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The comparative assessment of Watersheds 1 and 2 reveals how watershed morphology, land characteristics, rainfall variability, and conservation interventions collectively influence runoff behaviour, soil erosion, and carbon dynamics. Both watersheds demonstrate inherent vulnerabilities to erosion and carbon loss, but also show strong responsiveness to soil and water conservation (SWC) measures.

Watershed Characteristics and Hydrological Response

Watershed 1 exhibits a moderately elongated shape, as reflected by its form factor and elongation ratio. This geometry produces a relatively balanced hydrological response, characterised by moderated peak flows compared to circular watersheds. However, its high drainage density and short overland flow length indicate a well-developed drainage network that facilitates rapid surface water movement. While this enhances drainage efficiency, it also increases susceptibility to quick runoff generation and erosion during intense rainfall. The watershed’s moderate relief combined with a high ruggedness number highlights a terrain that is structurally prone to soil detachment and transport under high rainfall events.

Watershed 2 is more distinctly elongated, resulting in delayed peak flows and longer runoff durations, which inherently reduce flash flood risks. Despite this favourable shape, the watershed also exhibits high drainage density and short overland flow length, enabling rapid runoff conveyance. Moderate relief and a relatively rugged landscape further increase vulnerability to sediment transport during heavy rainfall events. As a result, both watersheds, despite differences in shape, face erosion risks driven by terrain and drainage characteristics.

Runoff Trends and Effects of Conservation Measures

An important finding across both watersheds is the measurable improvement in hydrological behaviour following the implementation of conservation measures, even under increased rainfall conditions in 2025 compared to 2023 and 2024. Runoff coefficients declined significantly in both systems, from 0.42 to 0.32 in Watershed 1 and from 0.41 to 0.28 in Watershed 2. This reduction indicates improved infiltration, enhanced water retention, and a transition toward more sustainable runoff regimes.

Soil Erosion Status and Improvements

Baseline soil erosion assessments underscore the severity of land degradation risks. Prior to conservation interventions, 48% of Watershed 1 and 54% of Watershed 2 fell under moderate to very severe soil erosion categories. The spatial concentration of severe and very severe erosion zones highlights the urgent need for targeted soil conservation strategies that address slope, land use, soil type, and rainfall intensity.

Following the introduction of SWC measures, both watersheds exhibited marked reductions in soil loss. In Watershed 1, average soil loss declined from 32.63 to 26.73 t/ha/yr in 2024, with a noticeable shift of land into lower erosion classes. Watershed 2 showed a similar response, with soil loss decreasing from 30.82 to 24.65 t/ha/yr and a larger proportion of land reclassified under slight erosion. These results confirm the effectiveness of conservation practices in improving soil stability and watershed resilience.

Projected outcomes following full implementation of recommended measures indicate dramatic long-term benefits. Annual soil loss in Watershed 1 is expected to decline further to 5.65 t/ha/yr, while Watershed 2 is projected to reach 4.75 t/ha/yr, representing substantial reductions from current levels.

Partial implementation scenarios also show positive outcomes. After treating 9 ha in Watershed 1 and 2.4 ha in Watershed 2, average annual soil loss decreased to 23.78 t/ha/yr and 21.59 t/ha/yr respectively, demonstrating that even limited-area interventions can generate measurable benefits.

Carbon Loss and Soil Organic Carbon Dynamics

Carbon loss analysis reveals significant depletion of soil organic carbon (SOC) prior to intervention, with average annual losses of 554 kg/ha/yr in Watershed 1 and 612 kg/ha/yr in Watershed 2. Such losses directly affect soil fertility, moisture retention, and ecosystem functioning.

SOC assessments show a consistent decline in carbon content with increasing soil depth in both watersheds. Natural vegetation areas maintain the highest SOC densities, underscoring their role as critical carbon reservoirs. In contrast, agricultural and barren lands exhibit substantially lower SOC levels, reflecting the influence of land use and management practices on carbon storage.

Implementation of SWC measures has significantly reduced carbon losses. Initial reductions lowered annual carbon loss from 412 to 120 kg/ha/yr in Watershed 1 and from 479 to 128 kg/ha/yr in Watershed 2 under full intervention scenarios. Partial implementation still resulted in measurable benefits, reducing carbon loss to 392 kg/ha/yr in Watershed 1 and 454 kg/ha/yr in Watershed 2. These findings demonstrate the role of conservation practices in enhancing soil carbon retention and supporting long-term sustainability.

Rainfall–Runoff–Carbon Relationships (2024–2025)

Rainfall-runoff dynamics during 2024 and 2025 highlight the strong influence of monsoonal patterns on sediment and carbon fluxes. In 2024, Watershed 1 recorded substantial rainfall between June and October, resulting in a total carbon loss of 19,354.6 kg. Watershed 2 experienced more variable rainfall, with July and August dominating runoff and producing a total carbon loss of 8,038.7 kg.

In 2025, extreme rainfall conditions provided deeper insights. Watershed 1 received 4,644.4 mm of rainfall, generating 4,827.16 mm of runoff and a runoff volume of 658,908 m³, resulting in a carbon loss of 54,634 kg. In contrast, Watershed 2 demonstrated high infiltration capacity, with the same rainfall producing only 578.48 mm of runoff and a carbon loss of 4,779 kg.

Monthly analysis reveals a decoupling between runoff volume and sediment or carbon loss. In Watershed 1, 2025 runoff decreased by 16% compared to 2024, yet sediment loads increased and carbon loss more than doubled. In Watershed 2, runoff increased in 2025, sediment loads declined sharply, while carbon loss rose dramatically. These patterns indicate that rainfall intensity, soil condition, land management, and antecedent moisture play a stronger role than runoff volume alone in driving sediment and carbon losses.