The climate varies somewhat with changing elevation along the Alpine region’s valleys. Variable topography and proximity to alpine peaks are the major factors that have a significant influence on the climate. The northward and northwestward movement of cool and sometimes cold air from the Victorian Alps through the Ovens & Kiewa River Valleys is a distinctive climatic feature of the Alpine Valleys wine region.
Long-term average yearly rainfall in the Ovens Valley ranges from 640mm at Wangaratta (elevation 150m), to 1220mm at Bright (elevation 400m) with about one third of this falling during the growing season from October to March. Along the entire system of Alpine Valleys' rivers, February is the driest month and June the wettest.
The increase in rainfall outlined above can be attributed to increasing elevation, narrowing of the valleys and the north-easterly-moving cyclonic system of moist cool air rising against the hills and mountains during the winter period.
In two of every three years there is a sharp drop in rainfall between October and November with the dry summer period often extending through March into April in the upper parts of the Alpine river valleys.
Newell calculated a yearly evaporation of 1041mm for Myrtleford and the actual evaporation figure at the Ovens Research Station is 1069mm per year. Other evaporation figures are not currently available.
Rainfall and evaporation figures show that in most years some irrigation of vineyards will be needed during the dry summer months to avoid acute stress.
This dry summer period, coupled with restricted irrigation practices such as Regulated Deficit Irrigation, enable berry size and associated components to be optimised. The use of Partial Rootzone Drying is being investigated and trials with sub-surface irrigation are in progress to ensure water use efficiency.
In general, average temperatures along the Alpine Valleys' river systems follow the inverse pattern to the rainfall; there is a decrease in average monthly temperatures with increased elevation.
There are appreciable variations within the Alpine Valleys due to aspect, slope and elevation.
Gladstones (1992) suggests that due to inflows of cold air from alpine peaks there will be a high variability in minimum temperatures in the Alpine Valleys Wine Region. This results in a high frost risk in areas where cold air drainage is limited.
In those vineyards where frost risk is moderate to high, frost prevention systems have been installed to ensure continuity of supply. Systems vary from low-tech overhead sprinkler type, to high-tech, low water volume micro-jets (Pulsators or Flippers).