Quantitative Evaluation of Spring Frost Risk to Agricultural and Horticultural Crops in Iranand Modeling

The purpose of this study is to quantify and mapping climatic damage risk of last spring frost for different agricultural and horticultural crops at various phonological stages over Iran and todevelop an applicable model for determining crop insurance premium rates. For this purpose daily minimum temperature data of 137 meteorological stations since their establishment date to 2004 were collected and submitted to quality control. Missed or debt full data were reconstructed using a cross control model. Finally the time series of daily minimum temperatures are formed for each station and then the date of the occurrence of these daily data were expressed by TDN (Thermal Day Number), using a thermal year calendar (from first of August each year until end of July next year). Thus the last spring frost (LSF) date of occurrence in each year is expressed by TDN. The time Series of LSF are accomplished for 13 standard temperature threshold q, from -9.8 to +4.8 Celsius degrees and for each station.Based on these series, the normalized values of TDNi named Zi is defined as a measure of frost risk severity for each thermal year i and each critical temperature (q).At next step, based on Zi values, each thermal year was placed in one of the four risk classes ofvery low, low, medium and high frost damage riskgroup. Then the probability of their occurrences(Po (andtheta;), P1 (andtheta;), P2 (andtheta;)and P3 (andtheta;)) were calculated for each station and all critical temperatureq. Finally the parameter P23 (q)=P2 (q)+P3 (q)i.e. the probability (in percent) of moderate and high frost risk were considered as spring frost risk criterion for various values of q. It has been shown that P23 (q) for all 13 values of qhas a significant linear relationship with longitude, latitude and elevation. Based on these regression equations and using error-correction procedures, spring frost risk maps with spatial resolution of 1andtimes;1 km2wereconstructed in GIS environmentfor 13 critical temperatures over Iran.Afterwardscritical temperatures (q) at different phonological stages based on FAO threshold data were coupled to frost risk maps. Ultimately, for practical applications,a new agro-climatic risk tool named AgroClimRisk was developed which can be combined with andnbsp;geo-statistical methods to calculate the quantities of maximum, minimumandnbsp; and averages of frost andnbsp;risk for 27 different crops and for three phonological main stages i.e. germination, flowering and fruit forming, over agricultural zones of Iran.