Cabot Conversations: Untangling the water system - surprising impacts of climate change

Cabot Institute for the Environment scientists, Dr Gemma Coxon and Dr Ross Woods, highlight some surprising facts about the water system and how nature based solutions to drought and floods may not serve the purpose we want, especially if implemented without sufficient prior research.

Transcript

00:00:07 Cabot Institute  

Welcome to Cabot conversations produced by the Cabot Institute for the Environment at the University of Bristol. 

00:00:13 Cabot Institute  

We are a diverse community of 600 experts united by a common cause protecting our environment and identifying ways of living better with our changing planet. 

00:00:23 Cabot Institute  

This podcast series brings together our experts and collaborators to discuss complex environmental challenges and solutions to climate change. 

00:00:31 Cabot Institute  

In this episode, Doctor Gemma Coxon and Doctor Ross Woods discuss untangling the water system, surprising impacts of climate change. You can find out more about the Cabot Institute for the environment at bristol.ac.uk/cabot. 

00:00:51 Dr Gemma Coxon 

Hello, my name is Gemma Coxon. I'm a lecturer in hydrology in the school of Geographical Sciences at the University of Bristol. 

00:01:01 Dr Gemma Coxon 

My research focuses on understanding and predicting change in hydro climatic extremes, so specifically droughts and floods little bit more on the drought side than on the flood side. 

00:01:15 Dr Gemma Coxon 

And and I build computer models essentially that. 

00:01:20 Dr Gemma Coxon 

Tell us what happens when a rainfall drops on the ground and how it kind of enters into our river flow River systems and and how that might change in the future. 

00:01:32 Dr Gemma Coxon 

How about you, Ross? 

00:01:34 Dr Ross Woods 

I work in the Department of Civil Engineering at the University of Bristol. In my work, I'm interested in lots of different aspects of the water cycle. 

00:01:45 Dr Ross Woods 

For the purposes of this chat, I'm mostly going to have my flooding hat on. 

00:01:51 Dr Ross Woods 

And. 

00:01:52 Dr Ross Woods 

But I'm also interested in all sorts of other things. 

00:01:57 Dr Ross Woods 

Different parts of the water cycle and differently in lots of different places. 

00:02:02 Dr Gemma Coxon 

Now I know we're here today to talk a little bit about impacts of climate change on the water system, and I know this features quite heavily in both of the work that we do. But maybe Ross, you can you can kind of start off by by outlining you know what what your thoughts are about the impacts of climate change on the water. 

00:02:24 Dr Gemma Coxon 

System and what might change in the future. 

00:02:27 Dr Ross Woods 

We differently anticipate significant increases in temperature, so we expect the atmosphere to get warmer. 

00:02:35 Dr Ross Woods 

That means quite a few different things for hydrology. 

00:02:39 Dr Ross Woods 

But one of the things that's important that it means is that the atmosphere. 

00:02:44 Dr Ross Woods 

Can hold more water and if the atmosphere because it's warmer. 

00:02:49 Dr Ross Woods 

And if the atmosphere can hold more water, that means that it can bring bigger rainstorms to places. And so we can get. We have now the potential with a warmer warming atmosphere for more intense rainfall. So one of the things that we'd anticipate. 

00:03:06 Dr Ross Woods 

Is that you get more intense rainfall and then the interesting thing to ask about that is. 

00:03:12 Dr Ross Woods 

What does that mean for floods? 

00:03:14 Dr Ross Woods 

And kind of the obvious answer is, well, heavy rainfalls cause big floods. 

00:03:20 Dr Ross Woods 

So if the rainfalls get bigger, then I guess the floods will. 

00:03:23 Dr Ross Woods 

Get bigger and. 

00:03:26 Dr Ross Woods 

That is what you might think. But sometimes nature has a way of coming up with surprises for us, and I think there is potentially one there because. 

00:03:38 Dr Ross Woods 

The way that floods get made is not always really straightforward, so sometimes it just rains really hard and it lands on your pavement or something like that. 

00:03:49 Dr Ross Woods 

And then the water runs across the pavement and into some drainage system. And if you put more rain on the pavement, you'll get more rain water in your drains. That's fair. 

00:04:00 Dr Ross Woods 

But sometimes floods get made because of a combination of how much it rained. 

00:04:05 Dr Ross Woods 

And. 

00:04:07 Dr Ross Woods 

What state the soil was in, how wet the soil was when it was raining. So if it was that, the heavier rainfalls that we got with climate change, if they came at a time of year when the soils were really dry. 

00:04:22 Dr Ross Woods 

Then maybe they wouldn't have much impact. 

00:04:25 Dr Ross Woods 

And maybe what would really matter would be how much the rainfalls increased at the time of year when the soils are really wet. So in the UK that. 

00:04:35 Dr Ross Woods 

Will be in the winter time. 

00:04:37 Dr Ross Woods 

So I think The thing is that. 

00:04:41 Dr Ross Woods 

Because hydrology does the land surface processes. When rain arrives on the ground because those do interesting and complicated things, then sometimes the impacts of climate change aren't quite what you'd expect. 

00:04:55 Dr Gemma Coxon 

Yeah, and often forgotten a little bit. We really regularly kind of focus on, you know, the climate change impacts and we think, right, changes in rainfall, changes in temperature. 

00:05:08 Dr Gemma Coxon 

And you know, that's kind of what's going on in the atmosphere. And often I think occasionally we sometimes miss that link between what's happening on the land surface and then those surprising elements of how those terrestrial water fluxes modify that climate signal to produce either a flood or a. 

