There's a Storm a Coming

The UK has just experienced its first named storm of Autumn 2016, Storm Angus, which hit the UK on the 20th November. As a result, there were some quite nasty weather conditions and impacts for the south of the UK - flooding, power cuts, ships running aground, and car accidents causing people to be hurt, though there were thankfully no fatalities. Take a look at this nice summary by the Met Office if you are interested in what happened. It is too early to say how much damage was caused by the storm, but this picture of a street in Bristol indicates the sort of issues that might have occurred:

Credit: Lee Gitsham/PA

In light of this recent storm, and following on from the article about jet stream research I posted a few weeks back, I thought it topical this week to explore the relationship between intense weather events and climate change, with a particular focus on the UK. At a global scale, there is consensus from the IPCC that climate change will lead to more extreme rainfall events in the future, but with a higher number of dry days. This is caused by the fact that in a warming world, air can hold more water vapour before it reaches the point where it must fall as precipitation. As such, there will be less rainfall events as a whole (it takes longer for the amount of water needed for there to be rain to build up), but the rainfall events that do occur will be more extreme in both their intensity and duration. There are obvious implications from this sort of climatic arrangement - an increased risk of flooding, damage, and loss of life during extreme weather events.

The discussion has already begun as to whether the recent Storm Angus has been influenced by climate change. The UK has experienced a succession of strong and destructive winter/autumn storms in the past 5 years, leading to widespread debate as to whether climate change is affecting weather patterns in the UK. During the recent severe floods of 2013/14 in southern England, Prime Minister at the time David Cameron told parliament that he 'very much suspected' anthropogenic climate change was associated with the event.  These floods were quite severe, and caused by continual low pressure storm systems moving in from the Atlantic across southern England, with a consistent amount of high level precipitation leading to flooding.

It is very hard to pin a single extreme weather event to climate change; it is simply one event in a chaotic system, and it is hard to tell whether that one event is due to a change in the boundary conditions of the system, or is simply a natural part of the chaotic system. Despite that, attempts have begun to examine whether anthropogenic climate change may have increased the risk of the occurrence of heavy storms and resultant flooding that have been recently been experienced in the UK.

The first piece of such research was published earlier this year by Schaller, et al. (2016), who examined the potential influence anthropogenic climate change had on the floods of 2013/14 in southern England. They conclude (through the use of a variety of climate model simulations) that along with the atmosphere being able to hold more moisture, anthropogenic warming has likely caused a small increase in the number of January days that have a westerly airflow, and a stronger jet stream. In combination, both of these factors increase the risk of the UK experiencing events of extreme precipitation.

The study then feeds this information into a hydrological model, in an attempt to understand how this event affected the River Thames - the area around the Thames is one of the key places flood damage to property occurred during 2013/4. It is found that under these the conditions experienced in 2013/4, the 30 day average of peak river flow in the Thames increased significantly. Combining these results with flood risk mapping, a small increase is found at the number of properties at risk from riverine flooding, though there is great uncertainty in the true value of the number. Despite this, similar events of a greater intensity could lead to even greater flood damage.

All of the aspects of this study have large bounds of uncertainty - the conclusions that have been drawn are simply the best estimates of the data available, reflecting how anthropogenic climate change has so far only had a subtle impact in increasing the risk of intense precipitation events in the UK. Far more attribution studies of this type are needed to begin to understand how climate change is affecting UK weather patterns. However, it is reasonable to suggest from this study alone that it is likely anthropogenic climate change may be beginning to influence extreme weather events in the UK - keep an eye on the weather forecast this winter! The next named storm we experience in the UK will begin with a B, so guesses for the name in the comments please! I'm going for Storm Bertha.

A Glass of Water - Part 2

In my last post, I explored how increases in temperature and rainfall as a result of climate change may affect the drinking water that we rely on as humans. There are some more factors to consider though, which I will cover in this post. Before we start though, why not go to the kitchen and pour yourself a glass of water from the tap? Drink it while you read this post. While you do that, I will run through some more potential effects of climate change on drinking water.

