impact of drought on sahra’s research on mount...

NSF STC for Sustainability of Semi-Arid Hydrology and Riparian Areas (SAHRA)

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Impact of Drought on SAHRA’s Research on Mount Bigelow

Media Briefing November 2003

Jim ShuttleworthNSF STC for Sustainability of

Semi-Arid Hydrology and Riparian Areas (SAHRA)

Department of Hydrology and Water ResourcesCollege of Engineering & Mines, University of Arizona


Rain mainly falls in winter and summer, with more monsoon rainfall on the mountains.

During the 1950s and in recent years, reduced winter rainfall has greatly increased the risk of fire.

Arizona Rainfall PatternsArizona Rainfall Patterns

Deficit after winter

Average

2001-2

2002-3


TOWER HEIGHT: 30 meters ~ 98 feet

LOCATION:Coronado National ForestSanta Catalina Range, Mt. Bigelow northeast of Tucson, AZ

SITE DESCRIPTION:Fir/pine, second growth sub-alpine forest~12m average tree height

COORDINATES: Latitude: 32° 25' 00" N Longitude: 110° 43' 31.85" W

STATION ELEVATION:2550 meters ~ 8400 feetabove sea level

INITIAL INSTALLATION: 15-Apr-02

SAHRA’sSAHRA’s Forest Tower on Mount Bigelow Forest Tower on Mount Bigelow

Measuring the energy, water, and CO2exchanges between the atmosphere

and “mountain island” forest


Mt. Bigelow

N

From May 21 to June 7, 2002, the human-caused Bullock Fire burned 30,563 acres, mainly in the northeast section of the Santa Catalina range.

From June 17 to July 12, 2003, the human-caused Aspen Fire burned 84,750 acres in the western portion of the Catalinas, consuming 333 structures.

Fortunately, the 2002 Bullock Fire had only minimal impact on our research, but fire prevention efforts during the summer 2003 included some tree removal within ~1km of SAHRA’s Mt. Bigelow EC tower site.

The area sampled by the instruments on the tower is now in the only remaining unburned area of pine / fir forest along the ridge line.

1km

Jan 2003: Sampled area after Bullock Fire

May 2002: Pre-fire view of the area sampled by tower instruments in the primary wind direction.

1km

Bullock Fire

1km

July 2003 Sampled area after Aspen Fire

Bullock FireAspen FireBack burn near base of Bigelow Tower

6-19-03 12:55pm Picture of webcam justBefore its removal

6-19-03 12:45pm Picture from tower as Aspen fire moves into Summerhaven

Impact of 2002 and 2003 fires near the Mt. Bigelow siteImpact of 2002 and 2003 fires near the Mt. Bigelow site


If winter rainfall is low, the soils dry out

In drought years, the soil is so dry by May that the trees shut downand wait for the summer monsoonThere is no transpiration, no CO2 uptake, and no growth

Soils Dry Out When Winter Rainfall is LowSoils Dry Out When Winter Rainfall is Low

Bigelow Soil Water Content

0%

5%

10%

15%

20%

% s

oil

wat

er c

on

ten

t b

y vo

lum

e

DEC JAN FEB MAR APR MAY JUN20032002

Amount of Water in the Soil

Already Dryin December Totally Dry

by May

Winter Storms


Measured Exchanges on the Bigelow Tower in 2002/3Measured Exchanges on the Bigelow Tower in 2002/3

Evapotranspiration in mm/hour

-0.1

0.1

0.3

12:00 AM 6:00 AM 12:00 PM 6:00 PM 12:00 AM

June 22-24, 2002

-1

-0.5

0

0.5

12:00 AM 6:00 AM 12:00 PM 6:00 PM 12:00 AM

June 22-24, 2002

-0.1

0.1

0.3

12:00 AM 6:00 AM 12:00 PM 6:00 PM 12:00 AM

Sept 15-17, 2002

-1

-0.5

0

0.5

12:00 AM 6:00 AM 12:00 PM 6:00 PM 12:00 AM

Sept 15-17, 2002

Time of day-1

-0.5

0

0.5

12:00 AM 6:00 AM 12:00 PM 6:00 PM 12:00 AM

Time of day

-0.1

0.1

0.3

12:00 AM 6:00 AM 12:00 PM 6:00 PM 12:00 AM

Jan 23-25, 2003 Jan 23-25, 2003

CO2 flux in mg /m2/s

Before thesummer monsoon

the trees areclosed down

During thesummer monsoon

the treesrecover

During the winterthe trees keep

growing

No transpiration

No CO2 uptake

transpiration

CO2 uptake

transpiration

CO2 uptake


Remote Sensing Tree Stress and Potential for FireRemote Sensing Tree Stress and Potential for Fire

June 26, 2002

Bigelow Tower in ForestTucson

Fra

ctio

n o

f P

AR

Ab

sorb

ed

0.6

0.65

0.7

0.75

0.8

0.85

0.9

0.95

1

1-Jan 2-Mar 1-May 30-Jun 29-Aug 28-Oct 27-Dec

Day in 2002

Monsoon onset

Jan/Feb Mar/Apr May/Jun Jul/Aug Sep/Oct Nov/Dec

Time variation for this area

Trees absorb CO2 by photosynthesis when active

Photosynthesis requires radiant energy from the sun at a particular rangeof frequencies, called “Photosynthetically Active Radiation” (PAR)

Fraction of the incoming PAR absorbed is a measure of the trees’ activity

When under stress due to lack of water, the absorbed fraction of PAR falls

Measured by MODIS

on TERRA satellite


SAHRA Rapid Response Research in SAHRA Rapid Response Research in SabinoSabino CanyonCanyon

Soil hydraulic properties

Immediately after the fire, SAHRA started new research to quantify this

Forest fires can cause soils to become hydrophobic,resulting in less infiltration and more overland flow and erosion

Water chemistry Hydrological models


OverviewOverview

● SAHRA’s forest tower on Mount Bigelow survived both the Bullock fire in 2002 and the Aspen fire in 2003. It now stands on the only remaining unburned area of forest along the ridge line

● Measurements on the tower show when winter rain is low in drought years, the forest shuts down in May/June due to shortage of water until the summer monsoon arrives

● Preliminary results suggest that it might be possible to detect severe water stress in the trees and the potential for fire using remotely sensed data from the MODIS instrument on the TERRA satellite

● Preliminary results from ongoing rapid-response research suggest fire reduces the ability of the forest soils to absorb rainfall, causing greater runoff of water that is contaminated

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