# Presentation: 759346

## Relating Air & Water Temperatures:Implications for Climate Variability & Change

- Roger Bales, Martha Conklin & Jean Morrill
- University of Arizona

- Climate change & stream temperature
- Previous work
- Current temperature data, methods & results
- Implications

## Climate Warming

- We expect an increase in surface air temperature of 3-5oC by the middle of this century

- 180 W

- -90 W

- 0

- 90 E

- 180 E

- Annual mean temperature change: 2040-2069 less 1961-1990

- +5

- +4

- +3

- +2

- +1

- 0

- -1

*Hadley CM3*

- oC

## What will be the impact on stream temperature?

## Climate Models

- 	Climate models simulate temperature over broad regions, on the order of 2-4o in size, and thus do not capture local variability

- Annual mean temperature change: 2040-2069 less 1961-1990

## Climate Models

- 	Climate models simulate temperature over broad regions, on the order of 2-4o in size, and thus do not capture local variability

## 	A rise in stream temperature will impact aquatic species that are sensitive to temperature, and to dissolved oxygen levels

## Science Questions

- Can air temperature be used as an accurate predictor of stream temperature?
- Can general relationships be developed that apply to a large number of water bodies?

## What affects stream temperature?

## What affects stream temperature?

- Distance from source (spring, lake, glacier, etc.)

## 15

- 0

- 0

- 30

- Stream Temperature, °C

- Air Temperature, °C

- 0

- 30

- Previous Work: Minnesota Streams

- Daily

- Weekly

## Methods

- Selected sites from the GLOBE data base
- moving fresh water (river, brook, stream)
- at least 50 measurements of stream temperature
- evaluated 26 sites
- Used linear regressions of stream temperature versus surface air temperature for 1, 3 and 7 days
- (noon) air temperature
- average of maximum and minimum air temperature
- Only for air temperatures above 0°C

## Location of Sites

## El Dorado Stream, Rossmoor Elementary School, Los Alamitos, CA 

- El Dorado Stream, Rossmoor Elementary School, Los Alamitos, CA

## Which air temperature to use?

- Stream temperature correlates with average of maximum & minimum air temperatures better than with noon air temperature

## Linear regressions were better for 3-day & 7-day means than for the same-day value

- Which air temperature to use?

## Sites with a 1:1 relation between air & stream temperatures

- Only 5 of the 36 sites examined fell into this category
- 1 in China
- 2 in Finland
- 2 in the U.S.

## Many GLOBE sites were in this category
Slopes ranged from 0.6 to 0.9 

- Slopes ranged from 0.6 to 0.9

- Air Temperature, oC

- Stream Temperature, oC

- Sites where stream temperature changes 0.7o for every 1o change in air temperature

- One previous study found slopes of 0.8-0.9 for 11 Mississippi basin streams

## Sites where stream temperature changes~0.4o for every 1o change in air temperature 

- Slopes of 0.2-0.6, with equally low R2 values
- Some sites at high elevations
- 6 sites had intercepts between 5-12o

## Summary of Findings

- 3 groups of air:stream temperature relations:
- 1:1
- 1:0.7
- 1:0.4
- For streams insensitive to air temperature:
- Several streams were warm even when air temperature was zero (groundwater fed?)
- Some higher-elevation sites had cold temperatures year round

## Future stream temperature in a 2  CO2 climate?

Changes in stream dissolved oxygen?

- Changes in stream dissolved oxygen?

- Implications

## Scippican River, Tabor Academy, MA, U.S.

- 4

- 6

- 8

- DO, mg/L

- 15

- 20

- 25

- 30

- 35

- Temp., °C

- Stream Temperature & Dissolved Oxygen

- Current

- Future

- 2

- Future

## Conclusions

- For over 80% of the sites evaluated, stream temperature will not increase as much as will air temperature under a 2CO2 climate scenario
- Summertime DO levels will decrease 0-3 mg/L
- Broad data sets, i.e. GLOBE, give general guidance as to changes in stream temperature; but  site-specific correlations may be needed for resource management

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