Characteristics of occurrence of heavy rainfall events over Odisha during summer monsoon season

Abstract

During summer monsoon season heavy to very heavy rainfall events have been occurring over most part of India, routinely result in flooding over Indian Monsoon Region (IMR). It is worthwhile to mention that as per Geological Survey of India, Odisha is one of the most flood prone regions of India. The present study analyses the occurrence of very light (0�2.4 mm/day), light (2.5 � 15.5 mm/day), moderate (15.6 � 64.4 mm/day), heavy (64.5 � 115.4 mm/day), very heavy (115.5 � 204.4 mm/day) and extreme (? 204.5 mm/day) rainy days over Odisha during summer monsoon season for a period of 113 years (1901 � 2013) and a detailed study has been done for heavy-to-extreme rainy days. For this purpose, India Meteorological Department (IMD) gridded (0.25� � 0.25� lat/lon) rainfall data and the European Centre for Medium-Range Weather Forecasts (ECMWF) Re-Analysis (ERA-Interim) (0.125� � 0.125� lat/lon) datasets are used. The analysis reveals that the frequency of very light, light and moderate rainy days persists with almost constant trend, but the heavy, very heavy and extreme rainy days exhibit an increasing trend during the study period. It may be noted that more than 60% of heavy-to-extreme rainy days are observed in the month of July and August. Furthermore, during the recent period (1980�2013), there are a total of 150 extreme rainy days are observed over Odisha, out of which 47% are associated with monsoon depressions (MDs) and cyclonic storms, 41% are with lows, 2% are due to the presence of middle and upper tropospheric cyclonic circulations, 1% is due to monsoon trough and other 9% of extreme rainy days does not follow any of these synoptic conditions. Since a large (nearly half) percentage of extreme rainy days over Odisha is due to the presence of MDs, a detailed examination of MDs is illustrated in this study. Analysis reveals that there are a total of 91 MDs formed over the Bay of Bengal (BoB) during 1980 � 2013, and out of which 56 (61.5% of total MD) MDs crossed Odisha. Further spatial analysis of extreme rainfall days exhibits that the maximum frequency of extreme rainy days is present over the south west region of Odisha. � 2018 Elsevier B.V.