The wildland-urban interface (WUI), a transition area where urban areas are intermixed with wildlands, is at high risk to wildfires due to human-caused ignitions in close proximity to areas with high fuel load. The expansion of urban areas over the next thirty years is likely to increase the size of the WUI globally. Combined with climate change and expected changes in temperature, the growth in the WUI is likely to increase the frequency of wildfires. Although there have been some studies of how urbanization affects the WUI and wildfires, there is little scientific understanding of how past patterns of urban land expansion globally has affected wildfire risk at the WUI and how future patterns of urban expansions will increase WUI fire risk. There are four major knowledge gaps about WUI. First, there are few available global WUI datasets and there is no global WUI dataset with temporal dynamics. Without information of changes in WUI, it is difficult to understand past trends and project future patterns of fire risk at WUI due to urban expansion. The second knowledge gap is the lack of understanding of urbanization and fire risk in the WUI. Urbanization may increase fire risk in the global WUI (GWUI): urbanization can increase the area extent of the WUI and increase the fuel load around buildings, both of which increase fire risk. However, densification can also decrease WUI area and fire risk as infill development removes vegetation and, thus, fuel. Third, there is limited understanding of how forest degradation occurs at the WUI and its effect on fire risk. Forest degradation may be a precursor to urbanization at an early stage of urban development, or a successor to urban development. Fourth, the dynamics of land surface temperature and how it affects fire risk at GWUI are not well understood. This project aims to fill these knowledge gaps using optical and thermal sensors, including Landsat, ECOSTRESS, MODIS and Sentinel 1. Although there are many pathways of how urbanization and forest degradation affect fire risk, we will investigate one mechanism in this project: land surface temperature increase due to urbanization and forest degradation and these combined effects on increased fire risk. Our hypothesis is that the spatial and temporal patterns of urbanization and forest degradation increase surface temperature and then increase risk of wildfires at GWUI. The overarching research question of this project is: How has urbanization affected fire risk at the global WUI, and how will future urbanization expand the GWUI? This project builds on and leverages past NASA-funded efforts, including projects on WUI (Radeloff), urbanization (Seto), forest degradation (Chen), wildfires (Balch), and urban forecasting (Huang, Seto). The project aims has five research goals: 1. Identify hotspots of historical urbanization within the GWUI and analyze the intensity of urbanization. 2. Assess forest degradation within urbanization hotspots in the GWUI. 3. Investigate the effects of urbanization and forest degradation on land surface temperature within urbanization hotspots in the GWUI. 4. Explore the effects of changes in land surface temperature on fire hazard. 5. Project future WUI in the urbanization hotspots and identify areas with potential high risk. In order to achieve these goals, this study will develop novel algorithms by combining shortwave infrared (SWIR), thermal infrared (TIR), and optical remote sensing data. The research questions of the proposed project are: 1. How has the intensity of urbanization, including building density and spatial patterns of development, changed over time in the GWUI? 2. How have forests degraded in the GWUI? 3. How have urbanization and forest degradation affected land surface temperature in the GWUI? 4. What is the relationship between land surface temperature and fire in the GWUI? 5. How will future urban land expansion increase the GWUI and fire risk?