Instant Genius - What has caused the heatwave and drought, with Prof Dann Mitchell

Episode Date: August 14, 2022

Prof Dann Mitchell, a climate scientist at the University of Bristol, reveals what has caused the current heatwave and drought, and what the future outlook could be. Hosted on Acast. See acast.com/privacy for more information. Learn more about your ad choices. Visit podcastchoices.com/adchoices

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Hello and welcome to Instant Genius, a bite-sized masterclass in podcast form. Are you feeling a little warm? Me too. I'm Alice Lipscomb Southwell, the managing editor at BBC Science Focus magazine. Because I was sweating in my office, I wanted to find out more about the current heat wave and drought. So in this episode, I talked to Professor Dan Mitchell, a climate scientist at the University of Bristol. He talks to me about the current weather conditions and reveals what is. caused it. I mean, I'm sitting here sweating while I'm doing this podcast. The UK and Europe is experiencing a heat wave at the moment. Now, how frequent occurrence is a heat wave like this,

statistically speaking? Well, this current heat wave isn't actually too uncommon. You know, we're getting temperatures of around 30 degrees, something like that. What's extremely uncommon is we've had two big heat waves almost back to back, so two or three weeks away. The first one, of course was a record-shattering event, so temperatures above 40 degrees. So having those two together is extremely unlikely. In fact, hasn't occurred in UK records yet. So what is the actual definition of a heat wave then? Well, so there are lots of different definitions of heat waves actually used throughout the world. In England, we have a threshold-based definition. So we talk about when temperatures exceed, say, 28 degrees or 29 degrees. But even that threshold-based definition in the

UK varies across the UK. So it's lower in Scotland and it's higher in England. And accompanying this heat weight, we've also got a drought. All our gardens are parched and do agriculture, struggling. So what's the definition of a drought then? Well, yeah, exactly. And, you know, the droughts, there's some fascinating satellite imagery at the moment showing our beautiful green country now looking brown and it really is quite clear how much of a drought it is. A drought is just persistent dryness and we've seen that in this case with say 10, 20% of the usual rain that we get in July in the south of the UK. So it really is much, much lower than usual conditions. So do heat waves always cause drought or is drought more related to rainfall than is

if it was really hot, but there were still quite a lot of rain, would things be okay? Yeah, it's a good question. And it's a very confusing one because normally they coincide with each other. So you normally see a heat wave and a drought. But actually, they don't have to, so they could be very different from each other. So the way to think about a drought is a persistent drying of the whole country for saying that could last for months or weeks. A heat wave is much faster timescales. So you might just get a heatwave for one or two days or in absolutely exceptional circumstances, they could last a couple of weeks. But the drought itself is actually one of the main drivers of a heat wave. There are other drivers, so you don't need to drought.

But if you get the drying out of the soils, then that has a negative feedback, which often causes very, very high temperatures in the atmosphere. So could heat waves and droughts be classed as natural disasters, then? Natural hazards, yes. Well, they are. We've always had heat waves and droughts. They've always been, you know, large. In all fairness, we could have potentially got a 40 degree heat wave like we did two or three weeks ago, even without any sort of human influence on the system. It's just what we find is the more we pump greenhouse gases and things like that into the atmosphere, the higher the likelihood of these sort of extreme events. So delving into that a little bit more then, what weather patterns have driven this current drought? So one, probably the leading order weather pattern is something

we call a blocking high. And that's when you get a high pressure system which sort of sits over the UK or sits over Western Europe. And we call it a block because all of the weather systems that come across the Atlantic, they smash into this block and then the displaced the side of the UK. And so it really stops all these weather systems coming through. So they're carrying the rain and the moisture and they're not getting to the UK. So if that happens for a long period of time, which it has for the entire summer, then you get these extreme drought conditions. And how long could this be going on for? Is it likely to carry on for weeks or months? Or can we project that far forwards? Well, we, you know, the seasonal forecasting,

so that's the forecasts which look at the weeks to the months ahead. Earlier this summer, I was looking at those forecasts, and they were predicting this much warmer than usual and dry than usual conditions. So over a month ago, I could have told you with some reasonable confidence that this was going to happen. Of course, things change at the last minute, but in this case it didn't, and our forecast models did the same thing. Now, we, for the rest of August, actually, we're still expecting it to be quite dry and hot. Hopefully it will get a bit cooler and a bit a bit wetter than it currently is, but we're strongly expecting it to be above average conditions still. We can't look further forward into September, October and into the winter?

Yeah, so we do have those forecasts again. Very different weather patterns are at play there. Different things are important. I haven't actually looked at those forecasts myself, so I can't tell you what they're going to do, but they do exist and we do have some skill in that forecast. So we all know about the bad side of droughts, you know, it's parched land, struggling as well. But are there actually any benefits to a drought? Does anyone benefit? Do any animals benefit from this situation? Well, it's hard to think of any positives coming out of a drought, to be honest. So no, I would probably say not. So how much rain would we need so we are no longer experiencing drought? Could we just have one big downpour and everything would be okay? Or would it

have to be a prolonged period now of quite wet weather? Yeah, so what a drought does is it changes is the properties of the soil. So by drying it out, it makes it actually a little bit more resistant to rain, which is quite counterintuitive, really. So as you've got a downpouring of rain, actually, you'd see a lot of that remaining on the surface and sliding off. So that's really what we don't want, because we can sometimes see some quite dangerous events when that happens. So we want to see more precipitation, but gradual and persistent across the next couple of weeks and months to really start refilling those ground soil moisture. When you say about dangerous events from just, say, one downpour, what sort of things do you mean?

