Identifying climatic drivers that dominate in determining crop yield variations at a regional scale is important for predicting regional crop production. In this study, a statistical method was used to quantify the relationship between reported shire wheat yields and climate factors during the wheat-growing season across the New South Wales (NSW) wheat belt in eastern Australia from 1922 to 2000. The results show that recent climatic trends have increased wheat yield by 8.5 to 21.2% in 4 different climatic regions of NSW over the last few decades: In the eastern slopes, growing season maximum and minimum temperatures and number of heat stress days (>34°C) were identified as the dominant climatic factors affecting wheat yield, accounting for 36% of its variation. The wheat yield variation in the remaining 3 regions were as follows: 41% in the northern region from maximum temperature, pre-growing season rainfall (December to April), and number of frost days (<2°C); 47% in the south from rainfall, temperature, and number of frost and heat stress days; while in southwest NSW, rainfall was the main factor responsible for 31% of the variation. Frost was less important in the eastern slopes because farmers manage frost occurrence by sowing late and using late-flowering cultivars. However, the opposite occurs in the northern parts of the wheat belt where farmers sow earlier and select short-season varieties to avoid heat stress, but thereby expose their crops to possible frost conditions. Understanding the impact of climate variations on crop yield is important for developing sustainable agricultural production under future climate change.