What process involves the stream at the valley head

answer:

headward erosion is a fluvial process of erosion that lengthens a stream, a valley or a gully at its head and also enlarges its drainage basin. the stream erodes away at the rock and soil at its headwaters in the opposite direction that it flows.

explanation:

for  example, forests have higher evapotranspiration than other ecosystems,  such  as grasslands, because of their deeper roots and greater leaf area. thus forests have a net moistening effect on the atmosphere and become a moisture source for downwind ecosystems.