Fig. 8

Comparison of three climate indices used to evaluate the relationship between fire year and antecedent precipitation conditions from 12 fire history studies on ponderosa pine (Pinus ponderosa) in Colorado, USA, used in the fire regime meta-analysis of 2017. Y-axis is the percent of all observations in each of three precipitation conditions: average precipitation, dry (below average), and wet (above average). Index categories are All, the combination of precipitation indices (n = 39); NINO3, sea surface temperature index (n = 7); PDS, Palmer Drought Severity index (n = 14); and TR, tree-ring growth index (n = 13). The four panels represent the number of years preceding a fire year: (A) y−1, one year prior; (B) y−2, two years prior; (C) y−3, three years prior; and (D) y−4, four years prior