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Senegal

Written by Michael Schultz Rasmussen and Karl-Erik Christensen

All over the world the living conditions of people changes from time to time. In some areas and in some countries the changes are fast and unpredictable, however, in other parts of the world, changes takes place slowly. In the areas south of the Sahara dessert in Africa, people are living in areas where serious changes take place from year to year because of changes in rainfall, fairly poor soil and lack of resources.
In the 1980’ies they experience serious drought and people died and they lost their cattle. The international community reacts in the most cases with providing assistance in terms of food and medical care, which is good, however, providing help and assistance to people without any need or only a limited need can equally be a problem, because if food is provided free of charge, the local markets are destroyed and this will have a serious effect on the local society. It can be extremely difficult to study if people’s livelihood is changing, because of the substantial annual changes. Satellite data can help us to understand the long term development of living conditions by studying the changes in the vegetation cover. Vegetation includes crops as well as grass to be used to feed the animals.

Senegal

In the following exercises we will try to answer the questions:

- is the daily lives and livelihood of people improving in Senegal?

- is the state of the environment deteriorating and causing what is known as desertification?

In Europe are the agricultural crops and the natural vegetation such as forests, wetlands, fallow land and protected areas growing steadily year after year. There may be minor differences, but the general picture is the same: our vegetation grows. In Senegal in West Africa, the rain is sparse and unpredictable and people here are very dependent on the growth of the vegetation. Either they are growing crops such as millet, groundnuts and corn, using the grass to feed the livestock or the forest for getting fuel wood and materials. The densities of people and cattle are high and the soils are sandy and not very fertile.

Therefore the condition of the vegetation is an excellent indicator of the livelihood of the people as well as the state of the environment in both Senegal and all the other semi-arid countries. The vegetation productivity decreases in years with low rainfall, in areas where the fields are not allowed to recover through fallow, where attacks from insects and maladies take place and where the density of grazing livestock is too high – just to mention the most important.

The condition and amount of vegetation can be estimated using satellite data. The principle is to keep track of the photosynthesis activities during the growing period. By the end of the season, we sum up the total photosynthesis or more correctly, we compute the net primary production (NPP) (also called biomass) for each pixel. If we know the NPP for some reference sites, we can compute a model that can estimate NPP for every pixel in the image. If we repeat this exercise every year, we get annual NPP or biomass maps and we can study the trend of the NPP for each pixel. This information can reveal if the environmental conditions and people’s livelihood are deteriorating or improving.

Keeping track of the vegetation development using Earth Observation is useful for many different purposes:

  • The growth of the global vegetation can be estimated and this provides information about the global CO2 sink. This is an important contribution to the studies and modelling of global change.
  • Estimate crop production in developing countries. This is used to assess food security and evaluate export potentials (and obtain better prices)
  • Support crop management for irrigation, pest management, water logging and insect attacks.
  • Estimate the availability and management of fodder resources for grazing animals
  • Identify long term environmental development and trends. Is a certain area experiencing a positive or negative development, e.g. increased or reduced crop production, reduced fertility of the soils and desertification.