Study Reveals Southward Shift of Precipitation Extremes over South Asia

Has your monsoon experience across India changed over the years?

The reason could be blamed on shifts in the spatio-temporal pattern of monsoon. In a recent study published in Scientific Reports by Nature Publishing Group, IIT Kharagpur researchers reveal that the pattern of monsoon and daily extreme rainfall is changing in India with more extremes expected over southern India and Himalayan foothills. They further predicted a continued southward shift of precipitation extremes over South Asia. 

The researchers have studied data of Indian Summer Monsoon precipitation for close to five decades, 1971 – 2017 (base period: 1930-1970). The data shows more increase in the magnitude of extreme precipitation over South India  (~18.5 mm/day for the worst climate change scenario) compared to Northern and Central India (~2.7 mm/day). 

“Our analysis of precipitation from the Coordinated Regional Downscaling Experiment, indicates a southward shift of precipitation extremes over South Asia. For instance, the Arabian Sea, South India, Myanmar, Thailand, and Malaysia are expected to have the maximum increase to about 18.5 mm per day for an RCP8.5 scenario in mean extreme precipitation,” said lead researcher Prof. Rajib Maity from the Dept. of Civil Engineering. 


Refer to the journal paper: Suman, M., Maity, R. Southward shift of precipitation extremes over south Asia: Evidences from CORDEX data. Sci Rep 10, 6452 (2020). https://doi.org/10.1038/s41598-020-63571-x


PhD student Mayank Suman, co-author added, “We based our predictions on average precipitation for the days with more than 99th percentile of daily precipitation. Our study showed a contrasting feature for North and Central India, and Tibetan Plateau with relatively less increase, to only about 2.7 mm per day for RCP8.5 scenario.”

Talking about the possible reason behind such a significant phenomenon, Prof. Maity remarked on the intensification of large-scale circulation phenomena over the tropical Indian Ocean (known as Indian Ocean Dipole) which could be leading to the contrasting trends across large regions in India. As a result of this intensification the Indian monsoon is expected to be enhanced across the country. The prediction is based on the analysis of air temperature at 850 mb and precipitable water for RCP4.5 and RCP8.5.

“Our convergence analysis along with the moisture flux show a change in the direction of the South-West Monsoon winds blowing towards the east over the Indian Ocean. This directional change will intensify the already observed precipitation contrast in future between South and North India, and cause more extreme precipitation events in countries like Myanmar, Thailand, Malaysia, etc.” remarked Prof. Maity

What could be the socio-economic impact of such change, particularly in the context of India? 

Prof. Virendra Tewari, Director, IIT Kharagpur, who has extensively worked with both industrial and rural sectors opined on getting ready for the monsoonal shifts based on predicted timelines and precipitation volume.

“South Asia, as we know, despite advances in irrigation systems, is highly dependent on the monsoons. Results of this study will be useful to the designers of water infrastructure and agricultural communities, especially in the southern parts of India and Himalayan foothills, to prompt a possible change in design criteria and agricultural practices including cropping pattern,” he said. 


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Project information: Prof. Rajib Maity, Dept. of Civil Engineering,rajib@civil.iitkgp.ac.in

Institute Information: Prof. B N Singh, registrar@hijli.iitkgp.ac.in;

Media Outreach: Shreyoshi Ghosh, shreyoshi@adm.iitkgp.ac.in

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A New Page in India’s History

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A breakthrough discovery by a study led by IIT Kharagpur has made the colourful Rann Festival of Gujarat a little more vibrant. The researchers have uncovered the earliest traces of the Old Iron Age which is older than 3000 years in the deep stretches of the Rann of Kutch and the Thar Desert. Most importantly the study reaffirmed the theories of human migration from the west to the east induced by climate change.

