Abstract
Changing climate is increasingly influencing the rainy seasons and posing significant challenges for agriculture and water resource management in vulnerable regions. The study examines the spatiotemporal variation of rainy seasons in the Upper Blue Nile Basin (UBNB) of Northwestern Ethiopia using projections from the CMIP6 climate models to assess potential impacts on agricultural and water planning. We analyzed observed and projected precipitation data across three Shared Socioeconomic Pathway (SSP) scenarios: SSP1-2.6, SSP2-4.5, and SSP5-8.5, spanning near-term (2015–2044), mid-term (2045–2074), and long-term (2075–2100) periods. To correct systematic biases in model outputs, a power transformation technique was applied to precipitation data from seven CMIP6 models. The finding of the study showed that the INM-CM5-0 model is the most accurate in simulating precipitation patterns, forming the basis for our detailed analysis. Our findings reveal significant shifts in the timing and duration of rainy seasons across all scenarios, with more pronounced changes under the highest emission pathways, SSP5-8.5. The SSP5-8.5 scenario indicates the most substantial extension in the length of rainy season, particularly in lowland areas, due to both earlier onset and delayed cessation. Conversely, highland and midland regions are projected to experience shorter rainy seasons, lasting between 82 and 130 days, driven by delayed onset and earlier cessation. These shifts could profoundly affect agricultural productivity, necessitating adjustments in planting and harvesting schedules by several months. Under high-emission scenarios, crop cycles may become misaligned with traditional planting windows, especially in highland areas where shorter rainy seasons may constrain crop viability. This study highlights the urgent need for adaptive strategies, such as the practice of early-maturing crop varieties, to enhance resilience to the change of projected seasonal rainfall patterns. Proactive measures, particularly in highland communities, are crucial for maintaining food security and effective water resource management to enhance adaptation options to climate change impacts in the area. These insights can guide targeted agricultural policies and resource planning, helping to mitigate the adverse impacts of climate change on food and water security.