Trend analysis of long-term climatic parameters in Dinhata of Koch Bihar district, West Bengal

Abstract

The monthly, seasonal and annual trends for five climatic parameters, such as rainfall, rainy days, temperature, relative humidity and sunshine hours were analyzed for the period of 1980–2015. The objective of this study was to detect the long term trend of climatic parameters of the study area. The non-parametric Mann–Kendall test and Sen’s slope estimators methods were used to determine whether there was a positive or negative trend in weather data with their statistical significance. The study area is characterized by high rainfall, receives an annual average rainfall of 3005 ± 820 mm, with an inter-annual variation 27% but analysis of long-term trends in the annual rainfall indicates a decreasing trend (− 14.31 mm year−1) and annual rainy days also significantly decreased (− 0.63 days year−1). In terms of seasonal rainfall, the pre-monsoon and monsoon months exhibited non-significant declining trends, while post monsoon months marginally increased. The result showed significant (P < 0.05) warming trend in annual minimum and mean temperature at the rate of 0.14 and 0.05 °C year−1 respectively and also showed similar significant (P < 0.05) increasing trend in summer (0.05 °C year−1) and winter (0.07 °C year−1) mean temperature. Decrease in maximum temperature during all the months except September and annual maximum temperature (− 0.04 °C year−1) is evident. The study area is experiencing a significant increasing trend in maximum (0.36% year−1), minimum (0.52% year−1) and mean relative humidity (0.13% year−1), with a significant decreasing trend of sunshine hours in pre monsoon (− 0.03 h day−1), post monsoon (− 0.04 h day−1) and mean (− 0.03 h day−1).