Water Unit Introduction Outline: Unique chemistry Distribution on planet - changes with time Hydrologic cycle - redistribution, climate effects Ocean circulation - basic wind & thermohaline

Chemically unique because it: exists in all three phases at atmospheric temp & pressure (high melting and boiling points for size & bond type- ammonia-NH3-mass 17, MP -78, BP 33) and is the only substance that does this! has covalent bonds for molecule, hydrogen bonds for liquid/solid phase (10x stronger than usual inter-molecular bonds, but weaker than metal or ionic bond)

Chemically and physically unique because it has: high heat capacity J/g/K- i.e., takes more energy to raise temp, therefore stores more, important for spreading planet’s heat high heat of fusion (solid <> liquid ~ 335 J/g/ºK) and vaporization (liquid <>gas ~ 2400 J/g/ºK) so more effectively transfers heat when changing phase in atmosphere/ocean conducts heat more readily as a liquid

Water is chemically and biologically unique because it: has high surface tension so forms drops & helps make good cell membranes can dissolve other compounds very easily (most common solute), so can transport many things, e.g. NaCl, nutrients mediates or facilitates most chemical reactions in living systems (e.g., takes water to photosynthesize) - neutral pH

Water is physically unique because it is less dense as a solid (ice) than as a liquid.

Distribution on Earth “Water, water everywhere, nor any drop to drink.” – Coleridge, Rime of the Ancient Mariner

Hydrologic Cycle (in 10 3 km 3 )

Global warming (temperature increase) Effects of global warming on water cycle Speeds up global water cycle More extreme weather events Droughts Droughts Storms Storms Floods Floods

Projected Changes in Annual Precipitation for the 2050s Source: The Met Office. Hadley Center for Climate Prediction and Research The projected change is compared to the present day with a ~1% increase per year in equivalent CO 2

Green = increasing, Brown = decreasing Global Precipitation Trends (% per decade) Source: Watson 2001

U.S. Precipitation Trends: 1901 to 1998 Source: National Climatic Data Center/NESDIS/NOAA Green = increasing, Brown = decreasing All stations/trends displayed regardless of statistical significance

Extreme Precipitation Events in the U.S. Source: Karl, et.al