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The Ewaso Ngiro North Basin represents one of Kenya’s most critical yet stressed water systems. Originating from the glacial peaks of Mount Kenya and the Aberdare Ranges in the humid highlands of Nyeri and Nyandarua counties, the river flows 700 kilometers northeastward through Meru, Laikipia, Samburu, and Isiolo counties, passing through progressively drier landscapes before terminating in the Lorian Swamp near the Kenya-Somalia border. Along this journey, the basin supports 3.4 million people across five counties—Nyeri, Meru, Laikipia, Samburu, and Isiolo—each with distinct water demands, livelihood systems, and levels of access to this shared resource (Kiteme & Giesen, 2004). The basin’s dramatic climatic gradient creates fundamental disparities. Upper catchment areas in Nyeri County (southwestern Mount Kenya slopes) and Meru County (eastern Mount Kenya slopes) receive over 1,200 millimeters of rainfall annually on the mountain’s humid zones, supporting intensive agriculture including coffee plantations around Nyeri town, tea estates in Kieni, and high-value horticultural exports in Timau and Meru North. The middle catchment across the Laikipia Plateau (1,600-2,300 meters elevation) experiences moderate rainfall of 400-750 millimeters supporting mixed farming around Nanyuki town, large-scale ranching across the plateau’s rangelands, and wildlife conservancies in northern Laikipia. Lower catchment pastoral zones in Samburu County (centered around Maralal and Archer’s Post) and Isiolo County (including Isiolo town and the Merti Plains) receive less than 300 millimeters annually and depend almost entirely on the Ewaso Ngiro River for livestock watering during critical dry seasons (Notter et al., 2007). This diversity, while ecologically rich, generates profound tensions over who gets water, when, and how much. Agricultural uses dominate water demand across the basin, consuming 70-80% of total abstractions. Commercial farms in Laikipia County, particularly along the Burguret, Naro Moru, and Likii river corridors, cultivate wheat and horticultural crops for export markets while operating extensive dairy enterprises. Smallholder irrigation schemes in Meru County around Timau and along the Kathita tributary produce vegetables and food crops. In Nyeri County, irrigation supports coffee wet-processing and horticultural production around Nanyuki. Downstream, pastoral communities in Samburu’s rangelands (from Archer’s Post northward) and Isiolo’s Merti and Sericho divisions depend on reliable water for livestock—the economic and cultural backbone of their societies. These competing demands, layered over climate variability and fragmented governance across five independent county governments, generate recurring conflicts that undermine the basin’s long-term sustainability (WRA, 2021). Water stress—the ratio of water withdrawals to available supply—provides a critical metric for assessing whether current patterns can be sustained. Previous studies have documented water scarcity challenges in specific sub-regions including the Burguret sub-catchment in Laikipia (Lanari et al., 2018) and the upper Ewaso reaches around Nanyuki (Mutiga et al., 2010), but comprehensive basin-wide assessment incorporating climate change projections and spatial differentiation across all five counties has remained limited. Understanding where stress is most acute, how it varies seasonally, and how climate change will reshape water availability is essential for developing equitable allocation policies and effective adaptation strategies.