In West Asia and adjacent dry farming and irrigation-agri-culture realms, adaptive social responses to altered dry farm-ing cereal production developed within decades of the onset and terminus of the abrupt megadrought of 4.2–3.9 ka BP (42oo – –39oo years ago, or c. 22oo –19oo BC). Relatively high-resolution and independent archaeological and palaeocli-mate records document that this period of abrupt climate change began with: 1. political collapse and regional aban-donments in rain-fed regions; 2. habitat-tracking to ripar-ian, paludal, and karst spring-fed refugia where agriculture remained productive; and 3. nomadisation (subsistence-transfer from agriculture to pastoral nomadism).
Adaptive social responses at the termination of the abrupt mega-drought included: 1. sedentarisation and resettlement; 2. political state formation; 3. increased and enhanced sur-plus agro-production; and 4. political-territorial expan- sion.These societal processes have previously been catego-rised archaeologically and historically in West Asia as com-ponents of the unexplained »Early Bronze/Middle Bronze transition«, »Intermediate Bronze Age«, »Akkadian col-lapse«, and »Amoritisation«. The highly resolved data cur-rently available for the 4.2 ka BP abrupt mega drought have focused many palaeoclimate and archaeological research programmes on the period, while century-scale Holocene abrupt climate changes also occurred at 8.2 ka BP, (Wenin-ger/Clare 2o14), 5.2 ka BP (Staubwasser/Weiss 2oo6), and 3.2 ka BP (Kaniewski et al. 2o13)