In China's drylands, deserts and areas prone to desertification constitute 44% of the landscape. The desert-oasis transition zone serves as a critical buffer between the desert interior and the oasis, playing an essential role in managing and preventing desertification. Despite its importance, the question of whether ecosystem functions exhibit multistability and experience regime shifts from functional to desertified states remains unresolved, particularly concerning the relationship between changes in vegetation patterns and ecosystem state transitions at the desert edges of arid and hyper-arid regions. In this study, we examined the stability landscapes of ecosystem multifunctionality and vegetation patterns in response to decreasing precipitation at both the inter-desert scale and within individual deserts, as the distance from the oasis to the desert interior increases. We compared the precipitation and distance thresholds for abrupt changes in vegetation pattern indices with those for regime shifts in ecosystem multifunctionality. Our analysis revealed that ecosystem multifunctionality can exist in both functional and desertified states when precipitation ranges between 104.37 mm and 152.56 mm. However, when precipitation drops below 104.37 mm, a complete shift from a functional to a desertified state occurs. The average precipitation threshold for abrupt changes in vegetation pattern indices—such as the size, shape complexity, and connectivity of vegetation patches, flow length, spatial skewness of the landscape, and the power law range, cutoff, and plexpo of the vegetation patch size distribution—is 201.69 ± 34.87 mm, which is higher than the threshold for ecosystem multifunctionality regime shifts. At the scale of individual deserts, changes in vegetation patterns precede regime shifts in ecosystem multifunctionality. These findings suggest that vegetation pattern indices can serve as early warning indicators for desertification in extremely arid desert-oasis transition zones. This study contributes to the enhancement of early-warning systems and supports the monitoring of desertification processes.

How to cite: Li, C. and Zhou, W.: Vegetation patterns as early warning signals for shifts in ecosystem multifunctionality in the desert-oasis transition zone of China’s drylands , EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-1786, https://doi.org/10.5194/egusphere-egu25-1786, 2025.

Spatial self-organization is a common response of arid and semi-arid ecosystems to water stress. It may result in periodic patterns such as dots, gaps and labyrinths, or in more irregular arrangements such as scale-free patterns, characterised by a power law distribution of patch sizes. As pattern formation occurs over large spatial domains, in the order of km² , it is often subject to heterogeneous environmental and soil conditions, which may lead to the anisotropic diffusion of resources.

In our project, we study the effects of anisotropic diffusion on pattern formation through the modelling of vegetation dynamics on complex network topologies. 

We employ the well-known reaction-diffusion vegetation model by Gilad et al. [1], in its simplified two-equation version by Zelnik et al. [2]. Two partial differential equations describe the dynamics of soil water and biomass densities.

In our implementation, the diffusive terms refer to network Laplacia, which allows us to the modify the topology on which the model operates.

When the diffusion networks of both water and biomass are regular two-dimensional lattices, we reproduce the observed progression of periodic patterns from gaps to labyrinths to dots for decreasing precipitation. 

To increase the complexity and connectivity of the network we implement the Watts-Strogatz small-world network model [3], in which a controlled number of random shortcuts is drawn over the two-dimensional lattice. Thus the number of shortcuts in the water and biomass diffusion networks become model parameters which may be used as proxies of heterogenous conditions affecting the diffusion of water and biomass respectively.

Our preliminary results show that an increase in anisotropic diffusion (number of shortcuts) has similar effects to an increase in isotropic diffusion in regards to the global variables of the ecosystem, such as average water and biomass densities. However, a small-world network topology induces the formation of steady-state non-periodic patterns, included scale free patterns, in a certain interval of network connectedness. 

Further, these steady-state scale free patterns appear unstable to the expansion of the largest gaps, leading to rapid desertification following a disturbance that may originate from grazing or human intervention. Hence, we uncover the existance of a bistability between two non-periodic patterns with very different ecological value. 

[1] E. Gilad, J. von Hardenberg, A. Provenzale, M. Shachak, and E. Meron. Ecosystem Engineers: From Pattern Formation to Habitat Creation. Physical Review Letters, 93(9):098105, 2004.

[2] Y. R. Zelnik, E. Meron, and G. Bel. Gradual regime shifts in fairy circles. Proceedings of the National Academy of Sciences, 112(40):12327–12331, 2015. 

