The Water Cycle and Water Insecurity - Edexcel A Level geography questions and answers)complete

What is the water cycle? - The cycle operates in a variety of spacial scales where physical processes control the circulation of water between stores on land, oceans, the cryosphere and the atmosphere. It works as a closed system with inputs (rainwater), outputs, stores and gravitational potential energy. It begins with evaporation where water vapour from the ocean is lifted and condensed in the atmosphere to form clouds. Moisture is then transported around the globe and returns to the surface as precipitation. When reaching the ground some water will evaporate back into the atmosphere whilst some of the water may percolate the ground to form groundwater. The balance of water that remains on the surface of the earth is called runoff and emptied into lakes, rivers and streams which carry it back to the oceans for the process to start again. This is therefore a closed system. What is the global budget? - The percentage contribution of water stores varies, with the majority of earths water being in saline oceans and freshwater being largely in ice caps and glaciers. The global budget limits water availability for human use and water stores have different residence times; some stores, such as those storing fossil water, are non renewable e.g. Ogalla aquifer in the USA High Plains stored fossil water from previous glacial melt so cannot recharge quickly. Ice Age vs. Now - Ice Age - more water was held within the cryosphere in solid form as snow and ice; as less was held in the oceans, sea levels dropped. Now - recent climate warming is beginning to reverse this with major losses of ice in Greenland and Antarctica meaning significant rise in sea level. What are the four major stores? - Largest is Ocean containing 96-97%, next is the cryosphere, then terrestrial surface groundwater and the smallest is the atmosphere. What affects residence time? - Some accessible stores e.g. soil, lakes = shorter residence times, it is easily lost to other stores by evaporation, transportation, groundwater flow or recharge. Atmospheric water has shortest residence timeStrong link with residence times and water pollution - stores with slower turnover = easily polluted as waters situ longer. Accessible water for human life support - 96-97% water stored in oceans - only around 2.5% occurs as fresh water. 69% locked in snowflakes, ice sheets, ice caps and glacier found in high latitudes and altitude locations - largely inaccessible for human use. 30% is groundwater, some very deep seated as fossil water therefore inaccessible. Only around 1% fresh water easily accessible for human use. Rivers main source of surface water for humans only 0.007% of total water. Technology is being used widely to extend availability of fresh water supplies e.g. by desalination of ocean water. What is the drainage basin water cycle? - It's a subsystem within the global hydrological cycle. An open system as it has external inputs and outputs causing amount of water in basin to vary over time due to different temporal scales, from short term hourly to daily, seasonal and annual. It's the area if land drained by a river and its tributaries frequently referred to as a river catchment - boundary of a drainage basin is the watershed (ridge of high land divides and separates water flowing to different rivers. They can be of any size, from a small stream without tributaries to international river flowing across borders of several countries.