Long-term marketable yields of horticultural crops in southern Ontario in relation to seasonal climate

In Ontario, Canada, marketable yields of certain annual horticultural crops increased steadily from 1940 to the mid-1980s, then dramatically decreased and became highly variable. This was not seen in field crops such as soybean and corn. Standard climatological variables showed little correlation with yields of vegetable crops such as tomatoes, cabbage, cauliflower, onions and rutabagas. The number of hot days (defined as days with maximum temperature greater than 30°C) and number of days with precipitation were better correlated with cool-season vegetable crop yield. With these climate measures we identified a period of milder growing season climate, from 1961 to 1986, and there was a greater frequency of hot days before and after this period. This analysis shows that horticultural crops are more sensitive to specific synoptic events, such as periods of hot days, than to overall growing season climate, and their yields may provide an indicator of a changing climate. Key words: Horticultural yields, historical climate, weather