The University of Arizona

NM Climate Division 1: Climate Reconstruction | CLIMAS

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NM Climate Division 1: Climate Reconstruction

Single-Year Reconstruction and Extremes

The graph below shows the cool season (November-April) precipitation reconstruction for New Mexico climate division 1. Values are expressed as a percentage of 1000-1988 average precipitation. The adjusted 2006 and 1950 averages, the two driest years during the dry periods of the 1950s and 2000s, are plotted in orange and red, respectively, for comparison. As the reconstruction shows, not many years in the past thousand years were drier than 2006.

R2 = 65%

View calibration/verification data

Reconstructed Average (1000-1988) = 113 mm

Instrumental Average (1896-2010) = 117 mm

 

Driest Year Wettest Year
Year Precipitation (mm) Percent Average Year Precipitaton (mm) Percent Average
1668 21.0 18.7 1840 222.7 198.0
1664 23.9 21.2 1484 222.3 197.7
1593 25.0 22.2 1839 217.6 193.5
1592 25.3 22.5 1065 215.5 191.6
1670 31.0 27.6 1196 213.6 190.0

Multi-Year Reconstructions and Extremes

The graph below shows the five-year average precipitation reconstruction for New Mexico climate division 1; values are expressed as a percentage of 1000-1988 average precipitation. The adjusted 1955-1959 and 1999-2003 averages for this climate division are provided for comparison (orange and red lines, respectively). Several extended dry periods stand out, particularly the late 1000s to early 1100s, late 1200s, early 1300s, late 1500s, late-1700s, and the mid-1900s.

 

R2 = 65%
View calibration/verification data

5-Year Reconstructed Average (1000-1988) = 113 mm/yr; 565 mm/5-yr

5-Year Instrumental Average (1896-2010) = 117 mm/yr; 585 mm/5-yr

Driest Five-year Period Wettest Five-year Period
Years Precipitation (mm) Percent Average Years Precipitation (mm) Percent Average
1664-1668 263.3 46.5 1837-1841 974.8 172.2
1589-1593 284.1 50.2 1865-1869 838.8 148.2
1214-1218 310.7 54.9 1200-1204 832.9 147.1
1778-1782 321.8 56.8 1115-1119 826.8 146.0
1250-1254 323.0 57.1 1617-1621 820.3 144.9

 

Instrumental Record and Extremes

While precipitation was below average for climate division 1 (46.2%) in 2006, the instrumental record for this division shows several years that were drier. Based on five-year precipitation averages, the driest period in the 2000s was between 2001-2005, measuring slightly above 64% of average.

Driest One-Year Period Wettest One-Year Period
    Year      Precipitation (mm) Percent Average      Year      Precipitation (mm) Percent Average
1904 37.6 32.2 1941 269.7 231.4
1972 48.8 41.8 1932 215.6 185.0
2006 53.8 46.2 1905 209.3 179.5
1977 54.1 46.4 1979 206.2 176.9
1902 57.7 49.5 2005 205.2 176.0
Driest Five-Year Period Wettest Five-Year Period
Year Precipitation (mm) Percent Average Year Precipitation (mm) Percent Average
1902-1906 359.2 61.7 1985-1989 828.3 142.3
2001-2005 373.1 64.1 1981-1985 819.7 140.8
1900-1904 389.1 66.9 1986-1990 797.8 137.1
1949-1953 397.8 68.4 1939-1943 792.0 136.1
1901-1905 409.4 70.4 1980-1984 784.9 134.9

Calibration and Verification Data

The graph below shows a comparison between instrumental and reconstructed November-April precipitation for New Mexico climate division 1. The graph shows excellent agreement between the tree-ring and instrumental records over most of the 20th century. The R2, in this case 66%, indicates the amount of variation in the instrumental precipitation record captured by tree rings. Higher R2 values indicate more reliable reconstructions.

How the Data Were Calculated

The 1000-year reconstruction of cool-season precipitation is presented as the combined neural network and linear regression reconstructions. The two separate reconstructions were combined in the following manner. If both the linear regression and neural network reconstructions were below the calibration in any given year, then the linear regression value was used. In all other instances, a simple average of the two reconstructions was used. The rationale for this approach is based on detailed analyses and the simple observation that the linear regression does a better job at capturing the drought years. The reconstructions for each division were “smoothed” using a centered 5-year running average.

These reconstructions were developed using millimeters as the measurement unit. However, it is sometimes easier to think of precipitation in terms of the percentage of the long term average. To convert these data to percentage of average each reconstructed value was simply divided by the average of the reconstruction. The same procedure was used to convert instrumental precipitation.

The threshold line for the most recent drought period was calculated by first determining the percentage of average precipitation received during the year or averaged over the last five years, then dividing by the long term averages. In the case of the five-year smoothed reconstructions the average is based on five year averages over the 1896-2010 period. Comparison of the most recent drought in the 2000s to the long term average is problematic, however, because these reconstructions only extend through 1988. In addition, tree-ring data do not match the variance contained within the instrumental data so an adjustment is needed to be made in order to make more reasonable comparisons. The 2006 value (or the 5 year average) was first adjusted relative to the 1896-1988 reference period by calculating the percentage of average over the entire period (1896-2010), then determining the value relative to only the common overlap period (1896-1988). For example, New Mexico Climate Division 1 recorded 53.8 mm of precipitation in 2006, which is 46.2% of the 1896-2010 average (116.6 mm). To put this into the context of the tree-ring reconstruction in terms of millimeters of precipitation, this value (46.2% or 0.462) was multiplied by the reconstructed average over the period 1896-1988 (118.7 mm), which yields an adjusted value of 54.8 mm.

A note about dates: while a single year or range of dates is given in the data for simplicity, cool-season precipitation estimates are for November-April. For example data listed for 2002 would actually be from November 2001 to April 2002.