HR: 17:15h
AN: H42M-06    [PDF]
TI: Role of Vegetation in Controlling Water Balance at the Land-Atmosphere Interface in Water Limited Ecosystems
AU: * Scanlon, B R
EM: bridget.scanlon@beg.utexas.edu
AF: Univ. of Texas at Austin, Jackson School of Geosciences, 10100 Burnet Rd., Bldg. 130, Austin, TX 78758 United States
AU: Levitt, D
EM: dlevitt@seabase.com
AF: Science & Engineering Associates, 3205 Richards Land, Suite A, Santa Fe, NM 87505 United States
AU: Keese, K E
EM: kelley.keese@beg.utexas.edu
AF: Univ. of Texas at Austin, Jackson School of Geosciences, 10100 Burnet Rd., Bldg. 130, Austin, TX 78758 United States
AU: Reedy, R C
EM: bob.reedy@beg.utexas.edu
AF: Univ. of Texas at Austin, Jackson School of Geosciences, 10100 Burnet Rd., Bldg. 130, Austin, TX 78758 United States
AU: Simunek, J
EM: jsimunek@ussl.ars.usda.gov
AF: US Salinity Laboratory, 450 W. Big Springs Rd., Riverside, CA 92507 United States
AU: Desotell, L T
EM: desotellt@nv.doe.gov
AF: US Dept. of Energy, Bechtel Nevada, Las Vegas, NV 89193 United States
AU: Lohrstrofer, C F
EM: lhorstcf@nv.doe.gov
AF: US Dept. of Energy, Bechtel Nevada, Las Vegas, NV 89193 United States
AB: Understanding the role of vegetation in the water balance at the land-atmosphere interface is critical for assessing the impact of changes in vegetation and climate on the near surface water balance. Monitoring nonvegetated and vegetated weighing lysimeters in the Mojave Desert in Nevada USA over an eight-year period demonstrated strong coupling between large increases in soil-water storage in response to El Nino cycles in 1994/1995 and 1998 winter periods and vegetative response that rapidly removed the infiltrated water through evapotranspiration (ET). Soil water storage in the vegetated lysimeter was about half of that in the nonvegetated lysimeter at the end of the 8 yr monitoring period, which indicates that even in this arid climate, vegetation is extremely important in removing water from the soil through ET. The lack of monitored drainage in the nonvegetated lysimeter is an artifact of the seepage face lower boundary condition, which prohibits drainage unless the soils become almost saturated. Modeling analysis indicated that increased soil water storage in the nonvegetated lysimeter should result in drainage if the seepage face is replaced with unit gradient conditions as in the natural system. Traditional approaches for water balance modeling that use vegetative parameters, such as Leaf Area Index (LAI), as forcing greatly underestimated soil water storage because they did not include the two-way coupling between water storage and vegetation dynamics. Inverse modeling was used to demonstrate the two-way coupling between soil water storage (related to climate) and vegetation dynamics and involved minimizing the sum of squared residuals between measured and simulated soil water storage by varying LAI, which was used as a surrogate of vegetation dynamics. Inverse modeling reproduced the measured water storage much better than forward modeling using prescriptive LAI because feedback between water availability and vegetation dynamics was included in the inverse modeling approach. This monitoring and modeling analysis reveals strong coupling between vegetation dynamics and soil water storage changes related to precipitation and underscores the need to incorporate this dynamic interaction between climate and vegetation in numerical simulations to reproduce the monitored water balance. The role of vegetation in controlling the water balance of these arid systems has important implications for water resources and waste containment. The tight coupling between vegetation and soil water storage indicates that land use change could significantly alter the water cycle and that vegetation changes associated with climate change could affect the impact of climate change on the water cycle.
DE: 1818 Evapotranspiration
DE: 1836 Hydrologic budget (1655)
DE: 1866 Soil moisture
SC: Hydrology [H]
MN: 2003 Fall Meeting