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

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

Trend in March-July average temperature, 1906-2012

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