One possible way to consider potential environmental impacts with events is to consider the Pressure-State-Response (PSR) model approved by the OECD (Organisation for Economic and Cooperation Development) and the UNEP (United Nations Environment Programme).
According to the PSR model, indicators can be classified as pressure indicators, state indicators and response indicators. State indicators reflect the environmental state of an event destination. The pressure indicators would reflect the event activities and their impacts on the environment, which would indicate whether the event activities exceed the limits of carrying capacity at the site. Response indicators therefore reflect the regulations, controls and standards that the municipal authority use to prevent degradation of the local environment.
Other way to estimate the environmental impact of visitors is to calculate their "ecological footprint". This is the area of land and water required to support the resource demands and consumption patterns of visitors, and is measured in terms of "global hectares" (gha).