The cashflow from tenants is more stable than that from equities, where values zigzag day by day and dividends can suddenly be suspended by the management.
There were, however, fluctuations in the climatic conditions, with the consequences that wet conditions were followed by dry ones, so that the availability of plants and animals oscillated brusquely.
There are several hypotheses, including warming or cooling of Earth, changes in seasonal fluctuations or ocean currents, and changing positions of the continents.