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Authors : Armand Kingbo , Oscar Teka, Augustin K. N. Aoudji, Bonaventure Ahohuendo and Jean Cossi Ganglo
Affiliated organization : Multidisciplinary Digital Publishing Institute
Type of publication : Article
Date of publication : April 29, 2022
Analysis of Average Annual Rainfall Parameters
The annual rainfall regime was characterized by high inter-annual variability with an average of 1210.85 mm/year. The period of excess covered the years 1954 to 1969, which resulted in a high frequency of wet years and having an inter-annual average of 1420.46 mm/year, i.e., an annual surplus of 12% compared to the inter-annual average (1211.85), with peaks in 1963 (2149 mm), 1968 (2020.3 mm) and 1965 (1769 mm). The rainfall deficit period was from 1970 to 2016 and corresponded to a relatively high frequency of dry years. The average annual rainfall for this period was around 1124.58 mm, which was an annual deficit of 28% compared to the inter-annual average. Strong deficits were observed for the years 1967, 1971, 1977, in 1998 and in 2015. These episodes of rainfall deficit reflect many drought years observed between 1970 and 2018.
Comparative Analysis between Rainfall and Temperature
The average maximum temperature is 30.36 ◦C. The curve of the inter-annual variation of the maximum temperature showed a large variation which was observed in an increasing way from 29°C around around 1954 to 31 ◦C around 1970 corresponding to a period of good rainfall in this region of Benin. However, after 1970, an increase in the average value of the maximum temperature was observed until 2016 when it increased to 33 ◦C. This period corresponds to low rainfall deficit being recorded.
The rainfall deficit period was from 1970 to 2016 and corresponded to a relatively high frequency of dry years. The average annual rainfall for this period was around 1124.58 mm, which was an annual deficit of 28% compared to the inter-annual average
The different variations presented by the climatic parameters confirmed that the climate in the southeast of Benin presented great variability distributed in two very distinct periods, the first period being before 1970, which seems to indicate the best rainfall with excess and had a maximum temperature between 29 ◦C and 31.5 ◦C. The second period, from 1970 until 2016, presented the worst climatic conditions, able to generate significant water stress for plants and trees which will have more difficulty in taking advantage of nature for their good growth and presenting the characteristic greenery of their good health. It was then more obvious for the forests to present more difficulties during this second period.
Analysis of the Dynamics of Land Cover and Use in the Forest of Dogo-Kétou in the Context of Climate Variability and Anthropogenic Pressures in Southeast Benin
The interrelationships between climate and land use have been assessed in this study. It allowed evaluation of the state of degradation of the natural forest of Dogo-Kétou and the real impacts of global changes as obtained through surveys among local populations in southeast Benin. The Normalized Vegetation Index (NDVI) reflects the health of the vegetation based on its cover density as well as its reflectance of sunlight. Indeed, the region of southeast Benin is experiencing visible transformations due to anthropogenic pressure accentuated by climate change. Analysis of satellite images has confirmed that for nearly 30 years the forest of Dogo-Kétou has suffered a sharp reduction in its density and forest cover.
However, the results of the present study have revealed from 1986 to 2018, a regression of dense forests and wooded savannas in favor of shrub savannas, agglomerations and bare soils
The results of this study reveal from 1986 to 2018 a regression of dense forests. In fact, over the period from 1990 to 2018 the normalized maximum vegetation index decreased from 0.9 in 1990, reflecting a high density of trees, to 0.6 in 2018. This period of decrease corresponds to a period where the local populations have reported the perceived impacts of climate change and human actions exerting simultaneously on the forest during the last decades. These rainfall deficits have increased the mortality of forest trees, making regeneration more difficult, destroying the grass cover, which was very sensitive to the lack of water, and increasing the pressure on surviving trees. This explains the various changes observed in the occupation and land use classes. A change in one element of the ecosystem has an effect on the other component. Understanding land use changes will impact policy for decision-making for an effective sustainable management of ecosystems, and this was how several authors have described the processes of land use dynamics in Benin.
The regression of dense natural forests has changed the landscape cover of the classified forest of Dogo-Kétou. Within the framework of participatory forest management, some vegetations as savannas were cultivated in the forest studied. The forests were invaded by populations who have their homes in permanent materials and schools in this forest
However, the results of the present study have revealed from 1986 to 2018, a regression of dense forests and wooded savannas in favor of shrub savannas, agglomerations and bare soils. The latter specified that under conditions characterized by a relatively high frequency of dry years, there is the destruction of mostly woody vegetation and an increase in the infiltration of rainwater and the appearance of species from dry areas. Seasonal attacks on forest vegetation by breeders in search of fodder and water resources were one of the main causes of the decline of dense natural vegetations. In addition, the population growth rate in the study, estimated at 4.02% from 2000 to 2013 [57], also reflects that strong pressure on natural resources and could also lead to considerable degradation if sustainable management measures of these ecosystems are not implemented.
The land cover consisted of forest gallery (37.16%), open forest (9.99%), wooded savannas (25.74%), tree savannas (0.47%), shrub savannas (2.93%), ferralitic soils (2.63%), ferruginous soils (16.33%), crops and fallow land (3.50%) and water (1.24%). The dominant formations of the vegetation being the gallery forest and the wooded savannas in 2014. But in 2018, this study confirmed that the areas of agglomerations have greatly increased reaching 7.8% of the forest area; tree and shrub savannas have also increased in area from 12.1% in 2000 to 38.9%. This increase could be explained by the impact of population growth, which has accentuated the deforestation of dense formations such as gallery forests and wooded savannas, since the latter fell from 52.6% in 1986 to 36.1% in 2000 then to 4.3% of the forest area in 2018. The wooded savannas have therefore almost disappeared with the increase of shrubby savannas. Indeed, the regression of dense natural forests has changed the landscape cover of the classified forest of Dogo-Kétou. Within the framework of participatory forest management, some vegetations as savannas were cultivated in the forest studied. The forests were invaded by populations who have their homes in permanent materials and schools in this forest.