The Earth’s environment is a dynamic system which includes many interacting components (physical, chemical, biological and human) that are constantly changing. The interactions and feedbacks among these components are complex and register high variability in time and space. Changes have always been present within the functioning of planet earth. But since 1950, human activities have produced an important impact in the Earth system (land surface, oceans, coasts, atmosphere, biological diversity, water cycle and biogeochemical cycles) causing changes well beyond natural variability (Vitousek 1992, Foley 2005, Levitus et al. 2012). The magnitude of these changes is increasing throughout the years due to the growing human population and the extension in scale of activities such as industry and agriculture.
After the industrial revolution, the world witnessed an increased gathering of its population in urban areas, as new job opportunities and improved living conditions increase. The 20th century witnessed the extreme and unprecedented growth of global urbanization. This trend is not new, but relentless and has been marked by a remarkable increase in the absolute numbers of urban dwellers, from a yearly average of 57 million between 1990-2000 to 77 million between 2010-2015 (MacLachlan, Biggs, Roberts and Boruff, 2017).
According to UN-Habitat (2016), the population in urban areas has increased from 14% in 1900 to 30% in 1950.With the world’s population evenly split between urban and rural areas in 2008, it is predicted by the UN that by 2050 the urban population will increase again to 66%with nearly 90% of this increase being concentrated in Asian and African cities. Nigeria alone is projected to add 212 million urban dwellers between 2014 and 2050. Whereas cities are hubs for positive social and economic transformation, urban centres are concentrations of industries, transportation, and other activities that release large quantities of greenhouse gases (Kara 2017).
An urban area is an area with an increased density of human created structures in comparison to the areas surrounding it (Enoguanbhor et al, 2019). These areas may be cities or towns, created and further developed by the process of urbanization. Urban areas are highly dynamic and are continually undergoing rapid changes, one of which is changes observed in land-use/land-cover (LULC) also known as land change. The knowledge of land use/land cover change is important to understanding certain occurrences on the earth’s biophysical composition. It entails a conversion of natural types of land to uses associated with growth of population and economy, transforming the landscape from its natural form to impervious urban lands termed cities and towns.
According to Hansen (2012), cities are the quintessence of man’s capacity to induce and control changes in his habitat. Through urbanization, man has created new ecosystems by interacting with the different components of the environment, thereby creating some imbalance in the system. This goes to say that urbanization is not without its consequences; most notable is the modification of land surface and atmospheric boundary conditions that lead to a modified thermal climate which leaves the cities warmer than surrounding non urbanized areas, commonly known as Urban Heat Island.
Birnin Kebbi land use and land cover change
Birnin-Kebbi is the administrative headquarters of Kebbi State. The total population of the city in 2006 was 268,620 and an estimated population of 366,200 in the 2016 demographic statistics released by the National Bureau of statistics, (NBS, 2016). The rate of urbanisation in the state has being largely influenced by the fast growing population. Despite having a Master Plan, the unchecked and uncontrolled development has led to the replacement of soil and vegetation cover with impervious urban materials and the creation of slums and squatter settlements. These may, directly or indirectly, affect the albedo and runoff characteristics of the land surface.
Land use and land cover change is a constant but gradual process occurring in any geographical location on the earth surface. This process may sometimes occur unnoticed over time and space. The Birnin-Kebbi land use and land cover analysis was examined using multi-temporal Landsat images between 1991 and 2018. The results (figure 3a) show that in 1991, with a population of 119,000 (UN-WPP, 2019) inhabitants, the urban/built-up areas were concentrated in the north-western part of the local government, with some isolated settlements in the other parts; development generally, was few and far between.
The urban/built up class covered only 1.4% (1,687 hectares) of the total land area. The low urban spread in 1991 is largely attributed to the fact that Birnin-Kebbi at this period was just elevated to the capital of a newly created state (Kebbi State), from Sokoto State. Also, vegetation covered 73,030 ha (58.5%), water body covered 0.04%, about 9,270 ha (7.4%) of the total land was used for agricultural purpose while bare land covered 40,773 ha (32.7%).
In 2000, (figure 3b), the population increased to 160,000 people (UN-WPP, 2019). The pattern of urban distribution indicates a gradual spread in the built up areas from the north-western part of the state capital, moving towards the western part in a linear pattern. There was also a rapid development of settlements in the southern part of the state capital. This led to the overall increase in the percentage of built up area in the year 2000 to 3.4% of the total land coverage. Also, vegetation covered 46.3%, water body covered 0.02%, and agricultural land covered 32.2% while bare ground covered 18.2%.
The growth in the built up area and agriculture is expected to come largely from bare ground and vegetation. This is because of the continuous increase in population due to migration and natural process, and the high demand on fuel wood for cooking energy (see plate II). So, the over dependent on fuel wood will lead to the destruction of vegetation. Similarly, the drive to make Nigeria self-sufficient in rice production will have a direct impact on vegetation, water body and bare ground in the future, as Kebbi state and Birnin Kebbi, in particular, is the major contributor to the total rice production in Nigeria.
It was discovered that there had been a steady increase in the rate of urbanisation and agricultural land (farmland) in the study area, with a corresponding decrease in vegetation cover and bare ground. The 2027 projection shows a similar trend and this is not environmentally sustainable.
There is a need to sensitive and re-orientate the people of Birnin Kebbi about the effect of using firewood as a source of cooking energy and it impact on climate change. The conscious reduction in the use of firewood for other sustainable alternatives like the LPG and electricity can lead to low patronage in the wood selling business and ultimately save the trees in the forest.
Sustainable skills development programmes, financial opportunity or material loans in terms of micro-credit schemes should be initiated by the government, through a coordinating ministry or NGO to provide LPG cooking system for private individuals and commercial food vendors at an interest-free loan to enable them stop the use of firewood.
The state government started a laudable project of planting trees within the urban areas in 2006-2007, this trees compensated for the loss in vegetation cover to farmland, leading to a small loss in vegetation between 2000 – 2009. The government should continue this project and encourage private organisations and individuals to plant trees. Primary and secondary school pupils can be motivated to plant a “Tree of Life” in their school environment.
The rate of land conversion from vegetation to agricultural purposes needs to be controlled, and more sustainable system of farming introduced.
Deliberate measures to control natural increase in population: if nothing is done to ensure a sustainable population size in the study area, all other effort to make Birnin Kebbi a sustainable city will be ineffective. The government need to synergize with Gate foundation, UNICEF and other aid organisation to invest more in the state in the area of family planning, education, poverty alleviation and green technology to improve child survival rate and ensure sustainable development.
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