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Background. Wildfire spread is influenced significantly by the weather variability. Wind speed and direction changes, resulting from synoptic weather systems and small-scale meteorological processes in complex terrain, can drastically alter fire intensity and spread. Aims. To investigate the use of vector wind change (VWC) integrated with the Fire Weather Index (FWI) as a new metric in fire danger. Methods. A 20-year FWI and modified FWI was calculated from weather station and gridded numerical weather simulation data. Key results. High VWC is found primarily on the South Island, inland and in areas of complex terrain. After incorporating VWC into the FWI, data from the modified FWI show spatiotemporal patterns that highlight the impact of wind variability in the fire danger. Conclusions. High VWC station data mapped with synoptic type suggest the primary factor in determining high VWC is meso- and micro-scale terrain-driven meteorology, not larger synoptic regimes. Implications. The current fire danger metric, the Fire Weather Index (FWI), does not include wind direction changes for high wind speeds. Therefore, the inclusion of VWC as an additional metric in fire danger calculations in a modified FWI could increase operational understanding of high-danger locations and terrain impacts on extreme and unpredictable fire behaviour. [ABSTRACT FROM AUTHOR]

Wildfire is a highly variable natural phenomenon, yet despite this, climate change is already making wildfire conditions measurably worse around the world; however, detailed knowledge about Aotearoa New Zealand's wildfire climate is currently limited. This study blends weather observations with regional climate model projections to assess Aotearoa New Zealand's 21st‐century wildfire climate. We find that in the 21st‐century, the emergence of a new—more severe wildfire climate will occur. Detailed analysis of observed and simulated wildfire weather finds that "very‐extreme" wildfire weather conditions matching the levels observed in Australia's 2019/2020 "Black Summer" bushfires are possible in regions formerly unaffected. While the extent of emergence is dependent on future emissions, the frequency of very‐extreme conditions for the areas affected can occur at any time and is independent of projected 21st‐century climate changes. Our findings have significant implications for many rural fire authorities, forest managers and investors, and climate mitigation and afforestation programs. Plain Language Summary: Combining highly detailed climate simulations with daily observations of weather and wildfire conditions, we simulate Aotearoa New Zealand's current and future wildfire weather conditions. We find that wildfire weather conditions will increase on average, both in wildfire season length and in the intensity of fires that may take hold, with the most severe wildfire dangers in the central‐south inland areas of the South Island. We find that the wildfire weather conditions will become noticeably worse for many regions than current conditions. For the first time, we find that very‐extreme conditions that led to the devastating 2019–2020 "Black‐Summer" fires in Australia can occur in Aotearoa every 3–20 year for areas of the South Island (Mackenzie Country, Upper Otago, and Marlborough). Our findings have important implications for communities near pine forests, the Government's tree planting plan to tackle climate change, and financial investment stored in plantation forests. Key Points: In the 21st‐century, the emergence of a new—more severe wildfire climate will occurWe discover that "very‐extreme" wildfire weather conditions are possible in regions formerly unaffectedWhile the extent of emergence is dependent on future emissions, the frequency of very‐extreme conditions is independent [ABSTRACT FROM AUTHOR]