The phrase "evaporation increases" means that the process of turning a liquid into a gas happens at a higher rate or becomes more intense. Full definition
They should find that the temperature gradient between the two points actually increases if the rate of evaporation increases. (newclimatemodel.com)
When temperatures rise, ocean water evaporation increases, denser clouds stop solar rays and surface temperatures decline.» (thehindu.com)
atmospheric absorption by CO2 and water vapor increases, reducing the solar heating at the surface, and surface evaporation increases faster with temperature than the transfer of sensible heat (due to the Clausius - Clapeyron relation), both of which tend to reduce the diurnal cycle. (realclimate.org)