Satellite and Tower Data Reveal Unique Climate Over the Southern Sierra Nevada

Eric WallerDepartment of Environmental Science, Policy, and Management

University of California, Berkeley

SSCZO Annual MeetingFresno, CA

8/4/14

MODIS Aqua (~1 PM)April Cloud Frequency,2003-2011

Average MODIS (Aqua) 2012 Diel Land Surface Temperature Range (Day – Night)

{Clear Sky Days!}

Δ 0C

Average Annual MODIS Diel Land Surface Temperature Range (C)

Aver

age

Annu

al M

OD

IS

Clou

d Fr

eque

ncy

(%)

R2 = 0.58Sequoia Points

Other Sierra NevadaPoints

405 meters

1160 meters

2015 meters

2700 meters

NoonFebruaryMarch

April

January

Average ½ Hourly Temperature by Month: 2015 meter site

Noon

Average ½ Hourly Dew Point Temperature by Month: 2015 meter site

Afternoonpeaks

Noon

Average ½ Hourly Relative Humidity by Month: 2015 meter site

Noon

Average ½ Hourly Relative Humidity by Month: 2015 m site, Clear Afternoons

Noon

Average ½ Hourly Relative Humidity for 4 Towers: April

Noon

No daytime warm-up at tower at 2015 meters

Average ½ Hourly Temperature for 4 Towers: April

°C

October minus April maximum temperature (California mountains unusually cold in April!)

Where’s this cold spring air coming from?

-still cold North Pacific

-Pacific high migrating north: winds/weather generally coming from

northwest rather than the west (confirmed by NCEP/NARR data)

-meridional flow: cutoff or closed lows

Regional and local conditions that favor Giant Sequoia:

-Low wind-Frequent high afternoon humidity and cloud cover-Late spring shift in precipitation -Cold spring storms: late spring shift in snowfall

A lot of these factors that could be beneficial to Sequoia could be reducing sublimation substantially as well.

A need for better Sierra-wide mapping of sublimation?

This area also has among the lowest average wind speeds in the world.

Giant Sequoia is responding to some combination of these climatic features – basically outcompeting other species in this unique climate regime.

In sum:

Unusually cloudy, particularly on spring afternoons (strongest predictor of Giant Sequoia distribution)

But there are a lot of (cor)related variables:• Unusually low spring temperatures (April COLDER than January)• Low diel temperature range (so spring afternoons especially cool)• Afternoon peaks in water vapor

• Highest relative humidity in the afternoon • Lowest vapor pressure deficit in the afternoon

• Extremely low wind

Much of this unusual behavior only evident at height

NOT PRE-DAWN!

Targeted climatic measurements above the surface

Daily patterns of temperature and humidity (rather than just min and max or average)

Extra measurements: wind, radiation (direct and diffuse), etc.

Relate to plant phyisological ecology and productivity

Some extra factors to consider in assessing climates