The region of Gujarat has been a part of many tales from the times of our mytho-history through various historical periods until modern times. Even the Harappan period can be traced to a few rocky islands in the Kutch region of Gujarat. However, till now the Rann which is a prominent geological feature of Gujarat was devoid of any sign of continued human settlement throughout the Early Iron Age to Early Historic Age (~3100 – 2300 years). The lack of evidence even led archaeologists term this period as ‘Dark Age of Gujarat’.

The recent explorations in the coastal settlement of Karim Shahi region of the Rann near Indo-Pak border, led by Prof. Anindya Sarkar from the Dept. of Geology and Geophysics at IIT Kharagpur, however, have unraveled the secrets behind this curtain of silence. The team has found the earliest evidence of human habitation dating back to 3000 years. They also found evidence of Historic to Medieval (~1500–900 years old) human settlement at Vigakot in the Thar Desert.

“We were conducting geological investigations for finding out the past climate change during and after the collapse of Harappan civilization funded by the INFOSYS foundation and IIT Kharagpur. During our explorations we came across numerous archaeological artefacts strewn over the surface of Karim Shahi and Vigakot,” said Prof. Sarkar.

The most intriguing finding is how the human habitation thrived in such water-deprived inhospitable terrain and survived from Iron Age to Medieval period although major Harappan cities were abandoned by that time, he opined. The researchers also did a total station survey to determine the landscape.

“What seems to be an arid landscape today have indications of an active river system and some amount of rainfall during that period as evidenced from the analysis of sediments, botanical remains like pollens and isotopes of oxygen in fossil molluscan shells,” said collaborator Dr. Navin Juyal from Physical Research Laboratory, Ahmedabad.

The researchers also referred to the historical travelogue of Al Beruni of 1030 AD which mentioned the presence of rivers in Kutch.

“Our study suggests that the Rann of Kutch and part of Thar desert were still a hospitable terrain for the sustenance of human settlements from the Early Iron Age till at least medieval times which led to the survival of the civilization under such climate threat situation following the Harappan decline,” he said.

It is long known that from Mature to Late Harappan period (5200 to 3300 years) the number of human settlements continuously increased from the Indus River valley in the west to the Ghaggar-Hakra in the east. This migration following the collapse of the old Indus Valley (Harappan) civilization has been attributed to the decline of monsoon or major droughts by many scientists. But what happened to the people after such collapse? Little is known about the people after the post-urban Harappan period. Some archaeologists believe that there was no demographic collapse as such. Rather populations persisted in smaller less complex settlements dispersed from the original river valleys of the Indus and Ghaggar-Hakra to more distant areas of the Ganga-Yamuna interfluves or Gujarat and Rajasthan until 3000 years before the present time. In northern India new kind of civilization rose afterward, namely, the Iron Age (or Painted Gray ware) between ~3000 and 2500 years before the present time that was followed by the Kushan period (~1900–1500 years).

“This was indeed a very critical transition, wherein human migration, as suggested by our findings, was far more expansive than thought before. We suspect that the gradual shift of Intertropical Convergence Zone, the main driver of monsoon from west to east over the last seven thousand years, forced people to migrate for greener pastures,” remarked Prof. Sarkar.

An earlier study by Prof. Sarkar on Haryana’s Bhirrana region had shown human migration from west to east due to the weakening of the monsoon. In a way, this created large climate refugees who took refugia were still some little rainfall was available.

“The United Nations framework convention on climate change and high commissioner for refugees in its report warned about such climate refugees due to impending climate change. If it could have happened in the past it will happen in the future too” reminded Prof. Sarkar.

Apart from the climatic conditions and sustenance of the settlements, the researchers have been successful in stitching a critical section of India’s Iron Age history which lay buried under the deep stretches of the Rann. The recovery of artefacts like pitcher, jars and bull figurines and also numerous animal remains like bones, teeth etc. have helped in reconstructing the social subsistence pattern of the region during the study period confirmed co-researcher Dr. Arati Despande Mukherjee from Deccan College PGRI Pune. The earliest evidence of Iron Age found in Gujarat till now was 2500 years old which has now been pushed back by several centuries in antiquity. At Motichher, a place close to Karim Shahi, iron objects, nuggets, and slags have been found and which would need further investigation. The researchers acknowledged the Indian Army for facilitating the explorations. The areas are so remote and close to an international border that no scientific investigation could have been carried out without the permission of the Indian army.

