Water scarcity remains one of the most significant constraints to agricultural productivity, particularly in semi-arid regions where irregular rainfall, increasing temperatures, and inefficient irrigation practices threaten sustainable food production. The emergence of Internet of Things (IoT)-based smart irrigation systems has transformed conventional irrigation management by enabling real-time monitoring of soil moisture, environmental conditions, and crop water requirements. This study examines the application of IoT-based smart irrigation systems in improving water use efficiency and crop productivity within semi-arid agricultural environments. A systematic literature review and comparative analytical approach were adopted to evaluate recent developments in IoT-enabled irrigation technologies, sensor networks, wireless communication, cloud computing, artificial intelligence, and automated irrigation control systems. The analysis reveals that IoT-based irrigation significantly reduces water consumption while improving irrigation scheduling, crop yield, operational efficiency, and environmental sustainability. Furthermore, integrating artificial intelligence, weather forecasting, edge computing, and precision agriculture technologies enhances irrigation decision-making and climate resilience. Despite these advantages, challenges relating to infrastructure costs, internet connectivity, energy supply, cybersecurity, technical expertise, and technology adoption continue to limit widespread implementation, particularly in developing countries. The study concludes that IoT-enabled smart irrigation represents a sustainable solution for addressing water scarcity and enhancing agricultural productivity in semi-arid regions. It recommends greater investment in digital agricultural infrastructure, farmer capacity development, supportive government policies, and affordable IoT technologies to accelerate adoption and strengthen climate-smart agriculture.