University of Birjand Water Harvesting Research 2476-6976 9 1 2026 03 01 Quantifying Roof Catchment Yields for Improved Water Security in a Populated Built Dryland Ecosystem: The Case of Kitui Campus of Kenyatta University, Kenya 40 56 3977 10.22077/jwhr.2026.10723.1196 EN Mary Makokha Department of Geography, Kenyatta University, Nairobi, Kenya. Fuchaka Waswa Department of Agricultural Sciences and Technology Kenyatta University, Nairobi, Kenya. Samuel Kimani Department of Geomatics Engineering and Geospatial Information Systems, Jomo Kenyatta University of Agriculture and Technology, Juja, Nairobi, Kenya. 0009-0002-3983-9308 Journal Article 2025 12 19 Water scarcity poses a significant challenge in semi-arid regions, with climate variability and growing demand exacerbating the strain on traditional water sources. As a contribution to sustainable water solution in a dryland region, this study reports the potential harvest from rooftop catchments in a populated built environment using Kenyatta University, Kitui Campus, in Kenya, as a case study. Roof catchment areas were computed using standard GIS procedures. Mean monthly rainfall was established using rainfall trends from 1981–2024. Estimated harvestable water was calculated standard formula for volume, but discounted for expected evaporation and seepage loses using applicable runoff coefficients. Results show that the entire campus can collect at least 11 million litres annually, with institutional buildings contributing 7.8 million litres and the staff quarters 3.4 million litres per year. With a population of about 1000 people coupled with water use efficiency, the campus can operate within a water secure scenario throughout the year. Seasonal analysis reveals that the October–December provides 361 mm of rainfall twice the volume of the March–May (MAM) which is 176 mm, necessitating strategic storage solutions to bridge dry periods. Based on the cost factor of above ground plastic tanks, this study proposes decentralized rainwater harvesting systems combining a series of large-capacity residential tanks available on the market (30,000-50,000 litres) for high-yield buildings and smaller tanks (5,000–20,000 litres) per individual residential houses. Lessons from this paper offer Kitui Campus, other learning environments, and households with ridged roof catchments, significantly opportunities through enhanced public health performance indicators and irrigation agriculture. https://jwhr.birjand.ac.ir/article_3977_b1c84b4b5ae8a71d7fd71909a46bb8ee.pdf