india

Updated: Jan 19, 2014 00:11 IST

The adverse effects of climate change are being felt on more than a fourth of India’s landmass over the last four decades. While some parts of the country have turned arid, others have witnessed more rainfall.

A study by the Central Research Institute for Dryland Agriculture (CRIDA) at Hyderabad has revealed that about 27% of the country’s geographical area has been directly impacted by climate change, a result of increase in mean surface temperatures coupled with changes in rainfall pattern between 1971 and 2005.

The study said the changes in weather have implications on agriculture, water availability, drought preparedness, and could be a possible trigger for climate-change driven disease.

Scientists working on climate-resilient agriculture said the impact of climate change on crops in states is a reality. “Demarcation of climate zones helps in adaptation methods such as identifying new technologies and carrying out research to bring out new seed varieties. But, the analysis must be studied further and should take a longer time period into account,” said a senior agriculture scientist, requesting anonymity, as he is not authorised to talk to the media.

An 11-member team from CRIDA used temperature and rainfall data from 144 weather stations and 6,000 rain gauge stations to compute the moisture index (MI) (see box 2), which is a fundamental variable on the basis of which climate was classified across India.

Their analysis found substantial increase in arid areas in Gujarat and a decrease of arid regions in Haryana. While Madhya Pradesh, Tamil Nadu and Uttar Pradesh have witnessed a shift from medium rainfall (dry sub-humid) to semi-arid, states of Chhattisgarh, Orissa, Jharkhand, Madhya Pradesh and Maharashtra have changed from being high rainfall (moist sub-humid) to dry sub-humid.

Areas that have seen maximum decrease in rainfall are Orissa, Chhattisgarh, Jharkhand and Madhya Pradesh, where 28 districts have changed from high rainfall (moist sub-humid) to medium rainfall (dry sub-humid). Meanwhile, Ladakh district in Jammu and Kashmir, which was earlier classified as a dry and cold region, is now an area with medium rainfall.

“While we cannot say that India is moving towards aridity, extremities are certainly increasing. Therefore, it was pertinent to revisit climatic classifications that will aid better planning and help in allocating funds to various government mega projects,” said B Venkateswarlu, director, CRIDA.

The changes in the climate zones listed in the present study as compared to the previous one are stark. The maximum shift from high rainfall (moist sub-humid) to medium rainfall (dry sub-humid), comprising 7.23% of the geographical area, was observed in Orissa (12 districts), Chhattisgarh (7 districts), Jharkhand (4 districts) and Madhya Pradesh (5 districts).

The earlier humid districts of Jammu and Kashmir, Uttarakhand and Himachal Pradesh are now moist sub-humid. It’s become per humid (continuous rain and therefore the wettest) in Mizoram and Tripura from being just humid. While Andhra Pradesh and Maharashtra has seen a marginal reduction in its semi-arid zone, about half of the districts with high rainfall in eastern India (other than West Bengal, which has shifted to being humid) received medium rainfall.

The study states that some regions, which now receive more rainfall, may no longer need that much irrigation, while regions that are showing declining rainfall, like Orissa and Chhattisgarh, may need more irrigation.

Stating that climate classification must be revisited every 30 years, Venkateswarlu said: “Many districts such as dry regions of Punjab and Haryana that once needed large funds are well irrigated and may not need that kind of allocation anymore. On the other hand, areas such as Orissa and Jharkhand are turning arid and hence may now be eligible for funds for water-shed programmes.”

The first climatic classification for Indian districts was given in 1988 based on temperature and monsoon data in the 1960s. “Back then, there were fewer weather observatories, rain gauges and even districts as compared to today. The last 30-40 years have seen changes in temperature and rainfall, as well as irrigation across the country,” added Venkateswarlu.

According to climate studies, the rate of warming in India has increased after 1970s, with mean annual surface air temperature of 0.21 degrees Celsius every decade as against 0.51 degrees Celsius every 100 years during the past century.

Scientists attribute global warming to an increase in carbon emissions from manmade factors such as vehicular emissions and biomass burning. A rise in temperature affects evapotranspiration, thereby increasing aridity. Evapotranspiration means the loss of water from the soil, both naturally and through vegetation.