The Water
Cycle and
Water
Insecurity
Enquiry Question 2: What factors influence the hydrological
system over short- and long-term timescales?
, 5.4 Deficits within the hydrological cycle result from physical processes but can have
significant impacts
A drought is a prolonged period of abnormally low rainfall, leading to a shortage of water
causing adverse impacts on vegetation, animals and people. The drought results from a
deficit in the water supply where the outputs from evapotranspiration are greater than the
inputs from precipitation. There are 4 types of drought that are sequentially related:
Meteorological drought - a shortfall in precipitation as a result of short-term
variability or longer-term trend, which increases the duration of the dry period.
Precipitation deficiency is usually combined with high temperatures, high winds,
strong sunshine and low relative humidity, all of which increase evaporation. It could
be caused by blocking high pressures, deforestation or longer term factors such as El
Niño events and climate change.
Agricultural drought - the rainfall deficiency from meteorological drought leads to
deficiency of soil moisture and soil water availability, which has a knock-on effect on
plant growth and reduced biomass. Some farming practices such as overgrazing can
accelerate the onset of agricultural drought.
Hydrological drought - associated with reduced stream flow and groundwater levels,
which decreases because of reduced inputs of precipitation and continued high rates
of evaporation. It results in reduced storage in lakes and reservoirs, often with
marked salinisation and poorer water quality. Hydrological droughts are also linked
with decreased water supplies for urban areas, which lead to water use restrictions.
Famine drought - a humanisation crisis in which the widespread failure of agricultural
systems leads to food shortages and famine with severe social, economic and
environmental impacts.
Physical Causes
1. El Niño
6. High 3. Low pressure =
pressure = clouds = rain =
drought floods
2. Air rises
5. Sinking air
1. Warmer than
4. Cooler than usual surface
normal water in water of coast of
Australia SA,low
Steers +8°C
pressure (rain,
cloud) around the
2. Blocking High Pressure (Anticyclone) high pressure, so
splits around the
anticyclones
Cycle and
Water
Insecurity
Enquiry Question 2: What factors influence the hydrological
system over short- and long-term timescales?
, 5.4 Deficits within the hydrological cycle result from physical processes but can have
significant impacts
A drought is a prolonged period of abnormally low rainfall, leading to a shortage of water
causing adverse impacts on vegetation, animals and people. The drought results from a
deficit in the water supply where the outputs from evapotranspiration are greater than the
inputs from precipitation. There are 4 types of drought that are sequentially related:
Meteorological drought - a shortfall in precipitation as a result of short-term
variability or longer-term trend, which increases the duration of the dry period.
Precipitation deficiency is usually combined with high temperatures, high winds,
strong sunshine and low relative humidity, all of which increase evaporation. It could
be caused by blocking high pressures, deforestation or longer term factors such as El
Niño events and climate change.
Agricultural drought - the rainfall deficiency from meteorological drought leads to
deficiency of soil moisture and soil water availability, which has a knock-on effect on
plant growth and reduced biomass. Some farming practices such as overgrazing can
accelerate the onset of agricultural drought.
Hydrological drought - associated with reduced stream flow and groundwater levels,
which decreases because of reduced inputs of precipitation and continued high rates
of evaporation. It results in reduced storage in lakes and reservoirs, often with
marked salinisation and poorer water quality. Hydrological droughts are also linked
with decreased water supplies for urban areas, which lead to water use restrictions.
Famine drought - a humanisation crisis in which the widespread failure of agricultural
systems leads to food shortages and famine with severe social, economic and
environmental impacts.
Physical Causes
1. El Niño
6. High 3. Low pressure =
pressure = clouds = rain =
drought floods
2. Air rises
5. Sinking air
1. Warmer than
4. Cooler than usual surface
normal water in water of coast of
Australia SA,low
Steers +8°C
pressure (rain,
cloud) around the
2. Blocking High Pressure (Anticyclone) high pressure, so
splits around the
anticyclones
