• SHRUTI VERMA

Articles written in Journal of Earth System Science

• Evolution of extreme rainfall events over Indo-Gangetic plain in changing climate during 1901–2010

Due to climate variability and climate change there is an increase in magnitude and frequency of extreme precipitation events. During the last few decades these extreme rainfall events have been increased in global as well as on regional scale. Our climate is very much affected by the changes in frequency of extreme rainfall events. Particularly, variability of extreme rainfall events has been studied over one of the most valuable Indian region i.e. over Indo-Gangetic plain (IGP). Long term trend in extreme events has been analyzed with the help of IMD classification. The classification is considered for moderate rain (2.5–64.4 mm; category I), heavy rain (64.5–124.4 mm; category II) and very heavy rain (124.5 mm or more; category III) and the categorization of rainfall events is based on daily rainfall for the period 1901–2010 during Indian summer monsoon (JJAS). The significant long term trend in frequency of extreme rainfall events is analyzed using the statistical test. Long term trend analysis shows the significant decreasing trend for categories II and III. However, an increasing rainfall frequency is observed for moderate rainfall events (category I) during the considered period. A significant interannual and inter-decadal fluctuation in rainfall frequency and magnitude were observed over IGP. Events of moderate and heavy rainfall increases during the withdrawal period of Indian summer monsoon, which might contribute in several cases of flood in the region of IGP. In term of distribution and contribution of rainfall in agriculture area categories I and II, rainfall events are more important but changes in rainfall pattern may lead to flood and drought risk over IGP. The policy making decision for disaster risk and food security should be based on spatial as well as temporal variability of rainfall pattern over IGP region.

• Abrupt changes in mean temperature over India during 1901–2010

Since eternity, the Earth’s temperature has varied or fluctuated; it has its cooling and hot timing dependency on its orbital position as well as the isolation received from the Sun. The global climate continues to change rapidly compared to the speed of the natural variations in climate. Therefore, the spatially complete representations of surface climate are required for many purposes in applied sciences. But in recent centuries, the main matter of concern is that Earth’s normal temperature fluctuation is being influenced by some external factors such as enhanced greenhouse gases because of extreme uses of fossil fuels, severe industrialization, advance urbanization, etc. This study presents a comprehensive surface temperature dataset of Climatic Research Unit (CRU) available since 1901 for India, which is used to document significant changes in Indian temperature over ten decades, during winter season (January and February), pre-monsoon (March–May), monsoon (June–September) and post-monsoon (October–December) to examine the patterns and possible effects of global warming. A strong increasing pattern is observed with the fast growing of the development after 1950 which has shown nearly doubled in the last 50 yrs. The mean temperature during winter for the 2000s shows a consistent pattern of warming over the Himalayan region, northwestern and southern India, and a pattern of the warming observed over northeastern India and extending southwestward across central India during post-monsoon.

• Assessment of climate change of different meteorological state variables during Indian summer monsoon season

Long-term assessment of basic meteorological field variability is an important factor that influences the Indian summer monsoon and consequently affects the socio-economic aspects of India. In this study, the spatial and temporal variation of meteorological parameters during summer monsoon season using NCEP/NCAR reanalysis datasets for the period of 70 years (1948–2017) has been analyzed in climatology, early-late phase and multidecadal epochs over India and its regions. Statistical techniques such as the standardized anomaly index of surface temperature, rainfall and zonal and meridional wind (at 850 and 200 hPa) and temporal analysis of Mann–Kendall trend test over six selected regions, viz., NorthIndia (NI), Central India (CI), Southern India (SI), Arabian Sea (AS), Bay of Bengal (BoB) and Equatorial Indian Ocean (EIO) reveal higher variability during summer monsoon season from 1948 to 2017. The significant spatial changes in the value of standard deviation and coefficient of variation confirm the early-late phase and multidecadal modulation of the seasonal variability of selected climatic parameters. The results indicate that the escalation in the surface temperature multidecadal variability and trend has dominating characteristics over NI, CI and SI regions at an alarming range (0.5–1.0°C). The major hotspots of increasing early-late phase and multidecadal variability and average precipitation have been found over BoB, EIO and SI (${\sim}$1–3.5 mm/day). The decreasing changes in the mean rainfall pattern and associated variability is strongly linked with increasing surface warming and significant reduction in the strength of surface zonal wind over BoB, IO, SI and CI region which cause the weakening of important atmospheric circulations such as the role of Somali jet and strong low-level jet (LLJ) during Indian summer monsoon season. Also, the meridional wind at the surface and upper level has shown significant enhancement over AS and EIO. The recent decadal anomaly (2008–2017) is really a matter of concern as precipitation and wind circulation anomaly at 850 and 200 hPa have shown decreasing trends over all the regions. In recent years, the variation in meteorological parameters and distribution are asymmetrical during summer monsoon season in changing climate.

• # Journal of Earth System Science

Volume 132, 2023
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Posted on July 25, 2019

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