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NM Climate Division 7: Climate Reconstruction | CLIMAS

NM Climate Division 7: Climate Reconstruction

Single-Year Reconstruction and Extremes

The graph below shows the cool season (November-April) precipitation reconstruction for New Mexico climate division 7. Values are expressed as a percentage of 1000-1988 average precipitation. The adjusted 2009 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 2009.

R2 = 42%

View calibration/verification data

Reconstructed Average (1000-1988) = 82 mm

Instrumental Average (1896-2010) = 77 mm

 

Driest Year Wettest Year
Year Precipitation (mm) Percent Average Year Precipitaton (mm) Percent Average
1782 9.7 11.5 1353 203.1 240.6
1668 12.7 15.1 1816 200.4 237.4
1168 14.8 17.5 1458 198.1 234.8
1218 16.0 18.9 1618 196.0 232.2
1542 17.6 20.8 1555 188.3 223.1

Multi-Year Reconstructions and Extremes

The graph below shows the five-year average precipitation reconstruction for New Mexico climate division 7; values are expressed as a percentage of 1000-1988 average precipitation. The adjusted 1953-1957 and 2006-2010 averages for this climate division are provided for comparison (orange and red lines, respectively). Several extended dry periods stand out, particularly the late 1000s-early 1100s, late 1200s, early 1300s, late 1500s, late-1700s, and the mid-1900s.

 

  

R2 = 42%
View calibration/verification data

5-Year Reconstructed Average (1000-1988) = 82 mm/yr; 410 mm/5-yr

5-Year Instrumental Average (1896-2010) = 77 mm/yr; 385 mm/5-yr

Driest Five-year Period Wettest Five-year Period
Years Precipitation (mm) Percent Average Years Precipitation (mm) Percent Average
1667-1671 214.9 52.4 1332-1336 748.8 182.5
1779-1783 223.3 54.4 1837-1841 712.4 173.6
1214-1218 239.2 58.3 1814-1818 710.5 173.1
1089-1093 239.9 58.5 1553-1557 702.0 171.1
1434-1438 241.0 58.7 1617-1621 687.6 167.6

 

Instrumental Record and Extremes

Precipitation was below average for climate division 7 (28.8%) in 2009. The instrumental record for this division shows few years that were drier. Based on five-year precipitation averages, 2006-2010 was slightly below average for climate division 7 (93.2%).

Driest One-Year Period Wettest One-Year Period
    Year      Precipitation (mm) Percent Average      Year      Precipitation (mm) Percent Average
1904 9.7 12.6 1919 197.4 257.0
1917 10.2 13.2 2005 190.8 248.4
1967 16.8 21.8 1941 187.7 244.5
2009 22.1 28.8 1915 184.4 240.2
1950 22.4 29.1 2004 181.4 236.2
Driest Five-Year Period Wettest Five-Year Period
Year Precipitation (mm) Percent Average Year Precipitation (mm) Percent Average
1952-1956 195.6 50.8 2003-2007 660.4 171.6
1954-1958 196.9 51.2 2005-2009 573.3 149.0
1953-1957 197.9 51.4 1985-1989 563.4 146.4
1955-1959 205.7 53.5 2006-2010 560.3 145.6
1951-1955 241.0 62.6 2004-2008 558.8 145.2

Calibration and Verification Data

The graph below shows a comparison between instrumental and reconstructed November-April precipitation for New Mexico climate division 7. The graph shows good agreement between the tree-ring and instrumental records over most of the 20th century. The R2, in this case 42%, 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 2009 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 7 recorded 22.1 mm of precipitation in 2009, which is 28.8% of the 1896-2010 average (76.8 mm). To put this into the context of the tree-ring reconstruction in terms of millimeters of precipitation, this value (28.8% or 0.288) was multiplied by the reconstructed average over the period 1896-1988 (80.8 mm), which yields an adjusted value of 23.3 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.