Perspectives of the Hydrology of the Arid and Semi-Arid Lands of Kenya

Introduction

Hydrology is important in water resources planning, development and management. Hydrological processes vary from region to region. Arid and Semi Arid Lands (ASALs) are characterized by low and erratic rainfall, periodic droughts, irregular agricultural productivity and high water scarcity. The hydrology of ASALs influences water security, environmental sustainability and agricultural production and availability of fish and energy resources. The influences are pronounced in the tropical environments where land degradation threatens the livelihoods of poor communities.

Catchment hydrological processes of ASAL areas are available in many studies. One good example is the Walnut Gulch Experimental watershed whose programmes included; erosion and sedimentation, climate change and carbon dioxide fluxes, remote sensing and decision support systems for the San Pedro River in South Eastern Arizona (Peter et al, 2000). Investigating hydrological processes and related variability helps in the understanding of water supply, water quality, and energy fluxes. By remote sensing, processes of evaporation, soil moisture and forage can be monitored for trends in plant and soil conditions. Surface soil moisture in ASALs can be modeled using remote sensing technology, simulation models and GIS.

In the Sahel, conservation and development studies have shown that degradation and desertification are the result of land use closely linked to demographic conditions (Amougu et al., 2010). These changes not only affect landscape productivity, but also increase aridity of the climate (Mahhanne et al, 2016). The increasing population and rapid economic development are key drivers of land use change (Mundia and Ariya, 2006). Land use change by human interference and climate change impact hydrological processes pertaining to water use that would determine water quantity and quality. For instance, the hydrological consequences of urbanization are reflected in high surface runoff, reduced lag time, reduced low flows, increased peak flows and channel erosion (Rose and Peters, 2001, Ondieki, 2005; Okoye and Kwamboka, 2016). Urbanization would greatly influence water quality and increase drought impacts and cause transboundary conflicts in water use. The changes induced in the pre urban landscapes often make urban environments vulnerable to pollution and drainage/flood hazards (Oyeabande, 1990). Urbanization impacts on ASAL runoff and storm water management strategy by increasing recharge have been studied by Pilgrim (1982). Ground water recharge can be increased by a storm water management strategy for ASAL runoff with influencing factors being vegetation, landuse/cover, temperature and soil moisture gradient in a basin (Flint, 2001). 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. Unsustainable land use and climate change will cause increased desertification and landscape degradation. Knowing the interaction between vegetation, soil moisture and surface runoff and; the subsequent erosion risk is imperative. This can be achieved by mapping the spatial and temporal variability of infiltration and runoff generation through infiltration experiments at various locations in a catchment and catchment scale modeling. An understanding of hydrological characteristics of ASAL watersheds is critical for sustainable development.