Hydroclimatology

Article By:

Oliphant, Andrew J. Department of Geography and Human Environmental Studies, San Francisco State University, San Francisco, California.

Last reviewed:2008

DOI:https://doi.org/10.1036/1097-8542.YB080340

As our understanding of the Earth's physical and biological systems has grown, it has become increasingly obvious that processes and patterns of the atmosphere, lithosphere, hydrosphere, cryosphere, and biosphere are dynamically linked over many space and time scales. This is very much the case for the Earth's climate and hydrologic (water) cycle. There is about 12,900 km³ of water (in all three phases) in our atmosphere. While this is a relatively small portion of the total global freshwater (∼0.04%), it has large turnover rates (∼495,000 km³ per year) because of the rapid cycling through evaporation, condensation, and precipitation and is transported effectively by atmospheric circulations. Atmospheric water also plays a key role in climate modification by absorbing, scattering, reflecting, and emitting radiation. This role is vastly different in the gaseous (water vapor), liquid (cloud droplets), and frozen (ice crystals) forms. Additionally, latent heat is absorbed and released during phase changes of water. Hurricanes (typhoons, tropical cyclones) and thunderstorms gain immense energy from the release of latent heat during condensation and freezing of moist air as it is lifted and cooled. Across the Earth's surface, large water and energy exchanges with the atmosphere occur through the processes of precipitation, evaporation, transpiration, sublimation, and the formation of dew and frost. Additionally, surface water has a large impact on the Earth's climate through albedo (reflectance). Snow and ice have a very high albedo, while oceans and lakes have a very low albedo. Consequently, the growth and shrinking of ice extent is dynamically linked with climate change. Hydroclimatology therefore focuses on the interaction and overlap between climatology and hydrology, including all of the atmospheric and surface components and fluxes of the hydrologic cycle (Fig. 1).

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