Najib Anwar
Is it an El Niño effect? Who knows?
According to a recent study, hill stations such as Srinagar, Shimla, Darjeeling and Kodaikanal had witnessed a rise in temperatures over the last 40 years. The study revealed that urbanization has played a pivotal role in contributing to the rise in temperature. The study has been conducted by the Indian Institute of Tropical Meteorology (IITM), Pune and the World Meteorological Organisation in Geneva, Switzerland recently and was published on 2nd September, 2016.
Hill stations apart, all the major cities like Kolkata, Delhi, Jaipur, Ahmedabad, Mumbai, Nagpur, Bengaluru, Hyderabad, Chennai and Pune had recorded significant temperature rise from 1971-2013. Kolkata is a metropolis where the annual mean temperature has risen substantially in the past 40 years. But the highest rise in mean temperature was in Jaipur (0.38 degree C). Bengaluru (0.23 degree C) and Nagpur (0.21 degree C) followed.
Meanwhile, Delhi is among the four cities which showed a decrease in mean annual temperatures from 1901 to 1970. But after that the trend got reversed. One reason for this reversal is ‘increasing urbanisation’. One of the authors of this report, IITM’s Dilip Rajaram Kothawale said that the analysis has revealed that industrialization and urbanization have played significant roles in contributing to rise in temperature in most major cities during the recent period. The effects are apparent on the minimum temperature, he said. All the coastal stations showed substantial rise in temperature, Kothawale commented.
Five hill stations had been used in this study. Three stations were located in North India and two stations in South India. All the hill stations show a significant increasing trend in annual mean temperature during the entire period. Only two stations, namely Shimla and Darjeeling showed a significant increasing trend in temperature, whereas three stations Srinagar, Kodiakanal and Medikeri do not show any trend. Annual maximum temperature anomaly shows a gradual increase up to 1970, and rapid increase during the period 1971-2010, however minimum temperature is trendless up to 1970 and after it shows an increasing trend up to 2010. The maximum and minimum temperatures are increased by 0.4˚C and 0.22˚C per decade respectively during the period 1971-2010. The analysis reveals that the maximum temperature increase more rapidly than the minimum, over the hill stations.
Nine major cities- Kolkata, Jaipur, Ahmedabad, Surat, Pune, Mumbai, Nagpur, Bengaluru and Chennai- showed substantial increasing trends in minimum temperature after 1971. During this period six major cities- Jaipur, Mumbai, Nagpur, Bengaluru, Hyderabad and Chennai showed significant increasing trend in temperature. So, Jaipur, Mumbai, Nagpur, Bengaluru and Chennai are having both the trends.
The report concludes that the minimum temperature increases faster than the maximum temperature over major and medium cities, while, maximum temperature increases faster than minimum over small and hill stations. The effect of urbanization on temperature is not uniform at all the stations. It may be due to the location of stations, spatial temperature variability, aerosols optical depth over that region as well as agricultural cropping patterns. The effects of urbanization are more pronounced on minimum temperature than that of the maximum temperature.
For the present study, altogether 36 locations were used classifying them into four groups- major, minor, small cities and hill stations. The seasonal and annual mean, maximum and minimum temperature data for the period 1901-2013 were taken into consideration.