Biggs, T., S. Christopher, G. Anju, J.-P. Venot, T. N. Chase, and E. Lee, and (2008), Irrigation and aerosol forcing of heat fluxes and surface temperature, southern India, Water Resources Research,

Abstract: Both land cover change and atmospheric phenomena have impacted the heat fluxes of south Asia in ways that may have altered the timing and magnitude of the monsoon. Multi-decadal budgets of water, radiation, and heat in the Krishna Basin (258,948 km2) in southern India demonstrate that irrigation impacted the sensible heat flux of the land surface (H) as much as or more than the atmospheric brown cloud (ABC) over 1960-2005. Annual discharge of the Krishna River fell from 226 mm during preirrigated conditions (1901-1960) to 64 mm by 1990-2005, when 14-20% of the basin area was irrigated. Annual evaporation increased by 166±32 mm (+28%) causing H to decrease by 12.8±2 W m-2 (-18%), compared to a maximum decrease in H due to anthropogenic aerosols of 10.7±1.8 W m-2. The rate of change in H during irrigation expansion (1960-1990) was between -3.4 and -5.0 W m-2 per decade (da-1) due to irrigation expansion and -1.8 to -2.3 W m-2 da-1 due to the ABC. The trend in H due to irrigation was negligible over 1990-2005 as irrigated area and evaporation stabilized. The maximum surface air temperature (Tmax) either decreased or remained the same in areas experiencing irrigation expansion but increased in a majority of unirrigated areas during the post-monsoon season, suggesting that irrigation changed both the sensible heat flux and air temperatures.