Temporal and spatial structure in a daily wildfire-start data set from the western United States (1986-96).

The temporal and spatial structure of 332 404 daily fire-start records from the western United States for he period 1986 though 1996 is illustrated using several complimentary visualisation techniques. We supplement maps and time series plots with Hovmöller diagrams that reduce the spatial dimensionality of the daily data in order to reveal he underlying space-time structure. The mapped distributions of all lightning- and human-started fires during the 11- rear interval show similar first-order patterns that reflect the broad-scale distribution of vegetation across the West and he annual cycle of climate. Lightning-started fires are concentrated in the summer half-year and occur in widespread outbreaks that last a few days and reflect coherent weather related controls. In contrast, fires started by humans occur throughout the year and tend to be concentrated in regions surrounding large-population centres or intensive-agricultural seas. Although the primary controls of human-started fires are their location relative to burnable fuel and the level of human activity, spatially coherent, weather-related variations in their incidence can also be noted. [ABSTRACT FROM AUTHOR]