Minimum temperatures on rise

Mumbai: While the current heat wave has led to a sudden rise in maximum temperature at most of the hill stations across Maharashtra, weather scientists studying changes in surface air-temperatures have shown that though very slow, the minimum temperatures at the hill stations too are on rise and have cited urbanization as the major reason for the increase.

The maximum and minimum temperatures at the hill stations have increased at least by 0.4˚C and 0.22˚C per decade respectively during the period 1971-2010, a research by Indian weather scientists, published in American Journal of Climate Change, has shown. The scientists have compared temperature data at several places across India between 1901 and 2013 and realized that a significant increase in mean temperatures at hill stations is clearly visible. The analysis also reveals that the maximum temperature increase more rapidly than the minimum over the hill stations. Interestingly, the annual maximum temperature show a gradual increase up to 1970 and rapid increase during the period 1971-2010, while minimum temperature is trendless up to 1970 and after it shows an increasing trend up to 2010. This clearly indicates the effect of rapid urbanization on local temperatures, the scientists have said.

Dilip Kothawale and Nayana Deshpande from Pune based Indian Institute of Tropical Meteorology and Rupa Kolli who is part of the World Climate Applications & CLIPS Division of World Meteorological Organization based in Geneva, Switzerland have made these observations. They went through the temperature data of past 110 to 113 years (1901-2013). The data was of various kinds - like the monthly mean (average of maximum and minimum), maximum and minimum surface air temperature. The scientists collected data from 36 places across India, which they had divided into four categories viz. major cities with more than 20 lakh population, medium cities with population between 4 and 20 lakh, small cities with population below 4 lakh and the hill stations that are at an altitude more than 1000 metres.

Since hardly any of the hill stations in Maharashtra is at an altitude of more than 1000 metres, they do not figure in the study. However, the observations made are pertinent since similar trends, which have been used in the past century, are still being followed in development of hill stations in the state.

The scientists examined trends in seasonal and annual mean, maximum and minimum temperatures at major, medium, small cities and hill stations for the three different periods, viz. entire period (1901-2013), past period (1901- 1970) and recent period (1871-2013). They realized that during the past period, less than 50% stations from each group showed a significant increasing trend in annual mean temperature, whereas in the recent period, more than 80% stations from all groups except small city group showed a significant increasing trend.

Another study by V Vizaya Bhaska of IMD Pune, published in 2014 has studied the hydro climatic characteristics of 18 hill stations between 1961 and 2010, too shows that there has been a drastic decrease in rainfall at hill stations between 1981 and 1990. It also observed that only one of the 18 hill stations studied had conserved its climate during the study period.