Defining drought

Characterized by unusual and persistent dry weather, drought is caused by shifts in global weather patterns such as El Niño, but also increasingly by human-induced climate change. Identifying drought is difficult, however, so there is considerable uncertainty about whether it is getting any worse (See Figure 1).

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Figure 1

Recent droughts

In 2011 and 2012, drought occurred on almost every continent, partly because of an unusually strong La Niña that caused record rainfall in Australia and led to severe water shortages in Sudan. Hundreds of millions of hectares of crops were destroyed, from wheat in Russia to sugar cane in India. The map (Figure 2) shows how rainfall deviated from the norm in this period and highlights the regions most affected by drought — many of which are major growing regions for the world's top four staple crops.

Figure 2: View the full-sized interactive map to see the percentage deviation from average annual rainfall, and highlights major droughts and their agricultural impact.
figure 2

SHEFFIELD, J. & WOOD, E. F. DROUGHT: PAST PROBLEMS AND FUTURE SCENARIOS (ROUTLEDGE, 2011)

View the full-sized interactive map to see the percentage deviation from average annual rainfall, and highlights major droughts and their agricultural impact.

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A long history

Serious droughts have occurred in Australia and Africa, among other regions, in recent decades, but more severe 'megadroughts' have occurred on virtually every continent throughout history. This timeline highlights some of the harshest (Figure 3).

Figure 3
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ZUMA PRESS/ALAMY / SEAN SEXTON COLLECTION/CORBIS / CORBIS / ALAIN NOGUES/SYGMA/CORBIS

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Land under threat

In many regions, climate change is expected to increase the amount of land at risk from drought and heat, and will threaten more arable areas. Each 1°C rise in global warming could cut grain yield by as much as 5%. Figure 4 shows the expected increase in the spatial extent of drought (left), how this will affect the amount of suitable land available to grow the four staple crops (centre) and overall how sensitive these crops are to changes in temperature.

Figure 4
figure 4

TEIXEIRA, E. I. ET AL. AGRICULTURAL AND FOREST METEOROLOGY 170, 206–215 (2013)

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