Quantitative assessment of hydrological multifunctionality of headwater wetlands

Headwater wetlands are integral to sustaining water security and downstream ecosystem integrity through their various hydrological functionality. Despite such relevance, previous research predominantly focuses on individual hydrological functions, leaving their combined roles underexplored. To fill this gap, we proposed a novel framework to discern the hydrological multifunctionality of basin wetlands. A distributed hydrological model integrated with wetland modules (riparian and isolated wetland modules) was developed to simulate basin hydrological processes. Subsequently, hydrological indicators including runoff variability, flood intensity, drought intensity and water conservation capacity were introduced to delineate hydrological characteristics and compared to quantify the multifunctionality of basin wetlands. The hydrological modeling was performed on the adjacent Black River and White River basins with distinct wetland patterns in headwater regions of the Yellow River to quantify hydrological multifunctionality, and our framework was validated. The results indicate that wetlands predominantly mitigate runoff variability by reducing the uneven distribution coefficient, complete adjustment coefficient, concentration degree, and change amplitude. They can also lower peak monthly flow rates and improve baseflow and low-flow conditions. Consequently, flows in March, July, annual maximum peak flow, and high flow in the Black River and White River basins decrease by 741.6 × 10⁴ and 181.7 × 10⁴ m³, 2427.8 × 10⁴ and 264.2 × 10⁴ m³, 1398.9 × 10⁴ and 36 × 10⁴ m³, 324.5 × 10⁴ and 14.27 × 10⁴ m³, respectively. In contrast, the mitigation services of wetlands lead to 19.9 × 10⁴ and 3.2 × 10⁴ m³ increase in low flow as well as 5.8 × 10⁴ and 4.2 × 10⁴ m3 growth in baseflow. For the two basins, wetlands augment water storage and water conservation capacities by −30.6 % and −2.1 %, as well as 19.8 % and 0.2 %, respectively, thereby improving basins’ resilience to hydrological extremes. This study highlights the roles of hydrological multifunctionality provided by headwater wetlands in enhancing resilience of a basin to hydrological risks. Therefore, wetlands are an extremely important land cover in the headwater regions, and it is essential to guide the restoration and protection of wetlands in these areas from the perspective of the importance of improving hydrological multifunctionality.