GeoLog

Soil Sciences

GeoTalk: Severe soil erosion events and how to predict them

GeoTalk: Severe soil erosion events and how to predict them

Geotalk is a regular feature highlighting early career researchers and their work. In this interview we speak to Matthias Vanmaercke, an associate professor at the University of Liège in Belgium who studies soil erosion and land degradation across Europe and Africa. At the EGU General Assembly he received the 2018 Soil System Sciences Division Outstanding Early Career Scientists Award.

Thanks for talking to us today! Could you introduce yourself and tell us about your career path so far?

Hi! So I am Matthias Vanmaercke. I’m from Belgium. I’m studied physical geography at the University of Leuven in Belgium, where I also completed my PhD, which focused on the spatial patterns of soil erosion and sediment yield in Europe. After my PhD, I continued working on these topics but with a stronger emphasis on Africa. Since November 2016, I became an associate professor at the University of Liege, Department of Geography where I continue this line of research and teach several courses in geography.

At the 2018 General Assembly, you received a Division Outstanding Early Career Scientists Award for your contributions towards understanding soil erosion and catchment sediment export (or the amount of eroded soil material that gets effectively transported by a river system).

Could you give us a quick explanation of these processes and how they impact our environment and communities?

We have known for a long time that soil erosion and catchment sediment export pose important challenges to societies. In general, our soils provide many important ecosystem services, including food production via agriculture. However, in many cases, soil erosion threatens the long term sustainabilty of these services.

Several erosion processes, such as gully erosion, often have more direct impacts as well. These include damage to infrastructure and increased problems with flooding. Gullies can also greatly contribute to the sediment loads of rivers by directly providing sediments and also by increasing the connectivity between eroding hill slopes and the river network. These high sediment loads are in fact the off-site impacts of soil erosion and often cause problems as well, including deteriorated water quality and the sedimentation of reservoirs (contributing to lower freshwater availability in many regions).

Matthias Vanmaercke, recipient of the 2018 Soil System Sciences Division Outstanding Early Career Scientists Award. Credti: Matthias Vanmaercke.

What recent advances have we made in predicting these kinds of processes?

Given that we live in an increasingly globalised and rapidly changing world, there is a great need for models and tools that can predict soil erosion and sediment export as our land use and climate changes.

However, currently our ability to predict these processes, foresee their impacts and develop catchment management and land use strategies remains limited. This is particularly so at regional and continental scales and especially in Africa. For some time, we have been able to simulate processes like sheet and rill erosion fairly well. However, other processes like gully erosion, landsliding and riverbank erosion, remain much more difficult to simulate.

Nonetheless, the situation is clearly improving. For example, with respect to gully erosion, we already know the key factors and mechanisms that drive this process. The rise of new datasets and techniques helps to translate these insights into models that will likely be able to simulate these processes reasonably well. I expect that this will become feasible during the coming years.

 

What is the benefit of being able to predict these processes? What can communities do with this information?

These kinds of predictions are relevant in many ways. Overall, soil erosion is strongly driven by our land use. However, some areas are much more sensitive than others (e.g. steep slopes, very erodible soil types). Moreover, many of these different erosion processes can interact with each other. For example, in some cases gully formation can entrain landslides and vice versa.

Models that are capable of predicting these different erosion processes and interactions can strongly help us in avoiding erosion, as they provide information that is useful for planning our land use better. For instance, these models can help determine which areas are best reforested or where soil and water conservation measures are needed.

They also help with avoiding and mitigating the impacts of erosion. Many of these processes are important natural hazards (e.g. landsliding) or are strongly linked to them (e.g. floods). Models that can better predict these hazards contribute to the preparedness and resilience of societies. This is especially relevant in the light of climate change.

However, there are also impacts on the long-term. For example, many reservoirs that were constructed for irrigation, hydropower production or other purposes fill up quickly because eroded sediments that are transported by the river become deposited behind the dam. Sediment export models are essential for predicting at what rate these reservoirs may lose capacity and for designing them in the most appropriate ways.

At the Assembly you also gave a presentation on the Prevention and Mitigation of Urban Gullies Project (PREMITURG-project). Could you tell us a bit more about this initiative and its importance?

