Landscape pattern change affect runoff and sediment yield in Nandong underground river system, Southwest China

In fragile karst watershed, landscape pattern mainly affects evapotranspiration, interception, surface runoff, soil water infiltration and groundwater formation through spatiotemporal variation of land use, vegetation pattern, and then influences the discharge and sediment transport. A new Vegetation-Topographic factor (VTF)was constructed by NDVI and DEM data from 2000 to 2018. Based on VTF classification , Vegetation-Topographic landscape index(VTLI) was calculated by FRAGSTATS to analyze the impact of VTLI change on runoff and sediment yield in Nandong underground river system（NURS）. The results showed that :(1) PD, IJI, LSI, SHDI were significantly positively correlated with runoff and sediment, while AI, CONNECT were significantly negatively correlated with runoff and sediment yield(P<0.05). LPI and DIVISION indices were not significantly correlated with discharge, but positively correlated with sediment yield. (2) PD, IJI, LSI and SHDI were the main promoting factors for runoff, while LSI and SHDI were the main promoting factors for sediment yield. CONNECT and AI were the main restrain factors of sediment yield, Which showed a downward trend. (3) In urban areas, VTF was decreased and has persistence trend. In basin-mountain margin areas, VTF was increased and has persistence trend. In mountain area, VTF was unchanged or not significantly increased but was anti-persistence trend. The change of landscape pattern indexes varied the runoff and sediment yield of NURS. The trend and persistence of VTF vary greatly in different geomorphic positions of NURS. These results will provide theoretical basis for watershed management and soil conservation of karst fragile ecosystem in southwest China.