M. H. Jorenoosh - Department of Irrigation, College of Agriculture, Shiraz University, Shiraz, I. R. Iran
A. R. Sepaskhah - Department of Irrigation, College of Agriculture, Shiraz University, Shiraz, I. R. Iran

ABSTRACT- Many fruits, vegetables and ornamental crops of tropical origin experience physiological damage when subjected to low temperatures. Protection of plants from the effects of lethally low temperatures is important in agriculture, especially in horticultural production of high value fruits and vegetables. The objective of this study was to develop a simple model to predict the daily minimum air temperaturefor prediction of frost occurrence in Bajgah and Kooshkak semi-arid areas, Fars province. Initially, the relationship between the minimum temperature of the early morning of a day with some meteorological parameters of the previous day was developed. Meteorological parameters used in this analysis are daily relative humidity, wind speed, pan evaporation, rainfall, sunshine hours, and estimated dew-point temperature. Dew-point is an important parameter which is related to the minimum temperature in different months with low temperature in Bajgah and Kooshkak areas. Many daily weather parameters used in the regression analysis showed no significant relationship with the daily early morning minimum temperature, except the dew-point and relative humidity. The regression equation between the differences between dew-point and minimum temperature with relative humidity as a simple model was proposed to be used to predict the minimum temperature and subsequently frost occurrence in the study regions. This model was validated by independent data set with an acceptable accuracy for the study regions.

Keywords:, Frost, Dew-point, Relative humidity, Minimum temperature