Harvest dates in ancient mesopotamia as possible indicators of climatic variations

Butzer (1958; also, Lamb, 1968) puts forward observations to the effect that about 2500 B.C. a period of increased aridity set in in the general area of the Near East, including Mesopotamia, and that rainier conditions returned after about 850 B.C. Because in the Mediterranean type of climate (winter rains) of the Near East winter temperatures and seasonal rainfall are highly correlated in a negative sense, we expect that the above mentioned period of aridity was also a period of relative warmth, whereas the period after 850 B.C. up to Roman times, was a period of cool winters. This negative correlation is thought to be due to the fact that in the Near East rainfall is usually produced in the migratory cyclones, especially close and behind the associated cold fronts which bring in cold air as well. A failure of these cyclones to reach the region in numbers, manifests itself both in reduced rainfall and comparatively high winter temperatures. In order to check on these ideas on temperature conditions, a search was undertaken of references to barley harvest dates in the literature (clay tablets) of ancient Babylonia comprising two periods: 1800-1650 B.C. (Late Old Babylonian Period = L.O.B.P.) and 600-400 B.C. (Neo-Babylonian Period = N.B.P.). It turns out that in the former, the harvest began late in March or early in April, while in the latter, it began late in April or in May, amounting to a difference of about a month or slightly more. In our own era, in what was once central and northern Babylonia, harvest begins in the second half of April or so. Thus in the L.O.B.P., harvest opened 10–20 days earlier and in the N.B.P. 10–20 days later than at present. The differences between the harvest dates of the two periods seem to be too large to be explained by changes in the barley varieties cultivated. On the other hand, the above mentioned inverse relationship between rainfall and winter temperatures supports the interpretation that the L.O.B.P. was warmer, and the N.B.P. cooler than the present era, and goes some way toward explaining the inferred differences in harvest dates.