ABSRACT
Water resources have been threatened in the Guinea and Sudano-Sahelian ecological zones by the persistent impact of climate change. Many previous studies in the area were based on historical trend analysis or hypothetical assumptions in projecting climate change impacts on water resources. Considering the sensitivity of the hydrological system to climate change, there is the need to adopt the current global paradigm shift from the use of historical trend analysis to the use of General Circulation Models (GCMs) with Representative Concentration Pathways (RCPs). This is yet to be adopted within the study area, which constitutes the research gap this thesis has identified. Thus, the aim of the thesis was to examine the impact of climate change on water resources availability in the Guinea and Sudano-Sahelian ecological zones of Nigeria. The objectives were to: analyse the sensitivity of the Guinea and Sudano-Sahelian ecological zones of Nigeria to climate change; determine the potential impact of climate change on water yield; identify the trend in the occurrence of extreme rainfall indices; and estimate the water stress resulting from climate change in the study area. The data used (observed and simulated) were from the archive of the Royal Netherlands Meteorological Institute Known as the KNMI Climate Explorer. The respective coordinates of each basin were used to derive the observed and simulated data. Mann Kendal statistical test was used to analyses trends in all the time series at the 0.05 significance levels. Projections were produced for three future periods namely: 20192048, 2049-2078 and 079-2100 using the multi-model ensemble mean of CMIP5 GCMs under RCP2.6, RCP4.5 and RCP8.5. The metrics were root mean square error (RMSE), Mean Absolute Error (MAE) and Nash-Sutcliffe Efficiency (NSE). The errors between the observed and simulated were within the acceptable threshold. Regional trend analysis of seasonal and annual temperature confirm significant positive trends for (2019-2048), (2049-2078), and (2079-2100) with respect to highest emission trajectories. On the other hand, seasonal and annual rainfall projections for the same time horizons confirm high level of variability unlike temperature. However, regional trend analysis confirms that Guinea and Sudano-Sahelian ecological zones of Nigeria will experience decreasing dry season water yield. As for wet season, it reveals that under 2019-2048 period there are no significant increasing trends. This is with respect to high emission scenario (RCP8.5) but significant in low and middle emission scenarios (RCPs 2.6 and 4.5). Furthermore, it is evident that regional trend analysis of maximum 5- day rainfall demonstrated that under 2019-2048 period there will be no significant positive trend. Regional trend analysis of heavy rainfall days point out that there will be no significant positive trends for RCP2.6 with respect to the three projected periods but significant with respect to 2049- 2078 for RCP4.5 as well as RCP8.5. Regional trend analysis of CWD established that there will be no significant negative trends. Conversely, CDD will increase within the range of 2-5 days and 6-10 days for all the three RCPs under the two baseline periods of (1959-1988) and (19892018) respectively. However, regional trend under the influence of population growth at constant climate observed that there will be significant positive trends in water stress for the three projected periods. This implies that future water scarcity is imminent and will be primarily caused by population growth and only secondarily by climate change in the Guinea and Sudano-Sahelian ecological zones of Nigeria. It was recommended amongst others that future research should explore the comparative analysis of CMIP5 and CMIP6 in reproducing historical seasonal as well as annual temperature and rainfall in the Guinea and Sudano-Sahelian ecological zones of Nigeria. This will facilitate a robust climate projection for the study area
CHAPTER ONE
1.0 INTRODUCTION
1.1 Background to the Study
Water resources include all sources of water that are valuable to humans (Habets et al., 2013). This includes groundwater, rivers, streams, lakes, reservoirs, basins and runoffs. It is imperative since it is required for life existence. Agricultural, industrial, domestic, recreational and environmental activities are the various uses of water. Nearly all of these human uses require fresh water. Felix et al. (2017) asserted that sustainable management of water resources is a function of the hydrologic cycle such that climate change has a vital link with it. Yang et al. (2011) state that the consequence of climate change on water resources is evident on the changes in water and its quality that are caused by climatic factors such as rainfall and temperature changes. The total amount of water resources in Nigeria are exaggerated by the alliance of climate change and human factors. The spatial pattern of climate, rainfall distribution as well as hyrdo-geological units from the coastal parts of the southern to the extreme northern Nigeria provide an outline for the recognition of the threats in terms of the quality and amount of water available.
