Isolating the indirect aerosol effects using a regional atmospheric model: impacts on
precipitation and soil erosion in northern India
Ralf Toumi and Hannah Nissan
We present a sensitivity study illustrating the potential effects of aerosol changes on
precipitation and soil erosion in northern India. Previous work suggests that indirect
aerosol effects dominate the precipitation response, but few have studied these in
isolation. We use a high resolution, convection-permitting regional model which isolates
the indirect aerosol effects only.
Consistent with previous studies, we find a reduction in precipitation in most areas and
weaker monsoon circulation for a tenfold increase in aerosols. This can be attributed to
local cloud microphysical changes, which induce a dynamic response opposing the
monsoon circulation. Erosion is estimated according to the widely used Universal Soil
Loss Equation. The change in erosion is greatest in the Western Ghats and the Ganges
Delta, both significant cropland areas. Both regions show reductions in soil erosion for
increasing aerosol concentrations, with locally isolated increases. These results suggest
that efforts to reduce anthropogenic aerosol emissions could adversely affect
agricultural productivity, but localised changes may be difficult to predict.