Drought

While it is never a good thing for water to contain pollutants, it’s best to have a small amount of pollutant in a large amount of water. This means the pollutant is more diluted in the water, with less pollutant per unit of water. Think of it in terms of a glass of orange squash – the ratio of the squash to water influences how strong the taste is, and it is the same with water pollution. You are more likely to get sick from drinking water concentrated with pollutants, rather than water in which the pollutant is more diluted.

Droughts reduce the amount of water in a hydrological system, due to a lack of rainfall and increased evaporation, but the amount of any pollutants in water remains the same. As such, droughts reduce dilution of pollution, increasing pollutant concentrations in water. The IPCC suggests it is likely that the frequency of droughts will increase in presently dry regions by the end of the 21^st century, and this could have significant implications for drinking water. There are still high levels of uncertainty in the quantification and projection of drought at a regional scale using climate models, but we know that droughts have increased in the Mediterranean, Central America and South Africa, and it is projected that they will increase into the future (Orlowsky and Seneviratne, 2013). 

The effect of drought in reducing the dilution is well documented. van Vilet and Zwolsman (2008) use existing water quality data to show a decline in the water quality of the Meuse river in north-west Europe during drought conditions, with increases in heavy metals, major elements, and the amount of algae in the river (the river flowing more slowly allows algae to develop, along with an increased nutrient concentration). As we saw in the previous post, algae have a negative effect on water quality. Bonte and Zwolsman (2010) show a similar effect for two man made lakes in the Netherlands, but in this instance using modelling to attempt to predict to effect of climate change induced changes in water quality. Using climate change predictions for 2050, the model suggests an intense salinisation (the water becoming more salty) of the two lakes due to increased chloride concentration as a result of low river flows, evaporation, and reduced rainfall. 

All of these effects are not good for human drinking water - hopefully that glass of water you are drinking isn't rich in heavy metals, algae and salt. They are not good things to put into your body. 

Sea level rise

Sea level rise is perhaps the most discussed topic in all of climate change, and as we all know is a major consequence of climate change and global warming. It could have significant impacts on drinking water quality as a result of a process called saline intrusion, which involves salty sea water workings its way into a freshwater aquifer, causing groundwater to be contaminated with salt. Take a look at this before and after diagram:

On the left is the normal state of things - the freshwater (light blue) separated from the salty water (dark blue). Remember that these are not bodies of water, but just the water that is stored in rock, deep beneath the sea bed. The well will be pumping up only fresh groundwater.  On right, is a situation likely to occur as a result of sea level rise - the sea level has risen, and as a result there has been an intrusion of salt water (towards the left, in this case). As a result, the same well will now be pumping up somewhat salty water. If we assume this well is used to supply a coastal village with drinking water, you can see the problems this process of sea level rise may create. 

This isn't just a process that will happen in the future - it is already happening in Bangladesh. Here drinking water in coastal areas has become contaminated with salty, as a result of rising sea levels causing saline intrusion, along with storm surges from extreme weather systems. Khan, et al. (2011) suggest that this explains a seasonal excess of hypertension (high blood pressure) in pregnancy in the area, as the estimated salt intake of the local population is exceeding recommended limits. The level of saline intrusion will only increase in the future, potentially causing long term health problems for the area - imagine that glass of water you are drinking with extra salt added, and think of the effects it would have on your body!

Disruption of water treatment facilities

This is a short but important point that I somewhat mentioned in the previous post, but warrants re-addressing here. Increased rainfall and resultant flooding means drinking water supply systems are vulnerable to climate change, as they may be unable to cope with the increased amounts of water, particularly if that water has become polluted. Howard, et al. (2010) make the assessment that that very few current water supply technologies are resilient to climate change. It is essential that we update these technologies. My view is that access to safe drinking water is a universal human right. We must work to preserve universal access to drinking water, both through trying to reduce the effects of climate change, and preparing technologies and infrastructure for these effects.

Article - Jet Stream Research

The second part of the drinking water post is on its way, but I thought I'd point out this news article, discussing research currently being undertaken on the jet stream - a powerful high altitude wind, one which is responsible for transporting stormy weather systems towards the UK, and thus plays an important role in flooding. Later in the blog, I will talk about how changes in weather patterns will influence flooding events. The article talks more about understanding the jet stream to aid weather forecasting, but this is relevant to the hydrological cycle - prior warning of a storm that could cause dangerous flooding is very important.