Aspects of Hydrology and Water Resource Management of ASALs in the Tropics

Introduction

Hydrology plays an important role in water resources planning, development and management. Hydrological processes in tropical Arid and Semi Arid Lands (ASALs) are characterized by low and erratic rainfall, periodic droughts, irregular agricultural productivity and high water scarcity. Water security, environmental sustainability, food security (crop and livestock production, fish production) and; fuel wood energy resources are critical in tropical ASAL environments where land degradation threatens the livelihoods of poor communities whose rising poverty levels create conflicts for marginalized agro-pastoral communities now worsened by land use and climate change dynamics. Climate change manifesting in recurrent droughts in the Kenya’s ASAL areas causing wildlife/ human conflicts. Sustainable agro-pastoral livelihoods require an understanding of the hydro-climatic patterns that would enable drought mitigation and coping mechanisms for food security.

Land use closely linked to demographic conditions has resulted in degradation and desertification in the Sahel with effects on landscape productivity and aridity (Amougu et al., 2010, Anyamba and Tucker, 2005, Descroix, et. al, 2011, Mahhanne et al, 2016). Unsustainable land use and climate change will cause increased desertification and landscape degradation. The increasing population and rapid economic development are key drivers of land use change that impact hydrological processes pertaining to water use which in turn determines water quantity and quality (Mundia & Ariya, 2006). High surface runoff, reduced lag time, reduced low flows, increased peak flows and channel erosion are a consequences of urbanization (Rose & Peter, 2001, Okoye and Kwamboka, 2016). Urbanization influences water quality and quantity and may cause transboundary conflicts in water use. Changes induced in the pre urban landscapes often make urban environments vulnerable to pollution and drainage/flood hazards yet for ASALs, the storm water can be managed by a strategy of increasing ground water recharge (Oyeabande, 1990, Pilgrim 1982). Ground water recharge for ASAL runoff is influenced by vegetation, landuse/cover, temperature and soil moisture gradient in a basin (Flint, 2001). The interaction between vegetation, soil moisture and surface runoff and; the subsequent erosion risk can be achieved by mapping the spatial and temporal variability of the processes. The recharge processes affect ground water quality and aquifer vulnerability to pollution and thus important in determining sustainable water abstraction levels and the ground water conservation zones in ASAL aquifer basins.

Hydrological networks equipped with suitable instrumentation with continuous monitoring of the variables would ensure adequacy of data for planning sustainable development and management. Effective rain fed agriculture and irrigation scheduling during droughts would reduce wastage and degradation of water quality. Research in hydrology has shown that ASALs are vulnerable environments and a classical example of hydrological processes study is the Walnut Gulch Experimental watershed in Arizona (Peter et al, 2000). In Africa, ASAL areas support large human, livestock and wildlife populations. Inadequate knowledge and diffusion of innovative technologies hinder sustainable development here due to inadequate understanding of the hydrological processes in the watersheds that are heterogeneous in soils and rainfall characteristics which would affect the availability of water for the increasing populations engaged in rain fed and irrigated agriculture, industrial production, recreation and maintenance of the environmental integrity (Chahine, 2007 ; Oki & Kanae, 2006; Gleick, 1998).