00:05:28 Dr Gemma Coxon 

Or a drought. 

00:05:30 Dr Gemma Coxon 

A. A similar kind of example from the kind of drought realm. 

00:05:36 Dr Gemma Coxon 

Is that? 

00:05:38 Dr Gemma Coxon 

So for the UK. 

00:05:41 Dr Gemma Coxon 

The UK sort of future climate projections, so those are UK CP 18. 

00:05:49 Dr Gemma Coxon 

Because they were produced in 2018, they are projecting that we'll get wetter winters and drier summers now. Overall, if you kind of average that out across the year overall kind of looks like we might get a small, you know, mean increase in rainfall. 

00:06:10 Dr Gemma Coxon 

So you think great, great for droughts, right? We weren't. 

00:06:13 Dr Ross Woods 

We water in the rivers in the. 

00:06:14 Dr Gemma Coxon 

Summer exactly, but bit more water in the rivers. 

00:06:17 Dr Gemma Coxon 

In the summer. 

00:06:18 Dr Gemma Coxon 

But because of the ways that we require water and we need water for, you know, public water supplies, so the water that's coming out of your taps and for agriculture, you know, we need lots of that water in the summer and our water supply system isn't really set up to store a whole load of water. 

00:06:41 Dr Gemma Coxon 

That comes in the winter. 

00:06:43 Dr Gemma Coxon 

To then be able to supply through the summer. So although we might get a small mean increase in our rainfall can lead to some water shortages because of those really severe decreases in rainfall in the sun. 

00:06:57 Dr Gemma Coxon 

And so again, it's how that climate signal is being modified. 

00:07:01 Dr Gemma Coxon 

By the by the terrestrial water system. 

00:07:06 Dr Gemma Coxon 

That's really interesting. 

00:07:08 Dr Ross Woods 

OK. So just to make sure I understood you right, So what you're saying is that you're expecting? 

00:07:14 Dr Ross Woods 

Overall, the total amount of flow in the river to get a little bit bigger maybe. 

00:07:20 Dr Ross Woods 

But. 

00:07:22 Dr Ross Woods 

If you look inside a year. 

00:07:25 Dr Ross Woods 

There's that extra water is coming in the winter, and they'll actually be less available than currently in the summer. 

00:07:33 Dr Gemma Coxon 

Yeah, and off often it's it's the summer when we most need that water or irrigation. We're taking a lot more showers and baths because of the hot weather, you know, filling up paddling pools and watering the gardens. 

00:07:51 Dr Gemma Coxon 

And so to be able to meet that water demand we, you know, it's not just about the total amounts of rainfall, but it's about the timing of that rainfall too. And I think that that links with your with the floods example of kind of when that intense rainfall is coming when you know how you know conditions. 

00:08:11 Dr Gemma Coxon 

Before play, a real strong part in determining whether we get a flood or a drought, for example. 

00:08:17 Dr Ross Woods 

Yeah. So I guess you've talked a little bit about some of the consequences of those preventable consequences. Do you think or? 

00:08:26 Dr Ross Woods 

Once we can reduce. 

00:08:27 Dr Gemma Coxon 

Sir James Bevan, who's the chief executive of the Environment Agency, gave a really interesting talk. I think it was a year or two years ago now where he spoke about the the jaws of death now. Not not quite. You know, like a. 

00:08:47 Dr Gemma Coxon 

Dark straws, but essentially. 

00:08:49 Dr Gemma Coxon 

And. 

00:08:52 Dr Gemma Coxon 

The projections for the UK are that you know, because of anthropogenic climate change, we're gonna get changes in our water supply. So how much how much rainfall is occurring and also how much evaporation is occurring from increases in temperature. 

00:09:09 Dr Gemma Coxon 

Actually one of the big drivers of kind of future droughts is how much water water we are using as a as a society. We have a rapidly growing population in the UK. 

00:09:25 Dr Gemma Coxon 

There it, which is centered around some quite densely populated urban areas. 

00:09:32 Dr Gemma Coxon 

And it's not just thinking about changes in water supply, but also changes in water demand. And Sir James Bevan gave this example where he was highlighting the fact that, you know, if we have water supply decreasing and water demand increasing, you get this point where they cross and and that's called the jaws of death because we don't have enough. 

00:09:53 Dr Gemma Coxon 

Water to meet water supply to meet demand. 

00:09:57 Dr Gemma Coxon 

Now. 

00:09:59 Dr Gemma Coxon 

Is part of that speech, he said that, you know, many areas of the UK will are projected to face severe water shortages by 2050 unless we do something now in terms of what we can do now, I think one of the key things is. 

00:10:18 Dr Gemma Coxon 

But this is really an interdisciplinary problem. 

00:10:22 Dr Gemma Coxon 

You know you've got the water supply, which is kind of. 

00:10:25 Dr Gemma Coxon 

More of the physical science side, you know how rainfall and evaporation transform themselves into a change in river flow, but then you've got water demand, which is very much, you know, more in a social science kind of realm. It's looking at behaviours of water patterns and water usage. It's thinking about how we can. 

00:10:45 Dr Gemma Coxon 

Change behaviour so that you don't leave a tap running for example, whilst you're brushing your teeth. 

00:10:51 Dr Gemma Coxon 

So I think one of the key solutions is that and I think actually hydrology is getting better at this is that we we need to work as an interdisciplinary community to be able to address some of these challenges and thinking about you know. 

