Background/Question/Methods: As we near the second decade of the 21st century, the majority of people worldwide are living in cities, compared to only 10% of the global population who were urban dwellers in 1900, a fact that by itself demands attention to these ecosystems. Research on urban ecosystems has generally focused on studies of individual cities, but understanding of urban ecosystem processes will advance most rapidly when considering urban areas in their physicochemical, social, geographical, and other contexts. Researchable questions include: How do ecosystem processes of human settlements depend upon their local biogeophysical context? Within similar biogeophysical settings, how do characteristics of the settlements themselves (i.e., size, shape, population characteristics) differentiate urban areas within regions? And finally, how do continental-scale gradients in biogeophysical properties combine with differences in settlement patterns (i.e., regularity of settlement distribution, isolation of urban areas, proximity to geographical features like coastlines) to influence ecosystem processes of urban areas? Using the concepts of material budgets and water provisioning ecosystem service, I develop hypotheses at each scale to explain the influence of both biogeophysical and social/geographic/economic contexts.
Results/Conclusions: Urban areas exhibit convergence in the overwhelming influence of human-mediated material imports, but local environmental contexts dictate the need to import water and modify water-delivery systems. Regional differences largely reflect history and variation in social contexts. Continental variation among ecosystem processes of human settlements reflects both types of contexts.