It is known and established in literature that there is intrinsic connection linking climate change and water resources. This is even more so as empirical studies in the recent past have shown the impact of the former on the later (Hagemann et al., 2013; Wenchao et al., 2014; and Adam, et al., 2016). Generally, global water resources are under heavy stress owing to the amplified climate change impact which varies from one region to another. However, its availability is controlled by the hydrostratigraphy of Nigeria that trail the pattern of prevalence of the aquicludes, aquitards or aquifers. The Intergovernmental Panel on Climate Change (IPCC) (2014), defined climate change as alteration in the state of the climate that can be identified using statistical tests to determine changes in the mean or the variability of its properties which persists for an extended period usually decades or longer. Eric et al. (2017) stated that it refers to any alteration in climate over time whether due to human activity or as a result of natural variability. This definition varies from that of the United Nations Framework Convention on Climate Change (UNFCCC).It defines climate change as the change of climate that is ascribed directly or indirectly to human actions that alters the composition of the global atmosphere in addition to natural climate variability observed over comparable time periods. However, the study adopts IPCC (2014) definition.
1.2 Statement of the Research Problem
The ecological zones of the Guinea and Sudano-Sahelian cover approximately 79% of the whole land mass of Nigeria. It is inhabited by over 50% of the country‘s 167 million people (Asemota et al., 2016). It is home to over two-thirds of the country‘s 250 ethnic groups (Asemota et al., 2016).Agriculture provides the major source of employment for the vast majority in these zones and presents the quickest way of reducing poverty (Babatolu and Akinnubi, 2014). About 80% of the inhabitants are engaged in crop and livestock production as well as fishing (Abdullahi et al., 2014). These zones allow for a diversity of crop production such as: sorghum, millet, maize, groundnuts, rice, cowpea, cotton, cassava and yam. Thus, making agriculture the largest water user (69%), then domestic (21%) and industrial (10%) (Doll et al., 2012; Schewe et al., 2013).
However, these water resources have been threatened by the persistent climate change impact. This is visible from the occurrence of drought to the continuous decrease in the quality and volume of water owing to the declined river flows and reservoir storage, drying up of wetlands and aquifers, as well as lowering of water tables (Esther et al., 2012). Lake Chad for example has shrinked from its initial 25,000km2 in 1960s to 1350km2 in 2005 (Yunana et al., 2017). Streams in these zones which hitherto were perennial have now become seasonal such that water can only be found in them during the wet seasons with little or no water in the dry seasons. Furthermore, a cursory examination of existing literature indicates that quite a lot of research has been undertaken in the areas of water resources and climate change. Notably, Yang (2011), Mohammed and Abdurrahman (2013), Wenchao et al. (2014), Jayasekera and Kaluarachchi (2015), Gijs et al. (2016), Heejun (2016), Hosea et al. (2016), Amar et al. (2017), Dehuaet al. (2017), and Pengpeng et al. (2017) all of which were carried out off the shore of Nigeria. Other researchers like Aizebeokhai (2011), Olaniyi et al. (2013), Ifabiyi and Ojoye (2013), Abdullahi et al. (2014), Babatolu and Akinnubi (2014), Salamiet al. (2015a), Asemota et al. (2016), and Ojoye et al. (2016) were undertaken in Nigeria. A common feature of these previous studies in Nigeria is that they were based on historical trend analysis or hypothetical assumptions in projecting the climate change impact on water resources availability.
Considering the hydrological system‘s sensitivity to climate change, there is the need for the current global paradigm shift from the use of historical trend analysis, to the application of Global Climate Models (GCMs) with Representative Concentration Pathways (RCPs).This is yet to be adopted within the study area; which constitutes the research gap this thesis has identified. Thus, it becomes inevitable to identify the impending impact on water availability of the area under consideration due to climate change.
1.3 Aim and Objectives
The aim of the thesis was to examine the impact of climate change on water resources availability in the Guinea and the Sudano-Sahelian ecological zones of Nigeria.
The objectives are to:
( i ) Analyse the sensitivity of the Guinea and Sudano-Sahelianecological zones of
Nigeria to climate change using climatic variables of temperature and rainfall.
