1. Freshwater and Groundwater THE MOST IMPORTANT RESOURCE OF ALL!!!!! John Solder Andrew McCauley

2. Natural State Globally 111,000 km 3 /yr of water precipitates onto the earth’s surface. 65,500 km 3 /yr evaporate and transpire directly back to the atmosphere. Humans use approx. 3800 km 3 /yr, only about 10% of the available freshwater discharge. 30% of ET is attributed to crops and rangelands, while 90% of water consumed goes to agriculture. Units in thousands of Km 3 (Jackson et al. 2001, fig. 2)

3. Natural Variation Freshwater availability is a direct result of global climate variability. 50% of total annual discharge occurs through flooding, largely due to seasonal precipitation variability.

4. Aquifer Use and Depletion Many areas depend on groundwater as major resource. Groundwater is seen as an infinite reservoir and use is commonly greater than the rate of recharge.

5. Groundwater Overuse Subsidence Drying up of current wells, drilling deeper for water. Reduction of local discharge. Salt water intrusion. Salinization Partly saltwater intrusion affects the salinity of water in the aquifer. Largely is the concentration of dissolved minerals from irrigation. Chemical Alteration Lowering of water table affects oxidation reactions in sub- surface. Sulphate soils become acidic. Release of arsenic. Release of stored carbon in peat bogs.