hadley Centre and the TAR emission scenarios of the IPCC. According to it, a shift towards wetter forest types in the northeastern region and drier forest types in the northwestern region is likely, thus impacting the biodiversity of the country. Also, the increase in atmospheric CO2 and warming could result in a 70 to 100 per cent increase in the Net Primary Productivity (NPP) of forests.
Climate change can also have a significant impact on health through vector-borne diseases because of changes in the survival and reproduction rates of the carriers, the intensity and temporal pattern of vector activity, and the lifecycle of pathogens within the vectors. In the context of malaria, the current climatic conditions and incidence rates suggest that the most malaria-prone areas are the central and eastern regions of India, covering Madhya Pradesh, Jharkhand, Chhattisgarh, Orissa, West Bengal and Assam.
The threat to the ozone layer is real, as the use of air-conditioners, as in this instance from Hyderabad, has increased manifold.
Considering the changed climatic conditions into the 2050s, Sumana Bhattacharya and others in their study, using a Hadley Centre RCM and the IPCC emission scenario, conclude that while malaria is likely to persist in Orissa, West Bengal and the southern parts of Assam, it may shift from the central Indian region to the south-western coastal States of Maharashtra, Karnataka and Kerala. Also the high-altitude northern States, including Himachal Pradesh, and the northeastern States of Arunachal Pradesh, Nagaland, Manipur and Mizoram may become malaria-prone. The duration of transmission windows, according to them, is likely to widen in the north and the west and shorten in the south. The extent of vulnerability to malaria will depend on the prevailing socio-economic conditions, the immune response to a new vector-borne disease, and the existence of associated health care infrastructure, they point out.
In spite of the vast spectrum of potentially adverse impacts that climate change can have on India and its population, it is strange that there was just one official from the Indian embassy during the release of the IPCC Summary Report for Policymakers in Paris. Contrast this with the Chinese, who had as many as 10 specialists at the same meeting.
Is this an indication of the official response to the imminent changes due to climate change? It would be sad if bureaucratic apathy blocked the adoption of appropriate measures to counter the serious effects of climate change.