​Hydrological connectivity of the Luanhe River Basin in northern China

Objective By quantifying the possibility of water and sediment connectivity in the Haihe River mountain area of northern China, the state and spatial distribution of runoff and sediment transport in the main water-producing areas of Haihe River were reflected from the perspective of landscape pattern, and the basis for water and sediment redistribution in Haihe River Basin was provided.

Method By using the vegetation factor and the normalized vegetation index of the general soil loss equation to calculate the connectivity index (IC₁ and IC₂, respectively), the hydrological connectivity of the Luanhe River Basin in the Haihe River mountain area was further obtained, and the influence of land use and other factors on the hydrological connectivity and its spatial scale effects were discussed.

Result (1) In 2019, the meane values of IC₁ and IC₂ in the control basin of Luanxian Hydrologic Station were −1.38 and −2.28, respectively, and the hydrological connectivity index values had a good positive correlation with the annual sediment transport modulus and runoff depth of the basin, and the connectivity index represented the sediment transport and runoff yield capacity of the basin well. (2) The hydrological connectivity of different land use types was different, and the hydrological connectivity of each category was arranged from the smallest to the largest in order as: water body < wetland < shrubland< grassland < arbor forest land < farmland < construction land < bare land. More than 80% of the area covered by wetland, shrubland and grassland had a hydrological connectivity value of less than 0, which was good for intercepting water and sand and maintaining water and soil. (3) Hydrological connectivity had significant scale effect.

Conclusion The mean, median of IC₁ and IC₂ in the Luanhe River Basin are logarithmic functions of the watershed basin area. More than 80% of the area covered by wetland, shrubland and grassland has a hydrological connectivity value of less than 0, which is good for intercepting water and sediments and maintaining water and soil. As the drainage basin area increases, the hydrological connectivity index initially decreases rapidly and then gradually flattens. The connectivity tends to a certain value when the drainage basin area exceeds 10 000 km².