Hydro-logical Cycle

Evaporation: The physical process in which a liquid changes to a vapour. Transpiration: The process by which plants lose water vapour through the stomata (pores) on their leaves. Evapotranspiration: The loss of moisture from the Earth's surface by means of both direct evaporation and transpiration from vegetation. Condensation: The process by which water changes from a vapour to a liquid or solid. Precipitation: The deposition of water in a solid or liquid form on the Earth's surface from atmospheric sources. Leaf drip and stem flow: The processes by which water flows off plants to the ground surface. Infiltration: The movement of water from the surface into the soil. The rate will depend on the permeability of the soil and its level of saturation. Percolation: The movement of water from the soil into the permeable bedrock or parent material. Surface runoff: The water leaving a drainage basin area in a stream or river channel.

Throughflow: The downslope movement of water through the soil or regolith (weathered bedrock). Groundwater flow (or base flow): The movement of water through the parent material or bedrock. Precipitation = Evapo-transpiration + Surface Run-off + Changes in Storage

Spatial Variations in Hydrographs -

Differences in Geology - Permeable rocks increase the percolation rate so less rainfall becomes surface runoff. Lowering the peak discharge and increases the lag time. The opposite occurs with impermeable rock

Differences if relief - High runoff rates will increase with higher relief

Differences in drainage basin shapes- Long Basin - lower and longer peak discharge Circular Basin - Shorter lag time and higher peak discharge Differences in drainage basin size - Small drainage basins, will have a shorter lag time and possibly a higher peak discharge

Differences in soil type - Thin soils mean they rapidly reach their field capacity, encouraging short lag times

Difference in drainage density - Strongly influenced by geology and antecedent events

Difference in land use - Woodland will increase interception and therefore lead to lower levels of surface runoff

Temporal differences -

Difference in the duration of rainfall - Prolonged rain fall leads to the rate of infiltration exceeding the soil's field capacity and becomes saturated

Difference in the intensity rainfall - Heavy rainfall may exceed infiltration capacity and lead to surface runoff

Snowmelt- Rapid melting can often lead to a rapid rise in discharge

Seasonal changes in vegetation - Less evapotranspiration in winter, deciduous trees will have low interception

Difference in temperature - Increase evaporation, reducing surface run-off

Precipitation -

Warm, moist air forced to rise, then the air pressure falls allowing the air to expand (Adiabatic cooling ) The cause of rainfall includes orographic, frontal and convectional processes