The United Nations Convention to Combat Desertification (UNCCD) to date has been signed by 195 parties, including the European Commission. Under the UNCCD the term desertification is defined as "land degradation in arid, semi-arid and dry sub-humid areas, resulting from various factors, including climatic variations and human activities". This definition highlights both the climatic and the socio-economic causes of desertification.
Desertification is a complex process of simultaneous degradation of soil, water resources and vegetation, which can affect natural, semi-natural and agricultural systems, as well as other human activities. Collectively, this degradation leads to a loss in resilience, soil quality and in ecosystem integrity and health. This results in a loss of both ecological and social capital. Desertion and desertification are related problems in rural areas. Whether causes of land abandonment are natural or socioeconomic is still subject to debate. Land abandonment occurs because of external driving forces, such as market changes, or as a consequence of land degradation which lead the system to cross some irreversible threshold, such as the critical soil depth for plant growth. Aridity, drought and desertification are distinct, but closely related, concepts. In addition to natural irregularities on water supply associated to climatic conditions, the public perception of desertification in Mediterranean areas has been heightened by water resources shortage arising from the human induced water problems.
Desertification to a large degree is indeed caused by inadequate and unsustainable land use under adverse climatic conditions, which all too often is linked to poverty and the lack of alternatives for subsistence. By inference, desertification is therefore the result of various land degradation processes largely human-induced (e.g. soil sealing, wind and water erosion, accumulation of contamination) but also occurring in nature (e.g. topographic/orographic changes, earth displacement through tectonic movements) or a mixture of both (e.g. climate change) which can be accelerated under severe drought conditions, and can occur under very diverse climatic conditions.
A common misunderstanding is that desertification is linked to the presence of deserts. The truth is that desertification can and does occur far from any climatic desert, as the presence or absence of a nearby desert has no direct relation to desertification.
Further basic facts on desertification can be found here.
Land degradation is the reduction in the capacity of the land to provide ecosystem goods and services and assure its functions over a period of time. It implies a reduction of the potential of productivity of the land (primarily, but not limited to, soil degradation and accelerated erosion, reduction of the quantity and diversity of natural vegetation) are widely spread in Europe, particularly in Mediterranean dry-lands but also in Central and Eastern European countries.
Like other natural hazards, drought has both a natural and social component. The risk associated with drought for any region is a product of both the region's exposure to the event and the vulnerability of society to the event. Vulnerability, on the other hand, is determined by social factors such as population changes, population shifts (rural to urban), demographic characteristics, technology, government policies, environmental awareness, water use trends, social behaviour, level of water development and/or exploitation, and water availability in general.
These factors change over time and thus vulnerability is likely to increase or decrease in response to these changes. Subsequent droughts in the same region will have different effects, even if they are identical in intensity, duration, and spatial characteristics, because societal characteristics evolve through time.
Drought is a natural hazard that differs from other hazards in that it has a slow onset, evolves over months or even years, affects a large spatial region, and causes little structural damage. Its onset and end, and the severity of drought are often difficult to determine. Like other hazards, the impacts of drought span economic, environmental, and social sectors and can be reduced through mitigation and preparedness. Because droughts are a normal part of climate variability for virtually all regions, it is important to develop plans to deal with these extended periods of water shortage in a timely, systematic manner as they evolve. To be effective, these plans must evaluate both a region's exposure and vulnerability to the hazard and incorporate these elements into a drought preparedness plan that is dynamic, evolving with societal changes.
Droughts differ from one another in three essential characteristics: intensity, duration, and spatial coverage. Intensity refers to the degree of the precipitation shortfall and/or the severity of impacts associated with the shortfall. It is generally measured by the departure of some climatic index from normal and is closely linked to duration in the determination of impact. Another distinguishing feature of drought is its duration. Droughts also differ in terms of their spatial characteristics. Drought impacts are closely related not only to the magnitude of the event, but also the timing of the onset, duration, and spatial extent. The spatial and temporal characteristics of drought affect the planning and responses.