See also: Dryness (homonymy)

The dryness (or dryness ) is the state (normal or momentary) of the ground and/or an environment, corresponding to a lack of Eau, over one period significantly long so that it has impacts on the natural or cultivated flora;

- this “ hydrous deficit ” to be episodically natural (ex: Interglacial glaciations/, cycles El Nino/El Nina, etc, perhaps amplified by the human gas emission with greenhouse effect).

- it makes following an unexplained rainfall deficit, over long periods during which precipitations are abnormally weak or insufficient to maintain the humidity of the ground and the normal Hygrométrie of the air.

- it can be worsened or explained by Pompage S, a fall of Ground water, the erosion and the degradation of the ground S (the Humus supports the retention of water), an increase in the evapotranspiration induced by plantations consuming water (Peuplier S, Maïs…)

The dryness can destroy harvests (partially or completely) and kill the livestock, and sometimes savages. It then becomes a factor of regional Famine and exodus, often accompanied by social disturbances then of armed conflicts, in particular in the areas with few economic resources.

The dryness is thus not only one physical or climatic phenomenon objective. It is also a relative concept which reflects the difference between the availability of water and the demand for water for the man, his agriculture and its cattle and certain uses of luxury (swimming pool, watering of the grasses, washing of car, etc.). This returns any definition of the dryness relating to the geopolitical and sociological context; the normal state “ ” of availability of water changes according to the zones biogeographic and the real needs or felt individuals and companies.

One generally distinguishes three types of dryness:

1. the weather dryness when there is one prolonged period of precipitations in lower part of the average
2. the agricultural dryness when there is not enough moisture for the cultures. This condition can take place even if precipitations are normal because of the conditions of the ground and the agricultural techniques, or of choice of unsuited plants (ex: corn or rices, very consuming water in zone dry).
3. the hydrological dryness when water reserves available in the water tables, lakes and tanks go down in lower part from the average. This can arrive even with normal precipitations or above the average when water is diverted for another geographical area or that it was overexploited, or when that a high water consumption exceeds the capacity of the tablecloth or the tanks to be renewed, or when the conditions of food of the tablecloths (permeability of the ground (See Loi of Darcy) are not met any more.

In the use the most frequent word dryness generally refers to the weather dryness.

- Scientifically speaking the dryness " is called; deficit climatique" cd. . Dc=P-ETP
P corresponds to pluviometry in milimètres.
ETP is the potential evapotranspiration of a plant in millimetres, i.e. its water loss by breathing and evaporation.

Dc=0 in the event of dryness.

- At the agricultural level the dryness corresponds to what is called the " deficit agricole" Da . Da=P-ETP+RFU
RFU is the easily useful reserve, it is water reserve in the ground available for the plants in millimetres. It is worth 2/3 of the RU which is equal to the water content X the depth of the roots.

The dryness in Africa

The drynesses are frequent and serious in much country of Africa Subsaharienne and have an impact devastator on their populations and their economies. The extreme vulnerability with precipitations in the arid and semi-arid regions of the continent as well as the low capacity of most of the African grounds to maintain the humidity make that almost 60 percent of these grounds are vulnerable to the dryness and 30 extremely vulnerable percent. Since the Sixties, precipitations in the parts of the Sahel and the Southern Africa also were appreciably in lower part of the 30 previous years standards. Moreover, the prospect for an effect EL Niño resulted in paying more attention on the impact of the dryness to sub-Saharan Africa.

Dryness and forest

The Forêt plays a crucial role for storage, the infiltration and the Cycle of water. The artificialized forest was often drained and genetically very impoverished. The important drynesses seem to have measurable medical impacts on the trees until 10 years afterwards. In addition the drynesses support the fires which if they are frequent strongly degrade the grounds and the possiblities of regeneration and storage of water, in particular in the semi-arid zones and on the slopes where the erosion is exacerbated. The primary Forest or with high degree of Naturalité profits from strong a impact strength. The foams, the Peat S, the humus rich in Mushroom S, formed starting from the Deadwood and of the excrements of the forest organizations, the embâcles natural, and in moderate zone the stoppings of beavers contribute have a strong value buffer. Moreover trees, if they are in their optimum stationnel lay out of strategies of avoidance of the hydrous stress vis-a-vis the not-exceptional drynesses . The pine S for example opturent precociously their Stomate S, and if the dryness perdure, they emit Hormone S which attract insects Défoliateur S, then Scolyte S which will kill the oldest trees (which évapotranspirent more) if the dryness perdure more than 2 years. Certain leafy trees of the dry tropical zones decrease their perspiration or lose their sheets in seasons dry. Those of the moderate zones only seem less capable of regular their evapotranspiration; Some lose part of their sheets, others seem able to attract défoliateurs in the event of acute stress. It should be noted that a natural forest rich in biodiversity generally associates gasolines which have varied zones of prospection racinaire, exploiting best the tablecloths as well in period of high tablecloth as of dryness. Conversely monocultures, especially if they are équiennes, exploit the water of the ground to the same depth by exacerbating the effects of the dryness which are much more brutal there.