Talking about a probable occupation of those people, Prof. Sarkar remarked, “both Karim Shahi and Vigakot probably acted as trade centers during this time. In fact, at Vigakot we found 1100 years old Chinese Qingbai porcelain probably manufactured in Guangdong province of south China and Sgraffiato potteries of 10th century Persia suggesting it to be a part of long-distance trade between West Asia and China”.

Prof. M.G. Thakkar from Kutch University and a collaborator emphasized the fact that the multidisciplinary study has proven the near-cultural continuity after the Harappans which the experts till now only hypothesized. He also harped on the point that this finding is going to bring Kutch under international limelight.

The findings have been published online in the prestigious Elsevier journal ‘Archaeological Research in Asia’. Download Paper

Graphic Credit: Suman Sutradhar

New Indian Monsoon Rainfall Prediction Model Developed by IIT KGP Researchers

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Researchers from Centre for Oceans, Rivers, Atmosphere and Land Sciences (CORAL) of IIT KGP have developed a new statistical model, which can be used to predict variability and trends in rainfall over different climate regions of India taking into consideration both local and remote factors causing weather change.

Many of these, local and remote, factors that affect weather conditions have been known to the scientific community. However, most weather forecast models typically consider local factors or a single factor that affects rainfall or use of statistical models of correlation to establish the impact of various factors. Because of this there used to be significant uncertainties in such predictions as each independent factor has a certain impact, which may not match with actual conditions.

“In our model we have used the multiple linear regression technique to assess contributions of different remote and local climate forcing to seasonal and regional inhomogeneity in rainfall. It removes the impact of individual factors to find the trends in rainfall. The model has three advantages; it can be used to find the contribution of individual factors to the rainfall and can be applied to estimate the trends and variability of rainfall. Apart from these, the model can predict any type of weather conditions, anywhere in the world only by changing the relevant factors affecting the changes. For instance, we have used a similar model for estimating trends in atmospheric trace gases such as ozone,” said Dr. Prijitha J. Nair, the lead researcher, who conceived and coordinated this study.

The novelty of the model has been reported through a research paper “The local and global climate forcing induced inhomogeneity of Indian rainfall” in the much-coveted Scientific Reports by the Nature.

“Our study finds that the Summer Monsoon Rainfall variability is governed by the surface temperatures of the Eastern Pacific, Central Pacific, Atlantic and the north Indian Oceans, and equatorial zonal winds. However, the winter Monsoon Rainfall variability is largely controlled by the surface temperature of the North Atlantic and extratropical oceans,” explained co-researcher Prof. Jayanarayanan Kuttippurath.

The model, which has been developed using data over a period of 38 years, has also predicted significant changes in Indian rainfall in a perspective of global climate change. The data analyses conducted during the study revealed significant positive trends (0.43mm/day/dec) in the North West for summer rainfall during the 1979–2017 period.

“There are scientific evidences of major climate shifts over centuries. These do not happen overnight but through gradual changes in weather conditions over time. The data shows there has been an incremental shift of Indian monsoon from east to west. However, this would require further studies,” said Prof. Arun Chakraborty, who supervised the research.

Dr. Hamza Varikoden, a scientist from the Indian Institute of Tropical Meteorology (IITM), Pune, and Dr. P. A. Francis, a scientist in the Indian National Centre for Ocean Information Services (INCOIS), Hyderabad (both are from the Ministry of Earth Sciences and are renowned for their significant contributions to Indian Monsoon research), are the other researchers participated in the study.