2.4 Data processing and analysis
2.4.1 The classification of alluvial fans.
The quantity of alluvial fans was large, and the area had lots of sizes
in our study area. In order to know the distribution of them, they were
classified into five sizes by the area of alluvial fans, i.e.,
1st: area≤0.1 km², 2nd: 0.1<area≤1
km², 3rd:1<area≤10 km², 4th:
area>10 km². And the quantity of all the sizes was counted.
2.4.2 Indicators for the land use
There were many types of land use in alluvial fans, for example
cropland, forest, grassland, shrubland, wetland, water body, tundra,
impervious area and bare land. In order to reflect the land use
characteristics of alluvial fans in LRB, the two indicators ofRlaf and Rllrb were used.Rlaf was the ratio between the area of a land-use
types in alluvial fans and the total area of alluvial fans.Rllrb was the ratio between the area of a
land-use type in alluvial fans and the area of the same land-use type in
LRB.
Rlaf = Ali / Aa·100% (1)
Where Ali (km²) was the area of land use iof alluvial fans; and i= cropland, forest, grassland…;Aa (km²) was the total area of alluvial fans.
Rllrb = Ali /Alrbi ·100% (2)
Where Ali (km²) was the area of land use iof alluvial fans, and i= cropland, forest, grassland…;Alrbi (km²) was the area of land use i of
LRB.
Meanwhile, in order to show the spatial distribution of land-use types
in alluvial fans, the alluvial fans are classified into 2 types by the
area of land-use type. The first type is the alluvial fans which area
are occupied as one land use i not less than 50%
(A50%i ), and i= cropland, forest,
grassland…. The second type is the A50%i which area are occupied as another land use j not less than 30%
(A50% i A30% j ), andj= cropland, forest, grassland….
2.4.3 Indicators for utilization potential.
The utilization potential is mainly depending on the distance between an
area and road, place and waterway. The centroids of all alluvial fans
were calculated in ArcGIS and used to analysis the distance between
alluvial fan and road, place and waterway respectively. According to the
fact of road in LRB and the needs of our study, the primary road,
secondary road, tertiary road, county, town and village were chosen to
analyses the distances. For the town and village, the places of their
government departments were used to get the distance. Meanwhile,
considering the background of water shortage in semi-arid monsoon
climate region, all kinds of waterways are important for this basin. So,
the data of stream with consistent low were added to the river data for
analyzing.
Another two ratio indicators including Rq andRa are used to show the utilization potential of
alluvial fans. Rq is the ratio between the
quantity of alluvial fans that their distance to road, place and river
are not more than some space and the total quantity of alluvial fans in
LRB. Ra is the ratio between area of alluvial fans that their
distance to road, place and river not more than some space and total
area of alluvial fans.
Rq =Qan /Q ·100% (3)
Where Qan is the quantity of alluvial fans not
more than n (km) to road, place and river, and n= 1, 5, 10,
20, 40; Q is the total quantity of alluvial fans.
Ra = Aan /Aa ·100% (4)
Where Aan (km²) is the area of alluvial fans not
more than n (km) to road, place and river, and n= 1, 5, 10,
20, 40; Aa (km²) is the total area of alluvial fans in LRB.
All figures are carried out with ArcGIS10.7 and Origin 8.5 software.