impact of drought on sahra’s research on mount...
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NSF STC for Sustainability of Semi-Arid Hydrology and Riparian Areas (SAHRA)
Intro PageIntro Page
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
NSF STC for Sustainability of Semi-Arid Hydrology and Riparian Areas (SAHRA)
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
NSF STC for Sustainability of Semi-Arid Hydrology and Riparian Areas (SAHRA)
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
NSF STC for Sustainability of Semi-Arid Hydrology and Riparian Areas (SAHRA)
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
NSF STC for Sustainability of Semi-Arid Hydrology and Riparian Areas (SAHRA)
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
NSF STC for Sustainability of Semi-Arid Hydrology and Riparian Areas (SAHRA)
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
NSF STC for Sustainability of Semi-Arid Hydrology and Riparian Areas (SAHRA)
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
NSF STC for Sustainability of Semi-Arid Hydrology and Riparian Areas (SAHRA)
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
NSF STC for Sustainability of Semi-Arid Hydrology and Riparian Areas (SAHRA)
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