Ancient desert agriculture in the Negev and climate-zone boundary changes during average, wet and drought years

Thousands of ancient terraces in the valleys of the Negev desert show that agriculture was conducted here in the past, based on the utilization of runoff and floodwater from local rainfall. A comprehensive collation and mapping is presented of the geographic distribution of such farming remains in the northern, central and southern Negev. The time range of these remains is also evaluated in detail with the inclusion of new data from the Neolithic to the present. Farming was and is conducted on a seasonal or annual timescale. However, proxy palaeoclimatic indicators in the southern Levant do not have such resolution. How do the ancient agricultural remains relate to climate? How do we define climate in order to make comparisons through time? How dry is dry? The conventional Köppen and Thornthwaite climatic classifications are cumbersome in both spatial and time-series analysis. This article presents for the first time the spatial positions of the climate zones in southern Israel based on the innovative P/PET climatic classification approach (P = annual precipitation; PET = annual potential evapotranspiration). Instrumental data from 13 meteorological stations were used for the required calculations and mapping. The decade 1990–2000 was selected, because of extreme climatic variations in this period, including the cold and wettest year ever recorded, 1991–92, as well as the warm and severe drought year 1998–99. Main conclusions are as follows: 1. The majority of remains of ancient runoff/floodwater farming are located south of Beer Sheva in the arid zone. 2. Only a few sites are situated in the hyper-arid zone in the southern Negev. 3. The southern and eastern borders of the ancient agricultural region in the central Negev coincide with the average decadal climatic boundary between the arid and hyper-arid zone (P/PET = 0.05). 4. The extremely wet year 1991–92 did not cause a significant displacement southward in the position of the arid and hyper-arid zones. Most runoff-farming areas remained within the arid zone. However, north of Beer Sheva the climatic zones shifted dramatically, as the humid zone, usually not extant in the southern Levant, and the sub-humid zone, moved into southern Israel. 5. The severe drought year 1998–99, on the other hand, caused a dramatic displacement northward of all climate zones. The boundary between the arid zone and hyper-arid zone (P/PET = 0.05) moved north of Beer Sheva and west of Arad. Most runoff/floodwater farming areas were situated in the hyper-arid zone. 6. An area with terraced valleys beyond the Negev in the southern foothills near Hebron experienced an arid climate in 1998/99, instead of average semi-arid conditions. This underlines the rational of runoff capture for drought mitigation in the semi-arid zone. 7. The investigation sets a modern standard of defined climate zones in the Negev and their shifts in wet and drought years as a basis for comparison with past climatic changes in relation to ancient agricultural remains.

► Collation, time range and mapping of ancient agricultural areas in the Negev desert.
► Novel climate zone mapping of the Negev with the annual P/PET aridity index.
► Climatic variability is mapped for average, wet and drought years during 1990–2000.
► Most ancient agricultural areas remain in the arid zone in average and wet years.
► Most ancient agricultural areas have a hyper-arid climate during drought years.