3.3 The land use of alluvial fans
The Table 1 shows the area proportion of different land use types of alluvial fans in LRB. The Rlaf of grassland is the largest with 68.70% in all land-use types. TheRlaf of impervious area covered by artificial buildings is only 4.52%, but Rllrb is 9.18%. The Rlaf and Rllrb of cropland had similar regulation with impervious area. TheRlaf of cropland is just 2.16%, butRllrb is 18.98% of the cropland area of LRB. Those illustrate the great contribution of alluvial fans about providing grass for livestock and food and residential place for human. TheRlaf and Rllrb of forest, shrubland, wetland, and water body are far lower than cropland, impervious area and bare land. The snow/ice almost can be ignored in all types of land use.
The spatial distribution of land-use types of alluvial fans is showed in Fig7. The grassland is the most in all land use types, especially in Damshung cunty. The cropland is mainly distributed in the south of LRB, including Taktse, Tolung Dechen, Chushur and the south part of Lhundup county. The distribution of imperious area is the same with cropland, including Taktse, Chenguan and Tolung Dechen. The bare land is mainly distributed in Damshung and Chushur county. Combining Google earth, the bare land of alluvial fans is covered by sand where is hardly grow vegetation.
There are only 3 kinds of alluvial fans which area are occupied more than 50% by one land-use type (A50%,), including A50%grassland, A50%impervious area, and A50%cropland (Fig8.). The A50%grassland exist all counties with 665 and area of 903.17 km². The A50%impervious area only exist in Tolung Dechen, Chenguan, and Taktsc. There is only an A50%grassland in LRB with the area of 0.07 km². There are 6 kinds of A50% which area are occupied more than 30% another land-use type (A50%A30%), and 4 kinds are about A50%grassland (Fig9.) the quantity of A50% A30% is far less than A50%. A50%grasslandA30%bare land is the most in A50%A30%, and distribute all counties except ChuChur. The A50%impervious area A30%bare land and the A50%impervious area A30%grasslanddistribute in Tolung Dechen and Chenguan.