16-Jun-2021: Cold desert Ladakh was actively flooding during the post-glacial warming: Study
Scientists have shown that the cold desert of Ladakh Himalaya once experienced large floods that rose much above the present-day river level. It implies that in the scenario of global warming, when the higher Himalaya regions are expected to respond dramatically, flood frequency in Ladakh may increase, which may call for serious urban and rural planning.
Large floods that naturally occur in major rivers of India fed by melting snow and glaciers and a continental scale precipitation regime of Indian Summer Monsoon (ISM) and Westerlies and East Asian Summer Monsoon (EASM) significantly modify the landscape and impact lives and economy of all that encroached into its geomorphic domain.
These floods are of various kinds and origin (Glacial/landslide lake outbursts, cloud bursts, excessively strong monsoon) and have different forcing factors and frequencies and therefore add large uncertainty in flood prediction models. An instrumental record of these floods is of ~100 years is not enough to understand the natural ramp of flood occurrences in the Himalayas, and therefore archive going deep into time is required.
A team of students and scientists lead by the Wadia Institute of Himalayan Geology at Dehradun, an autonomous institute of the Department of Science & Technology, Government of India, travelled through the tough terrains of Zanskar and Indus drained Himalaya and looked minutely into geological signatures of past floods in Ladakh region that date between 15-3 thousand years before present. This study was recently published online in the Geological Society of America Bulletin.
Flood leaves a stack of fine sand and silts at places along its channel where the flood energy drastically reduces, for example, wider segments of river valleys, confluences, behind rock embayments which is called as Slack Water Deposits (SWDs). The SWDs were located at several locations along the Zanskar and Indus rivers, counted vertically for the number of floods, and were dated using technology called Optically Stimulated Luminescence (OSL) and Accelerator Mass Spectrometry of 14C. The flood deposits were also analysed for their source.
This analysis showed that the cold desert once experienced a large flood that rose to more than 30 m above the present-day river level. The active flood plains nearer to river were also utilized by Humans, possibly as camping sites and cooking as indicated by presence of hearths at several locations and levels of flood deposits.
The chronology of the flood deposits pointed towards three phases of increased flooding occurred in Ladakh after the period called Last Glacial Maximum (14–11, 10–8, and 7–4 (1000 years) or ka). These were times when due to warming, the Indian summer monsoon was active in Ladakh as well. The results also suggest that Ladakh floods are chronologically out-of-phase with those occurring in North-Eastern Himalayas and mainland China during the past 15 thousand years. This implies that the modern relationship between the ISM and EASM goes deep into more than 14 thousand years. Further, the rocks of Higher Himalayan Crystalline and Tethyan sequences equally act as hotspots of erosion in the regions during the flood phases.
The preliminary study of hearths suggested that there was an inbound migration of people along the mountain corridors of Ladakh after the Last Glacial Maximum when temperatures were relatively warmer, and hydrology of the region was supporting. According to the WIHG team, a detailed genomic and isotopic-based study of these anthropogenic relics may further help understand the geographical antiquity of migrating humans and the kind of food and vegetation they were living on.
14-Jun-2021: The Northern Limit of Monsoon (NLM) continues to pass through Diu, Surat, Nandurbar, Bhopal, Nowgong, Hamirpur, Barabanki, Bareilly, Saharanpur, Ambala & Amritsar
ALL INDIA WEATHER SUMMARY AND FORECAST BULLETIN
The Northern Limit of Monsoon (NLM) continues to pass through lat. 20.5°N/ Long. 60°E, Diu, Surat, Nandurbar, Bhopal, Nowgong, Hamirpur, Barabanki, Bareilly, Saharanpur, Ambala and Amritsar.
Due to approaching of mid-latitude westerlies winds further progress of monsoon over remaining parts of northwest India is likely to be slow. The progress of monsoon is being monitored continuously and further update will be provided on daily basis.
The Low Pressure Area lies over south Jharkhand & neighbourhood with the associated cyclonic circulation extending upto mid-tropospheric levels tilting southwestwards with height. It is likely to move west-northwestwards. A trough runs from west Rajasthan to northeast Bay of Bengal in lower tropospheric levels and another trough runs from East central Arabian Sea to south Konkan in mid tropospheric levels. An off shore trough at mean sea level runs from south Maharashtra coast to north Kerala coast.
Under the influence of above systems:
Fairly widespread to widespread rainfall with isolated thunderstorm & lightning over most parts of East, Central & Northeast India during next 4-5 days. Isolated heavy rainfall over the region during next 4 days and isolated extremely heavy falls also very likely over Bihar on 15th June.
Widespread rainfall with isolated heavy to very heavy falls, thunderstorm & lightning very likely over Konkan & Goa, Karnataka and Kerala & Mahe during next 4 days. Isolated extremely heavy falls also very likely over Konkan & Goa and Coastal Karnataka on 14th & 15th June.
Scattered to fairly widespread rainfall with isolated thunderstorm & lightning over most parts of Northwest India during next 3 days and decrease in rainfall activity thereafter except East Uttar Pradesh where fairly widespread rainfall is likely to continue. Isolated heavy to very heavy rainfall over East Uttar Pradesh during next 5 days and extremely heavy rainfall also very likely over East Uttar Pradesh on 15th June.