00:11:11 Dr Gemma Coxon 

How we can work with a broader team of people I think is going to be really important. The other thing I think. 

00:11:22 Dr Gemma Coxon 

That we can do to address this, we've got lots of wonderful hydrological models. 

00:11:28 

That. 

00:11:28 Dr Gemma Coxon 

Provide us with projects projections of how flows might change in the future. I think those models need to be better adapted to reflect some of these water demand issues. 

00:11:42 Dr Gemma Coxon 

So. 

00:11:44 Dr Gemma Coxon 

Thinking about so, currently our our models are very good at kind of. 

00:11:50 Dr Gemma Coxon 

You know, taking an estimate of rainfall and transforming it into a river flow. What they're not so great at is thinking about, well, if if a farmer is going to abstract a lot of water just upstream. 

00:12:02 Dr Gemma Coxon 

You know and and apply that water to to his land. How might that affect the stream flow or how might that affect a decision maker further downstream or the behaviour of someone else because there's not enough river flow in your river. 

00:12:19 Dr Ross Woods 

Right. So there's a whole lot of other parts of the water cycle. 

00:12:25 Dr Ross Woods 

Beyond. 

00:12:27 Dr Ross Woods 

But but, but our model is used to representing. So yeah, lots of those models. 

00:12:33 Dr Ross Woods 

We've used them to put water. 

00:12:37 Dr Ross Woods 

To figure out how much water is at the beginning of the land cycle in effect. 

00:12:42 Dr Ross Woods 

Where it's the inflows to reservoirs, although recharge to groundwater, but there's actually a whole lot of other stuff going on. 

00:12:50 Dr Gemma Coxon 

What about the solutions, do you think on the flood site? Where do you think, yeah. 

00:12:55 Dr Ross Woods 

There's a bunch of different places where. 

00:12:59 Dr Ross Woods 

Things are needed. Some of that is to do with cities. 

00:13:03 Dr Ross Woods 

So. 

00:13:05 Dr Ross Woods 

In where? 

00:13:08 Dr Ross Woods 

Well as as. 

00:13:09 Dr Ross Woods 

Cities are built at the moment. There's not. There's not so much opportunity for water to be affected by the soil conditions of whether things are dry or wet or not. There's a lot more of the paved areas and things like that where you can't really store any water. And in those places it's actually quite challenging problem. It's quite a big. 

00:13:30 Dr Ross Woods 

Infrastructure problem because the pipes that we use to carry that storm water around, it's quite tricky to make them. 

00:13:39 Dr Ross Woods 

Yeah. 

00:13:40 Dr Ross Woods 

So yeah, I think one of the big challenges for cities is finding more space to put water when it first arrives on the ground. 

00:13:50 Dr Ross Woods 

And for cities that are already really densely inhabited, that's a big challenge. 

00:13:55 Dr Ross Woods 

For new build subdivisions. 

00:13:59 Dr Ross Woods 

We've got the opportunity to plan ahead and reserve some land. 

00:14:05 Dr Ross Woods 

And say this is a place where we'd like to store water when it rains and have it drain away slowly afterwards so that there's not so much extra water turning up in our stormwater drains at the time. 

00:14:22 Dr Ross Woods 

But yeah for. 

00:14:24 Dr Ross Woods 

Densely built cities. It's a big challenge. 

00:14:27 Dr Ross Woods 

The other thing that comes with that is. 

00:14:31 Dr Ross Woods 

Where we have combined sewers where? 

00:14:35 Dr Ross Woods 

The trains are carrying. 

00:14:38 Dr Ross Woods 

Not just our storm water, but maybe. 

00:14:43 Dr Ross Woods 

There's been some sewage that's either being carried by a drain or that's leaked from a pipe into our storm water systems. 

00:14:54 Dr Ross Woods 

UM. 

00:14:55 Dr Ross Woods 

Dealing with that pollution, it's going to be quite a big issue for us as well. So and there again, we've got quite big challenges because lots of that infrastructure is 100 years old and it's highly underground in the countryside, it's a slightly different story. 

00:15:12 Dr Gemma Coxon 

I was gonna. I was just about to ask you. What do you think about? 

00:15:16 Dr Gemma Coxon 

You know, nature based solutions and and in particular natural flood management, because there's something I'm really interested in as well. 

00:15:23 Dr Ross Woods 

Natural flood management. It's the idea that. 

00:15:28 Dr Ross Woods 

In places where there's space, we might be able to hold back some of the water during the flood. 

00:15:34 Dr Ross Woods 

And there's lots of different ways of doing that. Examples of that. 

00:15:40 Dr Ross Woods 

Might be. 

00:15:43 Dr Ross Woods 

Putting lots of pieces of wood and tree branches in the stream to partially block the stream so that it slows it up a bit. 

00:15:54 Dr Ross Woods 

Another option is. 

00:15:58 Dr Ross Woods 

Making use of ditches as. 

00:16:03 Dr Ross Woods 

Places to store water during floods, so this is good because it means that not all the rain that falls now has to be discharged into the stream. Right now that we can slow it down, which is a good thing. 

00:16:17 Dr Ross Woods 

I think the challenge with those is to get our expectations right for which events those can deal with that. There's only so much water that you can hold back. 

00:16:29 Dr Ross Woods 

On by holding it in places in the landscape. 

00:16:33 Dr Ross Woods 

And there are limits to that. So when we get to the most severe floods. 

