Let’s look at five periods on the graph Period 1 Early 19th century, peak in volcanic activity associated with the Dalton Minimum, a period of low solar activity. First fleeters suffered very badly from the ravages of drought. Period 2 mid 19th Century. Low in volcanic activity. In the 1850s and 1860s it was a low period of volcanic activity in the cycle and high point in solar activity. South Australia was growing half of Australias wheat, much of it north of the Gwyder Line, a line drawn on the map to show the expected northern boundary of land suitable for cultivation. North of the Gwyder Line was previously considered, and later proved, too dry for cultivation and pursuits such as growing wheat. Written accounts suggest much of inland Australia recieved more rain during this period. Accounts I have been given say Bushy Park near Boisdale had a 32 annual average rainfall, now probably around or slightly below 26. Period 3. Late 1880s-1920ish. Volcanic activity peaked and solar activity declined, drought gripped much of Australia. Sales rainfall which averages around 620mm (calculated mid 80s) dropped to around 450mm on a 5 year average. Period 4 Late 1940s to early 60s. low period of volcanic activity, resurgance of agriculture in inland S.A.. Sales rainfall got up 780mm on a 5 year average (1952) (ref 13). This indicates a 330mm (13.2) difference in the annual average rainfall for Sale, varying with the 70-90 year volcanic and solar cycles. Period 5. Late 80s onwards, heading towards another peak in volcanic activity, decades of below average rainfall.
Posted on: Thu, 11 Sep 2014 09:03:15 +0000
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