3.1. Soil erosion – RUSLE factors
At the national scale in this study, six RUSLE factors were calculated
at 1 km spatial resolution to compute annual soil erosion for 2005 and
2015. Out of six, soil erodibility (K), and slope-length (L) and
slope-steepness (S), factors remained consistent while rainfall
erosivity (R), cover management (C), and conservation practice (P)
factors varied for the 2005 and 2015 (Figure 3).
In the 2015 rainfall erosivity factor, >200 MJ
mm/ha/hr/year was observed over the larger areas of Azad Jammu &
Kashmir and Khyber Pakhtunkhwa which was much lower in 2005. Based on
the spatial distribution map we observed, overall precipitations of the
country increased from 2005 to 2015. The rainfall erosivity factor
values remained <11 MJ mm/ha/hr/year in 2005 and 2015 over the
entire Sindh province, Southern Punjab, large parts of the Balochistan
province and northern sides of Gilgit-Baltistan. A vast area of the
country consists of 11 to 130 MJ mm/ha/hr/year rainfall erosivity factor
values (Figure 3a).
Based on the LCLUC assessment, in four LCLU classes (Cropland,
Grassland, Wetlands/Snow cover, Settlements, and ‘Other land’)
increasing trend observed between 2005 to 2015, while only in ‘Forest
land’ decrease detected. In Punjab and Sindh provinces, a large area was
covered by ‘Cropland’ with 0.27 cover and use management (C) and 0.70
conservation practice (P) factors values. On the national scale, ‘Forest
land’ proportion was tiny as compared to the other LCLU classes. Across
Pakistan ‘Settlements’ are scattered with 0.08 cover management and 0.99
conservation practice factors values (Table 2). A huge area of
‘Grassland’ LCLU class was viewed across Gilgit-Baltistan, Azad Jammu &
Kashmir, Khyber Pakhtunkhwa, and Islamabad Capital Territory with 0.06
cover-management factor value (Figure 3b and 3c).
In the central parts of Punjab, Sindh provinces, slope-length (L), and
slope-steepness (S) factors indicated a lower range. Over
Gilgit-Baltistan, Azad Jammu & Kashmir, Khyber Pakhtunkhwa, and partial
areas of Balochistan, higher values of slope-length and slope-steepness
factors were observed with slight variations of low rage values (Figure
3d & 3e).
Figure 3f shows eleven soil erodibility (K) factor classes along with
one ‘wetlands’ LCLU class. In the soil erodibility (K) factor map, based
on the literature reviewed, 0.5 ton ha hr/ha/ MJ/mm value was assigned
to Cambic Arenosols (Qc) soil class and 0.33 ton ha hr/ha/MJ/mm was
assigned to Gleysols (G) soil class. Similar soil erodibility (K) factor
value was assigned to Orthic Acrisols (Ao) & Orthic Solonchaks (Zo)
soil classes i.e.0.23 ton·ha·hr/ha/MJ/mm, accordingly Haplic Yermosols
(Yh) & Calcic Yermosols (Yk) allotted 0.25 ton·ha·hr/ha/MJ/mm soil
erodibility (K) factor value and Calcaric Fluvisols (Jc) & Calcic
Xerosols (Xk) allocated 0.15 ton·ha·hr/ha/MJ/mm soil erodibility (K)
factor value. Lithosols (I) soil class covered the majority of the
Balochistan, Khyber Pakhtunkhwa, and Gilgit-Baltistan areas. Cambic
Arenosols (Qc) soil was observed in the Sindh and Punjab provinces along
the Indian border over the Desertic areas (Thar, Thal, and Kharan). The
Calcaric Regosols (Rc) soil class with 0.17 ton ha hr/ha/ MJ/mm lies
only in the Potohar plateau.