Quantifying connectivity patterns in dryland ecosystems is crucial for understanding how water and sediments flow across the landscape, crucial for mitigating the impacts of climate change and land use modifications. This study quantifies the multi-scale water-mediated connectivity within grassland and shrubland hillslopes using a weighted, directed network model. By integrating high-resolution elevation, vegetation data, and modeled event-based hydrologic and sediment transport, we quantify both structural (topology) and functional (dynamical) connectivity under varying rainfall and soil moisture conditions. Our findings reveal a marked increase in local connectivity metrics in shrublands compared to grasslands, with metrics such as betweenness centrality and the weighted length of connected pathways increasing up to tenfold. Despite these substantial local changes, global properties like link density and global efficiency show less drastic variations, suggesting a robust network topology that sustains geomorphic functionality across different vegetation states. This indicates that although local connectivity is highly sensitive to vegetation changes, the overall structure and functional connectivity of water and sediment at the global scale remain relatively stable. Functional connectivity is more strongly correlated with structural connectivity for sediment than for water. This difference is particularly pronounced under high rainfall conditions, yet shows little sensitivity to variations in antecedent soil moisture, highlighting the critical role of event-driven processes in shaping connectivity patterns. The study advances our quantitative understanding of how structural changes affect functional processes in dryland ecosystems. It offers a comprehensive framework for analyzing connectivity at multiple scales, which can inform targeted management strategies aimed at enhancing ecosystem resilience.

This study provides a new perspective on understanding the intricacies of water-mediated connectivity in ecosystems, bridging landscape ecology and geomorphology through network science. We highlight dryland and river floodplain ecosystems as distinct examples of contrasting water-controlled systems. We (1) discuss central considerations in developing Structural Connectivity (SC) and Functional Connectivity (FC) networks of water-mediated connectivity; (2) quantify the emergent patterns in these networks; and (3) evaluate the capacity of network science tools for investigating connectivity characteristics. Connectivity is quantified using seven parameters at both network and node levels. We find that Link Density, Betweenness Centrality, and Page Rank Centrality are highly sensitive to directionality; Global Efficiency and Degree Centrality are particularly sensitive to weights; while Relative Node Efficiency remains unaffected by weights and directions. Our study underscores the potential to transform how we quantify and understand water-mediated connectivity, especially in consideration of the role(s) of weights and directionality. This interdisciplinary review has implications for both theoretical insights and practical applications in environmental management and conservation efforts.

Gully erosion leads to soil loss and poses significant threats to availability of land for cultivation, food security and development of infrastructure. Hydrological changes driven by land-use changes are often identified as drivers of gully erosion. The aims of this paper are to assess the influence of changes in land use on gully catchment hydrology and relate these changes to gully erosion. To achieve these aims, we used The Soil Water and Assessment Tool (SWAT, 2012 version) to assess hydrological changes driven by land-use changes in 22 gully catchments in the Orlu region of southeast Nigeria between 2009 and 2018. In the absence of measured hydrological data, we used a mixed-method approach to validate modelling results: literature review, field observations and focus group meetings. Increase in surface runoff estimates was observed in 21 catchments where reductions in fallow cover were observed. In one catchment where increased fallow was observed, we identified reduction in surface runoff. Surface runoff erosion was identified as a dominant process of gully expansion in the study area, but there was no significant relationship between changes in gullied area and changes in runoff volumes (r 2 = 0.15, p = 0.08). Within-catchment variations in land-use configuration influences surface runoff volumes and pathways, and by extension, gully erosion. This was evident in the slow gully expansion rate/gully reduction identified at gullies with vegetated adjacent lands as opposed to active runoff incision observed in gullies with bare adjacent lands. Therefore, the key finding of this study is that it is important to identify and incorporate the uniqueness of gully catchments in gully management as a successful management technique in a particular catchment may not work in another.

Gully erosion is the dominant environmental problem in southeast Nigeria and has led to loss of human and material resources. In this study, we evaluated changes in gully characteristics in southeast Nigeria between 2009 and 2018 using a multi-method approach including geotechnical investigations, analysis of high-resolution satellite imagery (2 – 5 m) and focus group discussions. Gully numbers increased from 26 to 39 and mean gully length increased from 0.39 to 0.43 km. We found that the soils in the study area have low cohesion and high sand content which make them susceptible to dispersal by erosive forces. Land adjacent to rivers had the highest concentration of gullies, and there was a sharp rise in slope from 10 – 58.2% within a distance less than 500 m from the river. Regarding potential gully-drivers, land-use changes were observed. Non-vegetated lands increased from 58.6 km2 to 144.7 km2 between 2009 and 2018, while reductions in fallowed lands from 281.2 km2 to 57.8 km2 were observed. Results from focus group meetings indicate there was no gullying in the area before the Nigerian civil war. Although war-time activities which led to initiation of oldest gullies have ceased, land-use changes likely increase volume of surface runoff. We infer that interactions between soil conditions which potentially enhance seepage erosion and higher surface runoff resulting from land-use changes have propagated gullying in the study area post-civil war.