00:16:39 Dr Ross Woods 

Maybe the effect of those natural flood management techniques is not going to be so large that I think at the moment my understanding is they have their most value for medium sized floods. 

00:16:52 Dr Ross Woods 

Yeah you can. 

00:16:54 Dr Ross Woods 

Hold those back. Have the water drain off the land more slowly so. 

00:17:00 Dr Ross Woods 

For floods that are or for rainfall events that are currently pretty small but are going to get bigger. 

00:17:07 Dr Ross Woods 

And maybe turn from small ones into medium sized ones. 

00:17:11 Dr Ross Woods 

That water will not be able to hold back. 

00:17:14 Dr Ross Woods 

But for what's currently a big flood, that becomes even bigger if climate change means that atmosphere can hold more water and we get bigger rain storms. 

00:17:24 Dr Ross Woods 

There I think it's going to be challenged to hold those back. 

00:17:28 Dr Ross Woods 

I think. 

00:17:30 Dr Ross Woods 

The yeah, we've got to think about other things. 

00:17:36 Dr Ross Woods 

At least not rely entirely on natural flood management in the sense of holding water back as the solution, because there are limits to that. 

00:17:47 Dr Gemma Coxon 

Yeah, I think. 

00:17:49 Dr Gemma Coxon 

The combination of kind of measures is really interesting and when we're. 

00:17:57 Dr Gemma Coxon 

Thinking about adaptation measures and no, you know from a natural flood management side, there's been a really big drive recently, particularly in the UK to, you know, to quantify, to assess and estimate you know the the impact of these natural flood measures so that we can say. 

00:18:17 Dr Gemma Coxon 

You know well. 

00:18:18 Dr Gemma Coxon 

Actually, for these size droughts, yeah, droughts, floods. 

00:18:22 Dr Gemma Coxon 

But these size floods, they will have an impact. But you know, once you get to a really, really big event that you know we we need other measures in place. 

00:18:32 Dr Ross Woods 

Yeah. I think one of the really interesting features of those is connected to what you said about the. 

00:18:40 Dr Ross Woods 

This the more interdisciplinary side of our work that. 

00:18:45 Dr Ross Woods 

For these kind of nature based solutions to work, we really need to implement them in a lot of places because the floods that we see in really big rivers, those are made from the accumulation of water and lots and lots and lots of tiny little streams that all joined together. And those are all starting. 

00:19:05 Dr Ross Woods 

On the properties of individual land owners, landholders. 

00:19:09 Dr Ross Woods 

And for this kind of natural flood management to make a difference. 

00:19:13 Dr Ross Woods 

We need to do that when the stream is still really quite small. 

00:19:18 Dr Ross Woods 

Because once you've got a river that's five metres wide, you're not really going to be able to. 

00:19:23 Dr Ross Woods 

Put anything in there that's going to hold any water back unless it's a huge engineering structure basically. So if we want the nature based approach, we need to do it in small and in many, many places, which means talking to an awful lot of people because it's their land. 

00:19:40 Dr Gemma Coxon 

Yeah, and I think, UM, uh, the the government government sort of on quite a big drive at the moment to plant more trees. 

00:19:50 Dr Gemma Coxon 

Across the UK for various benefits, not not just for not just for water. 

00:19:58 Dr Gemma Coxon 

And finding space for that to happen and planting those trees critically in the right places so that they don't have unintended consequences on other aspects of the water cycle is really is really important. 

00:20:15 Dr Ross Woods 

Yeah, I I think that tree thing is a. 

00:20:17 Dr Ross Woods 

Really. 

00:20:18 Dr Ross Woods 

Multi dimensional idea. There's lots and lots and lots of interesting impacts. 

00:20:25 Dr Ross Woods 

So one of them that's good from a flooding point of view is that if. 

00:20:31 Dr Ross Woods 

If you plant trees, then more of the rain that lands in the place where the tree is. 

00:20:38 Dr Ross Woods 

If you if you put trees in where there was formerly a much smaller vegetation then. 

00:20:45 Dr Ross Woods 

Because it's a tree, it will catch more water on its leaves, and that has the opportunity to get evaporated away and its roots are deeper than a lot of other plants, so it can take more water out of the soil. So overall. 

00:21:00 Dr Ross Woods 

You do get drier soils. 

00:21:02 Dr Ross Woods 

If you have trees for other things, be equal. If you put trees in instead of grass, then you get drier soils. 

00:21:09 Dr Ross Woods 

And that's a good thing from flood reduction point of view, because if the soil is drier, there's more space to store water in it. And in the UK, having space in the soil to store water is the main way. 

00:21:21 Dr Ross Woods 

That. 

00:21:23 Dr Ross Woods 

Is a major control on the size of floods. 

00:21:28 Dr Ross Woods 

But yeah, the the story of the impact of trees is goes a lot further than what size of the floods. 

00:21:37 Dr Ross Woods 

So some some of it has an effect on your interest in droughts. Wonder if you want to. 

00:21:42 Dr Ross Woods 

Tell us a bit about that. 

00:21:44 Dr Gemma Coxon 

Yeah, so from a. 

00:21:45 Dr Gemma Coxon 

A drought perspective, you know, following on from your good description of what happens, you know when you plant, plant a tree, if you've got. 

00:21:54 Dr Gemma Coxon 

Got got less rainfall entering the soil system, so your soils are drier. You've got less water then you know flowing into your or kind of moving through the soil system into your rivers. But also you have less water recharging your groundwater systems. So in the UK. 

