How climate change affects the earth's rain

Michael Mann is from the University of Pennsylvania and author of ‘The New Climate War’. He told me what shifting patterns in rainfall will do to water availability in the UK and worldwide…

Michael - In a place like the UK, much of the water comes in the form of precipitation and streamflow, rivers and streams, that provide some persistence to the water resources that are available. In a large number of regions around the world, I believe it's as much as 25% of the world's population gets its drinking water primarily from glacial melt. And so this is one of the concerns as we lose glaciers around the world, we're losing that important source of water. And that's true certainly for parts of Europe, but for the UK again, much of that water comes from the basic hydrologic cycle where you've got the ocean, the Atlantic ocean to your west, and moisture evaporates off the ocean and then precipitates falls in the form of liquid water or in the winter. You get a little bit of that in London and much more in the Northern parts of the UK in the form of snow

Julia - With this rain water, how do we capture it so we can then drink it?

Michael - So there are various ways of storing water. Glaciers are a very important natural water storage device, but there's groundwater as well - aquifers. One of the problems is that these are not necessarily renewable water resources, at least on sort of the time scales of importance to us. So as we continue to tap these aquifers, we're depleting this longer term source, and eventually that will run out. So there's always a bit of a problem when we run into a deficit, when we're losing more water through evaporation, especially in the summer, then we're gaining in the form of precipitation primarily in winter. If that balance goes negative and we have to rely on tapping into aquifers for example, groundwater for example, then that poses a long term exposure to a very large population.

Julia - So we're seeing right now the impacts of climate change really on our water supply. And, you know, as the saying goes, it's hard to predict the weather. But with rainfall, do you know if we look ahead to the future, how that is going to change because of climate change and the trajectory that we're currently on.

Michael - Yeah. So we see more extremes at both ends of the scale, worst droughts and, and worse flooding events. And certainly we've seen that in the UK. We've seen that in Europe, we've seen that here in the United States. So that's one of the attributes of climate change, but then there are also the longer term average shifts. And we do actually expect to see more rainfall in the winter in parts of Europe and substantial parts of Europe because essentially, the atmosphere's warmer. When you get those winter storms, they're gonna produce more rainfall or in some cases snowfall. So over a large part of Europe and certainly Northern Europe, we expect to see increased winter rainfall. But here's the rub - we expect to see even larger losses of water through evaporation in the summer. And so, while we might see an overall increase in precipitation, especially in winter, that may be outpaced by an increase in water loss through evaporation. And so you get worse drought, even though you might expect to see higher rainfall amounts in the winters,

Julia - Is there a way then that we can take advantage of the higher rainfall that we potentially have in the winter by storing more rain water? Are there ways that we can capture more of this rain water when we're having it, and we're having a lot of it. So then in the summer, when the drought comes around, we're a bit more prepared.

Michael - There's a lot that we can do in the way of adaptation. That is to say we change our way of doing things. We're more efficient in our use of water. We store the water when there's excess water. Lots of things that we can do to try to limit our exposure to the impacts of climate change and so adaptation is really important. But if we allow climate change to proceed, if we allow the planet to continue to warm up and these effects to continue to get worse, we may soon exceed our capacity to adapt to these changes. And that's particularly true when it comes to perhaps the most vital resource that we rely upon as human beings - water resources,

Julia - 10, 20 years down the line, water's gonna be as precious as gold. If we keep going the way we're going, we're just not gonna have water on tap - pardon the pun - like we do now.

Michael - That's right. And we can see historical analogs for that, warnings from history. Much of the strife in the middle east, in the near east, ultimately has been driven by a long term shift in the climate towards drier conditions. In Syria, the Syrian uprising, the Syrian spring was driven in fact by a large part of migration of rural farmers, who could no longer make a go of subsistence farming because of what was, and continues to be, the worst drought in more than 900 years at least. And so this is really a warning to us that the battle for water resources will quickly lead to political and societal instability. If we, again, don't mitigate by reducing carbon emissions and stopping the continuation of the warming and put in place adaptive measures to deal with those changes that are now baked in, that we can no longer avoid.