Institute of Climate and Society

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    Impact of Climate Change and Variability on Surface Water Availability and Crop Water Requirement in Eastern Tigray, Northern Ethiopia: Implications for Dryland Water Management and Adaptation
    (Mekelle University, 2025-03-28) Amdom Gebremedhin Berhe
    Climate change and variability pose significant threats to agricultural productivity and water resources, particularly in vulnerable areas like Eastern Tigray. This situation underscores the urgent need for adaptive, integrated water management strategies to address the challenges climate change exerts on agriculture and water resources. Consequently, this study aims to analyze the impacts of climate change and variability on water availability and crop water requirement, as well as to identify adaptation strategies. This study employed various models and analytical tools to evaluate the impacts of climate change and variability on water availability, crop growing season characteristics, and crop water requirements. The research involved analyzing historical climate data and examining temperature and precipitation patterns to establish a baseline scenario. Future projections were developed using selected General Circulation Models (GCMs) from the Coupled Model Intercomparison Project, which were downscaled to accurately represent local conditions. Building on this data, the study assessed spatio-temporal patterns in crop water requirement and surface water availability across the research area. The hydrological simulations generated by the HEC-HMS model, along with irrigation demand estimates and additional inputs from various sectors, were integrated into the WEAP model. This comprehensive framework facilitated scenario-based analyses of water supply and demand within the watershed, providing a robust foundation for effective water resource management strategies. By synthesizing insights from climate models, hydrological simulations, and water management tools, this study presents a thorough examination of historical trends and projected climate shifts, focusing on their implications for agriculture and water resources management. The analysis of historical data revealed non-significant upward trends in rainfall, while temperature trends showed significant increases. There was high variability in Kiremt season rainfall (21–31%) and in the duration of dry spells (25–43%) during the observed period. The length of the growing period (LGP) ranged from 68 to 90 days, indicating a limited time frame for crops to mature. Furthermore, projected climate change scenarios suggest a shift towards wetter conditions. Despite such conditions, the combined impact of rainfall variability and warming is projected to reduce the LGP by 5.5% to 19%, restricting crop growth and maturation and posing challenges for agricultural productivity in the future. As temperatures rise, reference evapotranspiration rates are projected to increase across mid- and end-century periods under all scenarios and stations. Mean monthly crop water requirement is also expected to rise, with shifts ranging from modest changes to as much as 19.4% by the end of the century. Seasonal crop water requirements are projected to increase as well, varying between 6% and 13% depending on the period. Simulations from the HEC-HMS model further indicate that, under the SSP2-4.5 scenario, surface runoff may decrease substantially during most months in both the mid-term (2040–2069) and end-term (2070–2099) periods, with reductions ranging from 0.56% to nearly 25.8%. Under the extreme SSP5-8.5 scenario, surface runoff is anticipated to decline during the mid-term but could increase during several months in the end-term. Forecasts of future water demand produced by the WEAP model cover a range of "what if" scenarios and go through 2055. The findings show that population growth alone could increase water demand by 81%, even without the influence of climate change. If irrigation expansion is included, increasing from 10% to 30%, water demand could rise further, ranging from 86.6% to 98.3%. Moreover, water availability may drop by 12% under the mid-term SSP245 scenario, and unmet demand may double by 2055 due to both rising demand and falling supply. The findings highlight the growing complexities of water demand, influenced by population growth, economic development, and intensified irrigation practices, all of which exacerbate the risks of water scarcity in the context of climate change. As temperatures rise and precipitation patterns become more erratic, the region encounters additional challenges, including increased heat stress, variable crop water requirements, and potential flooding under extreme scenarios such as SSP585. Mitigating these risks will necessitate sustainable water storage solutions, enhanced irrigation efficiency, and integrated cross sectoral water management. These strategies, underpinned by flexible policies, are essential for achieving long-term resilience in water security and agricultural productivity throughout Eastern Tigray.
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    Institute of Climate and Society