Changes in the characteristics of rain events in India

Abstract

[1] Daily gridded (1°Â 1°) rainfall data prepared by the India Meteorological Department for the period have been used in this study to examine possible changes in the frequency of rain events in India in terms of their duration and intensity per day. So far as the duration is concerned, a rain event is classified as short, long, dry, or prolonged dry spell. Similarly in terms of intensity, a rainy day is considered as low, moderate, or heavy. Changes in the frequency of these events have great relevance from the point of view of climate change. Threshold and limiting values for defining the heavy and moderate rain days are calculated in accordance with the gamma probability distribution. Results show that the frequencies of moderate and low rain days considered over the entire country have significantly decreased in the last half century. On the basis of the duration of rain events it is inferred that long spells show a significant decreasing trend over India as a whole while short and dry spells indicate an increasing tendency with 5% significance. The characteristics of rain events are also examined over six homogenous rainfall zones separately since the spatial distribution of rainfall over India shows large variability. In this study, the changes in the frequencies of different categories of rain events suggest weakening of the summer monsoon circulation over India. This hypothesis of a weakening of monsoon circulation is supported by significant reduction in the 850 hPa wind fields in the National

Variation in the orographic extreme rain events over the Meghalaya Hills in northeast India in the two halves of the twentieth century

“…However, it should be mentioned that Goswami et al (2010), in their analysis of daily rainfall data from 15 stations between April and October in NE India, for the period from 1975 to 2006, found a decreasing trend of extreme events with more than 150 mm rainfall per day and that this exceeded the 99th percentile. This is in contrast to a detected increasing trend of such events in central India (Goswami et al 2006) and in the whole of India (Dash et al 2009;Dash et al 2011).…”

“…These stable conditions are seen not only on a regional scale but also at subdivision and station levels (Prokop and Walanus 2003;Dash et al 2012;Jain et al 2013). Dash et al (2009), using highresolution daily gridded rainfall data for the period , examined the changes in the number of rain events of different durations and intensities in the whole of India as well as over its homogeneous regions. They found that the frequency of heavy rain days and moderate rain days increased and decreased, respectively (significant at 5 % level), in northeast India in both the monsoon and post-monsoon seasons.…”

Trends in Precipitation Characteristics in Bangladesh from 1950 to 2008

“…Goswami et al (2006) found that the frequency and intensity of extreme rainfall increased in central India for the period 1951−2004. Dash et al (2009) demonstrated that heavy precipitation days increased in central northeast and northeast India during the monsoon season for the period 1951−2004, and moderate rain days decreased in these regions. In contrast to Dash et al (2009), Goswami et al (2010 reported that extreme rain event frequency tended to decrease at 15 stations in northeast India from 1975.…”

“…Dash et al (2009) demonstrated that heavy precipitation days increased in central northeast and northeast India during the monsoon season for the period 1951−2004, and moderate rain days decreased in these regions. In contrast to Dash et al (2009), Goswami et al (2010 reported that extreme rain event frequency tended to decrease at 15 stations in northeast India from 1975. Shahid (2010 analyzed trends in annual and seasonal precipitation for the period 1958−2007 in Bangladesh, and showed that the annual and pre-monsoon precipitation increased at the rates of 5.53 and 2.47 mm year −1 , respectively.…”

“…For Asian countries, trends in precipitation characteristics were investigated for India (Sen Roy and Balling 2004;Goswami et al 2006;Goswami et al 2010;Dash et al 2009), China (e.g., Zhai et al 2004;Endo et al 2005), and some other Southeast Asian countries (Choi et al 2009;Endo et al 2009). Goswami et al (2006) found that the frequency and intensity of extreme rainfall increased in central India for the period 1951−2004.…”