Steven Clemens on Climate Change and the Role it Played in the Pakistan Floods

Professor Steven C Clemens is a professor of Earth, Environmental and Planetary Sciences at Brown University, where he works with the Climate and Environment research group. Most of his academic research is trying to understand the evolution of the South Asian and East Asian monsoon systems at longer timescales (not necessarily the modern timescales discussed in the article). His aim is to understand how and why monsoon intensity and rainfall changes over time, as driven by large scale changes in the Earth's climate, like the glacial and interglacial cycles, or the large scale CO2 cycles that are known to happen naturally here on Earth.
Umer Lakani CMC '25 interviewed Dr. Steven C Clemens on on September 15, 2022.
Photograph and biography courtesy of Dr. Steven C Clemens.

Pakistan has experienced extreme flooding this summer with a very high death toll. How has climate change affected precipitation levels in South Asia? Was the recent flooding in Pakistan exceptional?

The recent flooding in Pakistan was exceptional. The last time this happened was sometime around 2010. It is still not yet understood whether the causes of those two events were the same. Generally speaking, it is a fairly easy concept. As the Earth warms, the atmosphere becomes warmer and warmer air can hold more moisture. The ocean surface temperatures, especially in the northern part of the Indian Ocean, are experiencing anomalous warming as well. Hence, the evaporation is larger. Anytime you have those two phenomena occurring, when it rains out, it rains harder. The long-term expectation is that the monsoon system will result in heavier rains, but not necessarily stronger atmospheric circulation. In fact, you can have the same wind regime taking place, and the winds won't necessarily strengthen, but the amount of moisture in those winds is going to strengthen. This is consistent with the types of floods that are going on in Pakistan right now.

Was glacial melting a significant contributing factor, given Pakistan's high amount of glacial ice? 

It could have been a contributing factor to the flooding, in that as more ice melts in the summer, there are larger loads on the rivers. Then, on top of that, more rainfall piles right onto the basins. In fact, there has been quite a bit of excess melting this summer as well, and the turbidity of the high-altitude streams has been noticeably higher. In addition, when rain falls on a glacier, it tends to undermine the glacier. These days, there are a lot of glacial dams in the higher Himalayas that are recently broken and causing flooding in and of themselves. This recent activity from the southern part of Pakistan is mostly atmospheric rainfall, at this point.

Could you just clarify what you mean by glacial dam?

As glaciers melt, they don't necessarily always run off right down streams into the lower levels. They can be blocked by ice dams that are literally dams, but they're made of glacial ice. Eventually, those let go and the result can be catastrophic. There was an instance of that this year in India, where a glacial dam broke and caused a lot of problems at a power generating station downstream with the loss of life as well.

What role did the heatwaves in Pakistan in May and June this year play in the increased precipitation levels and subsequent floods? 

That's really hard for me to assess. I've read that the heatwave in Europe this year actually had some type of impact on the South Asian floods. And in that case, they were calling on a stationary high that was set up over Europe. And that would, in fact, cause some deflections in the westerly wave patterns that could potentially bring moisture down south when it would normally head further north. I'm not sure exactly how the heat waves in Pakistan this year predating the onset of these anomalous rains are linked. Everybody is merely speculating. When this event is over, that data will be reassessed and analyzed. People will come up with some more concrete ideas as to what this particular event stems from. 

I've been looking a little bit at the genesis of the low-pressure systems that have come into this region. Low pressure systems are the atmospheric conditions that cause rainfall events; mainly atmospheric low pressure at the surface, causing cyclonic wind circulation, convergence and precipitation. And there's normally three or four per year in Europe. A few of those have been generated in the northern part of the Arabian Sea and migrated to the north and east up into the southern Pakistan region. In addition, there is anomalous warming in that area. So that's part of the signal that's coming in from these anomalous low-pressure systems that are forming in the northern part of the Arabian Sea. Moreover, some of the other systems that you'd normally find coming from all across the foothills into the northern part of Pakistan, those are there as well. In my initial look at the system, there are more systems usually being generated in the Arabian Sea. 

Is there any cause that we can link that to, specifically local to the region, or are those entirely anomalous?

