Download Hail (Frozen water)

Hail (Frozen water)
Hailstones grow in clouds where there are water droplets at below 0 degrees Celsius. The
incidence of hail wipeout of crops has been increasing in recent years in New Zealand.
Effects of hail

Physical damage
Strip
leaves
Reduces surface area
for light absorption
less
photosyn
thesis
Less
Glucose
produce
d
less
growth

Entry for pests and diseases requiring higher levels of spraying with
economic, social and environmental implications

Reduces the number of fruit and flowers with less yields, employment opportunities .
Most frequent in the west of NZ most severe in the east of NZ. Hail can occur at any
time of the year.
Other forms of water include
Dew – adding to soil water
Snow – once on the ground snow acts as an insulator preventing further heat loss from
the soil. If it thaws slowly it can be considered a reservoir of stored water that plants
can use in spring. If it thaws fast, such as when a hot north-west wind blows, it can
cause floods and valuable potential soil water is lost.
TECHNIQUES USED TO MODIFY THE EFFECT OF HAIL
o Hail netting. This is made of a strong knitted fabric protecting crops of all sizes
by a providing a physical barrier. It gives some shading but allows at least 85%
sunlight transmission. Best suited to high density orchards with dwarf
rootstocks or dwarfing root Netting is becoming more popular in NZ because it
is more effective than alternatives, cheaper and has a long life span. They
require labour to erect and have environmental implications being resistant to
biodegrading and changing the landscape. The decision to net an orchard or
any other crop has to be considered along with other priorities such as debt
reduction, frost control and further site development.
o Hail insurance. This can be a cheaper in the short term than nets but overall it
is an expensive option. In 2002 the cost for an apple orchard was
approximately 6-15% of the value of the fruit insured and there is a limit on the
payout in the event of a crop wipeout. NOTE insurance is not a technique used
to modify the environment but rather an economic response to damage.
o Hail cannon. These are acetylene powered devices that set off explosions that
send out shockwaves. The shockwaves are supposed to shatter hail forming
overhead. They are more effective when used in groups than individually. The
noise from these devices has social implications for neighbours especially when
orchards border residential areas.
Exercise: Select and Justify ONE technique used by growers to modify
a) The economic effects of hail. OR b) the social effects of the control
technique.