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.