The occurrence of exceptionally heavy rainfall events and associated flash floods in many areas during recent years motivate us to study long-term changes in extreme rainfall over India. The analysis of the frequency of rainy days, rain days and heavy rainfall days as well as one-day extreme rainfall and return period has been carried out in this study to observe the impact of climate change on extreme rainfall events and flood risk in India. The frequency of heavy rainfall events are decreasing in major parts of central and north India while they are increasing in peninsular, east and north east India. The study tries to bring out some of the interesting findings which are very useful for hydrological planning and disaster managements. Extreme rainfall and flood risk are increasing significantly in the country except some parts of central India.
Meteorological drought during the southwest monsoon season and for the northeast monsoon season over five meteorological subdivisions of India for the period 1901-2015 has been examined using district and all India standardized precipitation index (SPI). Whenever all India southwest monsoon rainfall was less than −10% or below normal, for those years all India SPI was found as −1 or less. Composite analysis of SPI for the below normal years, viz., less than −15% and −20% of normal rainfall years indicate that during those years more than 30% of country's area was under drought condition, whenever all India southwest monsoon rainfall was -15% or less than normal. Trend analysis of monthly SPI for the monsoon months identified the districts experiencing significant increase in drought occurrences. Significant positive correlation has been found with the meteorological drought over most of the districts of central, northern and peninsular India, while negative correlation was seen over the districts of eastern India with NINO 3.4 SST. For the first time, meteorological drought analysis over districts and its association with equatorial pacific SST and probability analysis has been done for the northeast monsoon over the affected regions of south peninsular India. Temporal correlation of all India southwest monsoon SPI and south peninsular India northeast monsoon SPI has been done with the global SST to identify the teleconnection of drought in India with global parameters.
The study is an attempt to analyze the extreme rainfall events of Andhra Pradesh, a coastal state of Peninsular India, where both monsoon and post-monsoon seasons contribute significant rain. A network of 155 stations having data of seventy years or more during the period 1901-2000 has been used for the study. These stations are well distributed over the state. One-day, two-day and three-day extreme annual rainfall series are made and the isohyetal analysis demarcates three heavy rainfall receiving zones. Probability distribution functions have been fitted for the regional estimates of climate changes in extreme rainfall series of each station. Both the extreme value distribution viz., Gumbel and log normal distribution fit well with latter one giving slightly better fit over the former. Goodness of fit of the distribution is tested with Kolmogorov - Smirnov Statistic.
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