STREAMFLOW and MONSOON RECONSTRUCTIONS for the LOWER RIO GRANDE BASIN, USA
Connie A. Woodhouse (1,2), David M. Meko (2), Daniel Griffin (1, 2), and Christopher L. Castro (3)
(1) School of Geography and Development, University of Arizona, Tucson, AZ 85721, (2) Laboratory of Tree-Ring Research, University of Arizona,
Tucson, AZ 85721, (3) Department of Atmospheric Sciences, University of Arizona, Tucson, AZ 85721
Shared seasonal droughts (droughts occurring in both cool and monsoon seasons of the same
year) impact both water supplies and demands. The effects of shared seasonal droughts are
compounded in the semi-arid Rio Grande region where water resources are becoming
increasingly stressed.
Photo: Reclamation
Key questions addressed here are: How does drought covary between upper Rio Grande water
year streamflow and lower Rio Grande monsoon precipitation, and how common are shared
seasonal droughts?
The southwestern US is on the northern fringes of the
North American monsoon region (upper left), with up
to 60% of the annual precipitation falling in JulySeptember. Monsoon regions have been identified by
Gochis et al. 2009 and others (numbered blocks). The
tree-ring data network (above) can provide
information about both monsoon and cool season
precipitation by measuring earlywood (EW) and
latewood (LW) separately, and removing the
dependence of the LW on the EW with regression
(Lwa) (left). Correlations shown are based on 4 sites
in southeastern Arizona.
Over the period of instrumental record,
Rio Grande water year flow and New
Mexico Division 5 JJA precipitation are
uncorrelated (upper right). Over the full
reconstruction period, the two records
are also uncorrelated (p< 0.01).
However, when smoothed, some
coherence between the two records is
noticeable (lower right). When different
decadal periods are examined, it is
obvious that while individual years may
not match, common period of time may
be characterized by wetness or dryness
(far right).
Monsoon
Otowi Flow
1600
Photo: D. Griffin
Otowi gage
New Mexico Climate Division 5 is outlined in red,
LWa chronologies selected as predictors are
shown as red triangles. Also shown is the Otowi
gage (blue square). Average monthly
precipitation totals for Division 5 are shown in
the inset.
New Mexico Division 5 total precipitation for
June-August (map, left) was reconstructed
using stepwise multiple linear regression.
The onset of the monsoon is captured
(June), as well as the two wettest months
(July, August)(inset).
From a pool of 14 candidate predictors,
three adjusted latewood width chronologies
were selected in a stepwise regression,
which explain 53% of the variance in the
instrumental data (upper right). Calibration
data are from PRISM (Daly et al. 2008),
1896-2008. Regression assumptions were
met, and the validation statistic, RE = 0.500,
indicates good skill. The full reconstruction
extends to 1600 (lower right), but the
reconstruction is most reliable after 1713
when sample number are more robust.
RECONSTRUCTION OF UPPER
RIO GRANDE FLOW
1660
The Otowi Bridge gage in northern New Mexico,
where allocations between New Mexico and Texas
are determined, was targeted for reconstruction (red
star, map). Water year flow values were estimated
from the sum of 10 relatively unimpaired upper basin
tributary gages (Colorado Division of Natural
Resources) plus the gains on the Rio Grande
between Lobatos at the Colorado/New Mexico
border and the Otowi gage (USGS) for the years
1958-2002.
39
38
37
36
NM
-109
-108
-107
-106
-105
Texas A&M AgriLife Research Center at El Paso, Texas A&M
The average of 17 ring-width chronologies, spanning
1450-2002, from CO, northern NM and southeastern
UT (green triangles on map) was used as the
predictor in a regression equation. The variance
explained by the tree-ring chronology average was
0.74 (RE = 0.71) and regression assumptions were
met.
Percent of average precipitation, June 15-Sept. 12, 2012.
From CLIMAS, Climate Assessment for the Southwest
1665
1670
1675
1680
1805
1810
1815
1820
1875
1880
1885
1890
1995
2000
2005
2010
20-year moving average
Otowi Flow
Monsoon
Otowi Flow
1870
OBSERVED
Monsoon
Rio Grande
Del Norte Flow
1990
Sequences of wet/dry/moderate monsoon
precipitation and Rio Grande flow years. Colors
represent wet (blue), dry(red), and middle
(white) tercile values for the two records for
select period. The last series shows the last two
decades of the instrumental record (Del Norte
instead of Otowi because of data availability).
