In conversation with Kieran Hunt, ‘J&K's snowfall decline, and flood risks increase linked to western disturbances’

Less snowfall, more rainfall and floods: climate change poses a great threat to India’s north-most region’s water and food security. But, how do these things go together? The answer is increasing western disturbances (WDs) and delayed northwest migration of subtropical jets. In the study published in the journal Weather and Climate Dynamics, Dr Kieran Hunt, from the University of Reading, assesses WD trends from  ‘70 years of European Centre for Medium-Range Weather Forecasts (ECMWF) reanalysis (ERA5) data’.

These WDs are responsible for ‘seasonal and extreme precipitation to the Hindu Kush, Karakoram, and western Himalaya in the winter months’, as stated in the study. Hence, WD intensity, frequent can impact both rainfall as well as snowfall patterns in the region. Rather, it has already. 

Western disturbances system has been delayed or weakened since 2019 i.e. India’s northern region has not received the storms with their utmost potential. As per the data, winter storms now occur frequently from April to July. This coincides with Indian summers and resulted in a 60% reduction in snowfall and an increased risk of catastrophic flooding in the Himalayan region. Most of Himachal Pradesh's agriculture is rainfed, therefore this change impacts the rabi crops and horticulture too.

Ground Report's Environmental Correspondent Wahid Bhat, interviewed the study’s author Dr Hunt elaborated on the changing patterns and surge in Western Disturbances due to climate change. As mentioned, the surge raises concerns about ecological balance, glacier health, and long-term water availability. Further discussions revolved around the effects of reduced snowfall on various seasons, including spring and autumn.

Q: How does the observed decrease in snowfall impact glaciers' health and long-term water availability in the South Asian region, considering its heavy reliance on water resources?

A: Negatively, I should think. It's a double-edged sword because as the climate warms, we not only see reduced snowfall and increased rainfall but also accelerated melting of glaciers and snowpack. Glaciers worldwide, including those in the Himalayas, are losing mass, making water security a significant concern. This situation is emblematic of climate change's impact on water resources, and urgent action is needed to address these challenges. 

Q: Have there been corresponding changes in temperature patterns, particularly in regions like Jammu Kashmir, Himachal Pradesh, and Uttarakhand, that might explain the decrease in snowfall?

A: Yes, there has been a noticeable increase in temperature in these regions. As the atmosphere warms globally, higher elevations experience a more pronounced warming trend, known as elevation-dependent warming. This means that the rate of temperature increase is higher at higher altitudes. As a result, we are seeing less snowfall and more precipitation falling as rain due to snow melting as it passes through warmer layers of the atmosphere. This phenomenon is a direct consequence of global warming and its impact on regional climate patterns.

Q: So, as you mentioned, there has been a consistent increase in Western disturbances in the region. What are the implications of reducing snowfall and increasing late-season rainfall on the ecological balance in the Himalayan region?

A: Yeah, so it's a big issue for water security. We are seeing that, again, there are kind of two effects going on here. During the winter, we're not necessarily seeing fewer Western disturbances, but the Western disturbances that are coming are interacting with the warmer environment and therefore causing less snow and more rain. This precipitation is carrying more rain and less snow. But then in the spring, we're just seeing a lot more rain, and often that can be quite heavy. And this has several knock-on effects. As you know, a lot of the Rabi crop in North India and in the upper Indus and Ganges regions, which is grown from February to May, relies on meltwater from the snowpack in the Himalayas, Hindu Kush, and Karakoram. That meltwater comes from glaciers and snow. If Western disturbances in the winter are not recharging that snow very effectively and instead just dumping water, by the time spring comes around, that water is not available.

On the flip side, Western disturbances in the spring are delivering a lot more water in the form of heavy precipitation, which is useless for irrigation because all it does is cause flooding. It's not that steady, reliable trickle of snowmelt but rather deluges that lead to localized flash flooding. So, you end up with this double impact on water security where you're losing a lot of that reliable winter snowmelt, and it's essentially being exchanged for these much more sporadic, intense, and localized rainstorms often later in the season, which not only damages the crop because there's less water available for irrigation but also harms the crop due to flooding. 

Q: So, what I want to understand is how these changes in snowfall, particularly in Jammu Kashmir and Himachal Pradesh, will impact the climate in the region, considering the increase in Western disturbances. How will climate change models and predictions for the Indian subcontinent account for these changes?

