## 2 Materials and Methods  
### Study Area  
This study was carried out at Alice Springs Mulga (ASM) and Ti Tree Ozflux stations, which are located in the Northern Territory, over a homogeneous Mulga woodland (ASM: \(-\)22.2828, 133.2493; Ti Tree: \(-\)22.2870, 133.6400) [11, 32] (Figure 1). Both sites are part of the Terrestrial Ecosystem Research Network's (TERN) OzFlux and Australian SuperSite networks that allow for the monitoring of land surface processes in Australia ([[https://www.ozflux.org.au/monitoringsites/alicesprings/index.html#intro](https://www.ozflux.org.au/monitoringsites/alicesprings/index.html#intro)]([https://www.ozflux.org.au/monitoringsites/alicesprings/index.html#intro](https://www.ozflux.org.au/monitoringsites/alicesprings/index.html#intro)); [[https://www.ozflux.org.au/monitoringsites/titreeast/index.html#intro](https://www.ozflux.org.au/monitoringsites/titreeast/index.html#intro)]([https://www.ozflux.org.au/monitoringsites/titreeast/index.html#intro](https://www.ozflux.org.au/monitoringsites/titreeast/index.html#intro)), accessed on 18 December 2024). These stations were selected since they are the only two existing in the Mulga woodland area. ASM was considered as the primary reference site, given that there is a lack of field data between 1 January 2020 and 19 November 2020 in the Ti Tree station. This last site was considered mainly to corroborate the relationship between variables. The mean annual rainfall is 312 mm (1987-2015) ([[http://www.bom.gov.au/](http://www.bom.gov.au/)]([http://www.bom.gov.au/](http://www.bom.gov.au/)), accessed on 18 December 2024), ranging from 25 to 955 mm [33]. In total, 86% of rainfall occurs between November and April [14]. Mean minimal and maximal air temperatures are between 5 \({}^{\circ}\)C and 22.6 \({}^{\circ}\)C (July) and between 22 \({}^{\circ}\)C and 37.5 \({}^{\circ}\)C (January), respectively, with absolute values between \(-\)4 \({}^{\circ}\)C (August) and 46 \({}^{\circ}\)C (January) [14]. The sites are located in a flat terrain (slope = 0.2%); the vegetation is similar in both sites, with high-density perennial Mulga savanna woodland (76% cover) consisting of _Acacia aneura_ and _Acacia aptaneira_[33]. Ti Tree is characterized by a Mulga (_Acacia aneura_) canopy with the presence of Corymobia. The highest canopy layer has an average height of around 4.8-6.5 m. The grassland and shrub layer is mainly composed of annual and perennial C4 species; the growth and photosynthesis of this layer strongly depend on rainfall amount and are more active in the summer [14]. During dry periods, the bare soil  
Figure 1: Map of major vegetation groups showing the location of Alice Springs Mulga (ASM) and Ti Tree Ozflux sites (data source: Dynamic Land Cover Dataset Version 2.1). surface is more widespread than during wet periods [34; 35]. Under wet conditions, the soil-plant system has the capability of a quick response, not only because of evaporation from the surface soil layer but also because of the transpiration of both vegetation layers that together explore surface and subsurface horizons [36]. The regional dominant soil type is red kandosol, with a sandy loam texture (74/11/15% sand/silt/clay) and organic matter content of 1.1% at the surface. An extensive siliceous hardpan is more common in this soil type in ASM, showing spatial variability, and its depth can fluctuate from the surface to more than 1 m. Above the hardpan, there is unconsolidated soil. Changes in hardpan depth produce differences in the subsurface storage of soil water and root development, mainly for _Acacia_, which has a dimorphic root system with deep roots. In these cases, a high concentration of roots can be expected above the hardpan [33]. In ASM, this mainly constitutes a limitation for infiltration during strong rainfall events, favoring soil saturation in deep horizons [14]. Access to groundwater by vegetation is hampered by the hardpan or the deep water table (usually around 49 m in depth) [33].