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This study reports impact of climate change on water resources availability in the Sokoto-Rima river basin (SRRB). SRRB is located in the North Western Nigeria and spread across four (4) States (i.e. Sokoto, Kebbi, Katsina and Zamfara) with ninety three (93) Local Government Areas, with a human population of more than 15million. The study uses Water Evaluation And Planning (WEAP) model to asses and evaluate the impact of climate change on surface water availability and investigate the sensitivity of SRRB to climate change. This model allows the simulation and analysis of various water allocations and scenarios. The available data was used to model the surface water resources situation, and then projected in to the present situation of the existing hydraulic condition of the basin. The hydrological processes that occur for the six major rivers within the basin during 1970 to 2013 was satisfactorily modelled and calibrated by visual observation and compared with the measured data. The calibration process of the model was done using the first twenty years climatological records (1970-1990) and validated with the remaining eighteen years data (1990-2008). Simulations were proposed for various climatic situations considering the global climatic models (GCM) predictions and linear trend of the data. Six (6) selected climate change scenarios of temperature increases (0, +0.5, +1 oC) coupled with decrease or increases in precipitation (0,-10%, +10%) were combined and applied for the study area in the WEAP model for simulation. The model was used to analyse the linkage between the water availability and the demand in some selected sections within the basin. Base on the human population, the hydraulic situation of the basin was projected to the future to analyse the water availability up to the year 2064. The runoff, evapotranspiration, and water demand series were obtained as output of the model. Results showed that climate change will reduce viii the runoff, and increase evapotranspiration and water demand in the basin, more especially the demand for irrigation. Results also indicated an annual reduction in the total available water by about 1.70 billion cubic meter and a maximum monthly water demand of 17.11 billion cubic meter for the month of April (which is the driest month in the basin) for the selected sites, under 10% reduction in the actual rainfall within the basin and increase in evapotranspiration under 1oC increase in temperature, this indicate reduction of the surface water in the future for the basin. In addition, the dependency of the basin on surface water sources make it imperative to apply some methods of efficient use of water resources, to ensure future sustainability.




1.1 Background of the study


Fresh water is crucial to human society, not just for drinking, but also for farming, washing and many other activities. It is expected to become increasingly scarce in the future, and this is partly due to climate change. The International Reports clearly stated the importance of freshwater to life support system and is widely recognised (Falkenmark, 1986; Dudgeon etal., 2006). Fresh water is indispensable for all forms of life and is needed in large quantities, in almost all human activities.


Climate, freshwater, biophysical and socio-economic systems are interconnected in complex ways, so a change in any one of these induces a change in another. Anthropogenic climate change which refers to the production of greenhouse gases emitted by human activity adds a major pressure to nations that are already confronting the issue of sustainable freshwater use. The challenges related to freshwater are: having too much water, having too little water, and having too much polluted water. Each of these problems may be exacerbated by climate change. Freshwater-related issues play a pivotal role among the key regional and sectoral vulnerabilities. Therefore, the relationship between climate change and freshwater resources is of primary concern and interest (Bates et al., 2008).


As climatic variability intensifies, changes in atmospheric conditions altered water resources, their distribution in space and time, the hydrological cycle of water bodies, and water quantity. The water cycle is altered by climate change, but because of the complexity of the hydrosphere in the Earth system, it is difficult to predict how precipitation patterns might change. Changes expected include the timing, amount, and location of precipitation and runoff. Such changes are major drivers of vulnerability and will alter the patterns of water availability in many regions, more especially the Sahel and Sudano-Sahelian belt that are areas with higher temperatures, low precipitation and most affected by droughts.


The large portion of Sokoto-Rima River basin (SRRB) is Sahel eco-climatic zone and Sudano-Sahelian belt in the south, which is characterised by strong climatic variations and an irregular rainfall. It is located in the North Western Nigeria and spread across four (4) States (i.e. Sokoto, Kebbi, Katsina and Zamfara) that have ninety-three (93) local government areas. The states rely heavily on its water resources for their socio-economic sustenance. The people living in those States consider rivers and streams within the basin as very important source of surface water for their municipal and agricultural demands. Therefore, even a small decrease in runoff within the basin could have dramatic effects on the welfare of the region.


