Impact of Sustainable Land Management (SLM) on Improving Water Security in the Rainfed Blue Nile Highlands
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Date
2023-05
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Addis Ababa University
Abstract
Securing water to meet ever growing human needs is a major global challenge. Particularly, feeding a rapidly expanding world population of 10 billion by 2050 presents a dominant water security challenge, with a projected water requirement of 12600 km3 yr-1 . To meet this demand, management and planning of water resources dominated by blue water whose availability is limited needs to be widened to include green water. Green water, which originates from naturally infiltrated rain, sustains 80% of the croplands globally. In sub-Saharan Africa, over 95% of the croplands are rainfed. While rainfall in vast regions of the world is sufficient to support agricultural production without large-scale irrigation, grain yields in rainfed systems are disproportionately low due to management-induced green water scarcity resulting from nonproductive rainwater losses of up to 70 – 85%. Investments in sustainable land management (SLM) initiatives in rainfed systems have led to reductions in nonproductive rainwater losses and increases in grain yields by 5 – 10 times. Largescale implementation of SLM initiatives in Ethiopia dates back to the early 1970s, which primarily involved the construction of terraces on agricultural lands. Such basic practices of SLM have contributed significantly to controlling soil erosion on agricultural land; however, they produced little impact on improving water security and agricultural productivity. This led to the emergence of a new approach of SLM, where every land use type within a catchment is treated for improving its productivity and ecological functionality. The main goal of the present thesis is to assess the impact of SLM on improving water security in the Blue Nile Highlands, where rainfed agriculture is the dominant economic activity. A paired-catchment approach provided an opportunity for using a combination of historical and newly recorded data for analysis. Runoff and causal rainfall data recorded from 26 experimental plots across xix three Blue Nile headwater catchments were used for an event-based water-budget analysis. Soil moisture data collected intensively at multiple sites and soil profile depths were used to assess the impact of SLM on soil water availability and soil moisture spatio-temporal variability. Relative to traditionally managed sites, sites under SLM practices presented computed runoff curve numbers reduced by -13.9 to - 21.6 units, revealing substantial increases in infiltration and water storage potentials of the agricultural landscapes in the study area. An increasing trend in the initial abstraction ratio was also observed across sites where the SLM interventions have been adequate, indicating a lag effect in runoff response. Sustainable land management practices in the study area reduced soil moisture temporal variability and spatial heterogeneity, resulting in increased soil moisture storage by 16 – 800%. The emerging SLM approach in the study area that leaves no land use type untreated within a catchment reveals great promises for improving rainwater infiltration and soil water storage potentials in the study area. Apart from securing water for sustaining rainfed production, SLM interventions have minimal effect on overall catchment runoff and, hence, on downstream water users and ecosystems. We conclude that a major effort needs to be exerted on mainstreaming water security into SLM initiatives to draw adequate attention among local land users, experts, and policy makers about the role of SLM for improving water security in the rainfed Blue Nile Highlands.
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Keywords
Green Water, Hydrologic Functionality, Infiltration-Runoff Dynamics, Management-Induced Water Scarcity, Rainfed Systems, Soil Water Storage, Sustainable Land Management, Water Security.