[3] M. E. J. Newman and D. J. Watts. Scaling and percolation in the small-world network model. Physical Review E, 60(6):7332–7342, 1999.

How to cite: Filippini, S., von Hardenberg, J., and Ridolfi, L.: Vegetation patterning dynamics induced by non-local connections, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-11850, https://doi.org/10.5194/egusphere-egu25-11850, 2025.

The study of how topographic and geological complexities drive vegetation dynamics over extended timescales, provides critical insights into the interactions between landscapes and ecosystems. Our study area encompasses the Greater Serengeti-Mara Ecosystem (GSME) in the Kenya-Tanzania transboundary region, renowned for its ecological richness and dynamic environments, most famously as the setting for the world’s largest terrestrial mammal migration. We focus on two case study regions: the Mara River Basin (MRB) and the Ngorongoro Conservation Area (NCA) to investigate localized interactions between geological, topographic, and ecological processes. The ecosystems are supported by a healthy and diverse vegetation cover, impacted by natural as well as anthropogenic factors. MRB is bounded in the north by active normal faulting dominated by Utimbara and Isuria faults whereas NCA is centred on Ngorongoro Crater, a large volcanic caldera. The tectonics of NCA is well-studied but subrecent faulting of Utimbara and Isuria was previously unrecognised and the impacts of these faults on uplift, subsidence and tilting of MRB has been revealed only recently. Previous studies have explored the relationship between precipitation and vegetation dynamics in the region. Limited research has focused on soil properties, primarily examining the effects of volcanic ash on the southeastern sector of GSME. However, the role of tectonics in influencing vegetation and, by extension, the broader ecosystem remains underexplored. We used remote sensing data (Landsat 5, 7, 8 and Sentinel 2) to create a time series analysis from the years 1984 until 2024 to examine the changes in the vegetation cover in the study area. Landsat 7 & 8 and Sentinel 2 data were processed in Google Earth Engine whereas those from Landsat 5 & 7 using Erdas Imagine. The normalised differential vegetation index (NDVI) shows a clear difference in vegetation cover during wet and dry seasons throughout the four decades for both the regions. MRB, which is covered by Quaternary sediments, has a higher vegetation cover throughout the year. NCA is affected by intermittent ash eruptions from Oldoinyo Lengai and has a vegetation cover, which varies at differing altitudes within the region and also shows a considerable seasonal variation at lower altitudes. Additionally, there is a significant difference in precipitation between MRB and NCA. In such a scenario, the vegetation cover in both the regions is likely to be a function of the interaction between the inherent soil properties and precipitation. Interestingly, stable vegetation also persists along active faults. Fault escarpments and fault-bounded wetlands provide seasonally stable vegetation cover, potentially due to localized influences on hydrology and soil properties and may serve as refugia during dry seasons. Our preliminary results highlight the need to integrate geo-tectonic analysis into broader ecosystem studies to better understand their role in sustaining biodiversity and ecosystem resilience.

How to cite: Purohit, C., Ludat, A., Said, A., Machunda, R., Hank, T., Kahle, B., and Kuebler, S.: Exploring the impacts of active faulting & tectonics on the vegetation cover of the dynamic Serengeti-Mara and Ngorongoro ecosystems of East Africa through spectral index analysis, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-3466, https://doi.org/10.5194/egusphere-egu25-3466, 2025.

Streamflow in several catchments in eastern Australia has decreased considerably (up to 40%) over the past 20 to 30 years, despite stable rainfall levels. This decoupling of streamflow and rainfall undermines the predictive accuracy of rainfall-runoff models used by catchment managers, which typically rely on the assumption of a stable relationship between these variables. Similar non-stationarity in streamflow has been observed in other catchments in the world, and evidence suggests that vegetation processes may be driving this non-stationarity due to increases in temperature and CO₂. Current rainfall-runoff models fail to capture the impact of these vegetation changes on evapotranspiration (ET). While these models account for ET's dependence on soil moisture, they do not consider changes in vegetation biomass and health, which can significantly alter ET and, consequently, runoff.

This contribution presents a methodology for estimating a vegetation-aware ET based on the Penman-Monteith equation and emulators that can account for changes in vegetation biomass and health. The emulators are developed using data from the Australian and New Zealand Flux Research and Monitoring network (TERN OzFlux). This network provides extensive measurements of energy, carbon, and water exchanges across various ecosystems, from which vegetation effects can be estimated under different environmental conditions, and across different vegetation types. Through this research we aim to contribute to understanding evapotranspiration dynamics and offer a reliable and simple tool for estimating vegetation effects, ultimately adding it to more realistic rainfall-runoff simulations.

