Tag Archives: monsoon

Aerosols increase drought severity over the Indian subcontinent

Abhay S.D. Rajput

Global view of fine aerosol particles (courtesy: earthobservatory.nasa.gov)

Pune: A team of atmospheric scientists from India, USA and Canada have found that aerosols in the atmosphere can increase the severity of droughts over the Indian subcontinent by as much as 17 per cent during El Nino years.

The team led by Dr.Suvarna S. Fadnavis of the Indian Institute of Tropical Meteorology (IITM), Pune has reported this in a new study published in Scientific Reports.

The El Nino phenomenon, which occurs when there is abnormal warming over the Pacific Ocean – is already considered as a deterrent for the Indian monsoon on the ground that it blocks the flow of moisture bearing winds from the oceans to the Indian landmass.

The new study has found that it further weakens the monsoon by transporting aerosols from the lower altitudes in East Asian region up and into the higher altitudes (12-18 km) forming an aerosol layer called Asian Tropopause Aerosol Layer (ATAL) over South Asian region. It remains hanging over there during monsoon. The thickening of this aerosol layer results in reduction in the amount of solar energy reaching the earth thus weakening the monsoon circulation and increasing the severity of drought conditions.

“The El Niño itself leads to a decrease in rainfall over India and the inclusion of aerosols further amplifies this decrease. Our study reveals that the combined effect of El Nino and aerosols produces an aggravated subsidence in rainfall over the Indian region compared to the individual effect of El Niño. By using satellite observations and a series of model simulations, we found that the severity of droughts during El Niño years over the Indian subcontinent is amplified by 17%”, said Dr. Fadnavis.

Noting that in recent decades there has been an increase in the frequency of El Nino events and the frequency of droughts over India, the researchers warned against any further increase in industrial emissions and thus aerosols from both East and South Asia. It can lead to a wider and thicker aerosol layer in the upper troposphere and potentially further amplify the severity of droughts.

“When India is already vulnerable to hydrological and weather extremes, the combined effect of El Nino and aerosols in increasing drought severity will only subject India to more hydrological stress, while affecting agriculture and the livelihood of millions of people. Reducing aerosol emissions is not only essential for improving air quality, but also for reducing drought conditions and avoiding negative consequences for millions of people living in the Indian subcontinent”,Dr.Fadvanis added.

Besides Dr. Fadnavis, the study team included T.P. Sabin and Chaitri Roy of Indian  Institute of Tropical Meteorology, Mathew Rowlinson and Alexandru Rap of School of Earth and Environment, University of Leeds, UK, Jean-Paul Vernier of National Institute of Aerospace, and NASA Langley Research Center, Virginia, USA, and Christopher E. Sioris of Air Quality Research Division, Environment and Climate Change, Toronto, Canada. (India Science Wire)


Twitter handle: @abhaysdr

Block level weather forecasts all over India by 2019

T.V.Venkateswaran and Jyoti Singh

New Delhi: The much expected south west monsoon has arrived ahead of its scheduled arrival date and is begun its four-month long over the Indian landmass.

The India Meteorological Department (IMD) under the Ministry of Earth Sciences (MoES) is tasked with keeping a track of the annual phenomenon and issue regular bulletins for the benefit of people. Since its inception in 1875, IMD has been striving to understand the phenomenon of monsoon and provide timely advance information on how the system would unravel.

In 1886, just 11 years after it was established, IMD came out with a monsoon forecast thus making India the first country in the world to introduce such a system of season-wise forecast. The model adopted for the forecast has been revised time and again as scientists keep acquiring newer knowledge on the science of monsoon system.

Scientists have predicted that the monsoon this year would be normal, with a rainfall of 96 per cent of the long period of average.

However, monsoon forecast is not the only forte of IMD. It has also been providing other short and medium range forecasts. Presently, the weather forecasters have a good skill for about four to five days. Efforts are underway to push the skills beyond to meet the requirements of various users.

Farmers particularly require weather forecast at the level of administrative block, which is one level higher than panchayat and one below the district. Presently, district level advisories are being issued. About 100 blocks would be covered by the end of this year and the rest will be covered by 2019.

In addition, the Department has been focusing on improving its capabilities for predicting severe weather events such as heavy rainfalls, severe convective storms and heat waves.

There is growing evidence that extreme weather events are increasing. The world has already witnessed more hot days and heat waves since the 1950s and the fifth IPCC (Intergovernmental Panel on Climate Change) report of 2014 warns that we will see more changes to weather extremes by the end of 21st century. -Rajeevan Madhavan Nair, secretary of MoES  and an internationally acclaimed meteorologist.

Apart from seeking to impart a quantum jump in weather forecast, the ministry has embarked on a mega project to explore and exploit deep oceans for living and non-living resources. Noting that the oceans are full of mysteries and only five percent has been explored by human civilisation so far, Dr Rajeevan points out that oceans can be a good source for valuable minerals as well as for alternate energy sources. “Many geophysical activities, like under the sea earthquakes that trigger tsunamis take place at the bottom of the sea. We are planning a lab at the bottom of the sea”.

In the area of polar research too, research efforts would be stepped up. India has permanent stations in Antarctica, the Arctic and one in the Himalayas. “Among the large number of questions identified, temporal changes in the extent of sea ice and their influence on atmospheric and ocean circulation is a prime area of knowledge gap,” Rajeevan said. “We need to understand and document these changes and examine their possible effects on Indian climate using observations and models. The on-going scientific activities at Antarctic, Arctic and the Himalaya are, therefore, being further strengthened.”

Dr Rajeevan, who obtained graduate and postgraduate degrees from Madurai Kamaraj University and Ph.D in physics from University of Pune, has over 30 years of operational experience in the different aspects of tropical meteorology. Before joining the Ministry, he was Director of Indian Institute of Tropical Meteorology at Pune.

His main research contribution include understanding monsoon variability, development of monsoon prediction models, understanding extreme weather events like heavy rainfall , Heat waves also cloud radiation interactions. He has received various awards for his outstanding work, noted among them is Young Scientist Award in 2007 for his research contributions in Atmospheric Sciences. (India Science Wire)