Hydrologic Variability and
Riparian Vegetation Response
in U.S.-Mexico Border
Watersheds
Thomas Meixner
University of Arizona, Dept.
Hydrology & Water Resources
1
Legacies from the past shape the present
Santa Cruz River
Tucson 1942
San Pedro River
US-Mexico border 1930
1989
2000
2
Precipitation Seasonality
Bill Williams
Santa
Cruz
San Pedro
3
Recharge Seasonality
4
Statement of the problem:
Mountain
Mountain
Front
Basin-Floor
Block
Recharge
Recharge
Recharge
WET
Ephemeral Channel
Recharge
MOIST
DRY
Basin
Groundwater
Flood
Recharge
5
Riparian Water Sources
δ 2H
Recharge during
monsoon runoff
Riparian Wells
-40 Charleston Baseflow
Highway 90 Baseflow
Hereford Baseflow
-50 Palominas Baseflow
LMWL
Basin
Groundwater
-60
-70
-10
•
•
•
•
•
-9
-818
δ O
-7
-6
Isotopes of water – natural tracer of source
Riparian wells span range between end members
Baseflow skewed toward monsoon runoff
Quantify % using simple mixing model
Uncertainty associated with runoff end member
6
Baillie et al., 2007 JGR
Hypotheses
1)The value of ecosystem services declines (increases) in
non-linear and stepwise fashion as water is extracted
(restored) from (to) dryland rivers
2)Hysteretic effects characterize stream re-watering: the
trajectories of changes in ecosystem value are
reversible, but the absolute magnitude of ecosystem
service recovery varies depending on the degree of
historic dewatering.
3)Climate change and population growth act together in a
synergistic way to decrease the water withdrawal levels
at which ecosystem services cross thresholds.
7
The Premise
•The Value of
Ecosystem
Services
Declines in a
Non-Linear
Fashion
Figure 1: From the Proposal
•Do Behavioral
Values Decline
in the Same
Fashion?
8