How to cite: Brieva, C., Jorquera, E., Quijano, J., Kuczera, G., Saco, P., Rodriguez, J., and Kibria, G.: Accounting for Vegetation Feedbacks in Hydrological Models Using a New Vegetation-aware Evapotranspiration Formulation, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-5142, https://doi.org/10.5194/egusphere-egu25-5142, 2025.

Salt-tolerant Tamarix chinensis roots are crucial in preserving wetland soil and carbon  sequestration, which is essential for wetland ecology. Soil-water-salt conditions influence the growth of these roots in coastal saline areas, but the specific factors and their effects remain unclear. Using principal component and partial least square structural equation modelling (SEM) methods, we studied T. chinensis root features in six Yellow River delta communities. Results showed varied root features across locations, with larger roots further inland. Root growth negatively correlated with soil texture and salinity and positively with groundwater levels. Soil texture and salinity decreased with distance from the coast, while groundwater increased with distance from the Yellow River. This suggests that geographical location influences soil water-salt conditions, impacting root characteristics. The principal component analysis–derived root feature index captured 56.7% of root feature variation. SEM revealed geographical locations indirectly influence root features, with the Yellow River’s proximity primarily affecting them through groundwater and coastal distance influencing via soil sand content and salinity. The study underscores the importance of these findings for wetland conservation and ecology.

How to cite: lizhu, S.: Soil spatial heterogeneity created by river–sea interaction influences Tamarix chinensis root features in the Yellow River Delta, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-5353, https://doi.org/10.5194/egusphere-egu25-5353, 2025.

Mangrove wetlands are one of the most significant and vulnerable ecosystems in the world, providing a wide range of services including habitat, flood control and carbon storage, among others. Their vulnerability under climate change scenarios has been well documented, but recent works have shown that coastal wetlands have the capacity to accrete following the trend of SLR under particular circumstances. Suspended sediment concentration (SSC) plays a critical role in the accretion mechanisms that support wetland survival.

Wetlands in the Pacific Islands are among the most vulnerable areas to climate change and they receive considerable sediment from croplands (sugarcane) of their inland catchments. This contribution focuses on mangrove wetlands at the mouth of rivers draining into the Great Sea Reef. The objectives of our research are to evaluate the sediment loads from the catchment upstream of the coastal wetlands and to model the ecogeomorphological feedbacks among catchment, wetland and coastal reef lagoon under current conditions and future climate change scenarios. The methodology simulates the hydro-sedimentological behaviour of the watershed, under current and future scenarios with changes in land use (cropland expansion/management) and extreme events (cyclones). The output of this simulation constutute the input for the eco-geomorphological coastal wetland modelling.

This integrated modelling approach provides a better understanding of the main processes and feedbacks among vegetation, sediments and hydrodynamics within the coastal wetland, considering its interactions with the adjacent terrestrial (catchment) and aquatic (reef lagoon) ecosystems.

How to cite: Jorquera, E., Rodriguez, J., Saco, P., Sandi, S., Quijano, J., and Breda, A.: Effects of climate and human activities on mangrove wetland evolution., EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-7458, https://doi.org/10.5194/egusphere-egu25-7458, 2025.

The different temporal scales of surface flow and vegetation growth represent a major challenge when simulating the dynamics of ecohydrological systems. The much faster surface flow is therefore commonly simplified by treating it as stationary and linearizing the equations. While the simplified equations can be solved efficiently, they do not resolve individual runoff events. However, the sequence of events can be relevant for the dynamics of dryland vegetation. The nonlinear flow during individual precipitation events can be resolved by employing more sophisticated numerical methods, such as adaptive-time stepping and implicit time-integration. However, this requires the iterative solution of a sequence of discrete linear systems at each time step. This is complicated by asymmetry of the discrete system, originating from the advection of the flow. Here, we explore strategies for the efficient simulation of the nonlinear flow during individual precipitation events when modelling vegetation dynamics over centuries.

How to cite: Kästner, K. and Hinz, C.: Efficient and realistic modelling of individual runoff events in ecohydrological systems , EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-9937, https://doi.org/10.5194/egusphere-egu25-9937, 2025.