Reduced sediment transport in the Yellow River due to anthropogenic changes

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1 DOI: /NGEO0 Reduced sediment transport in the Yellow River due to anthropogenic changes Shuai Wang 1,, Bojie Fu *1,, Shilong Piao 3,4, Yihe Lü 1,, Philippe Ciais 5, Xiaoming Feng 1,,Yafeng Wang 1, NATURE GEOSCIENCE 1

2 DOI: /NGEO Uncertainty discussion for the Sediment Identity approach Even the uncertainty introduced by the process of estimating hydro-climatic annual values is relatively low as they are the sum of consecutive daily measurements. It would come from the processing of collection and some spatial average calculates when the number of gauges is not enough for a large region. The Sediment Identity approach allows us only to attribute relative trends of sediment loads, not absolute ones. Also, the choice of the periods representing different regimes remains arbitrary and influences the attribution. Table 1. Proportional change rate of Sediment Identity factors in different periods. Factors P1-P3 P1-P P-P3 P (%) r (%) s (%) Sum (%) Table. Main tributary catchment characteristics and the long-term mean annual precipitation (P), potential evapotranspiration (E 0 ), runoff (R) and sediment load (S). Tributary Station Area (km²) Long-term mean annual value P E 0 R S (mm) (mm) (mm) (Gt) Huangfu(HF) Huangfu Kuye(KY) Wenjiachuan Tuwei(TW) Gaojiachuan Jialu(JL) Shenjiawan Wuding(WD) Dingjiagou Dali(DL) Suide Qingjian(QJ) Yanchuan Yanhe(YH) Ganguyi Beiluo(BL) Zhuangtou Jinghe(JH) Zhangjiashan Weihe(WH) Linjiacun Fenhe(FH) Hejin NATURE GEOSCIENCE

3 DOI: /NGEO0 SUPPLEMENTARY INFORMATION Change of runoff in different stages and impact factors We used seven variables describing runoff change during last few decades. Human restoration measures, together with precipitation are included. Our analysis found the dominant reason for runoff decrease shifted over the periods of 10s-10s, 10s- 10s and 10s-10s. Restoration measures including change of percentage area of terraces and check-dams, and change of annual precipitation act as the dominant factors in runoff decrease from 10s to 1 step by step, with re-vegetation becoming important from 10s-000s. Table 3. Impact factors of runoff change in different stages. 10s-10s 10s-10s 10s-10s 10s-000s ΔT (%) **(0.0) ΔD (%) *(0.43) ΔP (mm) *(0.3) *(0.0) ΔE 0 (mm) ΔL ΔV (%) ΔL V **(0.54) The relationship between runoff reduction and the dominant factors 10s-10s ΔR= ΔT (r =0.0) 10s-10s ΔR= ΔP (r =0.3) 10s-10s ΔR= ΔD (r =0.43) 10s-000s ΔR= ΔP -.3 ΔL V (r =0.4) ΔT and ΔD are change of percentage area for terrace and check dam respectively. ΔP and ΔE 0 is change of annual precipitation and potential evapotranspiration in the two compared periods. ΔL is change of GLASS LAI for each catchment. ΔV is change of the re-vegetation area observed by remote sensing. ΔL V is product of ΔL and ΔV. ** and * indicate the variable in the model is significant at p<0.01 and p<0.05 respectively. Otherwise the variable does not meet the 0.05 significance level for entry into the model of runoff change. NATURE GEOSCIENCE 3

4 DOI: /NGEO0 5 Figure 1. Double mass plot of annual sediment load versus annual water discharge. The gently increasing trend during 10s and a decreasing trend since 000s suggests both the water and sediment have responded to similar controls. 4 NATURE GEOSCIENCE

5 DOI: /NGEO0 SUPPLEMENTARY INFORMATION Figure. Sediment Identity factors including S, P, r, s are normalized to 1 in the turning-point year 1. Sediment load (S) is the combined result of several factors including precipitation (P), water yield capacity r (water discharge/precipitation) and sediment concentrationn s (sediment/water discharge). NATURE GEOSCIENCE 5

6 DOI: /NGEO0 4 5 Figure 3. Values of temperature and Sediment without normalization. (a) temperature, (b) P, (c) r and (d) s. Identity factors NATURE GEOSCIENCE

7 DOI: /NGEO0 SUPPLEMENTARY INFORMATION 5 Figure 4. Spatial variability of the sediment change trend and driving forces. The relative rate of change of the sediment load flux (S) and the contribution of each Sediment Identity factor for the 1 main tributaries of the YR in the LP. NATURE GEOSCIENCE

8 DOI: /NGEO0 Figure 5. The comparison between contributions of the tributaries. (a) Contribution of each of the 1 tributaries of the YR to the overall sediment load change between selected periods of time. (b) Same for the contribution of each tributary to the average sediment transportt in the YR in the LP region. NATURE GEOSCIENCE

9 DOI: /NGEO0 SUPPLEMENTARY INFORMATION Figure. The Budyko framework for all the 1 tributaries during the 3 periods. It describes the relationship between a catchment s potential evapotranspiration (E 0 ) and its actual evapotranspirationn (E), each normalized by precipitation (P) from which we can see the changes of landscape parameter n. R H (+) represents the human-induced water yield increase and R H (-) the reduction, R C (+) represents the climate change-inducedd water yield increase and R C (-) the reduction. NATURE GEOSCIENCE

10 DOI: /NGEO Figure. Vegetation coverage change and its effects on runoff and sediment reduction in the LP. (a) Vegetation coverage in the years 1, 1 and 0100 in the 1 sub-catchments on the LP based on remote sensing data. (b) The relationship between vegetation cover and runoff coefficient and (c) vegetation cover and suspended sediment concentration based on the data collected by Liu et al. 1,1, both with a negative linear relationship between the vegetation coverage and flow sediment concentration and runoff from the LP. 10 NATURE GEOSCIENCE

11 DOI: /NGEO0 SUPPLEMENTARY INFORMATION Figure. Effects of engineeringg measuress on sediment reduction in the LP. (a) Terracing as a percentage of total land area in the years 1, 1 and 00 in the 1 tributaries in the LP derived from the Yellow River water conservancy yearbook. (b) The relationship between percentage of terraced area and sediment reduction according to Ref 1. (c) The estimated amount of sediment captured by reservoirs and check dams during 10s, 10s and 000s according to the first national water census. NATURE GEOSCIENCE 11

12 DOI: /NGEO Figure. Prediction of the sediment production from the LP in the future. Using the output of 30 GCMs from IPCCC AR5 under the RCP 4.5 scenario, and the comprehensive management planning framework for this area, the vegetation coverage and terrace farming will continue to increase, but check dams and reservoirs will gradually lose their efficiency, resulting in a slight net increase in the sediment yield. 1 NATURE GEOSCIENCE