Introduction

In recent decades, rapid climate changes along with the intensification of land use and land cover (LULC) dynamics have emerged as the two main drivers of morphodynamic transformations in river basins. These transformations can fundamentally alter patterns of erosion, sediment deposition, and runoff connectivity, resulting in significant changes in watershed processes and river ecosystem stability. Among the latest conceptual frameworks in fluvial geomorphology, geomorphic connectivity has attracted growing attention for understanding and quantifying how sediment, water, and energy transfer between sediment sources, transfer pathways, and depositional areas within landscapes. This paradigm enables researchers and resource managers to assess both the structure and functioning of sediment transfer systems under environmental disturbances.



Geomorphic connectivity not only determines the continuity of material transfer from headwaters to downstream reaches but also reflects the sensitivity of watersheds to environmental changes such as climate variability and anthropogenic activities. A widely used quantitative metric to capture this concept is the Index of Connectivity (IC), which combines digital elevation models (DEMs) and surface characteristics to evaluate sediment transfer potential and structural connectivity across landscapes. The application of IC is especially relevant in semi-arid and dry basins where fragile topography and dependence on episodic precipitation events enhance connectivity sensitivity.

Most previous research has considered the separate or limited effects of either climate change or LULC transformations on geomorphic connectivity. However, the concurrent impact of both drivers, particularly over long-term periods and in environmentally sensitive regions such as Western Asia, has rarely been comprehensively studied. The Zarrinehroud River Basin, as one of the largest and most dynamic sub-basins of Lake Urmia’s watershed in northwest Iran, is exceptionally exposed to the combined effects of decreasing rainfall, increasing temperature, recurrent droughts, and rampant expansion of irrigated agriculture and built-up areas in recent years. This calls for an integrated, multi-temporal assessment of geomorphic connectivity to inform watershed management, erosion control, and water resource conservation under changing environmental conditions.



Methodology

This research aims to analyze the spatiotemporal dynamics of geomorphic connectivity within the Zarrinehroud basin over the period from 2000 to 2025, considering both climatic fluctuations and LULC changes. The study employs a four-phase methodology that integrates remote sensing, GIS, and advanced statistical analysis:

Data Collection and Preparation:

Spatial datasets—including 30-meter SRTM Digital Elevation Model (USGS), multi-temporal Landsat imagery (for 2000, 2010, 2015, 2025), river network vectors, and administrative boundaries—were acquired. Climatic data (annual precipitation, temperature, runoff) were sourced from ERA5 reanalysis and regional meteorological stations.



Land Use/Land Cover (LULC) Classification:

Landsat images were processed and classified into six main LULC classes: agricultural land, rangeland, built-up areas, barren, forest, and water. Classification accuracy exceeded 85% (Kappa coefficient). Change detection algorithms were applied to identify patterns and rates of LULC transformation across the study period.



Calculation of Index of Connectivity (IC):

The IC was computed following Cavalli et al. (2013), using DEMs, surface roughness, and hydrological flow properties in ArcGIS Pro and R software. The resulting IC maps reveal the spatial distribution of sediment transfer potential at four time slices: 2000, 2010, 2015, and projected 2025.



Temporal Analysis and Graph Theory:

Time series analysis of IC values was conducted at the sub-basin scale. Additionally, a graph-theoretical approach based on Heckmann & Schwanghart (2013) was used to model the sediment transport network, extracting centrality and betweenness indices for river nodes. Correlation and multivariate regression analyses (Spearman, Adjusted R²) were used to assess the relationships between changes in IC, LULC, and

Results and Discussion

Land Use and Climate Trends:

The classification results indicate a marked shift in LULC across the basin during the 25-year period. Agricultural lands have significantly expanded, especially along river corridors and in the downstream areas. Meanwhile, rangelands have shrunk, and urban/built-up zones have grown, particularly in the middle and lower sub-basins. Barren land has diminished, whereas forests and water bodies have experienced slight and localized changes.

Climatic analysis reveals an increase in average annual temperature from 12.3°C to 13.8°C and a decrease in rainfall by about 8% over 25 years. Future scenarios (RCP 2.6, 4.5, and 8.5) predict that rainfall could drop by 23-35%, with corresponding reductions in runoff by up to 39%. The runoff coefficient (runoff/rainfall) has risen in all scenarios, suggesting both increased rainfall intensity and reduced soil infiltration caused by LULC changes. There is an evident increase in drought events, particularly after 2010, impacting water availability for agriculture and hydrological regime stability.





Graph Theory and Network Analysis:

The sediment transfer network has become more centralized and vulnerable over time. The average path length for sediment transfer decreased by about 16%, indicating greater likelihood of direct sediment flow to the river channels. Critical nodes with high betweenness and centrality emerged, especially in sub-basins C and A, rendering these areas potential bottlenecks for sediment routing. Vulnerability is most acute in sub-basins with steep slopes, disrupted vegetation, and extensive agricultural development.



Statistical Relationships:

Regression and correlation results indicate that LULC changes, notably the expansion of croplands and built-up areas, are the dominant drivers of IC decline, explaining over 72% of the variance in IC reduction (Adjusted R²=0.72). While climate change (reduced precipitation and higher temperature) contributes to declining connectivity, its independent effect is less significant and often non-significant compared to human activities. The interplay between LULC and climate exacerbates connectivity loss in more than 60% of sub-basins, particularly where inappropriate management and environmental stress overlap. Notably, IC values plummet after the threshold of a 20% increase in agricultural areas is exceeded, and decline exponentially where expansion surpasses 40%.

Conclusion

The integrated assessment conducted in the Zarrinehroud basin clearly demonstrates that land use change is the primary factor controlling geomorphic connectivity dynamics and sediment transfer risks. While climate change augments basin vulnerability,