00:22:14 Dr Gemma Coxon 

1. 

00:22:15 Dr Gemma Coxon 

Of the key controls on river flows is. 

00:22:18 Dr Gemma Coxon 

The type of aquifer, essentially that underlays underlays the soil system and an aquifer essentially acts like a giant sponge. It soaks up all this water that's being infiltrated through the soils and gets recharged. 

00:22:37 Dr Gemma Coxon 

And then it slowly releases it out into the river. 

00:22:42 Dr Gemma Coxon 

Now if you have less water going into your giant sponge, you're going to have less water kind of being released into the river, and our groundwater systems are really important because they sustain quite a lot of water supply during the summer when rainfall is really low in the groundwater system. 

00:23:02 Dr Gemma Coxon 

You know that rain takes a long time to travel from hitting the land, going through the soil system, and then moving through that aquifer. 

00:23:11 Dr Gemma Coxon 

UM. 

00:23:12 Dr Gemma Coxon 

And so often in groundwater systems, you just get a nice, steady kind of base flow. 

00:23:18 Dr Gemma Coxon 

All throughout the year now, if you plant trees. 

00:23:22 Dr Gemma Coxon 

Might find that that base flow starts to get reduced and so we don't get that additional water that we would usually get in the summer. We don't get that water that's recharged, you know, from winter rainfall that's recharged back through the system. 

00:23:36 Dr Gemma Coxon 

And So what might be good for floods might not be so good for droughts. 

00:23:43 Dr Ross Woods 

I guess there's. 

00:23:44 Dr Ross Woods 

Lots of other dimensions of the tree planting question, the kind of outside the areas that we work in, things like. 

00:23:53 Dr Ross Woods 

Impacts on animal habitat and carbon capture. 

00:24:00 Dr Ross Woods 

Those sorts of things which are not really our field, they're also a really important part of deciding what would be a good policy for how we use our land. 

00:24:10 Dr Ross Woods 

And where would be really good places to plant. Trees will be places we might like to avoid. 

00:24:18 

And. 

00:24:19 Dr Gemma Coxon 

Building up the evidence base for that is actually it's quite challenging because as you said, we need to test it in a number of places because we know that you know, the terrestrial water system will act in interesting and surprisingly different ways depending on where we plant the trees. 

00:24:40 Dr Gemma Coxon 

We need to test. 

00:24:41 Dr Gemma Coxon 

That for a range of conditions and I don't know about you, Ross, but every time I've embarked on a project to study droughts, it's inevitable that, you know, the next five years there will be absolutely no droughts during during that period. 

00:25:00 Dr Ross Woods 

Well, maybe the water companies should hire you to get more research funded as a sort of insurance policy against. 

00:25:12 Dr Gemma Coxon 

Uh, that would be good. I'm so we need to test it in a lot of places we need to. 

00:25:18 Dr Gemma Coxon 

Test it for. 

00:25:19 Dr Gemma Coxon 

A range of events and you know we need to need to look at, look at, you know the different impacts like you were saying and I think it draws back into that interdisciplinary nature. 

00:25:32 Dr Gemma Coxon 

Of you know, we need to think about ecology and societal benefits of having a wetland and not just the impacts that it has ultimately on on the river flows and. 

00:25:47 Dr Gemma Coxon 

From a water perspective, I think you know, I think one of the reasons why we focus so much on rainfall changes, for example, is because they are easy to measure. 

00:26:00 Dr Gemma Coxon 

Relative relatively easy, easy to measure. Kind of the same as river flows, they're relatively easy to measure, but water flows through the subsurface because we can't see it. It's actually really difficult to measure, and I think that's why we get these surprises. 

00:26:18 Dr Gemma Coxon 

Because yeah, there are lots of things. 

00:26:20 Dr Gemma Coxon 

We still don't know. 

00:26:22 Dr Ross Woods 

If I was to say to you, if I allow you to put your hydrologist hat on for a moment and if you would be able to talk to. 

00:26:30 Dr Ross Woods 

A land use policy maker. 

00:26:33 Dr Ross Woods 

In the UK and you could have a chat with them. 

00:26:36 Dr Ross Woods 

About just the hydrological impacts of widespread widespread planting of trees, what would? 

00:26:43 Dr Ross Woods 

You say to them. 

00:26:44 Dr Gemma Coxon 

My my key message would be that we, yeah, we need to build this evidence base of what specifically these adaptations mean. 

00:26:55 Dr Ross Woods 

4. 

00:26:56 Dr Gemma Coxon 

Flies. 

00:26:57 Dr Ross Woods 

Yep. And would you say that on balance you'd expect the impacts of tree planting on droughts to be positive? 

00:27:08 Dr Ross Woods 

Would it improve the drought situation or might actually increase the risk of droughts? 

00:27:14 Dr Gemma Coxon 

I I honestly I I can't say that it. 

00:27:17 Dr Gemma Coxon 

It would kind. 

00:27:17 Dr Gemma Coxon 

Of depend on the drought event and where. 

00:27:21 Dr Ross Woods 

OK, it's a bit more subtle. 

00:27:23 Dr Gemma Coxon 

What do you think? Do you think there is? 

00:27:25 Dr Gemma Coxon 

A definitive answer. 

00:27:27 Dr Ross Woods 

What I think that in the places where the trees are planted. 

00:27:33 Dr Ross Woods 

Less of the water is going to get into aquifers and into rivers. 

00:27:41 Dr Ross Woods 

So I think that in those places. 

