Impacts of Climate Change and Land Use on Water Resources and River Dynamics Using Hydrologic Modelling, Remote Sensing and GIS: Towards Sustainable Development

Abstract

Water sustains life and ecosystems of the earth, making it an essential and important resource. However, it has become scarce, particularly in semi-arid regions of the globe, because of climate change, human population growth and growing economies. These factors can substantially impact on water resources, riverine ecosystems and services. Sustainable development of water resources and water system-related activities, such as agriculture, in river basins require an in-depth understanding of the present status and trends of hydrometeorological patterns, land use/land-cover and river channel dynamics in order to balance growth and integrity of vital environmental systems. Assessment of climate and land use impacts on water resources in the Tana River Basin (TRB), Kenya, as a typical example of Eastern Africa watersheds, was the main goal of this research. The focus was the Tana River Basin (TRB) in Kenya as a typical example of Eastern Africa watersheds. Land use/cover changes, hydroclimatic, hydro-geomorphology and morphometry of the basin including channel planform and floodplain corridor time series were characterised as well as historical modelling of climatic dynamics. The methods and tools applied were literature review, hydrological modelling, remote sensing (RS) and geospatial analysis techniques. Hydroclimatic data were obtained from Water Resources Management Authority (WRMA) of Kenya and remote sensing data were sourced from Survey of Kenya and Landsat Archive of United States Geological Survey (USGS). <br/> The first step of this investigation was a detailed literature review on the TRB and its adjacent Athi River Basin (ARB) to provide insights on the state of water resources. Limited scientific knowledgebase at watershed scale, inadequate data as well as gaps in the available data and the need for application of current state-of-the-art technologies were the major problems identified to affect whole basin water management and recommendations were made for better planning and management. The second step was to assess the spatio-temporal dynamics of land use/cover over a 28-year period in the upper TRB using digital change detection techniques. The results indicated substantial increase in agricultural land and builtup area and decrease in open land, waterbodies and vegetation. There was a large expansion of agricultural land to marginal semi-arid and arid areas (lower part of the basin) over the period. These changes have potential implications on water resources and environment. <br/> The third step was to investigate temporal variabilities and trends of rainfall and discharges in the TRB using statistical methods including Mann–Kendall non-parametric test and bootstrapping to capture and detect multiannual and seasonal variabilities and monotonic trends over a period of 75 years. The results suggested that the streamflow is largely dependent on increasing rainfall at the highlands which also seemed to be influenced by altitudinal factors. The precipitation exhibited spatio-temporal variabilities and trends. The streamflow also showed statistically significant upward monotonic trend and seasonal variability. The trends and time series data confirmed the potential evidence of climate and land use change and their impacts investigated in the previous step. <br/> The fourth step was to study recent hydromorphological characteristics and ecohydrological parameters using flow duration curve, freely available satellite data and geospatial analysis techniques. This study underscored the contribution of human and climate factors to streamflow changes and river channel morphology. The fifth step was to use Digital Elevation Model (DEM) to analyse morphometric parameters of the basin. This morphometric analysis of the basin provided the description of topography, geology and basin hydrological behaviour valuable for assessment and management of the basin water resources. The sixth step was to review methods for assessing probability distribution and associated parameter estimation procedures in the flood frequency analysis and apply the most efficient and robust approach in selecting the best models for fitting hydrological streamflow extremes in the basin. An assemblage of the latest computer statistical packages (fitdistrplus and HydroTSM) in an integrated development environment for the R programming language was applied. Maximum Likelihood Estimation (MLE), Goodness-of- Fit (GoF) tests-based analysis and information criteria-based selection procedures were used to identify the most suitable distribution models for forecasting hydrologic events and detecting inherent stochastic characteristics of hydrologic variables. This step provided a significant contribution on the current updates and understanding of predicting extreme hydrological events for various purposes, not only in the TRB but also in the methods that may be used in other regions. <br/> In the seventh step, river channel dynamics, in particular channel erosion and accretion, which are natural autogenic occurrences for fluvial rivers but accelerated by human modifications and climatic factors, were examined in detail. Remote sensing and geographic information system tools and techniques, aerial photographs, and satellite imagery were used to determine epochal channel erosion, accretion, and unchanged locations along the river. A geospatial methodological framework for monitoring river erosion and accretion was developed and applied to model and monitor, quantify and visualise the channel dynamics at reach scale. In the seventh step, another integrated remote sensing and GIS methodological framework was developed and used to study a total of 44 km reach of the channel morphological pattern changes (planform) and flood corridor dynamics of the river systems. In these studies, tremendous alteration in active channel and floodplain morpho-dynamics indicated substantial spatio-temporal dynamics and an overall vulnerability of the river condition. <br/> Lastly, scientific literature on modelling climate impacts on hydrology and water resources in river basins of the world was systematically reviewed and synthesized. The emphasis was on hydrologic modelling in terms of geography, global circulation models’ (GCMs), and downscaling, hydrologic models research topics and methods. Issues of uncertainties identified and discussed under this topic related to hydrologic model parameter estimation and hydrologic models themselves, GCM downscaling to application scale, stationarity in hydroclimatic variables, use of remote sensing products and geospatial analysis tools, and modelling of water quality. <br/> This research contributes information and knowledge that are of practical application to planning and management of water systems and policy decision-making in the water-foodenergy nexus within and without the basin. It provides guiding principles among other factors, for governments in this region in planning long-term viability and sustainability of riverine infrastructure and other regional projects such as those prioritised in the Comprehensive Africa Agriculture Development Programme (CAADP). The research also provides a basis for further modelling of river resources and environment under climate and human behaviour dynamics.