The worlds largest desert, the Sahara, has grown in size by 10 per cent since 1920. The reason behind such a growth in around a 100-year span has been credited to climate change, which is making the sand steadily shift to new regions, say scientists.

As temperatures rise across the globe and weather patters are thrown in turmoil, this kind of an expansion of extremely dry landscapes will not just be limited to the Sahara.

Though there have been many studies before mapping the rainfall pattern in these dry areas, this research was unique in the sense that it used rainfall pattern in the Sahara and Sahel to determine changes in the expanse of the desert on a century timescale.

HERE ARE THE HIGHLIGHTS OF THE STUDY:

1.The researchers looked into the annual rainfall data from the 1920s. Deserts get less than 150 millimetres of rain per year

2.Looking at the annual instead of seasonal trends, it was seen that the Sahara grew by 10 per cent within the period of 1920 to 2013

3.The expansion was as much as 16 per cent in the summer months

4.The highest amount of variations were found on the northern and southern borders of the Sahara

5.The Sahel region which is the connecting zone between the southern Sahara and the Sudanian Savanna was also examined closely

CHAD LAKE DRYING UP

The Chad Lake lies in the Sahel region, in the Chad basin located in the part of the Sahara pushing southwards. The lake is drying up, which shows the changing conditions along the Sahara border.

“It’s a very visible footprint of reduced rainfall not just locally, but across the whole region, said Maryland Universitys Sumant Nigam, the lead author of the study.

CLIMATE CYCLES AFFECTING THE SAHARA EXPANSION

The earth changes as a result of a number of climate cycles, and the worlds largest desert is affected mainly by two such cycles — the Pacific Decadal Oscillation (PDO) and the Atlantic Multidecadal Oscillation (AMO).

It is not possible to understand how these climate cycles affect our planet without long-term studies like this one as climate cycle such as the AMO run on 50-70 year periods.

“Deserts generally form in the subtropics because of the Hadley circulation, through which air rises at the equator and descends in the subtropics,” said Nigam.

The Hadley circulation could widen thanks to climate change which will facilitate the northward progression of subtropical deserts.

However, the Sahara is progressing southwards. This shows that a number of factors are causing this to happen, including climate cycles such as the AMO.

HOW HUMANS ARE AFFECTING THE SAHARA EXPANSION

Apart from climate cycles, researchers say that humans are also affecting the change and expansion of deserts through the climate change they usher in. One-third of the Sahara expansion can be blamed on humans.

As the population of the world grows, we need more and more land for agriculture and habitation. But the more these deserts expand, the less usable land we have.

Though the study was based only on the Sahara, it says a lot about the conditions of other deserts around the world.

Researchers want to continue with more such long term studies to properly access the long term trends of rainfall and temperature in the Sahara, understand the causes behind these trends and look at how they affect the Sahara and other regions.