In view of the above, this study focused on evaluating the impact of climate change on available water resources in the six major rivers (i.e. Bunsuru, Gagere, Rima, Sokoto, Zamfara and Ka) of the SRRB using a decision support system known as the Water Evaluation and Planning (WEAP) Model. WEAP is an analytical framework developed for the evaluation of climate change and other drivers that water managers commonly confront (Yates et al., 2006). WEAP model is one of the useful tools for integrated water resources management and it can be used as a database for forecasting and as a policy analysis tool, depending on the focus of the study. In this regard, the applicability of WEAP in assessing the impact of climate change as well as its main function as a sophisticated water allocation model was utilized in this study.


1.2 Justification of the study


The assessment reports produced by the Intergovernmental Panel on Climate Change (IPCC) and direct observations on the surrounding environment are increasingly providing evidence that climate change is actually happening much faster than initially assessed by the scientist. While the exact nature of the changes in temperature or precipitation, and extreme events are caused by climate change are not known, there is general agreement by the scientist that extreme events will get worse, and trends in most variables will change in response to warming and that the consequences are already visible in many areas of the world (Bates, 2008).


In Nigeria, the Federal Ministry of Environment (2003) analyses of available meteorological data from 1920 to 2003 on surface air temperature for Kano, Calabar and Lagos show evidence of increasing surface air temperatures of about 0.250C for Calabar and Kano and 0.25 to 0.500C for Lagos (Onyenechere and Igbozurike, 2010). Also, there are indications that other climate variables especially rainfall has declined both in magnitude and temporal distribution (Onyenechere and Igbozurike, 2010).

The impact of climate change on water resources will be overwhelming. Observational records and climate projections provide abundant evidence that freshwater resources are vulnerable and have the potential to be strongly impacted by climate change, with wide-ranging consequences for human societies and ecosystems (Bates; 2008). According to Rosenberg et al., (1999), water is considered as the most critical factor associated with climate impacts compared with many sectors of the natural and man-made environment that are expected to be affected by climate change. A similar idea is also highlighted by Houghton (1997) who stated that the most important impact of global warming is on water supplies which are in any case becoming increasingly critical in many places.

In contrast to the assessment of global or large scale variations of the climate driving forces for global hydrology by IPCC, the impact of climate change on the regional hydrology is still unknown for most regions of the world (Kim et al., 2006). Although climate change is a global phenomenon, the trends and impact may be different on a local scale.


In the continent of Africa, the observational records show that the climate has been warming through the 20th century at the rate of about 0.05°C per decade (IPCC, 2001).The water demand is continuously increasing due to lot of reasons, some of which are increase in population, increase in evapotranspiration and drought due to climate change, economic development, environmental considerations etc. As a result the risk that the required amounts of water will not be available is increasing more especially in semi-arid river basins areas, as such access to water needs to be secured in those regions. By 2025, it is assumed that 22 countries in Africa will experience a water-stress situation due to rapid population growth, expanding urbanisation, increased economic development and climate change (


Nigerians do not enjoy adequate water supply, and the rapid pace of population growth in the country has been accompanied by increased demand of fresh water for domestic, industrial and agricultural use. The problem of water shortage is more prominent and severe in the northern areas of the country that have limited rainfall water between May to October and harsh weather conditions associated with frequent drought.

Available individual and collective researches at regional levels show that Nigeria like most parts of the world is experiencing the basic features of climate change. Some localities are experiencing extreme weather conditions as a result of increasing temperature and an associated changing climate (Olaniran 2002; Ayoade 2003; Odjugo 2005). Ayoade (2003) recorded a slight drop in air temperatures within the late 1940s and early 1950s in Nigeria. According to Mabo (2006) and Ikhile (2007), a sharp increase in temperature between 1971 and 2005 could be linked to the effect of climate change and its associated global warming.


Temperature anomalies confirm the facts that global warming is unequivocal (IPCC 2007b). According to Odjugo (2010), increasing temperature is already present in Nigeria. The changes in climate such as temperature rise, erratic rainfall, sand storms, desertification, low agricultural yield; drying up of water bodies and flooding are physically present in the North Western region of Nigeria (Onyenechere and Igbozurike, 2010). Odjugo and Ikhuoria (2003) and Adefolalu (2007) report that increasing temperature and decreasing rainfall in the semi-arid region of Sokoto, Katsina, Kano, Nguru, and Maiduguri may have resulted in the increasing evapotranspiration, drought and desertification in Nigeria. Indeed, Sokoto basin is one of the few areas fingered for having the potential for more acute climate change impacts in Nigeria (Odjugo, 2010).


