a drought is a long period of time during which no rain falls
we speak of drought when precipitations
are unusually low compared to normal. In France and in neighboring
countries, it is called "absolute drought" a period
of at least 15 consecutive days without a drop of water (or
less than 0,20 mm per day).In the United States, it is said
that there is drought when a large area receives only 30%
or less precipitation than normal in twenty-one days minimum.
In Australia, there must be a region receives less than 10%
of rainfall compared to the annual average and India requires
that annual precipitation are 75% lower seasonal norms to
talk about drought.
In some cases it can last many years to see invade a large
part of a continent.
Often in summer waves of heat occur. These
are periods (ranging from one day to several months) of extreme
The minimum and
maximum temperatures average of the
summers in France from 1950 to 2003 (from June 1 to August
There are 3 types of droughts :
- Atmospheric drought is related
to lack of precipitation. It is judged by the amount of water
collected in the rain gauges ;
- Agricultural drought is based
on moisture content of agricultural soil to 1 meter deep.
When it occurs, the soil water reserve of plants runs out
and can have dramatic effects on plants. This slows the rise
of sap ;
- hydrological drought is the decrease
of streams and rivers. It comes after the depletion of water
reserves in the soil. At this level, we speak about hydrological
drought. When the situation gets worse, then the water tables
and the groundwater progressively disappear.
CAUSES OF DROUGHTS AND HEAT WAVES
and heat waves occur when a large anticyclone stays long standing
above the country and keeps away the Atlantic depressions
that bypass it.
coming to Europe
an anticyclone was above Europe so an air mass of Africa is
raised to England. It was 105,8°F (41°C) in Seville,
89,6°F (32°C) in London.
In many countries
droughts are related to anomalies of the surface temperatures
of the Pacific water. While El
Niño can affect droughts. When this climatic phenomenon
occurs the Indonesia, Australia, Japan, South Africa, Chile,
Brazil and Alaska are affected by droughts and severe heat
It said there would
be a dry or and hot weather with a cycle of 28 years in Western
Europe. In 1921 a very important drought occured in Europe
and in 1949 a hot, dry summer and the summer 1976 was also
very hot and dry and is 28 years after a major drought returned
in 2003. What is the cause of this cycle that it is not yet
OCCUR MOST OFTEN THE DROUGHTS ?
Droughts can occur almost everywhere in the
world. Except in the polar and subpolar regions the only areas
that don't go through drought.
A video on the causes and consequences
of the drought.
This map shows
us that drylands are everywhere, but especially in the tropics
of cancer and Capricorn.
Droughts in France:
the annual number average of sequences of more than
14 days without rainfall. In the Northeast, the Northern Alps
Massif Central, dry sequences are more common in winter than
THE IMPACT OF DROUGHT
As the drought continues, it causes a lot
of negative effects :
- The level of the water table down ;
- The level of lakes and rivers runs out
disrupting river traffic ;
- Water restrictions may affect crop irrigation,
domestic water uses such as watering gardens or industrial
- A reduction or even loss of crops
here to enlarge
In July 2003 a severe
drought has affected several European countries
including Austria, Romania, Hungary, Czech Republic, Italy
and France, and
disrupted river traffic on the Danube and in particular the
production of electricity.
here to enlarge
the Elbe with a high level during the rainy year
2002 and the Elbe with a low level during the 2003 dry year.
Régnier helped me correct mistakes, please you to visit
Im not english speaker, some improprieties can appear
to english masters.
Could you help me reporting by mail any fault you read. Thank
you for all.