( ii ) Determine the potential impact of climate change on water resources in the study area.
( iii ) Identify the trend in the occurrence of extreme rainfall indices under future climatic conditions in the study area.
( iv ) Estimate the water stress resulting from climate change in the study area.
1.4 Research Questions
( i ) What is the sensitivity of the Guinea and Sudano-Sahelian ecological zones of Nigeria to climate change?
( ii ) What are the potential impacts of climate change on water availability in the study area?
( iii ) What is the trend in the occurrence of extreme rainfall indices under future climatic conditions in the study area?
( iv ) What is the likely state of water stress resulting from climate change in the study area?
1.5 Justification for the Study
Understanding of climate change is continually improving, but the future climate remains uncertain (Ammar, 2015). Globally, it is estimated that by 2050 between 150 and 200 million people could be displaced as a consequence of phenomena, such as sea level rise and increased extreme weather events (Doll et al., 2012; Scheffran et al., 2012; Sadoff et al., 2015; Michael et al., 2017). In addition, the Global Environmental Outlook’s Baseline Scenario projects increasing strains on water resources through 2050, with an additional 2.3 billion people expected to be living in areas with severe water stress, especially in North and South Africa as well as South and Central Asia (Harding et al., 2014). Kwak et al. (2013) predicts the world could face a 40% global water deficit by 2030 under a business-as-usual (BAU) scenario. Africa‘s rising population is driving demand for water under accelerated degradation of existing water resources. More so, about 66% of Africa is arid or semi-arid and more than 300 of the 800 million people in sub-Saharan Africa live in a water-scarce environment (Charles et al., 2016). These statistics on the global and continental trend are indeed mind-bogging which calls for a study of this nature at local scale to unravel the impact of climate change on water resources.
Moreover, due to many changes, the climate in recent years in Nigeria has witnessed considerable variability across the various ecological zones. According to Babagana (2017), the Sahelian drought that started in 1969 which lingered on till 1973 to 1983-84 affected northern Nigeria and the calamity has had tremendous socio-economic impact on the area where pressure on available resources result in hydrological imbalance such as inadequate water supply, empty reservoirs, dry-upwells and crop damage. The severity of the drought was gauged by the degree of moisture deficiency, its duration, and the size of the area affected. This is also supported by details Chukwuma (2015) who contend that over the years, the Nigerian government had not given the much needed attention to the issue of climate change, particularly in the semi-arid northern Nigeria. The net effects were the shrinking of the Lake Chad and insecurity occasioned by the farmer-herder clashes and population displacement. For this reason, it is of vital importance to reflect on arrays of possible future climate conditions across these zones if any meaningful development is to take place in the water resource management and agricultural sector which has been of utmost priority in recent times (Mohammed et al., 2014).
1.6 Scope and Limitation of the Study
Spatial scope of this study covers the Guinea and the Sudano-Sahelian ecological zones of Nigeria. The study is limited to three basins namely: Kainji Lake Basin (KLB), Sokoto – Rima Basin (SRB) and Komadugu – Yobe Basin (KYB) that cut across the Guinea and Sudano-Sahelian ecological zones of Nigeria. The respective coordinates of each of the three basins were used to derive the observed and simulated rainfall and temperature records as well as evapotranspiration. The temporal scope covers scenario projections generated for three future periods namely: near-term (2019-2048), mid-term (2049-2078) and long-term (2079-2100) using the multi-model ensemble mean of CMIP5 GCMs under three CO2 emission trajectories (RCPs 2.6, 4.5 and 8.5) with references to the two baseline periods of (1959-1988) and (1989-2018).
1.7 The Study Area
1.7.1 Location of the study area
The study area lies between Longitudes 3°E and 15°E of the Greenwich meridian and Latitudes 8°N to 14°N of the equator. The area covers the Guinea and the Sudano- Sahelian Ecological Zones of Nigeria. It is bordered to the north by the Niger Republic, to the east by the Republic of Cameroun, to the south by the tropical rainforest and to the west by the Benin Republic.
