Water Cycle

• Systems are composed of inputs, outputs, stores, flows, and boundaries
• Inputs - the energy or matter that enters a system from outside it.
• Outputs - the energy or matter leaving a system to go somewhere else.
• Flows - the movement of energy or matter through a system over time.
• Boundaries - the limits of a system which define what is included and excluded.
• Stores- Where matter or energy is built up or held within a system.
• Open Systems- A system that is connected to other systems and is able to exchange matter and energy via flows and transfers.
• Closed systems- a system that is not connected to the outside world and is not allowed to exchange matter but cannot transfer energy.
• Dynamic Equilibrium- inputs equal outputs despite changing conditions.
• Negative Feedback- A chain of events nullifies the impact of the original event.
• In a local Water Cycle system, water may be lost through evapotranspiration and run off. But more water may be gained as an input through precipitation; as these are not balanced it is an open system.
• Precipitation is the main input into a local Water Cycle and includes rain, snow and hail. It comes from the atmosphere unlike rainfall.
• Transpiration is where plants lose water by turning it into vapor through their stomata (pores).
• Evapotranspiration (output)- The evaporation of water from the surface of the Earth and the transpiration of water through plants. Water goes out of plants into the atmosphere.
• Streamflow- All the water that enters a drainage basin leaves through the atmosphere or through streams which may flow as tributaries into other rivers or directly into lakes or oceans.
• Infiltration- water moves into the soil through cracks in the soil and into the ground. Grass crops and tree roots create these passages from the surface to the soil (increasing infiltration capacity) precipitation>infiltration capacity=overland flow
• Percolation (output)- The movement of water through the soil and porous rock layers to the water table.
• Throughflow (output)- Water flows through the soil and into the groundwater system, streams or rivers. The higher the field capacity of a soil, the slower the flow rate as smaller pores.
• Surface Runoff (output)- The water that flows over the surface of the ground.
• Groundwater Flow (output)- Water flows from the ground to the river, through the river and into the sea. Water moves through the rocks and ensures that rivers do not dry up.
• Water Cycle stores (local)- groundwater, soil water, lakes, river channels, oceans.
• Water Table- The upper level which pore spaces and fractures become saturated. Used to assess drought conditions, wetland health, and forest restoration success.
• Water Balance- changes seasonally due to variations of temperature and precipitation. Precipitation = Total Runoff + Evapotranspiration +/- Change in storage
• deforestation impacts (local)- soil erosion as more runoff from less tree interception, soil water storage decreases, transpiration decreases.
• Storm Events impacts (local)- quickly saturates the ground to field capacity, less infiltration, increased flooding as surface runoff increases, less effective at replenishing water stores than prolonged rainfall.
• Seasonal Changes impacts (local)- Spring = more vegetation growth = more interception, Summer = less rain = more impermeable encouraging surface runoff, Autumn = more rainfall = less interception as less crops, Winter = frozen impermeable ground = more runoff
• Agriculture impacts (local)- Pastoral tramples on land reducing infiltration, Arable increases interception and thus infiltration but drainage ditched increase streamflow, Hillside terracing decreases runoff (rice padis), Irrigation increases infiltration but decreases runoff thus groundwater depletion.
• Urbanisation impacts (local)- roads have drains which are impermeable surfaces with a reduction in infiltration but increased surface runoff = reduce lag-time = increase flood risk, Green roofs and Sustainable Urban Drainage Systems reduce the amount of impermeable surfaces.
• Soil Water Budget- annual balance between inputs and outputs of the water cycle and their impact on soil water storage. Never the same. Dependent on type, depth, and permeability of the soil and bedrock.
• Global Water Stores- hydrosphere (any liquid), lithosphere (water in crust/upper mantle), cryosphere (frozen water), atmosphere (water vapour).
• Aquifers- underground water stores unevenly distributed globally.
• Inter-Tropical Convergence Zone (ITCZ)- Low pressure zone on the equator, where the trade winds converge.
• Seasonal Changes (Global)- less precipitation and more evapotranspiration in summer, reduced water flows due to ice and reduced interception in winter.
• Storm Events (Global)- sudden rainfall increase, flooding and low replenishment of stores but not a long term change.
• Droughts (Global)- major stores depleted and flow activity decreases. May turn into a long-term change is climate change isn't reduced.
• El Nino is a natural phenomenon that occurs every 2-7 years and is caused by the warming of the ocean surface thus causing warm temperatures.
• La Nina is a cooling of the Pacific Ocean that causes a shift in the trade winds and a decrease in rainfall in the tropics, thus cooler temperatures. These could become more common with climate change
• Cryospheric processes (global)- glaciers and icecaps store freshwater in accumulation so with these meting from climate change, sea levels rise.
• Farming Practices (Global)- ploughing causes an increase in infiltration, arable farming increases interception and evapotranspiration, pastoral compacts soil reducing infiltration and increasing runoff, irrigation removes water from rivers decreasing their flow.
• Land use Change (Global)- deforestation reduces interception and evapotranspiration but infiltration increases, construction reduces infiltration and evapotranspiration but increases runoff.