Analysis of monthly rainfall data from 1911 to 1980 by the Federal Ministry of Environment (2003) reveals a changing pattern in annual precipitation. The results obtained suggest that, there appears to be a definite decline in the 1941 – 1980 eras. Other researchers show evidence of other indicators (Fasona and Omojola 2005; Chindo and Nyelong 2005; Ikhile, 2007; Nwafor 2007; Umoh 2007). Fasona and Omojola (2005), Obioha (2008) and Odjugo (2005, 2009) have observed decreasing rainfall in Nigeria especially in the northern part. The




decreasing rainfall, increasing temperature and evapotranspiration have resulted in either reduction of water levels or total drying up of some rivers and lakes in Northern Nigeria, while Lake Chad in Nigeria is reported to be shrinking in size at an alarming rate since the 1970s (Chindo and Nyelong 2005; Odjugo 2007). Nkomo et al., (2006), Molega (2006) and Nnodu et al,. (2007) confirm the existence of unusual or extreme weather related events such as erratic rainfall pattern, floods and sea level rise in Nigeria. Also, rainfall data analysis undertaken by Adejuwon (2002) indicates rainfall decline in several locations in Nigeria thereby authenticating the findings of previous researchers. Several past research studies on climate trends (Oladipo 1995; Anyadike 1993; Olaniran and Summer 1989; Clerk 2002; Nkeiruka and Apagu 2005) have also shown significant variation in temperature and other climatic elements.


Ekpoh and Ekpenyong (2011) proposed that further scientific studies be undertaken at regional levels of the Sahel, due to significant variations in the climate of the region predicted by General Circulation Models (GCMs) so as to provide society with accurate information on the real and potential impacts of climate change, as well as, the mitigation and adaptation options available.


Previous studies done within the study area have not focused on the impact of climate change on water availability. Most of the related studies in the region focus on water infrastructure development (Oyebande, 1990; Okoye and Achakpa, 2007;, 2015), irrigation (Adams, 2003; Yahaya, 2002; Wiggins, 2000) and Water quality (Hassan,, 2014).


Therefore, considering the above statements this study focused on the assessment of relationships between climate change, water availability, water demand and supply





management on a catchment scale, and analysis of how water quantity will be affected by climatic change in the SRRB. This was done by using integrated water resources planning system (known as ―Water Evaluation and Planning” WEAP) that calculates water demand, supply, runoff, infiltration, flows, and storage under varying hydrologic and temperature hypothetical scenarios.


This study will considerably improve our understanding of climate change, and can significantly improve early warning systems by providing prior information, which have become a powerful instrument for anticipating on and mitigating the negative effects of climate variability in many areas of the world. It will also provide data and method of analysis using WEAP for the determination of climate change impact on water availability to be used for management decisions and application to other basins. This is the first study of its kind that used this tool in the region. The reliability estimates described in this study also inform anticipatory adaptation actions such as investment in increased water use efficiency measures.




1.3 Aim and Objectives of the study


The aim of this study is to analyse how sensitive the SRRB is to climatic change with regards to its surface water availability, by developing a Model of the basin using WEAP and proposing some mitigation measures that can minimize the negative impact within the basin by the principle of mass balance of the hydrologic quantity of the whole area. The specific objectives are to:


  1. Evaluate the present hydrological condition (streamflow) of the entire SRRB using available data.






  1. Apply WEAP model to the SRRB to evaluate the impact of climate change for current and future water availability using water balance concept.


  • Calculate surface water availability and demand for each sub-basin within the entire River Basin by considering watershed characteristics and the demographic trends.


  1. Produce a simulation of the projected water availability and to compare the water availability with and without the effect of climate change in the study area and analyse the water resources trend in the part of the basin towards 2064.


1.4 Limitations of the study



The study focused on the application of the WEAP model to the SRRB for the purpose of defining how the basin could respond to major stresses of climate change in terms of the water availability at the catchment scale. However, it is beyond the scope of this study to identify the problem of flooding if it may happen under future climate scenarios. The study also does not take into account the effect of climate change on the ground water availability and water quality.




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