HR: 11:20h
AN: B22B-05    [Abstracts]
TI: Examining Severe Drought-Induced Vegetation Change and its Influence on Water Resources
AU: * White, A B
EM: amanda@lanl.gov
AF: Los Alamos National Laboratory, Earth and Environmental Sciences, MS-D452, Los Alamos, NM 87545, United States
AU: Springer, E P
EM: everetts@lanl.gov
AF: Los Alamos National Laboratory, Earth and Environmental Sciences, MS-701, Los Alamos, NM 87545, United States
AU: Vivoni, E R
EM: vivoni@nmt.edu
AF: New Mexico Institute of Mining and Technology, Department of Earth and Environmental Science, 801 Leroy Place, Socorro, NM 87801, United States
AB: A "global-change-type" drought that occurred in the southwestern U.S. from 2000 to 2003, accompanied by increased temperatures and bark beetle infestations, induced large-scale woodland overstory mortality, the consequent redistribution of water, radiation, and nutrients, as well as modification of the ecosystem phenology. Our objectives in this research are to examine these vegetation changes in detail and to determine whether they translated to changes in hydrological processes. We chose the Rio Ojo Caliente, a subbasin of the Rio Grande, as a study site since a significant portion of the woodland ecosystem (piñon-juniper) was affected. Examining a remotely-sensed vegetation index (1-km AVHRR NDVI from 1989 to 2006), there is an increasing trend in the mean NDVI from 1989 to 1998 (pre-drought period), a decreasing trend from 1999 to 2003 (drought period), and a dramatic increasing trend from 2004 to 2006 (post-drought period) in which the mean NDVI rebounds to pre- drought magnitudes. Streamflow records from 1932 to 2006 show the watershed to be primarily spring snowmelt-driven, although monsoonal summer precipitation also plays a significant role. We compare the temporal variability in the streamflow to the NDVI, including the mean, anomalies from the mean, and seasonally- based duration curves, and find significant correlations (correlation coefficient ρ = -0.61) between the streamflow and NDVI at approximately a three-month lag (NDVI lagging streamflow). In analyzing the three phases of the drought, the correlation is slightly stronger during the pre-drought (ρ = -0.64) and drought (ρ = -0.65) periods, yet markedly stronger during the post-drought period (ρ = -0.74). This suggests that the coupling between vegetation water use and streamflow is tighter after the drought. This may be attributable to the reduction in the less-responsive overstory (pinñon mortality) and increase in the more-responsive understory (grasses and shrubs exploiting newly available resources). Temporal patterns in gauge-based precipitation (frozen and unfrozen) and air temperature, and spatial-temporal patterns in PRISM precipitation, air temperature, and a soil moisture index are also compared to the NDVI. While the vegetation composition was altered to a great degree in the Rio Ojo Caliente Basin, the system rapidly recovered both photosynthetically and hydrologically during the post-drought wet period, although the dynamic between vegetation water use and streamflow was slightly altered. The aim of this research is to explore the consequences of a severe drought married with elevated temperatures on vegetation and water resources. As the intensity and frequency of droughts are expected to increase in the southwestern U.S. with rising temperatures (IPCC 2007), this research contributes to our knowledge of ecosystem and hydrologic response to the changing climate.
DE: 0439 Ecosystems, structure and dynamics (4815)
DE: 0480 Remote sensing
DE: 1605 Abrupt/rapid climate change (4901, 8408)
DE: 1812 Drought
DE: 1813 Eco-hydrology
SC: Biogeosciences [B]
MN: 2007 Fall Meeting