Changes in moisture and energy fluxes due to agricultural land use and irrigation in the Indian Monsoon Belt

We present a conceptual synthesis of the impact that agricultural activity in India can have on land-atmosphere interactions through irrigation. We illustrate a "bottom up'' approach to evaluate the effects of land use change on both physical processes and human vulnerability. We compared vapor fluxes ( estimated evaporation and transpiration) from a pre-agricultural and a contemporary land cover and found that mean annual vapor fluxes have increased by 17% (340 km(3)) with a 7% increase (117 km(3)) in the wet season and a 55% increase ( 223 km(3)) in the dry season. Two thirds of this increase was attributed to irrigation, with groundwater-based irrigation contributing 14% and 35% of the vapor fluxes in the wet and dry seasons, respectively. The area averaged change in latent heat flux across India was estimated to be 9 Wm(-2). The largest increases occurred where both cropland and irrigated lands were the predominant contemporary land uses.