Observed trends and variations in rainfall events over Ratnagiri (Maharashtra) during southwest monsoon season

Abstract

The observed trends and variations in rainfall during southwest (SW) monsoon season (June to September) of individual station Ratnagiri, have been analyzed by using 30 years (1980-2009) daily rainfall data. The analysis revealed decreasing but not significant trend in total amount of rainfall and number of rainy days, with increasing but not significant trend in average intensity of rainfall during rainy days of monsoon season. To verify this increase in average intensity of monsoon rainfall over the region, the trends in frequency of occurrence of rainfall events and percentage (%) contribution of rainfall events, to total monsoon rainfall in different categories of rainfall event, along with decadal variation during monsoon season are analyzed. The trend shows that frequency of occurrence of rainfall events and % contribution of rainfall events to total monsoon rainfall in category of light, moderate, rather heavy and heavy rainfall events decreased (but not significantly), whereas frequency of occurrence of rainfall events and % contribution of rainfall events to total monsoon rainfall in category of very heavy to exceptionally heavy rainfall events increased (but not significantly) during 30 years (1980-2009) over Ratnagiri indicating that increase in average intensity of monsoon rainfall is contributed by very heavy to exceptionally heavy rainfall events.
Decadal analysis also shows that frequency of occurrence of rainfall events and % contribution of rainfall events to total monsoon rainfall in category of light, moderate, rather heavy and heavy rainfall events have decreased per decade. Whereas in category of very heavy to exceptionally heavy rainfall events it has increased per decade. This increased frequency of very heavy to exceptionally heavy rainfall events over the region may lead to an increase in frequency of floods, landslides and spoil agricultural crops and hence requires attention.