In Sub-Saharan Africa, periods of low rainfall often lead to economic downturns. And economic downturns, in turn, lead to the toppling of autocracies.

At least, such is the theory put forth in a summary of a new paper by economists Marcus Bruckner and Antonio Ciccone, "Rain and the Democratic Window of Opportunity."

In his synopsis, Ciccone writes that "Four out of five Sub-Saharan African countries were autocracies in 1980, but twenty-five years later there were more democracies than autocracies." He then references the work of economists of Darin Acemoglu and James Robinson:

They show that democratization becomes more likely after transitory, negative shocks. These shocks give rise to a window of opportunity for citizens to contest power, as the cost of fighting ruling autocratic regimes is relatively low. When citizens reject policy changes that are easy to renege upon once the window of opportunity closes, autocratic regimes must make democratic concessions to avoid costly repression.

So what's most likely to cause a transitory negative shock in the agricultural-based economies of sub-Saharan Africa?

Drought.

In our sample, a 50 percent drop in rainfall reduces real income per capita by around 4 percent relative to trend. Putting the two pieces of the puzzle -- the effect of low rainfall on income per capita and its effect on the probability of a transition from autocracy to democracy -- together yields that a drought-driven recession that decreases income by 5 percent relative to trend raises the probability of democratization by around 7 percentage points.

Thus, the recent history of Sub-Saharan Africa provides empirical support for the idea that economic recessions put autocratic regimes in a position where they have no choice but to make democratic concessions.

On that final note, How the World Works feels compelled to observe that an uptick in claims for jobless benefits on Thursday morning has Wall Street running scared on recession fears again. Republicans, beware.