Recent Variability and Trends in Temperatures over India

Abstract

Present paper focuses on the variability and trends in annual, seasonal and monthly maximum and minimum temperature and other temperature parameters over India as a whole and over different homogeneous region designated as Western Himalaya (WH), North west (NW), North central (NC), Northeast (NE), Interior Peninsula (IP), East coast (EC) and West Coast (WC) during the period of 1975 to 2007. Analysis on the variability and trends in temperature is also presented over widely spaced 23 stations in different subdivision over India. Using the percentile values (extreme temperature indices), the number of hot and cold days in daily maximum temperature and number of hot and cold nights in daily minimum temperature were calculated for every month, season and year during the entire period of study. Annual mean temperature over India as a whole is observed to be 24.5oC with inter-annual variability of 1.1%. Diurnal temperature range (DTR) is found to vary by 1.73% over the India as a whole. The DTR during post monsoon season is most variable compared to other seasons over country. Variation in minimum temperature is higher than the maximum temperature over the country as a whole and in its homogeneous regions. Highest variability in annual mean maximum and minimum temperature is observed in WH region and most significant and accelerated increase in day and night temperature is also observed at the rate of 0.620C and 0.400C/decade in WH region. Annual mean maximum temperature is also significantly increasing in WH, NW and in WC regions while annual mean minimum temperature showed positive and significant trend in WH, NW, NC, NE and WC. Annual frequency of hot days showed comparatively increasing at higher rate in the subdivisions situated in peninsular and southern part of country. Significant and fastest increase in hot days is found during monsoon season at the rate of 2.1 days/decade. Occurrence of hot nights is observed to be significantly increasing annually at more accelerated rate in northern India. Annual frequency of cold night over the country as whole clearly showed significant decreasing trend at the rate of 9.0 days /decade. All the seasons in country as whole showed significant declining trends in frequency of cold nights and steeper decline is found in monsoon season.