In view of the underlying surface change for the implement of soil erosion
control and the Grain for Green Programme on the Loess Plateau, the paper took the
He-Long Region as typical study area, utilized the field survey, RS/GIS analysis
simulation, and the hydrological statistics methods to analyse the spatiotemporal
trends of environment including precipitation, vegetation, etc., discuss the erosion and
sediment yield variation characteristicon, and analyse the driving factors. The results
of this research are as follows:
(1) Spatial and temporal evolution of soil erosion and sediment yield
1) Precipitation and rainfall erosivity: Precipitation was not significantly reduced
from 1981 to 2010 at interannual scales. Areas of showing decreasing trend of
precipitation took 81.80% of the whole region. Rainfall erosivity was not significantly
reduced at interannual scales. Areas of rainfall erosivity showing decreasing trend was
7.72×10 4 km 2 . Overall, rainfall erosivity at Yanhe and Shiwangchuan reduced. Areas
of rainfall erosivity decreased took 26.62% and 57.13% of the corresponding basin
respectively at Kuyehe and Huangfuchuan.
2) Soil erodibility: Areas of soil erodibility decreased occupied 79.80% of the
whloe region from the late 1970s to 2010. Soil erodibility reduced in Kuyuhe and
Huangfuchuan. Areas of soil erodibility decreased constituted 58.65% and 14.03% of
the Yanhe and Shiwangchuan areas.
3) Vegetation cover: Vegetation cover increased highly significantly in the
growing season from 2000 to 2010. And vegetation cover increased the most significantly in July, August and September. The improve situation of vegetation was
best in Yanhe.
4) Soil and water conservation measures: The total area of soil and water
conservation measures increased from 12600 km 2 to 34300 km 2 during 1979 and 2011,
which was mainly for the increase of afforestation and grass. The largest change of
area was in Kuyehe, followed by Yanhe. The relative change of areas was largest in
Qingjianhe, and followed by Xinshuihe, Yanhe, and Kuyehe.
(2) Spatial and temporal variation of erosion and sediment load
1) Soil erosion: The soil erosion modulus was 2205.4t/km 2 ·a at 2011 on the
He-Long Region. Area of suffering soil erosion was 5.26×10 4 km 2 which occupied
46.72% of the whole area. Among of that, area of suffering moderate soil erosion was
largest with 1.70×10 4 km 2 which takes 15.08% of the whole area. The soil erosion
modulus was 1033.5 t/km 2 ·a in Hufuchuan, 1487.2 t/km 2 ·a in Kuyehe, 2986.7 t/km 2 ·a
in Yanhe, 1026.2 t/km 2 ·a in Shiwangchuan. The proportion of soil erosion area in the
basin area of the He-Long Region is largest in Yanhe.
The soil erosion area reduced significantly with 22783.6km 2 and a decrease of
30.22%, the erosion intensity descended, and the severe erosion changed the most
dramatic on the He-Long Region from 2000 to 2011. The the very strong and violent
erosion area reduced very severely at typical basins of different underlying surface
and the mild erosion increased significantly. And the erosion area variation degree
was largest in Shiwangchuan.
2) Sediment load: The multi-year average sediment load is 31044.8×10 4 tons
from 1980 to 2010, and 16020×10 4 tons from 2000 to 2010. The annual average
sediment transport modulus is 2747.3 t/km 2 ·a from 1980 to 2010, and is 1417.7
t/km 2 ·a from 2000 to 2010. Transition time is around 1998 on the He-Long Region
and typical watersheds.
The sediment showed a decreasing trend over time on the He-Long Region and
each typical basin, especially on the time period during 1998 and 2010, the the degree
of reduction is more dramatic and the zero sediment discharge days showed a
obviously growing trend. The sediment load reduced 50.2% after the Grain for Green
Programme compare with that before the programme at wet period, and the change value was -47.6% at dry period. The change of erosion and sediment yield is very
dramatic in Kuyehe and Huangfuchuan where the erosion and sediment yield is most
(3) Erosion and sediment yield driving factors as environment and human
1) Effect of precipitation to vegetation: Areas of NDVI being positively
correlated with precipitation constituted 73.3% of the whole region, among of which,
areas of showing significantly positive correlation occupied 22.14%.
Vegetation is positively correlated with precipitation on Huangfuchuan and
Kuyehe. On the contrary, the correlate relation is mainly negative on Yanhe and
Shiwangchuan where the precipitation is reduced, which illustrates that human
activities play an effective role.
2) Effect of precipitation to sediment load: Transition time of annual
precipitation was not significant. The fluctuating state of preicpitation is similar to
that of sediment load at the He-Long Region and the four typical basins, however the
change degree is small overall. The annual sediment load is small and shows a
reducing trend after 1998.
The sediment yield coefficient of precipitation changed dramatically on the
whole region and the four typical basins, and the significant of correlation coefficient
is very low after 1998 which illustrates that the sediment load is mainly influnced by
3) Land use change driving by human activities: The Grain for Green
Programme achieved good ecological benefits for the forestland increased
significantly, the sandland and farmland changed to grassland and forestland, and the
landuse types changed violently. Number of Patches increased severely, mean patch
areas increased significantly. The Land use structure are by beginning to
centralization from fragmentation and heterogeneity. The human activities increase
the forestland effectively on the He-Long Region.
The case of landuse change at the four basins is similar to the whole region
where the farmland reduced and grassland and forestland increased. Among of that,
the change degree is least in Shiwangchuan. 4) Effect of conservation measures to soil erosion: Conservation measures
averagely reduce the soil erosion modulus by 471.9 t/km 2 ·a, and the soil erosion area
by 14.52%. The conservation measures can reduce the extremely strong and strong
soil erosion area effectively. Soil erosion area reduced by 55.22% in Huangfuchuan
whose change degree is largest.
Key Words: Erosion; Sediment; Spatiotemporal trends; Factors; Drive; The He-Long