<P> Subsidence, or the gradual sinking of landforms, is another result of water scarcity . The U.S. Geological Survey estimates that subsidence has affected more than 17,000 square miles in 45 U.S. states, 80 percent of it due to groundwater usage . In some areas east of Houston, Texas the land has dropped by more than nine feet due to subsidence . Brownwood, a subdivision near Baytown, Texas, was abandoned due to frequent flooding caused by subsidence and has since become part of the Baytown Nature Center . </P> <P> Aquifer drawdown or overdrafting and the pumping of fossil water increases the total amount of water within the hydrosphere subject to transpiration and evaporation processes, thereby causing accretion in water vapour and cloud cover, the primary absorbers of infrared radiation in the earth's atmosphere . Adding water to the system has a forcing effect on the whole earth system, an accurate estimate of which hydrogeological fact is yet to be quantified . </P> <P> Apart from the conventional surface water sources of freshwater such as rivers and lakes, other resources of freshwater such as groundwater and glaciers have become more developed sources of freshwater, becoming the main source of clean water . Groundwater is water that has pooled below the surface of the Earth and can provide a usable quantity of water through springs or wells . These areas where groundwater is collected are also known as aquifers . Glaciers provide freshwater in the form meltwater, or freshwater melted from snow or ice, that supply streams or springs as temperatures rise . More and more of these sources are being drawn upon as conventional sources' usability decreases due to factors such as pollution or disappearance due to climate changes . The exponential growth rate of the human population is a main contributing factor in the increasing use of these types of water resources . </P> <P> Until recent 2015, groundwater was not a highly utilized resource . In the 1960s, more and more groundwater aquifers developed . Changes in knowledge, technology and funding have allowed for focused development into abstracting water from groundwater resources away from surface water resources . These changes allowed for progress in society such as the "agricultural groundwater revolution", expanding the irrigation sector allowing for increased food production and development in rural areas . Groundwater supplies nearly half of all drinking water in the world . The large volumes of water stored underground in most aquifers have a considerable buffer capacity allowing for water to be withdrawn during periods of drought or little rainfall . This is crucial for people that live in regions that cannot depend on precipitation or surface water as a supply alone, instead providing reliable access to water all year round . As of 2010, the world's aggregated groundwater abstraction is estimated at approximately 1,000 km per year, with 67% used for irrigation, 22% used for domestic purposes and 11% used for industrial purposes . The top ten major consumers of abstracted water (India, China, United States of America, Pakistan, Iran, Bangladesh, Mexico, Saudi Arabia, Indonesia, and Italy) make up 72% of all abstracted water use worldwide . Groundwater has become crucial for the livelihoods and food security of 1.2 to 1.5 billion rural households in the poorer regions of Africa and Asia . </P>

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