CURRENT RIO
GRANDE DROUGHT
The effects of persistent
drought, due to supply
deficits and demands, are
evident in the reservoir levels
for Elephant Butte and
Caballoe Reservoirs, the
major storage of Rio Grande
water in New Mexico (left).
SUMMARY
Ÿ
By analyzing latewood widths from tree rings, it is possible to
reconstruct monsoon precipitation, at least for a portion of the
monsoon season.
• When Rio Grande streamflow and monsoon observed data and
reconstructions are compared, there is no correlation between the
two on year-to-year time scales, but over decadal time scales, it
appears there is some coherence during some intervals of time.
• The occurrence of years with shared flow/monsoon conditions
and opposite conditions is variable over time. We find that low
runoff followed by a dry monsoon is not unusual, and over the full
reconstruction period, wet or dry conditions are shared in both
seasons more often than not.
The current Rio Grande basin drought, which began in 2000, does
not yet appear to be unusually severe in either the instrumental or
paleoclimatic context (analysis not shown here). However, the
impacts of this ongoing drought have been significant. Demand for
water now exceeds supply and climate change projections indicate
decreasing winter precipitation in the future.
REFERENCES CITED
Gochis, D.J., W. Shi, J. Schemm, and R.W. Higgins (2009), A forum for evaluating forecasts of the North American Monsoon: The
NAME Forecast Forum. Eos. Transactions, 90(29), July 21, 2009.
Top: Observed and reconstructed water year flow, 1958-2008.
Bottom: Reconstructed water year flow, 1450-2002, smoothed with a 10-year running average. Observed data,
also filtered, in red.
1620
Monsoon
Since 2000, nine out of 12
years have experienced
below average JJA total
precipitation. Of those years,
eight, flows have been below
average in the upper Rio
Grande (Del Norte CO
gage). In six years, both flow
and monsoon precipitation
have been below average.
CO
1615
Otowi Flow
Chi-square tests indicate the
distribution of values for these
three periods is not random (p <
0.05). The 2nd half of the 20th
century has the largest number of
years with opposite conditions, but
the difference is not significant
(table, right).
Top: Observed and reconstructed JJA precipitation, 1896-2008.
Bottom: Reconstructed JJA precipitation, 1600-2008, smoothed with a 10-year
running average. Observed data, also filtered, in red.
1610
Monsoon
When tabulated by half century
periods (wet and dry years are
again based on terciles) (right),
several periods stand out:
Ÿ
Early 20th century for shared
seasonal wetness, and
Ÿ
18th century (both halves) for
higher proportion of shared
conditions (wet or dry).
Overall, the distribution of values
among the 4 categories for all
years is not randomly distributed
(p < 0.05), suggesting shared
conditions are more common than
opposite conditions
1605
observed
1800
RECONSTRUCTION OF
LOWER RIO GRANDE
MONSOON PRECIPITATION
6.543826
2307845 1.695862
6.068428
2259428
5.581424
2540315 5.138255
2421309 7.511608
6.079773
2171983 3.046742
In regions of the world with bi-modal precipitation regimes such
as the southwestern US, water users and resource
management are vulnerable to multi-season droughts which
can have significant impacts on agriculture and ranching as
well as on urban water demand. In these regions, knowledge
of hydroclimate variability in both seasons is critical for fully
understanding drought and its impacts. Tree-ring data have
been used extensively to reconstruct past cool season
droughts in the Southwest, but until recently, information about
monsoon season droughts has been lacking. A new network of
tree-ring data (map, far right) now allows investigations of the
North American monsoon across the southwestern US,
including the Rio Grande basin of New Mexico, the focus of
this study. A reconstruction of monsoon precipitation is
compared with reconstructed upper Rio Grande flow, which is
largely snow-melt dominated, over the past four centuries.
Together, analysis of these two reconstructions documents the
variability of the dominant surface water supply for the region
with warm season precipitation, which also tempers surface
water and groundwater demand.
2153770 6.273424
2278093
2259088 3.409708
2063157
1082258
2486921
5.009638
2659322
LOW RIO GRANDE FLOW AND MONSOON DROUGHT
997414 2.858875
3.973974
INTRODUCTION
Daly, C., M. Halbleib, J. I. Smith, W. P. Gibson, M. K. Doggett, G. H. Taylor, J. Curtis, and P. A. Pasteris (2008), Physiographicallysensitive mapping of temperature and precipitation across the conterminous United States. Int. J. Climatol, 28, 2031-2064, doi:
10.1002/joc.1688.
ACKNOWLEDGMENTS: Research was supported by NSF grant no. 0823090 and an EPA Star Fellowship to D. Griffin.