Medium‐range forecasts of extreme rainfall events during the Indian summer monsoon

Abstract

Extreme rainfall events occur rarely but are integral elements of climatic conditions in any region. The frequency of occurrence of extreme events has been studied using 57 years of observed rainfall data over India and its neighbouring countries. In this study, the rank method has been used to compute the threshold rainfall amount based on past observations. If the model forecasted rainfall is above the climatological threshold, then that event is identified as an extreme at that grid point and for that specific day. The results show an increasing trend in the number of extreme weather events during monsoons. The National Centre for Medium Range Weather Forecasting (NCMRWF) uses the Unified Model (NCUM) for operational weather forecasting on a medium-range timescale. The capability of the model in predicting extreme rainfall events over India and its surrounding regions has not been evaluated so far. Therefore, this study has been undertaken to identify extreme rainfall events from the medium-range rainfall forecasts and compare the same with observations so that forecasts for extreme events can be obtained. The rank method has been applied to the NCUM forecast of rainfall during the period June to September 2014. Several extreme rainfall cases are identified during this monsoon. The frequency of occurrence of extreme events is compared with observations, and it is found that the model has reasonable skill to predict up to day three forecasts. However, this skill reduces when the forecast period length increases.

Assessment of two versions of regional climate model in simulating the Indian Summer Monsoon over South Asia CORDEX domain

“…ISMR exhibits significant temporal and spatial variability (Mooley and Parthasarathy 1984;Thapliyal and Kulshrestha 1991;Kripalani and Kulkarni 2001;Sahai et al 2003;Naidu et al 2015). Several scientists have investigated the inter-annual and intra-seasonal variations of monsoon rainfall and the associated phenomena over the last several years using observed data (Webster et al 1998;Gadgil et al 2003) and conducting modeling studies (Ratna et al 2011;Satyanarayana and Kar 2016;Pattnayak et al 2016a). The key features of Indian summer monsoon include the sudden onset and gradual withdrawal, which signify the beginning and end of the rainy season respectively.…”

Decreasing southwest monsoon rainfall over Myanmar in the prevailing global warming era

“…The region of highest rainfall coincides with the windward side of the prevailing monsoon southwesterlies; this is due to the earlier onset of the SWM over this region by at least 10 days as observed by Htway and Matsumoto (). While this distribution agrees with the earlier studies (Satyanrayana and Kar, ) where the distinction of south and north regions was identified, this study brings out an additional feature that the rainfall is maximum over the southwest coastal regions decreasing towards the northeast. A small region at the centre with minimum rainfall of <1,000 mm agrees with the arid zone reported by Roy and Kaur ().…”

“…APHRODITE rainfall data have been used in several research studies (e.g. Wang et al ., ; Yasutomi et al ., ; Lauri et al ., ; Pai et al ., ; Yatagai et al ., ; Satyanrayana and Kar, ). Monthly rainfall data for the period 2001–2010 at six stations in Myanmar were used for validating the APHRODITE rainfall data used in the present study.…”

“…APHRODITE rainfall data have been used in several research studies (e.g. Wang et al, 2011;Yasutomi et al, 2011;Lauri et al, 2014;Pai et al, 2014;Yatagai et al, 2014;Satyanrayana and Kar, 2016)…”

Variability and Trends of Rainfall Events in the Brahmaputra Valley of Assam

“…There are several studies in India on the variability of rainfall and its long term trends (Parthasarathy and Dhar, 1975;Mooley and Parthasarathy, 1984;Sarkar and Thapliyal, 1988;Thapliyal and Kulshresthra, 1991;Guhathakurta and Rajeevan, 2008;Krishnakumar et al, 2009;Kumar et al, 2010;Jain and Kumar, 2012;Bhatla and Tripathi, 2014;Das et al, 2015;Deka et al, 2016;Kothawale and Rajeevan, 2017;Sharma and Singh, 2017). Similarly, there are several studies which focused mainly on the intensity and trends of extreme rainfall events over India, Rakhecha andSoman (1994), Sen Roy andBalling (2004), Joshi and Rajeevan (2006), Rajeevan et al, (2008), Guhathakurta et al, (2010), Gill et al, (2013), Satyanarayana and Kar (2016) and Talchabhadel et al, (2018), to name a few. However, there are only a few studies available on the rainfall variability and trends over northeast India (Das and Goswami, 2003;Das et al, 2011;Deka et al, 2013;Jain et al, 2013;Das et al, 2015;Deka et al, 2016).…”