A: You're right that most climate models are developed in the Global North, but India also has some models like the IMD's dynamical climate model that are gaining recognition globally. However, there are challenges in incorporating regional complexities like changing snowfall patterns into global climate models. Climate models are based on weather models that are tuned for specific regions, which can lead to biases in other regions. The representation of mountainous regions like the Himalayas in climate models is coarse due to limited resolution, resulting in an underestimation of precipitation over these areas. This impacts the accuracy of projections for snowfall and rainfall over the Himalayas. So, while climate models provide valuable insights, researchers also rely on observations to better understand regional climate changes and their implications. 

Q: What are some numbers to understand the impact of temperature on snowfall? Specifically, for regions like Kashmir, what is the proportion of temperature increase to the decrease in snowfall?

A: I can’t produce a number off the top of my head, all I can say is that you do get more precipitation in general with a warmer atmosphere because the warmer atmosphere can hold more moisture. That rate is 7% per degree of warming. But that’s for precipitation as a whole. As for a decrease in snowfall, it depends on a lot of factors, and I wouldn’t want to put a single number on it largely because there’s a lot of threshold behaviour. It’s not a smooth transition; there will be some particular temperature often where you get a snap change, what we might call a tipping point. 

Q: Apart from floods, what are the other extreme weather events that might increase due to these trends?

A: Western disturbances are involved in various natural hazards related to precipitation. Besides flooding, avalanches and landslides can also increase due to heavy rainfall on slopes. Avalanches become riskier as snow weakens structurally with warmer temperatures.

Q: What specific hazards are associated with Western disturbances during spring in the pre-monsoon period?

A: Lightning is a significant hazard during this time, responsible for the majority of lightning incidents in North India between March and May. Fog formation, particularly over Delhi and surrounding areas, and cold waves due to winds from the north are also notable hazards.

Q: Which countries in the South Asian and Asia Pacific region will be impacted similarly by these trends, and how will it affect India and neighbouring countries?

A: Countries like Pakistan, India, Nepal, Bhutan, and even regions up to Turkmenistan and western China will be vulnerable due to changes in Western disturbance behaviour. India and Nepal, with their mountainous zones, are particularly susceptible, with India being the most vulnerable to these changes. Pakistan, especially regions like Baluchistan, is also at risk, experiencing significant rain periods in March. Nepal, although vulnerable, is less impacted due to Western disturbances weakening in the central Himalayas. 

Q: Alright, so how will decreasing snowfall and increasing Western disturbances impact the seasons, transitioning from the spring season into the late autumn season?

A: In the study, we found that spring will get wetter because you’re getting a lot more Western disturbances. Also, the risk of flooding is increased for several different reasons. Mostly because the precipitation is falling as rain and it’s typically falling on hard, arid ground. It’s not particularly absorbent, and it’s also often later in the spring interacting with more moist air. So spring’s wetter. As for autumn, we don’t know yet; we haven’t looked into that season specifically. 

Q: How do these changes in snowfall, particularly in Jammu Kashmir and Himachal Pradesh, affect climate change models and predictions for the Indian subcontinent?

A: The increase in Western disturbances due to changing snowfall patterns has significant implications for climate change models and predictions for the Indian subcontinent. The increase in Western disturbances and the shift from snowfall to rainfall are altering the water cycle in these regions. This shift affects water availability for agriculture, leading to crop damage due to flooding and reduced irrigation. Climate change models need to incorporate these changing snowfall patterns and their impacts on Western disturbances to provide accurate predictions for the future climate of the Indian subcontinent. 

Q: Can you explain how you identified and tracked Western disturbances in your study using ERA5 data, and what role this played in analyzing changes in snowfall patterns, especially in regions like Jammu and Kashmir?

A: We utilized the ERA5 data along with tracking algorithms to identify regions in the atmosphere exhibiting characteristics of Western disturbances such as high vorticity. By tracking these disturbances over time, we could analyze their frequency, intensity, and movement, which helped us understand their impact on snowfall patterns in regions like Jammu and Kashmir. This analysis forms the basis of our study on meteorological shifts impacting various regions and sectors in India over the past seven decades.

Q: How does the observed increase in Western disturbances align with the changing climate patterns in the Himalayan region, especially concerning the decline in snowfall, particularly noticeable in regions like Jammu and Kashmir?

