Climate-fire analysis. Santa Catalina Mountains, AZ (top), Black Mountain, NM (bottom). Proxy climate data, such as tree-ring records of precipitation, are compared with fire history records in order to determine the temporal pattern of precipitation associated with fire occurrence. These so-called "superposed epoch analyses" show the average of tree growth in precipitation-sensitive trees for all fire years (marked 0 on the x-axis) and several years before (marked -) and after (marked +) the year of the fire. A pattern frequently exhibited in Southwest fire-climate analyses is that of high precipitation in the years before a fire year. This pattern reflects (1) a build-up of fuels in the wet years and (2) a drying out of these well-developed understory fuels during the dry fire years. This pattern is typical of intense regional fire activity in the Southwest that occurs at the end of an El Niño (wet)-La Niña (dry) cycle.