00:27:44 Dr Ross Woods 

I think that there's going to be less water available than there have been. 

00:27:49 Dr Ross Woods 

And so, yeah, I I do think that the risk of droughts is likely to increase if those trees are planted in places. 

00:27:59 Dr Ross Woods 

That are at the moment. 

00:28:03 Dr Ross Woods 

An important part of the water resource. 

00:28:06 Dr Ross Woods 

It's not so easy when you get put on. 

00:28:07 Dr Ross Woods 

The spot. 

00:28:08 Dr Ross Woods 

Is it? 

00:28:12 Dr Gemma Coxon 

No, it's not. And it's it's a typical scientist thing, I think, to do to sort of say here's a statement. But here's 1000 caveats to to this to this particular statement. 

00:28:26 Dr Ross Woods 

Yep. And yeah, there's difference between. 

00:28:30 Dr Ross Woods 

The conversations that you might have in a science forum. 

00:28:36 Dr Ross Woods 

And the conversations that you might have in. 

00:28:38 Dr Ross Woods 

A policy forum. 

00:28:40 Dr Ross Woods 

Because I think you know, I think the need for information is different. 

00:28:46 Dr Ross Woods 

That for the policy people. 

00:28:50 Dr Ross Woods 

We need to give it. 

00:28:52 Dr Ross Woods 

Our best shot. 

00:28:55 Dr Ross Woods 

Which is on this side or on this side. 

00:29:00 Dr Ross Woods 

And we we can give opinions about how confident we are. 

00:29:04 Dr Ross Woods 

We can offer a judgment about how confident we are in that statement, but I think, yeah, in those forums we need to have we need to indicate a direction. 

00:29:14 Dr Ross Woods 

If we possibly can. 

00:29:16 Dr Ross Woods 

But yeah, I think in this case there's been enough experimentation to know which direction the effect goes. 

00:29:22 Dr Ross Woods 

In. 

00:29:25 Dr Ross Woods 

A tricky bit is about saying well. 

00:29:28 Dr Ross Woods 

Because there are a whole bunch of other benefits. 

00:29:32 Dr Ross Woods 

Like the benefits for reduction, flooding for carbon capture for improved habitat. 

00:29:40 Dr Ross Woods 

Figuring out how to weigh. 

00:29:41 Dr Ross Woods 

Those up. 

00:29:43 Dr Ross Woods 

And yeah, that's quite tricky. 

00:29:47 Dr Gemma Coxon 

What do you think the major? 

00:29:48 Dr Gemma Coxon 

Challenges are on the flood side. 

00:29:51 Dr Ross Woods 

I think one of our big challenges is. 

00:29:54 Dr Ross Woods 

Untangling. 

00:29:57 Dr Ross Woods 

All the different things. 

00:29:59 Dr Ross Woods 

That are going on to cause floods to be the size that they are. 

00:30:04 Dr Ross Woods 

I think I'm speaking maybe a bit more from a science point of view. 

00:30:10 Dr Ross Woods 

That a management point of view, but it's one of the things that I find is really interesting about my job, is that the reason that floods are the size that they are is a huge combination. Lots of different things to do with. 

00:30:25 Dr Ross Woods 

Lots of different dimensions of the climate. 

00:30:28 Dr Ross Woods 

And also how the lens being used and what kind of soils there, what geology and geological history it's derived from? 

00:30:40 Dr Ross Woods 

Yeah, there's a huge number of things all tangled up together, and then when someone asks you a question about, well, what if I was to change one piece in this puzzle? If I was to change just the intensity of their rainfall but nothing else, or I was to change just the way that the land is used. 

00:30:59 Dr Ross Woods 

But nothing else that for me that means I have to know exactly. 

00:31:06 Dr Ross Woods 

What part in the puzzle? 

00:31:08 Dr Ross Woods 

So. 

00:31:09 Dr Ross Woods 

Piece was playing or the land cover piece was playing or the climate piece was playing, and at the moment what we get to see when we make measurements of what's happening in rivers is. 

00:31:20 Dr Ross Woods 

A combination of lots and lots and lots of different things. 

00:31:23 Dr Ross Woods 

Yeah, so for me. 

00:31:25 Dr Ross Woods 

For me, that's a big science challenges untangling all of those pieces. 

00:31:31 Dr Ross Woods 

I'm. 

00:31:34 Dr Ross Woods 

And because I'm not yet very clear on exactly how to untangle them, it means that it's quite a big challenge to say well. 

00:31:43 Dr Ross Woods 

So what if this happened? What if something changed in this place? How different would it be if rainfall changed in the southeast of the UK versus in the Northwest? 

00:31:55 Dr Ross Woods 

What difference does that make? And that's quite a tricky question to answer. Or what if I plant tree? What if I plant more trees in the southeast versus planting more trees in the northwest? 

00:32:07 

And. 

00:32:07 Dr Gemma Coxon 

Then when you get to kind of a a policy point of view taking, taking those you know very tricky kind of science recommendations and turning those into a series of you know adaptation measures. 

00:32:22 Dr Gemma Coxon 

To ensure we're. 

00:32:24 Dr Gemma Coxon 

You know in. 

00:32:26 Dr Gemma Coxon 

We're resilient, I guess, to to future events I think is is really challenging. 

00:32:35 Dr Ross Woods 

But in the end, I guess people still have to make decisions. 

00:32:40 Dr Ross Woods 

And. 

00:32:42 Dr Ross Woods 

So I think one of the challenges for us is being able to say. 

