## 4 Discussion
### General Conceptual Model of LST, SM, and Vegetation Productivity  
Under homogeneous atmospheric conditions that determine similar water demand and under comparable incoming solar radiation, LST has been widely associated with SSM (e.g., [29; 69]). Not many studies have shown the effect of root zone SM on stomatal resistance to transpiration and evaporative cooling, i.e., ET and then thermal inertia [27; 30; 63]. Based on our results from in situ SM, GPP, and satellite LST, a general model of the relationship among those variables can be proposed (Figure 12), which has some differences from those previous works that reported linear relationships between SM and LST/optical indices. Given the homogeneous woodland cover in the study area [11], this model can be considered in order to spatially understand the effect of root zone SM on the vegetation status for this ecosystem. SM in the soil profile after significant wet pulses shows the incidence on ET and a cumulative effect on surface energy balance and the subsequent low LST associated with thermal inertia (B in Figure 12, left). That inertia can be considered the resistance of the land surface to thermal variations, being higher in wet surfaces than in dry soil/vegetation and displaying lower temporal temperature fluctuations associated with soil evaporation and transpiration under not limiting conditions. With a certain lag, the LSWI increases and GPP reaches its maximum values, suggesting a plateau for the highest SM in subsurface soil horizons (Figure 12, right). Differences in SM in Figure 12 (right) are mainly explained by the existence of a hardpan in ASM. The impact of rainfall on GPP in Mulga woodlands has been previously reported in different studies [11; 33; 34]; SM can be a valuable complement to rainfall data, given that it is a more integrative variable of the soil water balance. Figure 12 (right) also suggests the high sensitivity of Mulga woodland productivity to soil water availability, which is consistent with the high reliance of vegetation on subsurface soil water reported for semiarid lands of Central Australia [12; 70]; increases in this variable during the wettest periods can produce GPP values up to 5 times higher than those during dry seasons, which is consistent with rainfall amounts and the impact on productivity previously reported [5; 33; 71]. In Mulga woodlands, asymptotic adjustment suggests a minimum LST for late-spring and summer for high and extremely high SM that may be associated with thermal regulations of this ecosystem and can be more thoroughly explored in future studies. Furthermore, low-intermediate SM is associated with low thermal inertia (A and C, Figure 12, left); wet pulses that produce a slight increase in shallow SM have a low impact on vegetation productivity (Figure 12 right). Short-term fluctuations in LST, and not directly related to SM, were observed under this condition. Sub-daily analysis can improve the understanding of these fluctuations, whose contributions are probably more associated with heatwaves through land-atmosphere feedback processes or flash drought monitoring than the impact on vegetation productivity, given that during dry periods, such as the 2018-2019 season, vegetation did not show significant growth. Root zone soil moisture available for plant use has a key role in vegetation conditions in drylands, given that it strongly determines ETa and produces changes with a certain memory depending on the magnitude of rainfall pulses, vegetation access to water, and soil type, among others. In this sense, it is a scarcely explored variable for the early monitoring of vegetation water condition, given the uncertainties in its estimates. Direct estimations of SM from satellite data are frequently limited to the surface water content (typically 5-10 cm for microwave missions) or total water column (Gravity Recovery and Climate Experiment (GRACE) mission). Thus, the spatial evaluation of root zone soil moisture is difficult.