Ecosystem response to future climate change and the impact of vegetation feedbacks in the Southwest United States

Principle Investigator: Michael Notaro, University of Wisconsin-Madison, mnotaro@wisc.edu

Co-PIs: Zhengyu Liu and John W. Williams, University of Wisconsin-Madison
David Gutzler, University of New Mexico
Travis Huxman, University of Arizona
Robert Thompson, USGS

Abstract:: We will investigate potential changes in ecosystem structure, processes, and dynamics over the Southwest United States (SWUS) due to projected changes in temperature, precipitation, and CO2. We will evaluate the ecological responses to future changes in drought, fire, or heavy rainfall event frequency. We will quantify SWUS vegetation feedbacks through observational data and model experiments. We will assess the impact of vegetation feedbacks and variability on climate, including the monsoon’s intensity and timing.

Location: We will focus on the arid SWUS, which is primarily grassland and shrubland and climatically dominated by the monsoon. This region will likely experience springtime drying in the 21st century.

Hypotheses: While the recent IPCC experiments represent a major advance in predicting climate change, they neglect critical vegetation feedbacks and carbon fertilization. Warming over the SWUS will likely produce soil drying and vegetation loss, while carbon fertilization will contribute towards enhanced vegetation growth. Reduced rainfall and higher temperatures will likely result in expanded desert and reduced woody vegetation. Even without a change in rainfall, rising temperatures will increase the area’s vulnerability to drought. An increase in frequency of heavy rainfall events, without a net precipitation change, may produce soil drying and vegetation loss. Future changes in fire frequency will reflect a balance between diminishing litter availability and increasing soil dryness. Vegetation feedbacks likely play an essential hydrological role, although these feedbacks might be non-local. Vegetation variability potentially enhances decadal monsoon variability and prolongs droughts and pluvials.

Methods: We will perform offline experiments with the dynamic vegetation model, LPJ, using debiased, downscaled output from IPCC 21st century simulations, investigating the ecological response to predicted temperature and/or precipitation changes. Additional experiments will force LPJ with changes in heavy precipitation events, physiological CO2, drought occurrence, or ENSO. We will evaluate LPJ against observations and field measurements. We will statistically quantify local vegetation feedbacks for the SWUS using observations and output from two GCMs. We will develop new statistical approaches to quantify non-local feedbacks. We will explicitly assess SWUS vegetation feedbacks through initial value ensemble experiments with coupled models. We will assess vegetation’s impact on monsoon variability by contrasting simulations with interactive versus fixed vegetation.

Deliverables: This research will establish a range of potential ecosystem responses over the SWUS to future climate change, contributing to ecological predictability and decision-making. It will determine the role of vegetation feedbacks and lead to the development of an observed feedback dataset.

last updated: 15 April 2007 PLH