00:32:47 Dr Ross Woods 

How confident we are? 

00:32:50 Dr Ross Woods 

Or not? And how to have that information about confidence be useful? 

00:32:56 Dr Ross Woods 

To the people who are trying to make the decisions, because if someone asks. 

00:32:59 Dr Ross Woods 

Me and I say. 

00:33:02 Dr Ross Woods 

I think it's this much, but I really don't know. I mean, that's really not very helpful at all. 

00:33:07 Dr Ross Woods 

Just to say I'm uncertain. 

00:33:10 Dr Ross Woods 

But on the other hand, if I'm just to say or the answer is, 82 cubic metres per second. 

00:33:17 Dr Ross Woods 

That's not being very honest, because I I know that I don't know the answer that precisely. 

00:33:23 Dr Ross Woods 

There's uncertainty there, and that probably affects the way that people make decisions. 

00:33:30 Dr Ross Woods 

So yeah, handing over just the right amount of information about my uncertainties. 

00:33:38 Dr Ross Woods 

Yeah. Challenge something that. 

00:33:42 

I've. 

00:33:43 Dr Gemma Coxon 

Kind of been thinking about. It's also the the speed. 

00:33:48 Dr Gemma Coxon 

At which we need to make some of these decisions. 

00:33:54 Dr Gemma Coxon 

So you know, we have a climate. 

00:33:56 Cabot Institute  

That's. 

00:33:57 Dr Gemma Coxon 

You know quite rapidly changing. 

00:34:00 Dr Gemma Coxon 

We have a human population that is quite rapidly changing, dealing with those non stationary aspects, particularly when we don't have historic events to kind of base our understandings on. I think is a is a really interesting challenge. There's. 

00:34:21 Dr Gemma Coxon 

You know, how do you deliver the right information, but also at the right time. If you look at, for example, how the climate is projected to change in the next 30 or 40 years, if you look at the climate, you know the UK CPA team. So the UK climate projections from 2018. 

00:34:41 Dr Gemma Coxon 

If you look at look at that output and what they're projecting, I think in the in the sort of southwest for example, where we. 

00:34:52 Dr Gemma Coxon 

You know it's it's sort of around about a 3040% decrease in rainfall during the summer and around about 10 or 20% increase in rainfall during the winter. And those are quite, I mean those are significant shifts. 

00:35:07 Dr Ross Woods 

Yes, we haven't really been used to. 

00:35:10 Dr Ross Woods 

Planning for change? You know, we kind of we get in the habit. 

00:35:14 Dr Ross Woods 

Of thinking of. 

00:35:16 Dr Ross Woods 

Building stuff to suit the way things are now. 

00:35:21 Dr Ross Woods 

And it's. 

00:35:22 Dr Ross Woods 

I mean, although in the technical fields that we work in. 

00:35:26 Dr Ross Woods 

That idea of dealing with change is something we've been working on for 20 or 30 years, probably. 

00:35:34 Dr Ross Woods 

Getting that into the mindset of the entire society. 

00:35:40 Dr Ross Woods 

That's quite a big challenge. That's a. 

00:35:42 Dr Ross Woods 

So sort of cultural shift, almost that you don't expect the future to be quite like the past? 

00:35:49 Dr Gemma Coxon 

How do you think policy policymakers might? 

00:35:52 Dr Gemma Coxon 

Be able to. 

00:35:54 Dr Gemma Coxon 

Adapt to these changes or what do you think we need to be doing now to better adapt to these changes? 

00:36:03 Dr Ross Woods 

Some of it is. 

00:36:06 Dr Ross Woods 

Working with them on developing scenarios for how things might be different. 

00:36:13 Dr Ross Woods 

In the future, sort of imagining the future. 

00:36:20 Dr Ross Woods 

I think it's pretty difficult to actually imagine. 

00:36:24 Dr Ross Woods 

How things might be 30 years from now, what we might be wanting from water or dealing with water. 

00:36:31 Dr Ross Woods 

Don't really know, but I think. 

00:36:33 Dr Ross Woods 

Just the act of creating those scenarios. 

00:36:37 Dr Ross Woods 

Will help us maybe to realize that we might need some resilience to some kind of change and we might be guessing the wrong kind. 

00:36:46 Dr Ross Woods 

At the moment, because we can't see. 

00:36:49 Dr Ross Woods 

30 years ahead in the same way that when I was 20 year old, I couldn't have imagined the Internet. 

00:36:56 

Umm. 

00:36:58 Dr Ross Woods 

But I might have imagined that technology would develop and be different. 

00:37:03 Dr Ross Woods 

It's not in the particular way that it was that. 

00:37:07 Dr Ross Woods 

Having video calls with people was something that only happened on the Jetsons. 

00:37:12 Dr Ross Woods 

And not really anywhere else, but the concept of the video call exists and I think in the same way for future scenarios, imagining a scenario where we were. 

00:37:25 Dr Ross Woods 

Very short of water. 

00:37:27 Dr Ross Woods 

For some reason, and we can. 

00:37:29 Dr Ross Woods 

Create a scenario that helps that happen. That seems believable now, but it might not be. 

00:37:33 Dr Ross Woods 

Quite the right one. 

00:37:35 Dr Ross Woods 

But I think, yeah, the act of creating those scenarios and saying. 

00:37:40 Dr Ross Woods 

What if? What will? What will we do then? 

00:37:45 Dr Ross Woods 

Or what if what if floods were 20% bigger? 

