Global warming and drought conditions

[sweeteviljesus]

Lately, I have read a few unrelated articles claiming a connection between global warming and drought conditions in Africa. What is the mechanism by which this might occur?

Thanks for your help,
Rob

[Quartz]

[QUOTE=sweeteviljesus]
Lately, I have read a few unrelated articles claiming a connection between global warming and drought conditions in Africa.
[/QUOTE]

Hasn’t Saharan Africa been drying since the start of the last interglacial? As late as Roman times, North Africa was the breadbasket of the Med.

[Colibri]

[QUOTE=sweeteviljesus]
Lately, I have read a few unrelated articles claiming a connection between global warming and drought conditions in Africa. What is the mechanism by which this might occur?

[/QUOTE]

In general, warmer conditions will be expected to increase evaporation and thus to enhance drying trends. Drier conditions seem to be affecting many places besides Africa.

From the National Center for Atmospheric Research

The percentage of Earth’s land area stricken by serious drought more than doubled from the 1970s to the early 2000s, according to a new analysis by scientists at the National Center for Atmospheric Research (NCAR). Widespread drying occurred over much of Europe and Asia, Canada, western and southern Africa, and eastern Australia. Rising global temperatures appear to be a major factor, says NCAR’s Aiguo Dai, lead author of the study.

. . .

Dai and colleagues found that the fraction of global land experiencing very dry conditions (defined as -3 or less on the Palmer Drought Severity Index) rose from about 10-15% in the early 1970s to about 30% by 2002. Almost half of that change is due to rising temperatures rather than decreases in rainfall or snowfall, according to Dai.

“Global climate models predict increased drying over most land areas during their warm season, as carbon dioxide and other greenhouse gases increase,” says Dai. “Our analyses suggest that this drying may have already begun.”

Even as drought has expanded across Earth’s land areas, the amount of water vapor in the air has increased over the past few decades. The average global precipitation has also risen slightly. However, as Dai notes, “surface air temperatures over global land areas have increased sharply since the 1970s.” The large warming increases the tendency for moisture to evaporate from land areas. Together, the overall area experiencing either very dry or very wet conditions could occupy a greater fraction of Earth’s land areas in a warmer world, Dai says.

In addition to increased evaporation, changes in sea surface temperature can be expected to cause changes in rainfall patterns. This study traces drought in southern Africa to changes in surface temperature in the Indian Ocean.