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Evaluating the Influence of Precipitation, Temperature, and Soil Moisture on Upper Colorado River Basin Streamflow and Drought Connie Woodhouse, University.

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Presentation on theme: "Evaluating the Influence of Precipitation, Temperature, and Soil Moisture on Upper Colorado River Basin Streamflow and Drought Connie Woodhouse, University."— Presentation transcript:

1 Evaluating the Influence of Precipitation, Temperature, and Soil Moisture on Upper Colorado River Basin Streamflow and Drought Connie Woodhouse, University of Arizona Stephanie McAfee, University of Nevada, Reno Greg McCabe, USGS Denver Paul Miller, NOAA Colorado Basin River Forecast Center Greg Pederson, USGS Bozeman H31M-07 America n Geophysical Union Meeting December 17, 2014

2 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

3 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

4 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 Average values for each hydroclimatic variable across all years in a given drought period, color coded by drought 5

6 Individual years with in major droughts: percentile values of WY flow, and variables that influence flow WY flow Oct-Apr precipitation April temperature October soil moisture percentile 1930s 2000s 1950s percentiles

7 Individual years with in major droughts: percentile values of WY flow, and variables that influence flow WY flow Oct-Apr precipitation April temperature October soil moisture percentile 1930s 2000s 1950s percentiles

8 Lees Ferry flow and October-April total precipitation, in percentiles

9 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

10 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. Percentile values average for years with flows > relative to precipitation and years with flow < relative to precipitation

11 Trend in March-July average temperature, 1906-2012

12 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 Part 2

13 Observed and estimated flow, precipitation-only model Observed and estimated flow, precipitation-only and precipitation + temperature models

14 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

15 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.

16 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

17 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.

18 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

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20 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


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