2 Average monthly rainfall, runoff, and soil loss
Figure 3 presents average monthly runoff and soil loss data for all four landuses at plot level. The figure
illustrated that the ratio of runoff water from the degraded land was comparatively higher than that of the
all other landuses throughout the year. The proportion of runoff water increased during the monsoon
season (July-September) when rainfall intensity was normally high. In winter, a combination of
low-intensity rainfall and high infiltration rate caused small surface runoffs from agricultural, forest, and
pasture lands.
Figure 3 also shows the soil loss data for each landuse. The figure presents an increase in the soil loss
rate by increasing runoff amounts. Overall, the degraded land produced a high amount of soil loss
throughout the year, while soil loss increased sharply in June and July. A significant amount of soil loss
was observed from the agricultural plot in June when plant cover was not well established and early rains
eroded a considerable amount of soil from the land. Overall, average monthly runoff and soil losses were
higher from July to September due to high amount and intensity of rains, while they were lower in winter
when rainfall was low in amount and intensity. The figure clearly indicates that pasture, forest, and
agricultural lands generate very low soil loss during the winter months. It should be emphasized that all
major events in the agricultural plot were measured in May and June, which are sowing and weeding time.
Additionally, Fig. 3 shows fairly symmetric soil loss curves in plot-level for all landuses except in
degraded land. In degraded land, vegetative cover throughout the study period was not well established
while on all other land-uses vegetative cover was good enough to control runoff and sediment throughout
the year (i.e. in form of some grass on pasture, organic matter on forest plot and crop cover on agriculture
land). There are some significant runoff and soil loss events, which contributed to the major portion of
monthly/annual total runoff from the different landuses in the watershed even though the amount of
rainfall associated with those events was not very high. Generally, these events occurred in the
pre-monsoon period, when the land surface was desiccated, or in the early monsoon season when rainfall
intensity was high and vegetative covers were not well established and thus the lands were bare and
vulnerable to soil erosion.