1,2,1,1- 1National Centre for Groundwater Research and Training, College of Science and Engineering, Flinders University, Adelaide, SA, Australia (liu1545@flinders.edu.au)
- 2West Australian Biogeochemistry Centre, School of Biological Sciences, The University of Western Australia, Perth, WA, Australia (grzegorz.skrzypek@uwa.edu.au)
Understanding how rainfall alleviates vegetation water stress is critical for predicting ecosystem functioning in semi-arid regions under future climate conditions. This study quantifies vegetation water stress relief using the Crop Water Stress Index (CWSI) over the past 24 years in the Wanna Munna Flats of the Pilbara Basin, Western Australia, a semi-arid region characterized by a mean annual precipitation of 381 mm, a mean air temperature of 24 °C, and a potential evapotranspiration of approximately 2850 mm.
A modified Run Theory framework was employed to characterize individual stress relief events, defined as deviations of a reconstructed CWSI time series for a representative woody species (Mulga, Acacia aneura) from a reference stress condition (mean CWSI = 0.68). The results indicate that this woody species experiences persistent water stress, with a long-term mean CWSI of 0.52. In total, 191 stress relief events were identified over the 24-year study period.
On average, a relief event persists for 19 days (interquartile range: 8–36 days) and exhibits a relief magnitude of 1.9 CWSI·stress·day (range: 0.7–6.1), generated by 13.4 mm of cumulative precipitation (range: 3.8–42.6 mm) distributed over several days. Event-scale cumulative precipitation is the dominant control on both relief magnitude and duration. However, for comparable annual precipitation totals, higher rainfall intensity reduces stress relief efficiency.
Random Forest analyses further indicate that vegetation growth responses are primarily triggered by stress relief events associated with precipitation exceeding 17 mm, which account for 41.9 % of all recorded events. A pronounced step change in stress relief occurs when event-scale precipitation exceeds 56 mm, although only 42 such events were observed during the 24-year period.
Overall, this study provides a quantitative framework for characterizing water stress relief dynamics and reveals the nonlinear vegetation responses to rainfall in natural semi-arid ecosystems.
How to cite: Liu, Z., Skrzypek, G., Batelaan, O., and Guan, H.: Vegetation water stress relief by rainfall pulses in a semi-arid region, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-8692, https://doi.org/10.5194/egusphere-egu26-8692, 2026.
