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Detection of forest water stress under future climate change in drought prone ecosystems of the Southwestern United States

Warter, Maria Magdalena 2022. Detection of forest water stress under future climate change in drought prone ecosystems of the Southwestern United States. PhD Thesis, Cardiff University.
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Terrestrial ecosystems are becoming increasingly vulnerable to climate changes that negatively affect the spatial and temporal water availability, especially in waterlimited regions of the Southwestern USA, which may yield potentially irreversible consequences to biodiversity and species distribution across this dryland region. Substantial uncertainties remain regarding future climate variability and the associated vegetation responses to extreme climatic events, especially droughts that produce prolonged water deficits. Projected climate scenarios are still quite variable across this region, ranging from hotter/drier, to hotter/wetter/stormier. These variations pose potentially compounding challenges for terrestrial vegetation ecosystem functioning. Therefore, an improved understanding of the key climate drivers of vegetation functioning is needed which is capable of quantifying potential vegetation responses to future climate change and variability. This new capability would provide land managers with a modeling tool to explore climatological and hydrological scenarios and ecological responses. Such models would inform sustainable, adaptive management strategies of vulnerable habitats in response to the “new normal” climate conditions, thus increasing the future resilience of ecosystems to such altered climate conditions. In this thesis, climate-vegetation interactions are analyzed through data and models across different biomes and spatio-temporal scales. Using multi-decadal climate records, remote sensing information and several new numerical models that characterize ecohydrology, past and potential future vegetation responses to varying moisture availability were quantified. First, by using local climate and in-situ soil moisture records, as well as a simple soil moisture balance model, I quantified vegetation responses of two contrasting Southern California grassland ecosystems to prolonged moisture deficits that occurred under the recent period of extreme drought and more extreme droughts that might be expected in the future. I show that shifting climate conditions towards warmer and drier will arguably increase vegetation water stress, affecting vegetation phenology and threatening the integrity of grassland and forest ecosystems. Next, to address current limitations to dynamically model plant phenology in response to changing climate conditions, I developed a dynamic vegetation module (DYNA-VEG) that improves the quantification of vegetation interactions in dryland ecosystems within the existing dryland water partitioning model DRYP. The functionality of the module was evaluated through synthetic experiments to test its effectiveness in capturing climate-soil-vegetation interactions under different future scenarios of climate change. The results from these model simulations highlighted the diverging sensitivities between shallow rooted soil moisture and groundwater dependent riparian species to alterations in recharge and groundwater levels and precipitation, respectively. Most significantly, simulations showed the compound effects of altered climate conditions and hydrological changes on riparian forest responses, where declines in water tables of several meters resulted in peak physiological stress. Simulations highlighted that climate induced changes to recharge and water table dynamics are the key drivers of future vegetation responses, which has broader implications for exploring adaptive management strategies. Indeed, for sensitive riparian habitats future ecologically sustainable groundwater thresholds and managed aquifer recharge can be explored through ecohydrological modeling framework and translated into future management approaches.

Item Type: Thesis (PhD)
Date Type: Completion
Status: Unpublished
Schools: Earth and Environmental Sciences
Funders: US Department of Defence
Date of First Compliant Deposit: 29 March 2023
Last Modified: 30 Mar 2023 12:02

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