The impact of climate change on rivers and lakes Climate change and human interference are altering our water systems on land. Lakes and rivers are undergoing dramatic transformations which impact nature, ecosystems and ultimately us. Rivers, streams and lakes give us water and food, rich biodiversity and sustain industries, so when they change, you can expect disruption. Can scientists help work out solutions before our waterways are dangerously dried up and degraded? By Richard Forsyth
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hilst we often think of climate change in terms of rising sea levels and coastlines under threat, climate change is also fundamentally changing the planet’s precious lakes and river systems. Consider that 97 percent of the water on Earth is saltwater, leaving only three percent as fresh water. Around two thirds of that fresh water is frozen in glaciers and ice and most of the remaining is subsurface groundwater. That leaves a tiny fraction as water above the ground or in the air. The warming effect of climate change is transforming the water cycle and when, where and how much precipitation occurs. It triggers severe weather events as more water evaporates, so with the higher levels of water vapour there is more frequent and heavy rainfall, which in turn can lead to flooding. The drier land with less vegetation means the soil does not so easily absorb the downfalls. Add farming fertilisers to the runoff from fields into waterways and it can lead to algae blooms which can be detrimental to the natural wildlife in the rivers and lakes. Rivers and lakes affected by climate, can change the weather and affect environment in and around the water. In more than one way, today, our natural water sources are altering in nature, and faster than we could have predicted. Combine this with our interference with nature’s water systems, building dams and excessively using fresh water and you have the makings of a potential crisis.
No snow, no meltwater High-up glacial meltwater is often the source for rivers but with less precipitation and warmer climates, the ice and snow vanishes. This leads to some rivers and lakes drying up and even disappearing, as with Lake Poopó, which was Bolivia’s second biggest lake prior to 2015. This was largely due to the loss of the Andes glaciers, which provided the meltwater. The huge lake was reduced to marshland after December 2015 and is unlikely to recover. The lost Bolivian lake provides a glimpse at a scenario that is likely to be repeated across the world. Rivers are facing the same challenges as lakes. Pakistan held an urgent online meeting, organised by Global Water Operators Alliance in June, precisely to acknowledge that water from melting glaciers has been affected by climate change and the country’s river water was running dry. Ironically, in conjunction there have been unpredictable torrential rains which led to flooding in urban areas and to the destruction of crops. About half the world’s river networks are running dry. To highlight this closer to home in Europe, impacts of this nature have already
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begun. The Rhine and the Danube for example, have headwaters that originate in the Alps. The Alpine glaciers of Europe are melting faster than the snow can top them up, due to the warmer temperatures. In recent years there have been unprecedented low water levels in these rivers. In 2018, Germany’s Rhine levels were so low that shipping was impossible, which had a knock-on impact for industry, cutting off factories from supply ships. In 2020, at one key point in the river at Kaub, it dropped to about 1 metre on 3 June, the lowest in two decades. Researchers at the University in Canada found that over half of the Earth’s rivers stop flowing for at least one day a year and more are expected to run dry. In this study, the reasons for halted flow vary, from freezing up, such as in the Himalayan streams, drying out as in the Sahara or when there is too much water extraction for irrigation of crops. This is a situation expected to get worse with escalating climate change. The World Health Organisation estimates that half of the world population will be living in areas that are water stressed by 2025.
Washed away As previously mentioned, on the other side of the challenge of drying up rivers and lakes, climate change can increase rainfall. This can cause some rivers to burst their banks and flood, at times which are not in line with established ecosystem processes. Researchers from University of Glasgow and Umeå University in Sweden found that the thermal growing season for plants (where temperature rises consistently above 5°C) was starting earlier in the year, closer to the time when the highest river floods occurred. This means that seeds and vegetation get washed away, which in turn denies a food source for animals, with implications for farming too.
The changing influences of water Rivers and lakes are changing all around the world, that is clear now. A recent study published in the journal Science, by an international team led by ETH Zurich, analysed 7,250 measuring stations around the world and combined with computer modelling, the study proved river flow changed systematically between 1971 and 2010. Some rivers were drying out and some were increasing volume. The common factor was that significant changes were occurring. Patterns emerged from the study revealing the nature of the changes. Regions like the Mediterranean and north eastern Brazil had become drier and in other places like Scandanavia the volume of water had increased. Studies like this can also provide data for projecting ahead, and that can be crucial for management of land, resources and to see how migration patterns of animals and people could occur.
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