SPRING FROST RISK IN ORCHARDS FORECAST AND PROTECTION

SPRING FROST RISK IN ORCHARDS - FORECAST AND PROTECTION METHODS Federica Rossi, Franco Zinoni CNR-Institute of Biometeorology Bologna Meteorological Service Regione Emilia Romagna

Spring frosts: when temperature falls below the melting point (0°c) sensitive crops can be injured Scarring, distortion, russet Style, ovary, petals necrosis Dehydration, brown tissues

Whether or not there is frost damage at a particular minimum temperature plant species, crop variety, hardening, cultural practices (pruning, fertilization, irrigation), presence of INA bacteria, weather conditions.

Most countries with temperate climates experience frost damage to crops and even tropical countries can have frost damage at high elevations. Coffee region

Farmers have been always cohabiting with such a meteorological hazard

Now…. More sensibile cvs Cultural practices Climate change: higher winter temperatures early blooming. Increase of low-temperature episodes in spring Needs to protect local and traditional crops (sustainable- GAP)

Average economic losses due to the occurrence of late frosts - Emilia Romagna 300 M Euros 38% Gross Production Value 65 M Euros 50 % Gross Production Value

How to improve frost protection ? Define meteo & micrometeorological conditions during frost events Develop knowledge and instruments able to evaluate the risk Define the more appropriate methods for protection in relation to the climatic hazard and sustainable resources management Communicate to farmers how to avoid or mitigate the detrimental effects (active-passive protection)

Passive protection (low-cost – high-benefits) Awareness of the meteorological risk Selection of low-risk sites Avoid low-spots, select slope orientation Planting species and cvs blooming later in the spring Maintain soil water content to obtain high thermal diffusitivity Minimizing or removing cover crops Proper pruning, nutritional management

Active protection (high costs) Awareness of the meteorological risk Selection of the appropriate protection method: • Crop • Location Effectiveness • Climate Efficiency • Costs Risk

Active protection High effectiveness (all kind of freezing) Heaters Low efficiency High consumption rates (50 % of efficiency) Expensive to operate (2000 €/ha/night) Total efficiency is proportional to the number of heaters and depending on the air temperature

Active protection Break up of b. l. – mixing of warm air aloft with surface colder air Effectiveness: radiative frosts Efficiency: low labour requirement, low operational costs (10 €/ha/h) but high capital cost and high ‘standby’ charges. Possible in every location. Environmental friend, but noise pollution Wind machines

Active protection Over-plant sprinklers Under-plant sprinklers Efficiency: Low operational costs. High installation costs but sprinklers can be used for irrigation, fertilizer applications, evaporative cooling…Disadvantages: large amounts of water needed Water freezing: when 1 Kg of water freezes at 0°C, the phase change converts 334 k. J of latent to sensible heat

Over-plant sprinklers Uniform application, continuous and adequate water amounts. Problems under windy conditions. Errors in operating (late starting, early stopping, accidental interruptions) can induce major damages

Under-plant sprinklers The goal is to maintain the wetted cover crop temperature near 0°C

Efficiency: Intermittency low amounts of water (higher sustainability, lower costs). The same sprinklers can be used for irrigation. Useful to protect large surfaces Effectiveness: Radiation frosts

Meteorological Base S. Pietro Capofiume 44° 65’N – 11° 62’E 11 m a. s. l. Test- site for microclimatic characterization to identify the atmospheric features correlated to frost events

400 cm 200 cm 100 cm 50 cm 22. 5 cm

ATMOSPHERE STATUS - CLOUD COVER ARE THE MAIN FACTORS CONDITIONING SPRING FROSTS Radiation frosts: calm wind - clear sky: heat is lost in form of radiant energy. Temperature falls faster near the surface causing a temperature inversion To optimize orchard protection, it is important to understand the interaction between radiation and turbulent processes in complex canopies.

Evaluation of the effectiveness in orchards: Micrometeorological observations - energy and radiation balances Air and plant tissue temperatures

Height (cm) Irrigated Non irrigated + 3°C Temperature °C

Under-canopy irrigation: the temperature of the lower part of the canopy becomes higher because of the release of latent heat. Bud t (overcanopy irrigation) Bud t (undercanopy irrigation

WHY FARMERS NEED PREVISIONS ? Awareness of the risk Active protection What a probability for a frost occuring tonight? Can thermal levels predicted compromize my crops at this stage ? Shall I activate my protection devices? What will be the ratio cost sustained/cost of the possible damage? 10% damage kiwi apricot peachi apricot pea ri

Frost forecasting target 7 – 2 days forecast EPS Farmers to dispose protection devices 2 – 1 day EPS-Kf < 12 hrs Nowcasting Reclamation consortiums to make water available Alert to activate and optimize protection

Rischio gelo nelle prossime notti Riceviamo dall'ARPA-SMR e diffondiamo il seguente bollettino ARPA - Servizio Meteorologico Venerdì 4 aprile 2003 Speciale Bollettino Agrometeorologico per Rischio Gelate. A seguito della perturbazione che ha interessato la regione a partire da Mercoledì 2 Aprile e prodotto piogge diffuse ed un notevole calo delle temperature massime, è previsto l’arrivo di aria fredda e secca da nord-est che apporterà condizioni di cielo sereno o poco nuvoloso. Queste condizioni sono favorevoli a forti abbassamenti termici dovuti sia all’arrivo di aria fredda (avvezione) che alla perdita di calore dal terreno durante la notte (irraggiamento). Nei prossimi giorni sono quindi previste intense gelate. La temperatura dovrebbe scendere al di sotto dello zero nella notte tra Domenica 6 e Lunedì 7, ma i valori potrebbero essere ancora più bassi nella notte successiva, tra Lunedì 7 e Martedì 8

WHY FARMERS NEED PREVISIONS ? Awareness of the risk Passive protection Selection of low-risk sites !!!! Crop selection

A regional topoclimatic model including phenological and growth models is under development to be used operationally • Definition of the risk maps for the different crops • Weekly agrometeorological bullettins • Climatic regional data-base for land capability

Topoclimatic analysis to create frost risk maps as a tool for agricultural land planning and site selections Climatologic component Spatial interpolations of previsional data from meteo models Geographical component Generation of DEM: Plan & hill domains Correlation analysis between orography and climatic variables Minimum temperature prediction maps Correlation between frost indexes and minimum temperatures Frost index values for the different species Biological component

Needs: • to improve accuracy and resolution of DEM • take into account other meteo variables affecting frost • more and proper distributed meteo stations • remote sensing imagery to retrieve night surface temperature maps

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