The Atmospheric Infrared Sounder (AIRS) experiment on NASA's Aqua spacecraft provides a four-year record of water vapor profiles from the surface into the upper troposphere, along with simultaneous observations of temperature, minor gases, clouds and surface properties. The dense sampling and multi-year record from AIRS gives a uniquely detailed and comprehensive picture of climate and hydrologic phenomena. The AIRS observations are advancing our insights into several important hydrologic processes, including tropical intraseasonal oscillations, the oceanic boundary layer, upper tropospheric hydration, and cloud distributions. We present an overview of phenomena currently being studied with AIRS observations, along with some of the outstanding questions to be addressed in the near future.