Influence of nature values on environmental assessments in the ESGAP framework
Environmental metrics are used to describe the state of the environment in order to help actors responsible for implementing public policies for development and environmental protection to evaluate the effectiveness of their actions. To describe the state of the environment in Senegal, we use the ESGAP method, which consists of evaluating each dimension of the environment in biophysical units, in order to estimate at the national level, the capacity of natural capital to perform its environmental functions. The strong environmental sustainability (SES) index informs the gap between the current state of the environment and the environmental sustainability objectives. Four functions (the renewal of natural resources, the capacity of ecosystems to absorb pollution up to their critical load, the maintenance of biodiversity, and the impact of the environment on health and well-being) are measured by 33 indicators.
The main challenge in Senegal is to understand the respective influences of the data quality supporting indicators, the choice of one indicator instead of another to inform one dimension of the environment and the weight of each environmental dimension on the aggregated SES index. For that, we performed a global sensitivity analysis (GSA). We found that the weights of dimensions with low uncertainty and extreme score (‘UNESCO sites’, ’Terrestrial ecosystems’ and ’Soil resources’) are highly influencing the aggregated SES index. They are responsible of 66 % of the SES index variability in the GSA. Then the choice between indicators with very different scores to inform one dimension of the environment was the second group of influential variables. For example, the choice between the ‘biodiversity intactness index’, the ‘red list index’ or the ‘mean species abundance’ to inform the ‘terrestrial ecosystem’ dimension is highly influencing the aggregated SES index because they give different scores (respectively 89, 94 and 51). Finally, the choices between databases given different results for the same indicators are the third influential group of variables. For example, the choice between two data sources to inform the soil resource in Senegal is responsible of significant part of the SES index variability in the GSA. We concluded that participatory approaches to introduce negotiated values in the evaluation of the state of the environment through weights between the dimensions of the environment was highly important, but only for well-informed indicators. Thus, the participatory process and the data gathering are complementary to evaluate a robust and relevant state of the environment.