A report on How forests attract rain: A new hypothesis in International Society for Agricultural Meteorology”(June 3,2009) states: Pressure gradients driven by temperature and convection are considered to be principal drivers of air flows in conventional meteorological science. Makarieva and Gorshkov argue that the importance of evaporation and condensation have been overlooked. At the global average lapse rate water vapour rises and condenses. The reduction in atmospheric volume that takes place during this gas to liquid phase change causes a reduction in air pressure. This drop in pressure has routinely been overlooked. So atmospheric volume reduces at a higher rate over areas with more intensive evaporation. The resulting low pressure draws in additional moist air from areas with weaker evaporation. This leads to a net transfer of atmospheric moisture to the areas with the highest evaporation. Sheil and Murdiyarso (2009) discuss various local consequences. Forest loss and diminished evaporation can for example reduce the penetration of monsoon rains and reduce the duration of the wet season. Clearing enough forest within a larger forest zone may switch net moisture transport from ocean to land into from land to ocean, leaving forest remnants to be dessicated. Clearing a band of forest near the coast may suffice to dry out a wet continental interior.
