The trends of rainfall have a great impact on the hydrologic cycle and therefore affect both the quality and quantity of water resources. There is therefore the need to examine the trend of rainfall in Sudano-Sahelian Ecological Zone of Nigeria comprising Kebbi, Sokoto, Kano, Jigawa, Yobe, Katsina and Borno States. The study examined the trend in rainfall patterns over a period of fifty years i.e. 1960-2009 so as to know the effect of rainfall variability in the occurrence of drought and flood in the zone. The study makes use of rainfall data, which were collected from the Nigeria Meteorological Agency, Oshodi, Lagos. The Standardized Anomaly Index was used to test for fluctuations in rainfall while the Spearman Rank Statistics was used to look for the trend in rainfall. The study revealed that there was a downward trend in rainfall amounts in the 1970s and 1980s which was responsible for the drought episodes of 1972/73 and 1980 and an upward trend in the amount of rainfall between 1990 and 2009 which accounts for the flood episodes in Northern Nigeria. There is a general increase of 5% in annual rainfall over the entire fifty years under study in the zone due to an observable 5.4% increase in mean rain-days and 4% increase in the rains that fall as heavy rain, which was found to be responsible for the increase in runoff, ground water recharge and the frequent flood episodes in the zone. Based on this study, it can therefore be concluded that the Sudano-Sahelian Ecological Zone of Nigeria has been experiencing an increase in the annual rainfall with little recession in 1970s and 1980s, the rainfall has been very high and this has significant consequences on water resources in the zone with the zone becoming prone to flood events, erosion and sedimentation which may have adverse effect on both quantity and quality of water available for human consumption. The study therefore recommends that a study of the interactions between the ecosystems due to the distortion in the hydrology of the zone should be carried out among others.

Abstract

This study examines the impact of climate change on hydrologic resources of selected rivers and lakes in the Sudano- Sahelian Ecological Zone of Nigeria. Climatologically data acquired were rainfall, temperature and evaporation from Nigeria Meteorological Agency, Oshodi, Lagos. Similarly, the hydrological data of river discharge and lake levels were obtained from Nigeria Hydrological Services, Kaduna. We used the Standardised Anomaly Index to test for fluctuations in rainfall, temperature, runoff and water level in lakes. Mann Kendall statistics were used to examine the trends in the climate variables. Pearman correlation was adopted to test the relationship between runoff and the rainfall variables. The findings revealed a general downward trend in rainfall amounts in the 1970s and 1980s. The findings also detected an upward trend in the amount of rainfall from 1990 to 2019. The correlation results of rainfall attributes and runoff showed significant relationships in annual rainfall (r= 0.61), annual rain-days (r=0.61), rain days of heavy rainfall (r= 0.57) and wet season rainfall (r=0.54). These attributed when combined, revealed a 51% contribution to the overall regression with (r=0.51) at 95% probability level. The study concluded that the Sudano-Sahelian Ecological Zone of Nigeria experiencing an increase in the annual rainfall. The increase in rainfall point to the recovery of the rainfall from the great Sahelian drought of the 1970s and 1980s. The rise in the annual rainfall is a possible influencing factor to the frequent occurrences of flooding in recent time across the ecological zone.

In Nigeria, the climate in recent years has witnessed significant variability across the various ecological zones due to climate change. Thus, the objective of this study was to analyse the 21st century trend of water yield in river basins of Guinea and Sudano-Sahelian ecological zones, Nigeria. The data and computation were done using KNMI Climate Explorer. The coordinates of the basins were used to derive the annual and seasonal water yield. Projections were produced for near-term (2019-2048), mid-term (2049-2078) and long-term (2079-2100) using ensemble mean of CMIP5 under RCP2.6, RCP4.5 and RCP8.5. Findings revealed that water yield during dry season demonstrates decreasing range of (-0.05 to-0.1 mm/day). It was observed that the decrease were only significant for RCP8.5 but not under middle and low emission trajectories. As for wet season, it reveals significant increasing trends at 0.05 significant levels with respect to RCP8.5 but not significant in low and middle emission scenarios. Regional trend analysis of average annual water yields reveals no significant positive trends for all the RCPs. This is to say that despite the projected increasing pattern of average annual water yield observed over Guinea and Sudano-Sahelian ecological zones, incidences of water crisis cannot be ruled out. Contribution/Originality: This paper's primary contribution is finding that river basins of Guinea and Sudano-Sahelian ecological zones of Nigeria will be significantly affected by the anthropogenic climate change at highest emission trajectory. The result can act as guidelines for strategic planning against water crisis as envisaged by the projection. 1. INTRODUCTION Climate projection is usually a statement about the likelihood that something will happen several decades to centuries in the future if certain influential conditions develop. Scenarios however, represent alternative possible ways in which the future may unfold [1]. 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 [2-5]. Furthermore, the Global Environmental Outlook's Baseline Scenario OECD, (2012) cited in Adefisan [6] 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 and South and Central Asia. WWAP (United Nations World Water Assessment Programme) [7] 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