doi:10.1038/nindia.2013.41 Published online 23 March 2013
The vulnerable north eastern states of India — which bear a significant brunt of the global climate change phenomena — have finally got some serious attention from climate scientists. The eight states, least studied so far, have been thoroughly analysed over a 34-year period in a new study1. Based on the trends observed from 1971 to 2005, the scientists predict a rise in the regional annual mean temperature as well as mean rainfall in future.
The mega study, led by Sushil Kumar Dash of the Centre for Atmospheric Sciences at the Indian Institute of Technology Delhi, looked at present‐day climatic conditions prevailing in the region. The team examined the regional trends based on actual observations at the meteorological stations of India Meteorological Department (IMD) and on the gridded data.
The eight states – Assam, Arunachal Pradesh, Tripura, Nagaland, Manipur, Mizoram, Meghalaya and Sikkim – were studied for the two most important climatic parameters – temperature and rainfall. The region is blessed with ample monsoon rains and houses the world's wettest place Mawsynram, which receives an annual rainfall of about 1187.3 cm.
They also used data from the 'Regional Climate Model version 3' (RegCM3) of the Abdus Salam International Centre for Theoretical Physics (ICTP), Trieste, Italy to examine the projected changes in climatic parameters of temperature and precipitation in the region.
The model projected an increase in the annual mean surface temperature by about 0.64 °C in the 30 years from 2011 to 2040 and by 5.15 °C at the end of the century (2071–2100). It also projects increase in annual mean precipitation by about 0.09 mm/day in the near future and by 0.48 mm/day at the end of the century.
"The model simulations during 1971–2005 were compared with the IMD gridded datasets to validate the performance of RegCM3," Dash told Nature India. The team found that the model was able to simulate the trends in annual mean temperature for the period correctly. However, it overestimated the rainfall scenario. "Major parts of north east India show a wet bias in the model precipitation," he said.
The simulated annual mean temperatures for the region showed a good correlation with the gridded temperature values. Based on the IMD gridded datasets, the team examined extreme temperature events of daily maximum and minimum temperatures.
One of the key results that Dash and colleagues arrived at was the observation that warm nights were more frequent in the region in summer months than warm days. Their future simulations indicate more frequent warm events than cold events.
Climate change assessments for north eastern states of India have earlier been done by India's ministry of environment and forests. These were based on the projections of climate for 2030s at a sub-regional scale (such as the Himalayan region, North-Eastern region, Western Ghats and Coastal regions) simulated by a regional model developed by the UK Hadley Centre. That model used the greenhouse gases (GHG) forcing for the future under the IPCC A1B scenario. The results indicated likely increase in annual mean precipitation by 0.3% to 3% in the northeast region by 2030. It also anticipated an increase in temperature of the region by 1.8 °C to 2.1 °C by the end of 2030.
"Since there are uncertainties in the model projections depending on the type of model used, it is important to use another regional model over the Indian domain and assess the changes for the future," Dash said.