The Bigger Picture

Earth is a wonderfully diverse place. As a planet, we are incredibly unique – no other planet (that we are aware of) can claim such environmental diversity. We always come first in the Known Universe Gardening Competition (as judged by the Vogons).

'Second place again?' Image Credit: Apak Studios

                                                           
Our unique atmosphere and range of environments means that different regions are likely to react quite differently to climate change. In the context of river discharge, this makes prediction quite difficult. There are many different natural and anthropogenic forces that may force changes in river discharge, and each may act with a different magnitude. 

Climate change will likely accelerate the hydrological cycle – this could increase discharge (more precipitation), or decrease it (evapotranspiration operating as a counterbalance). Discharge will increase in some areas of the world, decrease in other areas, and not change at all in others. Our blue marble responds in varying ways to the new pressures it has likely never experienced before. 

A map of projected percentage changes in discharge (from the mean) around the world. From Nohara, et al. (2006)

Modelling work using complex Global Circulation Models has generally been consistent in identifying how different regions of the world will be affected. Discharge is projected to decrease in the Mediterranean, Central America and southern Africa. In contrast, discharge is expected to increase in the high latitudes, southern/eastern Asia, and central Africa. These changes will occur because of changes in annual mean precipitation, evaporation and runoff – if precipitation is greater than evaporation, there is more runoff, and greater discharge (and vice versa).

It is clear that this whole idea of changing river discharge and climate change is not a simple exercise. Many have claimed that global river discharge has increased during the 20^th century, but some studies would suggest neither discharge nor precipitation changed much during the last half of the 20^th century. If this is true, viewing the problem of changing discharge though a global lens may be a naïve approach – each region of the world has rivers that will react in very different ways.

This is going to be harder than we thought.

Setting the Scene

A poorly fitting blazer. A textbook of infinite boredom. A hastily drawn scribble and definition of an oxbow lake. Reeling off case studies like you do it all day. Boasting to your parents that you know what a thalweg is.

I fear that these may be many peoples memories when you mention the words ‘geography’ and ‘rivers’ are mentioned in the same sentence. Based on my own school experiences, I would not blame anyone for reaching those conclusions. School geography is often hopelessly dull, particularly seeing as rivers is revisited every single year. The ‘luckiest’ students might have even gone on a field trip that involved standing in the middle of a small stream in wellies (that didn’t fit properly and gave you horrible blisters), cold and miserable, with little to no interest in rivers. Perhaps even a resentment against any hydrological theory.

At risk of sounding over enthusiastic, rivers are actually rather interesting, and incredibly relevant in the state of global affairs we find ourselves in. I don’t mean relevant in a ‘well, this scientific theory is interesting way’, but a ‘this is something that is going to have significant impacts on people around the world’ way. We’ve all heard about climate change, and climate change has the potential to seriously impact the way rivers function – functions that are often important to human beings.

In this blog, I hope to communicate the potential impacts of climate change on river discharge and flood regimes on a global scale, and how this will affect both the natural environment and humans that rely on rivers. The best introduction to the issues I will be tackling is provided by some of the main points raised in the recent IPCC (Intergovernmental Panel on Climate Change) AR5 report:

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• As greenhouse gas emissions increase, the risk of adverse impacts to freshwater systems increase.

 

• In dry subtropical regions, climate change is projected to significantly reduce both surface water and groundwater resources. This will affect regional water energy water and food security, as there is less water available.

• Projections for changes in flood magnitude and frequency are less clear, but there is evidence to suggest variations in flood frequency around the world.

• Freshwater ecosystems will be negatively impacted by changes to streamflow and water quality caused by climate change.

• Rivers fed by snowmelt and glaciers will see increased seasonality and variability in flows as result of climate change.

All of these changes have the capability to impact humans – water is an important economic and social resource. Attempting to predict these changes is a difficult business, dependent on environmental modelling; in effect attempting to predict the future. Predicting the future is a hard business – according to Tomorrow’s World we would all have robot butlers by now. However, environmental modelling is a very powerful tool, and allows informed decision making about future risk. This sort of knowledge can help us understand the likely future impacts on rivers and the people dependent on them.

Hopefully it is evident that the real issues surrounding rivers are quite different to the geography plied at secondary schools up and down the country. I hope to explore the science behind these issues in this blog, the potential impacts, and what this means for humans around the world. I hope you will join me on this voyage into the unkown.