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Evaluating the Influence of Precipitation, Temperature, and Soil Moisture on Upper Colorado River Basin Streamflow and Drought
Connie Woodhouse, University of ArizonaStephanie McAfee, University of Nevada, RenoGreg McCabe, USGS DenverPaul Miller, NOAA Colorado Basin River Forecast CenterGreg Pederson, USGS Bozeman
H31M-07America n Geophysical Union MeetingDecember 17, 2014
Research Question:
What is the role of cool season precipitation, spring/summer temperatures, and antecedent soil moisture on flow (particularly low flows) in the upper Colorado River basin (UCRB)?
Part 1. Examination of droughts
Part 2. Identify and quantify contributions of temperature and antecedent soil moisture on Colorado River flow
Data
• Gridded climate data from PRISM for total monthly precipitation, average monthly temperature (4 km resolution)
• Monthly soil moisture storage from McCabe and Wolock (2011) monthly water balance model
• Water year natural flow estimates for the Colorado River at Lees Ferry
• Analysis period: 1906-2012
• Data have been converted to percentiles in comparative analyses
Analysis Variables
• October-April total precipitation• March, March-May, March-July average temperature• October or November soil moisture
Colorado River at Lees Ferry, natural flows, 1906-2012
Major Droughts*
Part 1
*below average flows broken by no more than 1 year of above average flow
5
WY flow O-A precip AprT MarMayT MarJulT OctSoil NovSoil0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
Major UCRB Droughts
1930s 1950s 1960s 1970s 1980s90s 2000s
perc
entil
e
Average values for each hydroclimatic variable across all years in a given drought period, color coded by drought
Individual years with in major droughts: percentile values of WY flow, and variables that influence flow
WY flow
Oct-Apr precipitation
April temperatureOctober soil moisture
perc
entil
e1930s
2000s
1950s
perc
entil
espe
rcen
tiles
perc
entil
es
Individual years with in major droughts: percentile values of WY flow, and variables that influence flow
WY flow
Oct-Apr precipitation
April temperatureOctober soil moisture
perc
entil
e1930s
2000s
1950s
perc
entil
espe
rcen
tiles
perc
entil
es
Lees Ferry flow and October-April total precipitation, in percentiles
Gray bar = 1 standard deviation from the mean; these are years when Lees WY flow is markedly greater or less than Oct-Apr total precipitation
+ = flow greater relative to precip
- = flow less relative to precip
Flow is > relative to precipitation when temperatures are cooler and soil moisture is slightly higher than average.
Flow is < relative to precipitation when temperatures are warmer and soil moisture is slightly lower than average.
WY flow Oct-Apr precip
March temp
Mar-May temp
Mar-Jul temp
Nov soil moisture
Flow > precip n=14
0.624 0.344 0.345 0.302 0.306 0.519Flow < precipN=16
0.397 0.661 0.682 0.544 0.646 0.483
Percentile values average for years with flows > relative to precipitation and years with flow < relative to precipitation
Quantifying the contribution of temperature and antecedent soil moisture in annual flow
Stepwise model with pool of 6 predictors (Oct-Apr precipitation; March, March-May, Mar-Jul temperature; Oct , Nov soil moisture), 1906-2012
Step Multiple Multiple R-square F - to p-level Variables
+in/-out R R-square change entr/rem included
OctAprP 1 0.813312 0.661476 0.661476 205.1700 0.000000 1
MarJulT 2 0.859178 0.738188 0.076712 30.4723 0.000000 2
novsoil 3 0.870644 0.758021 0.019834 8.4423 0.004488 3
Part 2
Observed and estimated flow, precipitation-only model
Observed and estimated flow, precipitation-only and precipitation + temperature models
Does the addition of temperature to the precipitation-only model improve the model fit during particular periods?
Years of highest and lowest tercile Colorado River flows are plotted with periods when model with temperature improves or worsens model fit
Does the addition of temperature to the precipitation-only model improve the fit during periods of major drought?
Years of highest and lowest tercile Colorado River flows are plotted with periods when model with temperature improves or worsens model fit. Shading indicates periods of major drought.
Does the addition of fall soil moisture to the precipitation + temperature model improve the fit during particular periods?
Years of highest and lowest tercile Colorado River flows are plotted with periods when model with soil moisture improves or worsens model fit
Does the addition of fall soil moisture to the precipitation + temperature model improve the fit during particular periods?
Years of highest and lowest tercile Colorado River flows are plotted with periods when model with soil moisture improves or worsens model fit.Shading indicates periods of major drought.
Colorado river flow values (in percentile) for the 10 years with the most improved fit when temperature is added to the precipitation-only model
Colorado river flow values for the 10 years with the most improved fit when soil moisture is added to the precipitation + temperature model
Summary
• Major low flow years are characterized by low precipitation, high spring/summer temperatures and low antecedent soil moisture
• In years with less flow relative to winter precipitation, high temperatures may be a factor (and vice versa); these types of years have been more prevalent in recent decades
• While cool season precipitation explains most of the variance in water year flow, temperatures may contribute in low flow years, while soil moisture may influence flows in the very wettest years
• Next steps: consider antecedent moisture metrics; repeat these analyses on the 3 UCRB sub-basins, and reconstruct metrics with tree rings