Models of floods, disease, lakes, and fish don’t arrive ready-made – they’re patched together from code, data, software, theory, habits, and disagreement. Anja Klein follows that patchwork in action through fieldwork with two interdisciplinary research groups: a project in Accra tracking diarrhea and flood risk under climate change, and a Stockholm-based group building simulation models of social-ecological systems. How do materiality, difference, and complexity get handled in the daily work of modeling? What gets to be included and what is left out and why? Moving between ethnography and equations, the study traces moments of frictions and surprise that shape what a model can or cannot say about the world. In a grounded account of ›earthly modeling‹, the volume shows the potential of working across ethnography and simulation for knowing better our planet in crisis.