A: Yes, it's a multi-dimensional issue. Western disturbances are increasing both in the winter season, albeit slightly, and significantly more in the spring and summer. The growth of these disturbances in winter is attributed to baroclinic instability in the atmosphere, which has increased due to climate change. Additionally, the migration of the subtropical jet northward during the monsoon has been delayed, extending its presence over northern India until late June or even July. This delayed migration allows Western disturbances to continue affecting the region, especially during the summer when moist monsoonal air masses interact with them, leading to heavy precipitation events like floods witnessed in recent years. 

Q: Are there specific regions within North India that have experienced more pronounced shifts in Western disturbance timing and rainfall patterns?

A: Yes, apart from Jammu and Kashmir, other regions in North India have also experienced notable shifts in Western disturbance timing and resulting rainfall patterns. The delayed northward migration of the subtropical jet impacts a wide area, and we've observed similar trends in areas like Himachal Pradesh, Uttarakhand, and even parts of the Indo-Gangetic plains. These shifts are crucial to understand as they directly impact the frequency and intensity of extreme weather events like heavy rainfall and floods in these regions. 

Q: Other than the specific regions within North India, have other areas experienced a more pronounced shift in Western disturbance timing and rainfall patterns?

A: Yeah, so it's a good question. Western disturbances have a really large footprint, they're quite big storms, but their impacts tend to be quite localized because most of the precipitation associated with Western disturbances is caused by their kind of moist low-level winds impacting the mountains. So the basic idea, if you could see my camera, but you'd have the wind that, let's say, you have a sudden low-level wind that strikes the mountain, it then gets forced upwards and as it cools, the water in that air condenses and precipitates. And so most of the precipitation associated with Western disturbances falls along the Himalayan foothills, particularly the Western Himalayan foothills and slightly higher altitudes as well. So the regions that get most affected by Western disturbance precipitation and are thus most affected by changes in Western disturbances are the states of Himachal Pradesh, Uttarakhand, and Jammu and Kashmir. 

Q: So, are there any geographical or topographic factors specific to Jammu and Kashmir that contribute to the observed decrease in snowfall?

A: It's the increase in temperature that is leading to the decrease in snowfall; the total amount of precipitation is either staying about the same or slightly increasing, but snowfall is universally decreasing. That's purely because surface temperatures in the region have been increasing by approximately one and a half degrees over the last 100 years. If you imagine being in a region near the edge of a snowpack and the temperature rises from zero degrees to one and a half degrees, you can appreciate that snow will melt much more quickly and not hang around. So, what you see is less area of the mountain covered in snow, and the altitude at which snow persists is raised. 

Q: How much is deforestation or land destruction playing a role in this change?

A: I need to figure out the specific impact of deforestation or land use changes in that region regarding snowfall patterns. Studies are showing that deforestation can lead to increased runoff and flash flooding due to reduced soil moisture absorption, but local research on the climate effect of deforestation in that part of India is limited. 

Q: Do changes in these mountain ranges affect cyclones and storms reaching certain areas?

A: Western disturbances are not greatly affected by changes in specific mountain ranges or deforestation in those regions. These disturbances are quite large storms with a spatial scale of several thousand kilometres. Removing trees from the mountains does not significantly impact these disturbances. However, if the Himalayas were removed altogether, Western disturbances might penetrate further into central and eastern India. 

Q: Where is this European NGO getting its data from to create the ERA5 reanalysis?

A: They gather data from various sources including automatic weather stations, weather balloons, satellite data, ocean buoys, and other observation systems worldwide. These data are then ingested into a comprehensive model to create a grid-based weather product that researchers like me can use for detailed analysis and tracking of meteorological phenomena like Western disturbances. 

Q: How widely accepted is the ERA5 data, particularly by governments such as India, and is it primarily used for post-analysis or also for predictive modelling?

A: ERA5 data is highly regarded and widely used globally, including by government weather agencies like the India Meteorological Department (IMD). It serves primarily for post-analysis due to its reliance on historical data, but the same modelling systems are also used for predictive weather and climate modelling by organizations like ECMWF. 

Q: What specific meteorological data did your study utilize to determine the increase in investment in urban areas and among Indians over the past 70 years?

A: Yeah, so I used mostly ERA5 data, which stands for the fifth generation of the European Centre for medium-range Weather Forecasting's atmospheric reanalysis. This data combines observations with high-resolution models to create a detailed three-dimensional view of the atmosphere over the last 80 years. It helps us understand phenomena like Western disturbances crucial for snowfall and rainfall patterns in northern India.

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