The global Wildland-Urban Interface and associated wildfire risk to people

Posted 08/22/23

The Wildland-Urban Interface is an area of potentially severe human-environmental conflict such as settlement exposure to wildfires or biodiversity loss. A group of SILVIS researchers and external collaborators now offer a global perspective on the Wildland-Urban Interface and identify many previously unknown hotspots. Covering about 5% of the land surface, the Wildland-Urban Interface is home to nearly half the global population, with hotspots across all continents.

The Wildland-Urban Interface (WUI) is where houses and wildland vegetation meet or intermingle. This makes that area a place of potentially severe human-environmental conflict, where settlements are exposed to wildfire, habitat is fragmented, and the risk of spreading zoonotic diseases is increased. While there is evidence for WUI across Australia, Europe, and North America, the worldwide distribution of the WUI is yet unknown.

A group of SILVIS researchers and external collaborators recently presented a global map of the 2020 WUI at 10 m resolution using a globally consistent approach based on remote sensing-derived datasets of building area and wildland vegetation, and identified hotspots of wildfire hazard in the WUI. The total global WUI area in 2020 was 6.4 million km2, or 4.9% of global land area, which is about twice the size of India. Globally, 3.3 billion people live in the WUI, of which two thirds live in landscapes dominated by forests, shrubland, and wetland, and one third in landscapes dominated by grassland. While WUI hotspots could be identified across all continents, Europe and North America have the highest land area share of WUI (12% and 6%). Patterns are highly diverse on a country level with regard to WUI land area share, population living in the WUI and dominant land cover types (Fig. 1).

Fig. 1: Wildland-Urban Interface area and population share by world region (top) and for selected countries (bottom). Some US states were also included for better comparability to previous research. F/S/W: Forest/Shrubland/Wetland, Grass.: Grassland.

Wildfires are of increasing concern across the globe, as their frequency, intensity and season-length has increased due to various factors, including climate change, more human ignitions, and rising fuel loads. Wildfires are a particular problem in the WUI, as they cause substantial losses of homes and lives there. Indeed, nearly two thirds of all people affected by wildfires since 2001 lives in the WUI, while only a small share (2% – 10% across regions) of all global wildfire occurrences in that period were in the WUI. Differences among world regions and countries persist here. In North America, 85% of the population affected by wildfire lives in the WUI, but in Africa only 50% does (Fig. 2).

Fig. 2: Wildfire and the Wildland-Urban Interface (WUI). A: Share of area affected by wildfire within and outside of the WUI. B: Share of population that experienced wildfire within 1 km of their home within and outside of the WUI. Africa (AF), Asia (AS), Europe (EU), North America (NA), Oceania (OC), and South America (SA).

As fire-prone areas expand globally, a global perspective on WUI data can help guide proactive actions to prepare for future wildfire in the WUI. This is particularly useful in areas where there is a high probability of becoming areas of increased fire hazard towards the middle of the 21st century, such as Temperate Broadleaf and Mixed Forests and (Sub-Tropical) Moist Broadleaf Forests, two biomes that represent 61% of the global population.

The global Wildland-Urban Interface. Percent area of the Wildland-Urban Interface (WUI) in ca. 2020 per hexagon with 50 km diagonal length.

Story by Schug, Franz