Tuesday, July 10, 2018

The Tropics - Most Prone to Erosion - New Study Published

Those who live there are unlikely to be surprised by the conclusions in the study, but it does attempt to quantify those areas where it is most severe.

The north of Australia is among some of the most severely impacted areas but has some respite due to seasonal issues - little rain for a number of months in the middle of the calendar year helps reduce the problem.

The first world erosivity map provides a picture of those areas where it is worst.  And it is likely to get even worse with an  increase expected with changing climate and more frequent extreme rainfall.

Regions in the tropical climate zones suffer the greatest rainfall-related soil erosion, reports an international study.

The study, published last month (July) in Scientific Reports, has developed the first-ever Global Rainfall Erosivity Database and a Global Erosivity Map. It notes that while rainfall provides moisture critical for plant growth, it is also one of the prime causes of soil degradation, referred to as rainfall erosivity, which threatens food and water sustainability. 
[study available here in full - https://www.nature.com/articles/s41598-017-04282-8] 

For experts, model predictions of global erosivity are very important because they help assess risks as well as plan and implement effective soil mitigation and restoration strategies.

According to the study, erosion by rainfall remains poorly quantified despite its significance. This is because it is a complex event influenced by various factors including rainfall intensity, duration, amount and frequency — factors which are not captured in current erosivity estimates.

To model annual rainfall erosivity for different regions, the international team relied on rainfall data gathered from 3,625 stations scattered across 63 countries. Their analysis shows that annual mean rainfall erosivities for countries in the tropics are more than double the global average of about 2,190 megajoule millimetres per hectare per hour per year.
South America (particularly Brazil, Columbia and Peru), South-Eastern Asia (Cambodia, Indonesia, Malaysia, the Philippines and Bangladesh), the Caribbean, and Western and Central Africa have annual mean rainfall erosivities that are greater than 5,000 megajoule millimetres per hectare per hour per year.
Cold and dry regions like Canada, the Russian Federation, Northern Europe, Northern Africa and the Middle East have the lowest annual mean rainfall erosivity.
“The tropical forests and the monsoon zones (covering Amazonia part of Brazil, Central Africa and Southeast Asia) have intense rainfall but also excess monthly precipitation (greater than 1,000 millimetres for two consecutive months),” says Panos Panagos, study leader and scientific officer at the Joint Research Centre, European Commission. “The Mediterranean zone (a typical temperate climate zone) has seasonal rainfalls which are less intense than the ones in the tropical zones.”

“This is a great effort,” says Anton Vrieling, assistant professor of geo-information science and earth observation at the University of Twente, the Netherlands. However, he observes that calculating rainfall erosivity at different times in a year would be more useful than having an annual average value.
“In a given year, there are rainstorms of different intensity and duration. Other factors like the protective vegetation also vary throughout the year,” notes Vrieling.

With extreme rainfall events becoming more common as a result of climate change, soil erosion is expected to increase — leading to further impacts on agricultural production, and a greater contribution to disaster-related risks such as flooding and landslides.
Panagos says the emerging risks can be managed through good agricultural practices like reduced tillage, cover crops, grass margins and contour farming

Northern Australia - a small area by global standards is in the second highest zone, according to the mapping.  Small areas may of course be a little different.

Annual mean rainfall erosivity above the global average, by region
RegionAnnual mean rainfall erosivity (in mega Joule millimetre per hectare per hour per year)
Global mean2,190
Caribbean countries8,000
South-East Asia7,400
Western Africa and Central Africa7,000
South America5,874
Erosivity map

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