Drought arises from periods of insufficient precipitation, leading to deficits in both surface and subsurface water resources. In this chapter, various factors affecting hydrological drought have been evaluated. Also, hydrological drought has been investigated using the Standardized Streamflow Index in a case study (Karun 4 basin in Iran). For this purpose, the monthly discharge data of Armand station during the years 1987–2020 have been used. First, these data were examined in terms of homogeneity, outliers, and trends. Then the 3-month SSI was calculated. Our case study reveals a trend of increasing drought severity from 2000 to 2018, with extreme droughts in 2008 and 2018, indicating an urgent need for intervention. The use of GIS and spatial data has improved real-time monitoring and assessment of droughts, providing valuable data on their severity and duration. Understanding the spatial distribution and dynamics of droughts, influenced by local catchment characteristics, is essential for effective management, especially in regions with variable drought conditions. The study emphasizes the threat of climate change and land use changes, which can alter and disrupt the hydrological cycle, increasing vulnerability to drought. To address these challenges, the study suggests a focus on emerging technologies like remote sensing, the development of early warning systems, drought management plans, and water conservation strategies. It advocates for transboundary cooperation and continuous research to enhance resilience against droughts, ensuring sustainable water management. This serves as a call to action for coordinated efforts to mitigate the impacts of hydrological droughts.