Urban mega-gullies are a growing concern in many tropical cities of the Global South. These urban gullies are typically several metres wide and deep and can reach lengths of more than one kilometre. They typically arise from a combination of intense rainfall, erosion-prone conditions, inappropriate city infrastructure and lack of urban planning and are often formed in a matter of hours due to the concentration of rainfall runoff.

Urban gully in Mbuji-Maji, Democratic Republic of Congo, September 2008. Credit: Matthias Vanmaercke

Given their nature and location in densely populated areas, they often claim casualties, cause large damage to houses and infrastructure, and impede the development of many (peri-)urban areas.  These problems directly affect the livelihood of likely millions of people in several countries, such as the Democratic Republic of Congo, Nigeria, and Angola. Due to the rapid growth of many cities in these countries and, potentially, more intensive rainfall, this problem is likely to aggravate in the following decades.

With the ARES-PRD project PREMITURG, we aim to contribute to the prevention and mitigation of urban gullies by better studying this problem. In close collaboration with the University of Kinshasa in the Democratic Republic of Congo (DRC) and several other partners and institutes, we will study this underestimated geomorphic hazard across several cities in DRC. With this, we hope to provide tools that can predict which areas are the most susceptible to urban gullying so that this can be taken into account in urban planning efforts. Likewise, we hope to come up with useful recommendations on which techniques to use in order to prevent or stabilise these gullies. Finally, we also aim to better understand the societal and governance context of urban gullies, as this is crucial for their effective prevention and mitigation.

Interview by Olivia Trani, EGU Communications Officer

Imaggeo on Mondays: Namibia’s mysterious fairy circles

Imaggeo on Mondays: Namibia’s mysterious fairy circles

The grassy Namibian desert is pock-marked with millions of circular patches of bare earth just like these shown in the picture between linear dunes.

Viewed from a balloon, they make the ground look like a moonscape. Commonly known as fairy circles, the patches range from two to 12 metres across and appear in a 2000 kilometre strip that stretches from Angola to South Africa.

For many decades, the fairy circles extending uniformly over vast areas in the landscape, have puzzled laymen and scientists alike. They are subject to a lively debate and contrary hypotheses on their origin exist. Some researchers claim fairy circles were caused by termites, others propose they are the result of vegetation self-organization.

Description by Hezi Yizhaq, as it first appeared on imaggeo.egu.eu.

Imaggeo is the EGU’s online open access geosciences image repository. All geoscientists (and others) can submit their photographs and videos to this repository and, since it is open access, these images can be used for free by scientists for their presentations or publications, by educators and the general public, and some images can even be used freely for commercial purposes. Photographers also retain full rights of use, as Imaggeo images are licensed and distributed by the EGU under a Creative Commons licence. Submit your photos at http://imaggeo.egu.eu/upload/.

Imaggeo on Mondays: Arctic cottongrass in Svalbard

Imaggeo on Mondays: Arctic cottongrass in Svalbard

In the High Arctic, where vegetation is limited in height, cottongrass stands out as some of the tallest plant species around.

This photo shows a wispy white patch of Arctic cottongrass growing amongst other tundra vegetation in the Advent river floodplain of Adventdalen, a valley on the Norwegian archipelago island Svalbard.

Svalbard is of particular scientific interest as it is a relatively warm region for its high latitude. This is due to the North Atlantic Ocean, which transports heat from lower latitudes to Svalbard’s shores.

The photo was taken in September 2014, towards the end of the region’s growing season. In the background, you can see that the season’s first snow had already blanketed the valley’s neighboring mountain tops.

Cottongrass generally loves wet conditions and scientists sometimes even use this plant genus (Eriophorum) as an indicator of the ground’s fluctuating water level, especially in areas that begin to develop peat, an accumulation of more of less decomposed plant material in wet environments. The waters feeding this region’s wetland come from melted snow and ice travelling down the adjacent mountains and floodwater from the Advent river, which is primarily meltwater fed.

Arctic cottongrass also can exchange gases with their underground environment through their roots and even have been shown to alter the local carbon budget of regions where they grow. It is therefore a very important species to account for when studying permafrost carbon dynamics.

Gunnar Mallon, currently a teaching fellow at the University of Sheffield (UK), took this photo while on a fieldwork expedition together with Andy Hodson, a glaciology professor at the University Centre in Svalbard, for the LowPerm project.

