Climate Change

Farmers’ climate perceptions guide adaptation, but previsouly they have been tested against weather stations rather than soil moisture, which matters more for crops. We used surveys of 1,171 Zambian farm households after the 2016 harvest recalled onset dates for recent and earlier seasons. In our analysis each farmer’s own onset rule was compared with local rainfall and modeled soil moisture. Some 88% reported rains arriving 21.9 days later than a decade ago, yet the mean perceived onset for the latest season nearly matched the physically derived mean. Recall bias sets in as early as a year after harvest, and planting rules track maize planting dates, so policy should target current variability over future change.

Köppen-Geiger classifications, which categorize the world into cliamte types such as tropical, arid or polar, underpin ecology and climate impact work, but the global versions in wide use were drawn at about 10 kilometers or coarser resolution, without any uncertainty quantification. We developed new maps at about 1 kilometer for 1980-2016 by merging several precipitation and temperature datasets and quantifying its confidence value. A companion map projects 2071-2100 under a high-emissions scenario. Against 22,078 weather stations the new map classified 80.0% correctly, versus 66.1 to 73.4% for the earlier maps.