Southwestern US seasonal precipitation and fire frequency from tree rings

1.  Southwestern US seasonal precipitation and fire frequency from tree rings Woodhouse, Griffin, Faulstich, and Swetnam AGU 2012 Session GC049. The North American Monsoon: Past, Present, and Future

2. GC049. The North American Monsoon: Past, Present, and Future Southwestern US seasonal precipitation and fire frequency from tree rings Woodhouse, Griffin, Swetnam, Faulstich Abstract Precipitation and drought drive wildfire in the southwestern US. Since the natural fire regime has been disrupted due to a variety of human activities since the early 20th century, proxy records are needed to assess the relationships between fire occurrence and seasonal precipitation. Fire scar data from tree rings have long been used to assess the natural fire regime for this region, and more recently, reconstructions of both cool and monsoon precipitation have been generated from partial ring-width chronologies for southwestern US. These proxy data allow an evaluation of the seasonal variability of precipitation and its relationship to fire. In this study, we examine and compare seasonal precipitation and fire in southern Arizona and New Mexico, from 1650-1899. In general, most fires occur before the onset of the monsoon, during the dormant season through spring, and are most closely related to cool season moisture deficits. In addition, a weaker but still significant positive relationship is evident with early season fires and the prior year’s cool season precipitation, and more strongly so for Arizona. A comparison of the major fire years (top 20th percentile) in the two regions suggests nearly 40% of these occur across the entire region, and these are clustered in time, primarily in the 19th century. Differences in the occurrence of largest fires (top 5 here) may be due to the climatic influences on major fires, with wet conditions in prior cool seasons playing a more important role in Arizona than New Mexico, where persistence dryness through antecedent seasons seems more critical. Late spring and summer fires, while much less widespread and frequent, are not significantly correlated to precipitation in either cool or monsoon seasons, but the largest appear to occur in the same years of major pre-monsoon season fires.

3. Fire Scar Data: • Arizona: SE AZ sky island sites • New Mexico: Sandias • New Mexico: Jemez area • Percent of recording trees scarred, averaged across the sites within the two regions, for D, E, M, L, A, (no Us). • 1650-1900 • Reconstructed Climate Data: • Arizona, NAM2 region , 7-month and 3-month SPI • New Mexico, Rio Grande rectangle from Cochiti to Elephant Butte Dams, total seasonal precipitation • Cool season = Oct-April; Monsoon = JJA • 1650-1900

4. Location of NAM2 and CEB regions for cool and monsoon precipitation reconstructions. These correspond to 2 NAM forecast regions (CEB falls with NAM3). CEB NAM2

5. Jemez Regional Analysis: All files within yellow circles were combined for Jemez-wide analysis VG samples from surrounding Valle Grande Erica Bigio

6. Valle San Antonio group: VSA -- 45 trees (Dewar/Falk) VSR -- 21 trees (Dewar/Falk) VSLD -- 11 trees (Dewar/Falk) VSC -- 19 trees (Dewar/Falk) Valle Grande group: VG -- 95 trees (Dewar/Falk) -- surrounding Valle Grande VJ -- 44 trees (Dewar/Falk) VGR -- 11 trees (Baisan/Morino) Bandelier group: BA2 -- 13 trees (Swetnam/Allen/Caprio) BA3 -- 18 trees (Swetnam/Allen/Caprio) BA4 -- 23 trees (Swetnam/Allen/Caprio) CPU -- 8 trees (Touchan/Swetnam/Allen) Pajarito Mountain Group CMN -- 20 trees (Touchan/Swetnam/Allen) CME -- 6 trees (Touchan/Swetnam/Allen) CAS -- 31 trees (Touchan/Swetnam/Allen) PME -- 17 trees (Touchan/Swetnam/Allen) PMR -- 23 trees (Touchan/Swetnam/Allen) PMW -- 11 trees (Touchan/Swetnam/Allen) Monument Canyon MON -- 198 trees (Don Falk) All files combined for Jemez-wide seasonality percentages Erica Bigio

7. Jemez-wide combined: 613 trees Erica Bigio

8. Sandias sites Erica Bigio

9. Sandias Sandias: 48 total trees (Baisan/Caprio/Swetnam) BON -- 21 trees (includes BON, FBR, MFL, MLO, MLR) CDE -- 14 trees CPC -- 3 trees LLT -- 9 trees PNO -- 1 tree Erica Bigio

10. SE Arizona fire scars Pinalenos, Huachucas, Rincons, Catalinas, Santa Ritas 636 total trees for all SE AZ sites Compiled by Holly Faulstich

11. Analyses Performed: How closely linked is seasonal climate to fire occurrence in these three regions? Correlations between seasonal precipitation and percent scarred in respective regions, different combinations of scar positions for current year, and lagged forward 2 years (two years of prior climate) How widespread are fires (across the three regions)? Correlations between DEM and LA fire years in the 3 regions. Top 20th percentile DEM scarred years, time series plotted. Plot of these fire years common across all regions or 2 of the 3. What are the corresponding cool season, and prior monsoon and cool season anomalies that accompany big widespread fire years? Identification of large DEM fire years (top 20th pctl) shared across all 3 regions (10 total) and associated season precipitation anomalies, current and prior year (antecedent climate conditions). What patterns of seasonal climate anomalies are associated with the larges fires in each region? Bar plots of the precipitation anomalies for the current and prior cool and monsoon precipitation for the top DEM 20 years in each region. *May also add season climate patterns for back to back fire years, an analysis that focuses on role of the monsoon more specifically, and/or a quick and dirt regression using climate and prior fire to predict DEM series

12. Correlations between fire scar series and regional climate • NAM2 cool and monsoon season SPI with SE AZ fire scars • CEB cool and monsoon season precipitation with Jemez and Sandia fire scars • red = sig @ p < 0.05

13. AZ NM – Jemez AZ NM Jemez NM Sandia Correlations of fire scar series between the three regions, total (DEMLA), pre-monsoon (DEM), and summer (L+A) scars

14. Top 20th percentile DEM scar years for each of the three regions AZ

15. Combinations of regions with shared large (20th percentile) DEM fires: 1) Across all 3 regions, 2) AZ and Jemez, 3) AZ and Sandia, and 4) Sandia and Jemez --with large shared L+A fires (AZ, Jemez)

16. 10 big fire years common to all 3 regions, with associated climate

17. Widespread Regional Fire and Associated Seasonal Climate Seasonal climate for 10 years with large DEM fires in all three regions. Precipitation by percentile in cool season of fire year, and cool and monsoon seasons for the prior two years Results for SE AZ fires/NAM2 climate and NM fires/CEB climate

18. 20 largest fires for each of the 3 regions with current and antecedent climate conditions • current yr cool season dry conditions key, esp. in NM • antecedent cool season wet conditions also notable, but somewhat variable among regions; Sandi a most notable • dry prior monsoon seems important to Jemez only, in yr n-1, while in yr n-2, wet monsoons seem to prevail