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
•Climate
•Costs
Effectiveness
Efficiency
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 kJ
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
26 January 2000 23:00 GMT
900
800
400 cm
700
Height (m)
600
500
400
300
200
100
200 cm
0
-5
-4
-3
-2
-1
0
1
2
Temperature (°C)
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
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.
4
T air at ground
3
T air 2 m
2
h= 2m
1
h= 1m
0
-1
-2
-3
-4
22:3023:3000:3001:3002:3003:3004:3005:3006:30
Ora solare
Bud t (overcanopy
irrigation)
T (°C)
T (°C)
5
5
4
3
2
1
T air at ground
T air 2 m
h= 2m
h= 1m
0
-1
-2
-3
-4
22:30
23:30
00:30
01:30
02:30
03:30
04:30
05:30
06:30
Ora solare
Bud t (undercanopy
irrigation
WHY FARMERS NEED PREVISIONS ?
Awareness of the risk
Active protection
What a probability for a frost occuring tonight?
Can the 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?
Sensibilità al gelo - danno del 10 %
10%
damage
0
-2
-4
T (°C)
-6
-8
-10
-12
Actinidia
kiwi
apricot
peachi
apricot
Pero
pea
germogliamento
ri
Albicocco
Pesco
-14
-16
fioritura
allegagione
fase di sviluppo
frutticini
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
Tmin  a  H rel  b  I n   z  sea
valley top
Hc
computation point
Dc
Hf
valley bottom
Df
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
Thank you