Moderate to severe thunderstorms accompanied by frequent cloud to ground lightning and strong gusty winds very likely over Uttarakhand, Uttar Pradesh, Madhya Pradesh, Rajasthan and Bihar on 14th & 15th; over Jharkhand on 14th; over Punjab and Haryana on 15th June. This may cause injuries leading to casualties to people and animals staying outdoors.
17-Dec-2020: Research reveals that Disturbance from North Atlantic could be possible reason why Indian monsoon derails in August; needs to be factored in to improve monsoon predictability
A planetary wave from the North Atlantic is capable of derailing the Indian monsoon on which the Indian economy is heavily dependent, suggests a study published in the journal Science.
The findings suggest that modelling efforts ought to focus on including the influence of mid-latitudes, in addition to the Pacific and Indian oceans, for getting a better handle on predictability of the monsoon, its variability as well as droughts.
A team from the Centre for Atmospheric and Oceanic Sciences (CAOS), Indian Institute of Science (IISc), who carried out the research, supported in part by DST under their climate change programme, showed that, in the past century, Indian monsoon droughts that occurred in non-El Niño years were sub-seasonal, as against El Niño droughts, where the deficit persists throughout the season.
The research team analysed daily rainfall during the two categories of droughts from 1900 to 2015 and noticed dramatic differences in the evolution of rainfall deficit. Rainfall deficit in El Niño droughts sets in early around mid-June and becomes progressively worse. By mid-August, the deficit is very high and spread across the country, with no sign of recovery.
During non-El Niño droughts there is a moderate decrease in June rainfall, followed by signs of recovery during mid-July to mid-August ‒ the peak of the season. However, in late August, there is an abrupt and steep fall in rainfall, resulting in drought conditions.
“We tried to trace this late August break to a forcing agent or system that influences the behaviour over India. We looked at the winds that were prevalent in these non-El Niño drought years,” said Jai Sukhatme, Associate Professor at CAOS, and one of the senior authors, in an IISC statement.
“The interaction between upper-level winds and deep cyclonic vorticity anomalies located above anomalously cold North Atlantic waters during late August to early September results in an atmospheric disturbance. This disturbance, a Rossby wave, curves in towards India and, apparently squeezed in by the Tibetan Plateau, disrupts the flow of the monsoon winds,” V Venugopal, Associate Professor at CAOS, and a co-author explained.
The atmospheric tele-connection studied in this paper whose first author was a PhD student Pritam Borah with DST inspire fellowship, offers an avenue for improved predictability of droughts, especially in the absence of tell-tale signs in the Pacific.
9-Jun-2021: Novel technique could help detect tropical cyclones for Bay of Bengal Basin earlier than satellites
Indian Scientists have found a promising technique for early detection of development or strengthening of tropical cyclones in the atmospheric column prior to satellite detection over ocean surface in North Indian Ocean region.
Early detection of Tropical cyclones has wide socio-economic implications. So far, remote sensing techniques have detected them the earliest. However, this detection was possible only after system developed as a well-marked low-pressure system over the warm ocean surface. A larger time gap between the detection and the impact of the cyclone could help preparation activities.
Prior to the formation of cyclonic system over the warm oceanic environment, the initial atmospheric instability mechanism, as well as the vortex development, is triggered at higher atmospheric levels. These cyclonic eddies are prominent features in the vertical atmospheric column encompassing the disturbance environment with a potential to induce and develop into a well-marked cyclonic depression over the warm ocean surface. They could be used for detection of prediction of cyclones
A team of Scientists including Jiya Albert, Bishnupriya Sahoo, and Prasad K. Bhaskaran from IIT Kharagpur, with support from the Department of Science & Technology, Government of India under the Climate Change Programme (CCP), devised a novel method using Eddy detection technique to investigate the formative stages and advance detection time of tropical cyclogenesis in the North Indian Ocean region. The research was published in the journal ‘Atmospheric Research’ recently.
The method developed by the scientists’ aims to identify initial traces of pre-cyclonic eddy vortices in the atmospheric column and track its Spatio-temporal evolution. They used coarser grid resolution of 27 km for identification and finer resolution of 9 km to evaluate the characteristics of eddy vortices. The study was conducted with cases of four post-monsoon severe cyclones –Phailin (2013), Vardah (2013), Gaja (2018), Madi (2013), and two pre-monsoon cyclones Mora (2017) and Aila (2009) that developed over North Indian Ocean.
The team observed that the method could bring about genesis of prediction with a minimum of four days (~ 90 h) lead time for cyclones developed during the pre-and post-monsoon seasons. Initiation mechanisms of genesis of tropical cyclones occurs at upper atmospheric levels and are also detected at higher lead time for pre-monsoon cases, unlike the post-monsoon cases. The study made a comprehensive investigation on the behavior of eddies in an atmospheric column for non-developing cases and compared these findings with developing cases.
The technique was found to have potential for early detection of tropical cyclogenesis in the atmospheric column prior to satellite detection over ocean surface.