Ground Frost

Primary reference(s)

WMO, 1992. International Meteorological Vocabulary, WMO-No. 182. World Meteorological Organization (WMO). Accessed 13 October 2019.

Additional scientific description

A ground frost refers to the formation of ice on the ground, objects or trees, whose surfaces have a temperature below the freezing point of water. During situations when the ground cools faster than the air, a ground frost can occur without an air frost. A grass frost, an un-official type of ground frost, can occur when other surfaces – such as concrete or road surfaces – do not experience a frost, due to their better ability to retain warmth. It is possible for a grass frost to occur in late spring or even early summer when the risk of more widespread frosts has disappeared (UK Met Office, 2019).

Metrics and numeric limits

Not available.

Examples of drivers, outcomes and risk management

The Food and Agriculture Organization of the United Nations (FAO) has published a summary of frost protection methods. Rather than cold temperature, frost damage to crops results mainly from extracellular (i.e., not inside the cells) ice formation inside plant tissue, which draws out water and dehydrates the cells causing injury to the cells. Following cold periods, plants tend to harden against freeze injury, and lose this hardening after a warm spell. A combination of these and other factors determine the temperature at which ice forms inside the plant tissue and when damage occurs (FAO, no date).

The FAO recommends risk management methods which include passive and active protection methods:

• Passive protection includes methods that are implemented before a frost night to help avoid the need for active protection. The main passive methods are site selection; managing cold air drainage; plant selection; canopy trees; plant nutritional management; proper pruning; plant covers; avoiding soil cultivation; irrigation; removing cover crops; soil covers; trunk painting and wraps bacteria control; and planting date for annual crops. Passive methods are usually less costly than active methods and often the benefits are sufficient to eliminate the need for active protection (FAO, no date).
• Active protection methods include heaters; wind machines; helicopters; sprinklers; surface irrigation; foam insulation; and combinations of methods. All methods and combinations of methods are undertaken during a frost night to mitigate the effects of sub-zero temperatures. The cost of each method varies depending on local availability and costs. In some cases, a frost protection method has multiple uses (e.g., sprinklers can also be used for irrigation) and the benefits from other uses need to be subtracted from the total cost to evaluate fairly the benefits in terms of frost protection (FAO, no date).

Examples of national alerting parameters include those for a Frost Advisory by Canada (Government of Canada, 2019) and a Frost Warning by China (China Meteorological Administration, 2012).