Dendroclimatology and wheat production in Algeria

Drought is one of the main natural factors in declining tree-ring growth and the production of agricultural crops in Algeria. This paper addresses the variability of growing conditions for wheat in Algeria with climatic data and a tree-ring reconstruction of January-June precipitation from ten Pinus halepensis tree-ring chronologies. A regression-based reconstruction equation explains up to 74% of the variance of precipitation in the 1970-2011 calibration period and cross validates well. Classification of dry years by the 30% percentile of observed precipitation (131 mm) yields a maximum length of drought of five years (1877-1881) and increasing frequency of dry years in the late 20th and early 21st centuries. A correlation-based sensitivity analysis shows a similar pattern of dependence of tree-growth and wheat production on monthly and seasonal precipitation, but contrasting patterns of dependence on temperature. The patterns are interpreted by reference to phenology, growth phases, and - for wheat - agricultural practices.