Floods and Climate Change

Hello. My name is Dr Linda Spate

and I'm a lecture here at the University of Oxford.

I work in hydro meteorology.

That means I work in the interface between hydrology and meteorology.

And I look at how do we make sure that we make the

best use of weather forecast so we can have efficient flood warnings?

And that's the topic I'm going to talk to you about today.

So water is essential to life on earth.

Too much of it, or too little of it can spell disaster. They

only extreme storms like hurricanes, caused more damage than floods.

The impacts of floods can be catastrophic.

Immediate, there's damage to infrastructure,

buildings and potentially loss of life.

Then there's economic impacts,

disruption to business and life as we know it,

or potentially damage to crops,

meaning that the food prices go up or famine could occur.

This impacts to health.

It's not good to have dirty water mixed with clean water,

washing down the streets and into our houses.

And then the longer term we could have impacts

from water borne diseases spreading when water is inundated.

The floodplain,

then last but not least, is the emotional impacts of floods.

If you have water in your house,

it can take years to get overcome the trauma of that situation.

According to insurers,

the 2021 floods in Western Europe was one of the costliest natural catastrophes

in modern European history.

But it wasn't just Europe that was affected.

In July 2021 alone,

there was 124 floods reported in 24 countries around the world.

That was just one month snap snapshot.

This is playing out,

over and over again and we're seeing more and more floods happening.

Our experiences in 2021 show that nowhere is prepared for

flooding on the scale that we are starting to see.

So let's talk a little bit about floods and climate change.

The latest IPCC report, released earlier this year,

stated this unequivocal that humans have warmed our planets.

This statement is based on an in

depth analysis of changes to global average temperatures

when it comes to floods, though were not really interested in averages.

It's the extremes

that we're concerned about, particularly the extremes of rainfall,

so there's an image that you can look at here,

which shows that when we change the mean of the distribution,

we also move the extreme tail of the distribution.

That means that it's more likely that we'll see extreme events.

So

the image here is looking at a temperature.

The relationship between temperature and rainfall is complicated,

but put simply, warmer air can hold more water.

That means that you can evaporate more water from the oceans, and when it rains,

it really pours

So using attribution, SCIENCE

Post Event reviews has shown that recent events around the world

have not just become more likely due to climate change,

but virtually impossible without it.

But it's not just climate change,

which is making floods more impactful and more damaging.

Alongside the changing climate,

we've had increasing populations and changing ways in which we

use the land and manage the way we use water.

This also increases the stress on natural systems.

I mean, they're less able to cope when we see these extreme rainfall events

and with more people living on the floodplain,

more impacts will happen when it floods because there's

just more people in palms in harm's way.

There's an argument that states that there's really

no such thing as a natural disaster.

The decisions that humans make in the way that we live and

manage our society make these impacts when these natural hazards happen.

Worse.

So today we're talking about flood forecasting and warning.

This is one way that we can build resilient communities, but it's not the only way.

Flood warning alone won't reduce all the impacts of floods.

We also need to consider flood defences to keep water away

from the places that are most vulnerable or most economically important.

We need to manage catchments.

We don't actually want the water to get down to our towns and cities.

We want to keep upstream

in the rural areas where we can perhaps make the best

use of natural storage to slow down the flood peaks.

We want to build cities with space for water.

So we have green areas where water can pool

rather than rushing down the streets and into houses.

We want to build resilient communities where

people know and understand about flooding,

so that made people realise that they are at risk

of flooding and that they can do something about it.

It's not something that we want to have a

fear topic It's something that we want to say.

This is something you need to understand so that when the worst events happen,

you already

and actually have designed their houses so that when water does come in,

then they can quickly dry them out and get back to normal.

Flood warnings can save lives,

and that's why I think is really important and really

interesting and why I want to work in this area.

But first, let's start with some definitions.

So flood forecasts, combined weather information,

current river levels and understanding about where water

will go in a catchment when it rains.

They used to predict river flow and water level.

It's not an exact science as we'll discuss later,

and there's lots of uncertainties along the way.

Flood warnings are a way of communicating the flood forecast

that enables people, businesses and organisations to take action.

You'll probably find out I use the two terms interchangeably in this lecture,

whose flood warnings are really the penultimate

step in a flood forecasting system.

You can see that system in the diagram here,

Um, it's a chain of events, a chain of activities,

and they're all linked together through these bridges So the

idea of this diagram is showing that the mountains,

the things we know about and the bridges are the links between them.

The high mountains are supposed to indicate that we know more about these areas

and the smaller mountains, areas where we're still researching and working on it.

So you can see that the flood forecasting chain starts with observations.

We then move on to the weather forecast and the hazard forecast in this case, floods.

We want to try and understand a little bit about impacts,

and we can find all this information together to reduce the warning.

Then the final stage is a decision.

Uh,

warnings really have no value unless someone can take

action on them and make an appropriate decision.

So, in a break from tradition,

I'm actually going to start at the end with the decision making