Economic impact of the dryness

The economic dryness is defined like referring to the effects of abnormally low precipitations, apart from the normal parameters envisaged with which an economy is equipped. As such, its impact depends on the interaction of an event or a weather anomaly with the changing dynamic structure and the health of an economy. It also depends on the forecasts relating to the probability of the dryness and all changes which result from this in the various economic enterprises.

To concentrate more clearly on the characteristics structural of an economy which interpose between the effects of the dryness like a climatic and hydrological event, one is established to distinguish three situations from country in terms of impact of the dryness. There exist simple, intermediate and dualistic economies.

The simple economies are agricultural economics, of breeding, and semi-subsistence strongly influenced by the rains, having a limited infrastructure, having bottom grades of incomes per capita, and the elevated levels of self-sufficiency within the rural population. The impact of the dryness as a whole can be particularly enormous because of the relative importance of the agricultural sector. However, translating weak intersector relations, elevated levels of self-sufficiency and not-agricultural sectors relatively small, the multiplier effects of a shock of the dryness in the remainder of the economy are well limited.

In the intermediate economies, the effects of the dryness are very largely widespread in the economy, reflecting a more close overall integration and more solid intersector relations between the incipient agricultural sectors and manufacturing sectors. It is probable that the intermediate goods constitute most of the imports, implying that a compression of the imports due to the dryness will have additional multiplying implications on the domestic production. In meanwhile, the renewal of activity after the dryness can be very delayed insofar as the manufacturing sector continues to face the lack of inputs and with the slowness of the revival of the request. The implications on public finances can also be very serious, since the government is likely to face itself with most of the costs of the efforts of recovery, rather than to count almost entirely on the international assistance.

Lastly, in dualistic economies, which have great sectors of mining extraction, unless the sector of extraction is with great water intensity, economic impact of the dryness is limited to the variability of the agricultural sector with a small multiplier effect. Thus, the macro-economic impact of the dryness appears still weak, although it can have major effects in the agricultural sector whose the majority depends on the population.

History since 1000 years in Europe

• 1303 : the most important dryness of the millenium. The Rhine could be crossed with dry foot.
• 1540,1719,1874,1906,1911,1921,1945,1947,1949,1953,1957,1964,
• For the recent period, the drynesses of 1976,1988 1989,1990,1991,1992 and 2003 had significant impacts on the ecosystems and the cultures in Europe, like on health (surmortality related to the heat wave)

Solutions?

They pass at the same time by adaptations to the dryness, a better management of water, and by a fight against the anthropic causes of many phenomena of aridification or Désertification, which can be of long run if it is estimated, in accordance with the repeated conclutions of GIEC that climate warming is well mainly of human origin.
De many solutions ecotechnic are proposed, in particular passing by the restoration of the vegetation and of the Humus destroys by the methods of modern agriculture, but difficult to implement (the programs of green belts or timbering in the Sahel often suffered from the aggravation of the drynesses, of the weakness of the means implemented, in particular for the protection of the trees against the goats and herds). Techniques using best the resources of the Biodiversity and the gasolines local pionnières (as developed by Akira Miyawaki) forcing the root S to be inserted more deeply (plantation in a pipe dégradable, with initial watering starting the capillary increase of deep water) or of the rétenseurs of water such as the polyter were effectively tested, but without development with large scales.
Les promoters of GMO asserts that one can transform plants to adapt them to dry grounds and/or salinized, but their detractors propose the risk that they pump the water little there which remained there, by increasing the salinisation and while eliminating from other species still present, with the detriment of fauna and the biodiversity perhaps. Technical solutions (Dessalinisation of sea water) also exist, but which are expensive and sometimes with strong Empreinte ecological. The great programs of irrigation often generated downstream from the disastrous consequences (pollution and lowers level of the Mer of Aral for example).

Conclusions

The shocks due to the dryness have effects important, but highly differentiated on the unit from the economy. The frequency, the scale and the probable nature of these effects depend on the interaction of the economic structure and the equipments in resources, as well as of the short-term economic factors. Contrary to the intuition, some of the economies more developed relatively or " more complex " sub-Saharan Africa, such as those of the Senegal, the Zambia and the Zimbabwe, is more vulnerable to the shocks of the dryness than those of the less developed and more arid countries, such as those of the Burkina Faso, or the countries which know conflicts like the Somalia. Consequently, a country less developed such as the Ethiopia could initially become more sensitive to the dryness while its economy develops. Then, as the economies become more complex and diversified, they become less vulnerable to the dryness thereafter.

See too

• Draining of the Sea of Aral
• special Alarm of FAO (http://www.fao.org/WAICENT/faoinfo/economic/giews/french/alertes/2000/sa304naf.htm)
civil
• Locusts and disorders worsens the effects of the dryness (http://www.lefaso.net/article.php3?id_article=5231)
• the dryness in Africa: an urgent call to solidarity (http://www.protestants.org/docpro/doc/1243.htm)
• Historical of the drynesses in Europe (http://la.climatologie.free.fr/secheresse/secheresse1.htm)
• Drynesses in France (http://www.notre-planete.info/actualites/actu_631.php)

External bonds

• Random links:

  Ashy heather | Babel (cartoon, Angel) | Saint Martin's day (Belgium) | Chris Parks | Mike Mussina