They are not entirely anomalous. But, once again, this is pure speculation. Ultimately, the Westerlies can certainly factor into the generation of low-pressure cells in a part of the Arabian Sea. The Westerlies normally go above the plateau at this time of year. However, with respect to the Arabian Sea, there are many regions on Earth with regional warming of the ocean surface waters.  The northern Arabian Sea is one of them. They are starting to be called ocean heat waves.  They are not unique to the Indian Ocean or the Arabian Sea.

To what extent were the floods an anomaly based on current models? Could they have been predicted at all? Could the government have been better prepared?

You run these models under future conditions. You can see that there is increased rainfall, and increased variability in that rainfall, especially in the context of having more moisture in the air. So, from a statistical standpoint, the floods were not at all unexpected for this particular set of events. The data need to be analyzed in the coming year. 

Moreover, we can all be better prepared. Where I am in Rhode Island, we just had 10 inches of rain in one day, and our freeways flooded. We're designed for big events, meaning three or four inches—not a 10 inch rainfall. Everybody's being caught by surprise. In the case of Pakistan, they are one of the regions on earth that are expected to get harder hit by rain than other places. The government probably is and does need to be more proactive and think about drainage. It has to think about where new construction is built and how it's built. There's always something the government can do, but all politics is local. Local governments must decide where to put their money. Interestingly, however, the most recent modeling suggests that Pakistan has a 1% chance of such flooding each year, which means they are likely to experience one such event every 100 years, yet Pakistan has now had two in the past 20 years!

From a policy perspective, what do you think Pakistan could do to be better prepared in the future? What could they do to combat the effects that they're feeling right now in the short term?

We all build in floodplains, right? That's where fertile soil is, where the water is. Floodplains are notoriously prone to flooding when there is excess rainfall. We see the exact same thing in the Mississippi River Valley that Pakistan is seeing now. There is a lesser loss of life, though, because the events aren't as extreme. In Pakistan, that's happened twice now: 2010 and 2022. Hopefully, that'll be a wakeup call for people to start considering what to do in these classic cases, like planning for evacuation,  relocating people and emergency supplies. Those are the kinds of things about which you need to be proactive in order to try and mitigate the impact of future events, if you can't mitigate the future events themselves. 

How important do you think it is for Pakistan to start taking environmental measures , especially local measures? As you mentioned earlier, there was some linkage between European heat waves and increased precipitation in South Asia, which is completely out of its control. So how much does local environmental policy help? How much could that go towards helping prevent future floods?

It is important only in the context of mitigation and preparation for the event itself. Nobody's going to prevent floods, right? We're all in this game together. If it's not excess flooding, it’s excess drought. Pakistan has both floods and droughts. I don't think you can change environmental policy to stop these events, but you can mitigate the impact. Lobbying on the global stage for everybody to reduce greenhouse gas emissions is an important thing. As part of the global community, the rallying cry, always helps.

What do you think are the main obstacles that are preventing the adoption of these sorts of measures on a larger scale? Or maybe on a more local scale?

I can speak from experience in the US. Here there are lobbying arms that seek to block the policies needed to reduce our carbon footprint and our carbon emissions. Fortunately, from my perspective, I see that decreasing rapidly and our young people are very tuned in to these ideas because they've grown up with it. My hope is that as the younger generation starts to take the reign of powers, it will get better; at least the US will get better at what it should have been doing for decades. Again, it's hard to speak for Pakistan given the local political issues surrounding climate change.

What do you think is the obstacle for a global unity in adopting environmental measures?

The obstacle is the prevalence of available fossil fuels. It's sad—easy accessibility of fossil fuels is certainly a problem. As long as they're the least expensive source of energy, we're going to continue to use them. That's certainly been my experience over the past couple of decades. But I do think that that is changing, it certainly changes with each administration. Globally, there's a much better feeling something must be done. This is spilling into US politics as well, albeit slower than I would like. But it is happening, so I'm reasonably optimistic.  

Umer Lakhani CMC '25Student Journalist

Ali Hyder Junejo, CC BY 2.0 <>, via Wikimedia Commons

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