1.7.2 Climate of the study area
The two predominant air masses that influence the weather and climate of these zones are the Tropical Continental (cT) air mass and the Tropical Maritime air mass (mT)(Abdulkadir et al., 2015). The former is dry and dusty which originates from the Sahara Desert, while the latter is dense and moist whichoriginates from the Atlantic Ocean. The Guinea savannah is located around the middle part of the country and is the most extensive of all the zones. With a unimodal rainfall distribution, it shows a mean of 1120mm but attain 1500mm on the Jos Plateau. The temperature shows an annual mean of 24°C to 30°C. The Sudan zone is found in the Northwest. It has an annual average rainfall of about 700-1100mm with a prolonged dry season of about 6-9 months. The Sahel is located in the extreme northeastern part of the country. The region is also associated with greater extremes of temperature as high as 44°C before the onset of the rains and can drop to as low as 6°C during the cool harmattan air around December to February. In this zone dry season can last for as long as 9 months and the maximum annual rainfall is about 600mm (Abdullahi et al., 2014).
1.7.3 Relief and Geology of the study area
In general, the topography of the area consists of plains interrupted by plateaus and hills. The Sokoto Plains lie to the northwestern corner of the country, while the Borno Plain is in the northeastern corner extending as far as the Lake Chad basin. The Lake Chad basin and the western parts of the Sokoto region in the far northwest are underlain by soft, geologically young sedimentary rocks. Gently undulating plains, which become waterlogged during the rainy season, are found in these areas. The characteristic landforms of the plateaus are high plains with broad, shallow valleys dotted with numerous hills or isolated mountains, called inselbergs; the underlying rocks are crystalline, although sandstones appear in river areas (Abaje et al., 2013). The Jos Plateau rises almost in the centre of the country; it consists of extensive lava surfaces dotted with numerous extinct volcanoes.
1.7.4 Hydrology of the study area
The Guinea and Sudano-Sahelian ecological zones of Nigeria are well drained with a close network of rivers and streams. Some of these, particularly the smaller ones are seasonal. Out of the four major drainage systems in Nigeria, two are found in the Guinea and the Sudano-Sahelian ecological zones. They are: The Niger River Basin Drainage System with its major tributaries of Benue, Sokoto-Rima, Kaduna, Gongola, Katsina-Ala, Donga, Tarabe, Hawal and Anambara Rivers; and the Lake Chad inland Drainage System comprising the Kano, Hadejia, Jama‘are, Misau, Komadougou-Yobe, Yedoseram and Ebeji Rivers (Ojoye et al., 2016).
The Hadejia/Nguru Wetlands in the northeast of the country receive their water from the Hadejia and Jama‘are rivers, which meet to form the Komadougou-Yoberiver, flowing northeast into the Lake Chad. So far, more than half of the wetlands have been lost due to drought and upstream dams. New development could divert still more water from the wetlands for irrigated agriculture in upstream areas, affecting both the ecology and the irrigated agricultural production in the floodplain using water from the shallow groundwater aquifer, as recharging would decrease further. Inappropriate agricultural practices, such as lack of crop rotation, adoption of maximum tillage, inadequate or total lack of fallowing, inadequate fertilization, overgrazing, absence of mulching, and the opening up of riverbanks have led to silting of riverbeds and loss of watercourses.
1.7.5 Water use in the study area
Long-term average internal renewable surface water resources are estimated at 214 000 million m³/year and renewable groundwater resources at around 87 000 million m³/year, but 80 000 million m³/year is considered to be overlap between surface water and groundwater, which gives a value of total internal renewable water resources (IRWR) of 221 000 million m³/yea. Total annual water withdrawal was estimated at 12 475 million m³ for the year 2010. Agriculture is the sector withdrawing the largest share of water, with about 5 510 million m³ (44 percent) made up of 4 549 million m³ for irrigation, 233 million m³ for livestock and 728 million m³ for aquaculture (Aizebeokhai, 2011). Around three quarter of the municipal water withdrawal is from groundwater resources, the remaining coming from surface water. Industry is the sector with the smallest withdrawal with 1965 million m³ (14 percent). Figure 1.1shows the study area.
This material content is developed to serve as a GUIDE for students to conduct academic research
CLIMATE CHANGE IMPACT ON WATER RESOURCES AVAILABILITY IN THE GUINEA AND SUDANO- SAHELIAN ECOLOGICAL ZONES, NIGERIA
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