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Riyadh Al-Naseri

Candidature

PhD Candidate

Thesis title

Modelling Australian vegetation physiology and phenology within an operational land surface model

Research project

Riyadh Al-NaseriVegetation processes influence the energy, carbon and water fluxes between the land surface and the atmosphere. Land Surface Models (LSM) need to accurately represent these processes such as leaf photosynthesis, stomatal conductance (gs) and the timing of leaf out and senescence, which affect weather patterns and are critical for accurate weather predictions. However, current LSMs such as the Joint UK Land Environment Simulator (JULES) often struggle to simulate these processes, specifically in regions with diverse and unique vegetation like Australia, as most of them are primarily developed and calibrated for Northern Hemisphere ecosystems. Additionally, most studies usually investigate the coupled photosynthesis–stomatal conductance models and leaf phenology separately, which limits our understanding of how these processes interact to influence energy, carbon and water fluxes estimations. My thesis aims to improve the representation of these key physiological and phenological processes within JULES and thereby improve the energy, carbon and water fluxes simulations in Australian ecosystems. Empirical approach will be implemented to estimate key parameters such as the stomatal slope (g1) from the Medlyn stomatal conductance model, maximum carboxylation rate of RuBisCO Vcmax) and maximum rate of electron transport (Jmax) from the Farquhar leaf photosynthesis model. This parametrization will be derived from large number of observations from different types of datasets, including leaf gas ex-change, stable isotope discrimination and eddy covariance flux data. The current plant functional types (PFTs) classification system in JULES will be modified to account for the distinctive types of Australian vegetation. Additionally, a new leaf phenology model tailored for Australian ecosystems will be developed, accounting for precipitation as a key driver of plant growth in water limited ecosystems such as arid and semi-arid areas which cover around 75 % of the total Australian land surface area. The new parametrisation will be integrated into JULES and tested at both ecosystem (Australian flux sites) and continental scales.

Ultimately, this study will enhance JULES’ ability to simulate vegetation-atmosphere interactions in Australia providing a more reliable representation of land-atmosphere fluxes to improve weather prediction in diverse Australian ecosystems.

Supervisors

Distinguished Professor Belinda Medlyn, Dr. Clare Stephens (UNSW, Dr. Siyuan Tian (BOM), Dr. Valentina Marchionni (BOM)