Precipitation at the Third Pole: the race to understand Himalayan rainfall

11 December, 2024 Long reads, science

Water is one of the pillars of humanity’s survival – and yet there’s still much to explain about the processes that bring water to some of the world’s largest populations. Seeking to change that is Dr Siddharth Gumber, who discusses his research into climate, clouds and Himalayan water cycles.

‘Into each life some rain must fall’, wrote the poet Henry Wadsworth Longfellow in 1841. Though the poem is metaphorical, this statement is also literally true, yet very few of us give much thought to the mechanisms behind rainfall and the benefits of finding out more.

Not Siddharth Gumber. He dedicated his PhD to studying cloud behaviour in minute detail at Vellore Institute of Technology, India and believes that the knowledge gained could help millions of people in parts of the world that are prone to flash flooding.

Siddharth grew up in the foothills of the Himalayas, where disasters caused by landslides and flooding are occurring more frequently as a result of the climate emergency. He spent his PhD analysing clouds at a microscopic level to understand rain initiation within. His recent publication in Scientific Reports details the first observations of cloud droplet dynamics: behaviour that was theorised 20 years ago by Dr Satyajit Ghosh and published in Proceedings of the Royal Society. Ghosh was his PhD supervisor and also a co-author on the current paper.

Limited understanding of cloud processes — cloud microphysics  — poses a challenge in accurately predicting weather, and strengthening models through research could improve early warning systems in vulnerable regions.

By focusing on the tiny details of how droplets are flung around clouds by microscale whirlpools, Siddharth and colleagues can support modelling efforts to better predict rain. Their paper describes how different sized droplets behave and this can better determine when rain will start, when it will finish and the magnitude of the rainfall.

In Siddharth’s words,

“At the moment, weather models simply assume that you have a cloud, within which are droplets of water falling in still air as if there was no turbulence at all. We have shown that, in fact, cloud droplets of a certain size range (6-18μm) are flung around quite violently by tiny eddies. Smaller droplets can travel further than larger ones, while larger ones recruit smaller ones, grow in size and yield rain amounts. Understanding these effects allows us to better estimate cloud conversion and ultimately predict rain with better accuracy.”

Siddharth studied at Pinewood School in Uttar Pradesh, India, where students were taken on nature trails. He says he was “struck by the beauty of stately pines and junipers against the backdrop of the Himalayas.”

“I have always been shy and reticent and very observant of nature’s beauty. The landscape stayed fresh in my mind, and I started painting the mountain-scape as soon as I returned. Over the years, the Himalayan valley with its meadows and the ever-smiling mountain folk have always been part of my life and I keep returning again and again.”

He studied chemical engineering as an undergraduate and during the course he took some climate science modules, starting to see overlaps with atmospheric physics and chemistry. It was during his PhD that he became interested in cloud microphysics, which is an established field in the UK but still relatively new in India.

The research is part of the ‘Cloud Aerosol Interaction and Precipitation Enhancement Experiment’ (CAIPEEX), in which the team fly monitoring aircraft through clouds over Solapur city in the rain-shadow region of the Western Ghats in India. The plane’s state-of-the-art probes record microsecond observations, allowing researchers to zoom in and watch the process in detail. In the past, probes could only take a measurement every few seconds, and newer high-frequency technology provides far greater detail than has been available until now. The resulting data could lead to more accurate rainfall prediction.

In India, millions of people depend on monsoon rains for their livelihoods. As the earth warms, extreme weather events are more likely to occur and flash flooding at catastrophic levels will require hundreds of thousands to evacuate, while droughts will devastate food production.

Advances in understanding rainfall patterns can feed into adaptation and mitigation planning, as well as potential engineering solutions such as cloud seeding where clouds are manipulated to encourage rainfall.

Higher up in the mountains there is another reason to study precipitation, in this case snowfall. While more extreme weather impacts people living at lower altitude, it is also melting the glaciers housed in the high Himalayas.

Glaciers are formed over millennia as snow accumulates and compacts into ice. As the ice gains weight the glacier begins to ‘flow’ downhill where on warmer, lower slopes it begins to melt. As the earth warms, most glaciers are shrinking, and many are predicted to disappear altogether.

The Himalayas are known as the planet’s ‘Third Pole’ because their ice fields are the largest permanent ice cover outside of the polar regions. They contain some of the largest reservoirs of freshwater on earth, providing water to one billion people downstream. Unlike in the Alps in Europe or Rockies in North America, which have multiple weather stations, in the high mountains in Asia, there is just one single active weather station capturing snowfall at over 4,000 metres over a vast 100,000 square kilometres.

As a child in Saharanpur, in Uttar Pradesh, India, Siddharth went on vacation in the mountains:

“We did not know then and we still do not know how much snow falls in these high-mountain regions. Even at the famous hill stations such as Manali and Shimla people would come to know about snow falling in the Himalayas only from reports after the events have taken place.”

British Antarctic Survey’s Big Thaw is an ambitious project to examine global mountain water resources by studying the Himalayas and the Alps. It is predicted that mountain glaciers around the world will lose between 20% and 60% of their ice, posing a threat to water, food, energy, and livelihood for millions.

The field team, led by Dr Hamish Pritchard and Dr Federico Covi, are deploying novel state-of-the-art sensors to capture data on the timing and intensity of snowfall in high mountain regions. Siddharth is working with Dr Andrew Orr to analyse this data to assess snowfall, extreme weather events and mountain water runoff.

Until now, observations are inadequate to support modern modelling, so mountain water resources are underestimated and misunderstood across all mountain ranges.

The new measurements will fine-tune modelling to estimate how much snowfall reaches a region, which will enable estimates of the thickness of the glaciers and how long they will last in the face of warming.

Siddharth knows that the work of the team has potential to impact millions as we develop climate adaptation and mitigation strategies. Though he is not climbing mountains or flying aircraft through clouds, he does step away from modelling and data analysis to engage in science communications efforts.

“The modelling of tiny details can have big implications for understanding weather systems affecting people living on the front line of climate change. It’s important to explain the research in layman’s terms to the public, so I make time to get out to do that.”

From the foothills of the Himalayas to BAS’s headquarters in Cambridge, Siddharth’s research is providing valuable insights into cloud behaviour and rainfall prediction, helping improve our understanding of water resources in a changing climate and supporting better preparedness for the communities that depend on them.

Dr Siddharth Gumber spoke to writer Ruth Francis.