Well, if you get a very convective system and you get a lot of rain, say, in a short period of time, so over one or two or three hours, then if that rain doesn't have anywhere to go to, then, of course, it leads to some sort of flash flooding, that sort of thing. And that's what I'd be starting to be worried about coming into September, October, over November, where we might start getting some more of these precipitation systems. They would try to get down to the soils, but again, because of this sort of semi-water repellent property that it has when it's so dry, then that water would just do flood in one direction. And if you're in a flood zone, then that could be quite dangerous.

There are some parts of the world where maybe that wouldn't be such a problem. They're used to dealing with the soil drying out a lot and then it being wet. Is it something about the UK soil or just our weather that makes us less resilient to that sort of scenario then? Yeah, so I mean, there's lots of different examples of where we've changed the land surface and that's resulted in negative impacts of these sort of precipitation events. And the most obvious one is concrete. That's completely repellent to water. If you concrete over a whole area like we do, of course, in cities,

then you create very little space for the precipitate. precipitation to go. So countries where they do have a lot of very highly convective systems on various different land surface types, they have learned to adapt, or many of them have anyway. And we from the UK could potentially look at that. It is a very strong signal that we detect. We're expecting to see more of these drier events. So it is something that we should look at. Is there any way that we can sort of tell the cost of this drought so far? I mean, been fires already and crops are drying out. Can we actually calculate that? That's extremely complex. And so people do try and do it, but to get an accurate number is next to impossible.

As you pointed out a few of the things, but then let's start thinking about things like healthcare, you know, how many more people in the UK are going into hospitals because of the heat wave and because of dehydration and heat stress. You talked about agriculture. there's the loss of crops, that's one thing, but there's also what the farmers are doing to adapt to these sort of droughts. So they're investing time, energy, finance, into drought resilient crops, for instance. They're essentially crops which have got longer routes

so they can get deeper into the soil and get those water supplies. So how much is that farmer spent on that sort of adaptation as well? So it's not just the actual impact of the event, it's how we're adapting and evolving to these vents. as well. You say about it's adapting there. And on a personal level, are you doing anything differently? Are you planting different things in your garden? Are you stockpiling water? Or you're just going to move underground for the end of days? Well, I'm not in my household. I actually was one of those

silly people who bought a north-facing house. And actually during a heat wave is about the only time where I'm glad of doing that. So our house is quite cool, which is nice. What I am doing and what I've advised a lot of friends and colleagues to do is I'm checking up on my my elder relatives, my more vulnerable friends, and it can be really simple things. So it can be just dropping them a text saying, you know, make sure you've got a bottle of water next to you, make sure it's been in the fridge or the freezer, closing your curtains, all these sort of things. It's those more vulnerable people that are really at risk during these sort of droughts and heatways. They're the ones we need to really look up to. As a climate scientist, how do these record-breaking temperatures

and dry conditions make you feel about the overall outlook? Are you optimistic or are you quite pessimistic about it? Well, it's a strange one. You know, as a climate scientist, for the past, I'd say six to seven years every summer, I come on. I probably give the order of a hundred interviews on whatever heat wave or drought is on. The me, you know, many sectors of the media are very good at picking up on this. In the last couple of years, they're very good at explaining the dangers to their audiences. But the government's just smile and nod and give you the thumbs up, but we don't see the action from the governments. And that's the real problem is they don't have, I guess the ability to think on timescales of climate, which are at the odds of decades to centuries. They think on

re-election cycles. And there's not necessarily criticism of who's in power. It's a criticism of the way our government works is they have to get re-elected each four years. And if they put lots of money into the climate problem, they might not get re-elected. So it's a fundamental issue we need to change to really solve this climate problem. And are there easy wins that we could do? I mean, you touched on it earlier that just the way our country has been built up with all the concrete, that that's made us more vulnerable. Are there any easy wins we can do to turn that round? Well, in terms of adaptation to heat, for instance, or drought, it really is all in the communication and the future planning. And one easy win is just to really get on board the major media centres, that's social media and traditional media, and get them repeating the messages.

You know, this is dangerous because of X, Y and Z. This will become more worse because of whatever the thing is causing it. And that doesn't happen as much as you would like to think. We're often in our bubbles in social media. So we listen to the people we follow or we have our certain channels we switch on. But other people are in other bubbles. And we saw with the heat wave two or three weeks ago that there was some really quite nasty attacks on meteorologists and climate scientists just for saying what the dangers of the heatwave would be. So what does the future hold for us then, do you think? Well, at some point, at some point the system's going to crack.

You know, we are getting to the stage where we're seeing these extreme heat waves so frequently, we're seeing droughts so frequently. This is a, in the UK in particular, these hotter, drier summers are not a surprise to scientists. We've predicted this for decades. We've looked in the data and we've seen that happening for at least a decade now. and all our climate models show that this is a very clear trend in climate change. There are other things that are less certain, but this is a very certain thing. So how do we respond to that in the future?

Well, at some point, it's going to get to the point where we do have significant proportions of our summer where we have certain restrictions on the water use and things like that. And at that point, we're going to be spending so much money in adaptation that the government will have to act. Of course, if they just acted earlier, then in the long run it would save a hell of a lot of money and even more it would save lives. But that's what's going to happen. Thank you for listening to this episode of Instant Genius. That was climate scientist Professor Dan Mitchell talking about the current heat wave and drought.

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