The LowPerm project aimed to understand how nutrients are transported within permafrost landscapes in Norway and Russia and how that may affect the production of greenhouse gases, such as carbon dioxide (CO2) and methane (CH4). The study brought together scientists from the UK, Norway, Denmark and Russia and results from the extensive field and laboratory work are currently being analysed and made ready for publication.

Imaggeo is the EGU’s online open access geosciences image repository. All geoscientists (and others) can submit their photographs and videos to this repository and, since it is open access, these images can be used for free by scientists for their presentations or publications, by educators and the general public, and some images can even be used freely for commercial purposes. Photographers also retain full rights of use, as Imaggeo images are licensed and distributed by the EGU under a Creative Commons licence. Submit your photos at http://imaggeo.egu.eu/upload/.

Geosciences Column: Landslide risk in a changing climate, and what that means for Europe’s roads

Geosciences Column: Landslide risk in a changing climate, and what that means for Europe’s roads

If your morning commute is already frustrating, get ready to buckle up. Our climate is changing, and that may increasingly affect some of central Europe’s major roads and railways, according to new research published in the EGU’s open access journal Natural Hazards and Earth System Sciences. The study found that, in the face of climate change, landslide-inducing rainfall events will increase in frequency over the century, putting central Europe’s transport infrastructure more at risk.  

How do landslides affect us?

Landslides that block off transportation corridors present many direct and indirect issues. Not only can these disruptions cause injuries and heavy delays, but in broader terms, they can negatively affect a region’s economic wellbeing.

One study for instance, published in Procedia Engineering in 2016, examined the economic impact of four landslides on Scotland’s road network and estimated that the direct cost of the hazards was between £400,000 and £1,700,000. Furthermore the study concluded that the consequential cost of the landslides was around £180,000 to £1,400,000.

Such landslides can have a societal impact on European communities as well, as disruptions to road and railway networks can impact access to daily goods, community services, and healthcare, the authors of the EGU study explain.

Modelling climate risk

To analyse climate patterns and how they might affect hazard risk in central Europe, the researchers first ran a set of global climate models, simulations that predict how the climate system will respond to different greenhouse gas emission scenarios. Specifically, the scientists ran climate projections based on the Intergovernmental Panel on Climate Change’s A1B socio-economic pathway, a scenario defined by rapid economic growth, technological advances, reduced cultural and economic inequality, a population peak by 2050, and a balanced reliance on different energy sources.

They then determined how often the conditions in their climate projections would trigger landslide events specifically in central Europe using a climate index that estimates landslide potential from the duration and intensity of rainfall events. The index, established by Fausto Guzzetti of National Research Council of Italy and his colleagues, suggests that landslide activity most likely occurs when a rainfall event satisfies the following three conditions: the event lasts more than three days, total downpour is more than 37.3 mm and at least one day of the rainfall period experiences more than 25.6 mm.

The researchers also incorporated into their models data on central Europe’s road infrastructure as well as the region’s geology, including topography, sensitivity to erosion, soil properties and land cover.

Overview of a particularly risk-prone region along the lowlands of Alsace and the Black Forest mountain range: (a) location of the region in central Europe and median of the increase in landslide-triggering climate events for (b) the near future and (c) the remote future.

The fate of Europe’s roadways

The results of the researchers’ models suggest that the number of landslide-triggering rainfall events will increase from now up until 2100. Their simulations also find while that these hazardous rainfall events slightly increase in frequency between 2021 and 2050, the number of these occurrences will be more significant between 2050 and 2100.  

While the flat, low-altitude areas of central Europe will only experience minor increases in landslide-inducing rainfall activity, regions with high elevation, like uplands and Alpine forests, are most at risk, their findings suggest.

The study found that many locations along the north side of the Alps in France, Germany, Austria and the Czech Republic may face up to seven additional landslide-triggering rainfall events as our climate changes. This includes the Vosges, the Black Forest, the Swabian Jura, the Bergisches Land, the Jura Mountains, the Northern Limestone Alps foothills, the Bohemian Forest, and the Austrian and Bavarian Alpine forestlands.

The researchers go on to explain that much of the Trans-European Transport Networks’ main corridors will be more exposed to landslide-inducing rainfall activity, especially the Rhine-Danube, the Scandinavian-Mediterranean, the Rhine-Alpine, the North Sea-Mediterranean, and the North Sea-Baltic corridors.

The scientists involved with the study hope that their findings will help European policy makers make informed plans and strategies when developing and maintaining the continents’ infrastructure.