Constraints to productivity of subsistence dryland agroecosystems in the Fertile Crescent: Simulation and statistical modeling

Authors: Jaradat, Abdullah; Timlin, Dennis

Submitted to: American Society of Agronomy Special Publication
Publication Type: Book / Chapter
Publication Acceptance Date: 8/13/2021
Publication Date: N/A
Citation: N/A

Interpretive Summary: The large and diverse Fertile Crescent of West Asia was identified as a major food-deficit region of the Old World where subsistence farming is increasingly impacted by climate change. The region encompasses several countries that share general similarities due to the overall effect of the Mediterranean climate but displays large within- and among- country differences in their natural endowments. This contribution is part of a global move towards enhancing agricultural research and precision management of resources for subsistence farming in developing countries by integrating system models and experiments. The objectives of the study were to identify constraints to sustainable crop production of subsistence farmers and predict yield gaps that can be attributed to projected climate changes during the 21st century. Twenty-eight locations have been selected for the study and represented the two-major agricultural and geographical zones in the Fertile Crescent, i.e., the Mediterranean and Mesopotamia. These locations represent all major soil types and rainfall patterns, as well as temperature regimes and subsistence farming systems in the Fertile Crescent and the larger Middle East region. While the impact of simulated climate change on subsistence farming was widespread over the Fertile Crescent, it is expected to be more noticeable in the central and northern parts of the Levant, a region most impacted by the Mediterranean climate. The probability of producing subsistence crop yields will decrease over time, if no actions are undertaken to curb the negative effects of decreasing rainfall and rising temperature. Results of this study provide important insights into the many interacting factors that can be addressed to improve subsistence crop production.

Technical Abstract: Subsistence farming in the Fertile Crescent functioned as a quasi-sustainable buffering strategy to counterbalance climatic instability, and may have slowed down, albeit for a while, the inevitable depletion of natural resources and the gradual decline of agroecosystem services. In retrospect, adaptive subsistence farmers in the Fertile Crescent of West Asia seemed to have managed the unavoidable and avoided the unmanageable in response to climate change. An integrated approach, combining simulation modeling and statistical approached was employed in studying features of subsistence farming in the Fertile Crescent. Annualized yields of traditional and alternative crop rotations derived from field experiments and from archived records for all countries in the Fertile Crescent were used in a simulation and statistical modeling study. The objectives were to identify constraints to sustainable crop production of subsistence farmers and predict yield gaps due to projected climate changes. Spatial (longitude and latitude coordinates of 28 locations in the Fertile Crescent) and temporal variation (the years 2010, 2050 and 2100, respectively corresponding to RCP2.6, RCP4.5, and RCP8.5 Representative Concentration Pathways) in soils, maximum temperatures, rainfall amounts and monthly distribution, accounted for major differences in projected annualized crop rotation yields. Consequently, the growing season will be shortened; thus, widening current yield gaps between actual and potential crop rotation yields and forcing significant changes in the farming systems and the choice of crops that can be grown by subsistence farmers. With 50% probability, subsistence farmers may be able to achieve as large as 67.0% (under RCP4.5) or as small as 34.0% (under RCP8.5) of their water-limited crop yields; however, whether these yield gaps can be closed agronomically, ecologically, and sustainably, remains an open question. Spatiotemporal variation in heatmaps of annualized crop rotation yields, although large and dynamic, did not respond linearly to changes in RCPs suggesting that complex interactions are behind this response. While the impact of simulated climate change on subsistence farming was widespread over the Fertile Crescent, it is expected to be more pronounced in the central and northern parts of the Levant, a region most impacted by the Mediterranean climate. As a follow-up to this study, strategies will be developed in silico that will target each of the 28 locations in the Fertile Crescent where yield of subsistence crop rotations are well below their current water-limited yield.