Hydroclimatic changes in a climate-sensitive tropical region

Abstract

In this study, the hydroclimatic variables of Orissa, a tropical region in eastern India, and the cyclonic disturbances over the Bay of Bengal were analysed to assess trends and variations using nonparametric statistical procedures. The trend results revealed pronounced warming pattern in the monthly maximum temperatures and cooling pattern in the monthly minimum temperatures for the period 1987–2001. The differential forcing mechanisms of greenhouse gases and aerosols were considered as a reason for the temperature extremes. For the period 1960–2003, significant upward shift was observed in June rainfall, particularly over the region where orography influences the rainfall. This study provides strong evidence suggesting the occurrence of abrupt shifts in the cyclonic disturbances over the Bay of Bengal. For the period 1901–2003, the monsoon depressions and cyclonic storms, which contribute a substantial amount of rainfall in Orissa and central India, exhibited significant downward abrupt shifts during 1971 and 1950, respectively. However, severe cyclonic storms in the post-monsoon season showed significant upward shift during the 1961–1965 pentad. More cases of non-significant decreasing trends were observed in the monsoon rainfall for the period 1980–2003 in spite of high inter-annual variability. These trends may be attributed to the significant downward shift in the monsoon depression from 1983 onwards analysed for the period 1960–2003. Results also show that the observed trends are highly sensitive to the season of analysis and the period of records.