00:37:50 Dr Ross Woods 

For now, now what would we do? 

00:37:53 Dr Ross Woods 

Where would we? 

00:37:55 Dr Ross Woods 

Where we want to live, where would we want to do things? 

00:38:01 Dr Ross Woods 

Which pieces of land would we treat as stable? 

00:38:06 Dr Ross Woods 

And secure. 

00:38:09 Dr Ross Woods 

Yeah. So I think those are useful thought exercises to have. Now we can have the opportunity. 

00:38:17 Dr Ross Woods 

To imagine bits of the future, at least. 

00:38:20 Dr Gemma Coxon 

I think that would be would be really productive and it's I guess it's not just policymakers that that you would need to build those scenarios and talk through those scenarios with it. It would be farmers and. 

00:38:36 Dr Gemma Coxon 

Land use policymakers and water resource managers and a whole. 

00:38:42 Dr Gemma Coxon 

Host of other other people. 

00:38:45 Dr Ross Woods 

People who might use water industries, water or food production or energy production. 

00:38:54 

War. 

00:38:55 Dr Ross Woods 

Waste management. 

00:38:58 Dr Ross Woods 

All aspects for dilution. 

00:39:01 Dr Ross Woods 

So maybe Jim, do you want to say a bit about? 

00:39:06 Dr Ross Woods 

What sorts of things make Bristol an interesting place and an yeah an interesting place for you to do this kind of work? 

00:39:14 Dr Gemma Coxon 

I'm in a good place to be able to talk about that, cause I I did my undergraduate at Bristol a very long time ago now. 

00:39:23 Dr Gemma Coxon 

And I I've never left, which I think I think tells you something about hopefully the strength and diversity of the water group at Bristol. I think we are incredibly fortunate. 

00:39:45 Dr Gemma Coxon 

To be part of a really thriving and interdisciplinary group and one of the things that I think makes. 

00:39:56 Dr Gemma Coxon 

The water group at Bristol, quite unique is that we have, you know, a lot of people. 

00:40:05 Dr Gemma Coxon 

Who work, you know, kind of in in similar areas but on different aspects, but we have a lot of people kind of who call themselves, you know, a hydrologist or a water resource specialist or someone who looks at the social aspects of water, for example. 

00:40:27 Dr Gemma Coxon 

UM. 

00:40:28 Dr Gemma Coxon 

And that means that we have these conversations frequently, you know, about how we can translate our science into something that has impact. And also we've spoken a lot in this discussion about. 

00:40:49 Dr Gemma Coxon 

You know, interdisciplinary measures and kind of working as part of the the water group, also through Cabot. 

00:41:00 Dr Gemma Coxon 

I think is is a really great way to kind of fuel those collaborations. 

00:41:07 Dr Gemma Coxon 

Anything else you'd like to add, but I know you've. You're a long time too now. 

00:41:12 Dr Ross Woods 

Not quite. As long as you almost, almost. I think one of the things I moved here about eight years ago and one of the things that I've really enjoyed is the feeling that I'm in a team environment. 

00:41:26 Dr Ross Woods 

And I really enjoy that a lot. 

00:41:30 Dr Ross Woods 

Yeah, it. I'm just tremendously lucky with the people I get to work with. It's fantastic. 

00:41:36 Dr Gemma Coxon 

So, boss, what's your key point you would like to get across to policymakers about the impacts of climate change on the water system? 

00:41:48 Dr Ross Woods 

The thing that I'd like to say is. 

00:41:50 Dr Ross Woods 

If you're going to use planting of more trees as. 

00:41:56 Dr Ross Woods 

One of the ways of reducing the impacts of climate change. 

00:42:01 Dr Ross Woods 

Then try to look beyond just the impacts on the carbon cycle and on carbon storage carbon capture, but also think about the impacts on the water cycle that planting more trees has a positive effect on the water cycle from the point of view of in some places reducing the size of floods. 

00:42:22 Dr Ross Woods 

Which is really great because the floods are significant source of damage for society. 

00:42:28 Dr Ross Woods 

But also think about the impacts of planting trees on droughts, because planting trees is likely to exacerbate make worse the risk of droughts. So. 

00:42:40 Dr Ross Woods 

Just a plea to weigh up all of those factors when you're looking for recommendations about how to mitigate impacts of climate change. 

00:42:51 Dr Ross Woods 

So, Gemma, if you were to have. 

00:42:56 Dr Ross Woods 

One message for policymakers about the impacts of climate change, what would you say to them? 

00:43:03 Dr Gemma Coxon 

I would say. 

00:43:04 Dr Gemma Coxon 

That a lot of the impacts of climate change are going to be felt through the water system. So whether that be. 

00:43:15 Dr Gemma Coxon 

Increased rainfall, potentially a resulting in a in a flooding event that you know impacts homes and families, or whether those changes in rainfall will result in more droughts. That means that we need to think about public water supply and. 

00:43:35 Dr Gemma Coxon 

How much water we have to irrigate crops? 

00:43:39 Dr Gemma Coxon 

It's not just. 

00:43:42 Dr Gemma Coxon 

Changes in our climate that are important, but it's thinking about how those changes in rainfall and temperature get translated into a change in how water moves through the terrestrial system. And so to engage with hydrologists to think about. 

00:44:03 Dr Gemma Coxon 

How those impacts of climate change will will manifest themselves. 

00:44:13 Cabot Institute  

You can find out more about the Cabot Institute for the environment at bristol.ac.uk/cabot.