Evaluating Nature Based Water Management Solutions for biodiversity in urban areas in England

Urban Nature Based Water Management Solutions (UNBWMS) used in England include natural wetland creation, bioswales, street trees, green roofs and walls, and most recently, ecological bus-shelters. The value of each UNBWMS to biodiversity depends on the water retention time, the type of vegetation present, flower structure and length and time of flowering coupled with the overall connectivity (capacity for animals to disperse) between each habitat. Measuring the value of a given habitat to biodiversity can be complex and time consuming. The Biodiversity Net Gain (BNG) metric developed by Natural England is a standardised approach that provides an indicator of habitat distinctiveness. It allocates a baseline score to a predefined list of habitat types, scores that are multiplied further by up to three additional factors as a function of habitat quality, ecological connectivity and strategic position within the landscape. Profiling the biodiversity value of UNBWMS by adapting the BNG metric allows the implementation of UNBWMS while simultaneously enhancing the value of the urban landscape to biodiversity. A further approach, also used in the planning application process, are habitat suitability indices (HabSI). The indices are based on key habitat requirements and have been developed for a limited number of species protected by legislation, such as the northern great crested newt (Triturus cristatus Laurenti). The derivation of T. cristatus HabSI for different UNBWMS options provides an indicator of their potential conservation value for this species, enabling the prioritisation of water management solutions to enhance populations.