Evaluation of temporal and spatial trends in relative humidity and dew point temperature in Bangladesh

Abstract

Trend analysis of climatic variables on different spatial and temporal scales has been of great concern during the past century because of the attention given to global climate change by the scientific community. In this study, trends of the annual and seasonal relative humidity and dew point temperature time series have been investigated for 15 stations all over Bangladesh during 1961–2010. The magnitude of the climatic trends was derived from the slopes of the Sen’s estimator. The statistical significance of the trends was determined by means of the Mann–Kendall test. Pre-whitening was used to eliminate the influence of serial correlation on the Mann–Kendall test. The percentage of stations showing a significant trend is moderate in the case of relative humidity, but is a lot higher in dew point temperature series at the 95 % confidence limit. On average, relative humidity is increasing at 0.53, 0.86, and 1.18 % per decade on annual, winter, and pre-monsoon (summer) scales, respectively, in the western part of the country. Significant negative trends of relative humidity series are apparent in monsoon season. On the other hand, there is no significant decreasing trend in both annual and seasonal dew point temperature time series at any station. Again, a higher magnitude of the significant trends is observed in the western part of the country. The majority of the slopes are above zero, indicating an increasing nature in annual and seasonal dew point temperatures over Bangladesh. This warming of dew point temperature in Bangladesh is analogous to the global trend.