The long-term trend in the diurnal temperature range over Sri Lanka from 1985 to 2017 and its association with total cloud cover and rainfall

Abstract

This study is focused on studying the long-term trend of the diurnal temperature range (DTR) in three temperature zones in Sri Lanka using daily maximum and minimum temperature data set for the recent 33-year (1985–2017). We investigate the potential reasons for the long-term trend in the DTR by studying the response of the DTR to Total Cloud Cover (TCC) and rainfall on a seasonal basis. On an annual basis, results indicate that the DTR significantly decreased per decade by −0.14 °C, −0.16 °C, and −0.18 °C over the high elevation temperature zone (HT), low-elevation temperature zone one (LT-2), and low elevation temperature zone two (LT-2), respectively. The annual decreasing trend of DTR in three temperature zones is mainly due to the larger increase in minimum temperature over the HT (0.13 °C/decade), LT-1 (0.23 °C/decade), and LT-2 (0.14 °C/decade) zones than the maximum temperature from 1985 to 2017. Furthermore, a decreasing trend in DTR is observed during the southwest monsoon (SWM), first inter-monsoon (FIM), second inter-monsoon (SIM), and northeast monsoon (NEM) seasons, where the most prominent decreasing trend in HT, LT-1, and LT-2 is seen in NEM (−0.19 °C/decade), SIM (−0.24 °C/decade), and SWM (−0.40 °C/decade) seasons, respectively. The strong inverse correlation between the DTR and TCC in all seasons indicates that increasing TCC influences the decrease in DTR over the HT, LT-1, and LT-2 zones. Concomitant increasing trends in rainfall during NEM, FIM, and SIM seasons may be one of the possible causes of the DTR decreases in the aforementioned seasons over three temperature zones in Sri Lanka.