Investigating the Role of Temperature in Mediating Relationships between Cool Season Precipitation and Water Year Streamflow in the Upper Colorado River Basin

Connie Woodhouse, University of Arizona Greg Pederson, USGS, Bozeman MT Kiyomi Morino, University of Arizona Greg McCabe, USGS, Denver CO PACLIM 2015 Asilomar, March 8-11

This work is being funded by a DOI Southwest Climate Science Center grant. Other co-PIs include Adam Csank, Steph McAfee, and Steve Gray with numerous water management partners

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 for comparative analyses

Upper Colorado River Basin

Analysis Variables Selected: • October-April total precipitation • March, March-May, March-July

average temperature • Prior October or November soil

moisture

Correlations with Colorado River water year flow, 1906-2012 (prior July – September)l Monthly total precipitation

Monthly soil moisture storage

Monthly mean temperature

Quantifying the contribution of cool season precipitation, 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

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 1MarJulT 2 0.859178 0.738188 0.076712 30.4723 0.000000 2novsoil 3 0.870644 0.758021 0.019834 8.4423 0.004488 3

March-July temperature accounts for only 8% of the total variance explained, but is it more important in certain years?

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

Trend in March-July average temperature, 1906-2012

A closer look: 4 flavors of years

Colorado River flow

A closer look: 4 flavors of years

Colorado River flow

Water year flow and cool season precipitation, averaged for each set of years

Years with flow < precipitation above median flow yrs below median flows yrs

Years with flow > precipitation above median flow yrs below median flows yrs

N = 4 N = 9 N = 10 N = 7

• Below median flow years • Flow < relative to precipitation • Above median temperatures. • Soil moisture corresponds more closely to

precipitation

• Above or below median flow years • Flow > relative to precipitation • Below median temperatures • Soil moisture corresponds to moisture

anomalies

Water year flow, cool season precip, March-July temperature, and November soil moisture averaged for each set

• Above median flow years • Flow < relative to precipitation • Temperatures are not warmer but nearly

average…..

Water year flow, cool season precipitation, March-July temperature, and November soil moisture averaged

• Above or below median flow years • Flow > relative to precipitation • Below median temperatures • Soil moisture corresponds to moisture

anomalies

• Below median flow years • Flow < relative to precipitation • Above median temperatures. • Soil moisture corresponds more closely to

precipitation

These 7 years coincide with some of the wettest ranking winters. How do they compare with 7 wettest winters with correspondingly high flows?

WETTEST COOL SEASONSWY Oct-Apr, percentile

1973 0.9912005 0.9811941 0.9721952 0.9631979 0.9541993 0.9441980 0.9351997 0.9261942 0.9171920 0.9071909 0.8981995 0.8892011 0.8801907 0.8701986 0.8611906 0.8521985 0.8431978 0.8331917 0.8241984 0.8151929 0.8061958 0.7961999 0.7871932 0.7781914 0.7691911 0.7591916 0.750

Above median flow years with flow < ppt

Wettest winters with similarly high flows

Total cool season precipitation, in percentile, averaged for 2 sets of years, by month

Differences in Distribution of Precipitation over the Cool Season?

Entire cool season precipitation Oct- Apr wettest winters - ppt<flow yrs

Seasonal patterns vary, but in general, the wettest winters with correspondingly high flows show greater precipitation in headwaters regions, particularly for the Yampa, main stem, and Gunnison.

Early cool season precipitation Oct-Dec wettest winters - ppt<flow yrs

Mid to late cool season precipitation Jan-Apr wettest winters - ppt<flow yrs

mm

m

m

mm

Mean temperature, in percentile, averaged for 2 sets of years, by month

Differences in Average Monthly Temperatures, March-July?

March mean temperature wettest winters - ppt<flow yrs

July mean temperature wettest winters - ppt<flow yrs

In comparison to the wettest winters, in above median flow years with flows lower relative to precipitation, March temperatures are warmer in the upper portion of the Upper Basin. In July, temperatures are slightly warmer in these years, except in the southwestern part of the basin.

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Summary

• March-July mean temperatures do not explain a large part of the total variance in water year flow, but….

• When flow is > than expected given the cool season

precipitation –in high or low flow years-- temperature, (and maybe antecedent soil moisture) appear be playing a role.

• Ditto when flow is < than expected given the cool season precipitation –in low flow years.

• When flow is < than expected given the cool season precipitation –in high flow years -- drier antecedent conditions (headwaters region) and less cool March temperatures (northern basin) may be responsible.

• Are trends in warmer temperature driving a higher

frequency of years with lower water year flows, given cool season precipitation -- essentially, less efficient cool season precipitation? Implications for the future?