Radial drainage -a pattern of streams radiating from a central point or area e.g. off a mountain.

Radiation -the emission of energy as electromagnetic waves.

Radiation fog -a fog formed when warm moist air is cooled to the dew point by the ground.

Rain -liquid precipitation from the atmosphere in drops of at least 0.5mm in diameter.

Rain gauge -an instrument used to quantify the amount of rain falling in a particular location over a period of hours. Consists of a beaker marked out in millimeter intervals and a funnel leading into it. The beaker will be set in open ground to avoid water from drips or splash.

Rainshadow -the area on the leeward side of a mountain range which experiences drier conditions than the windward side. This is due to the air being drier as it has experienced condensation and precipitation on the windward side, plus the fact that the air will be sinking and therefore warming meaning relative humidity is falling and condensation cannot occur.

Rainsplash -soil erosion caused by the force of impact of raindrops.

Raised beach -a relict beach left dry by a relative fall in sea-level.

Ramsar Convention -The Convention on Wetlands of International Importance especially as Waterfowl Habitat held at Ramsar in Iran in 1971. Now known as the Convention on Wetlands. Seeks to identify, conserve and use wisely, areas of wetland that may be under threat from human encroachment. The Convention entered into force in 1975 and had 158 signatories lodged with UNESCO by 2009. www.ramsar.org

Ranching -vast, extensive livestock farms, usually found in remote, marginal areas which are not viable for other types of farming.

Range -in human geography, the maximum distance that people are willing to travel to obtain a good or service. Accuracy is limited by multiple local factors plus the subjective nature of the idea, but generalizations can be drawn.

Rank-size rule -the size of a settlement is inversely proportional to its rank i.e. the second largest city is half the size of the largest etc. If the largest city is much larger than all others, primacy exists. If two cities are broadly similar and larger than all others then it is said to be a binary situation.

Rationalization -the reorganization of a company to increase efficiency, usually by cutting costs especially labour costs.

Ravine -deep, steep-sided valley, gorge or cleft cut into a rocky landscape.

Raw materials -unprocessed inputs to an industrial process.

Reforestation - is the restocking of existing forests and woodlands which have been depleted, with native tree stock.

Reclaimed land -artificial land created in coastal areas.

Recreation -any activity people do during their leisure time. Some definitions require it to be activities away from home but that take up less than a day, after which they become tourist activities.

Recreational forest -forests maintained for recreation activities such as bird-watching, cycling, horse-riding, camping etc.

Recycling -the re-use of materials that would otherwise be deemed rubbish.

Redevelopment -the regeneration of urban areas that have fallen into poverty and disrepair. May involve renewal of existing infrastructure, or wholesale demolition and rebuilding.

Red tide -a bloom of surface algae, red in colour, found in coastal waters when a heavy nutrient load is washed from the land stimulating the algal growth.

Reduction -a chemical reaction involving the removal of oxygen.

Refraction -the tendency for waves to become more parallel to the coastline as they approach it. Caused by the slowing of waves at their base as they enter shallower water.

Refugee -a person who flees their home country through a fear of persecution on the grounds of race or religion, or membership of some other group.

Regelation -the refreezing of water into ice after pressure which caused it to melt is released.

Regeneration - see redevelopment.

Region -an area defined from its surroundings by common characteristics of physical landscape, economy or function.

Regolith -rock material that has been weathered from the original bedrock.

Rejuvenation -the increased erosional activity of a river brought about by a relative fall in sea-level which means the river must flow further and at increased gradient thus giving it more energy.

Relative humidity -ratio of water vapour in the air compared to the maximum possible at that temperature and pressure, expressed as a percentage. 

Relief -the shape of the land particularly as it pertains to elevation.

Remembrement -the consolidation of fragmented land parcels, split by inheritance practices over many years, back into larger units.

Remote-sensing -the study of the surface from data gathered at high altitude by photography and other technology carried on aircraft and satellites.

Rendzina -a thin soil developed on limestone or chalk bedrock.

Renewable resources -flows or living things which are either never-ending or grow quickly enough that their use does not lead to exhaustion.

Replacement rate -the fertility rate required to maintain a population at its current size. It is 2.1 children per woman to allow both mother and father to be replaced.

Reservoir – a body of water usually held behind a dam. Reservoirs can also be held in underground compartments. Usually multi-purpose such as holding freshwater supply for increased water security, flood control and/or recreational use.

Residential area -an area where the dominant land-use is for homes.

Residential type -the housing tenure of an area: owner-occupied, rented privately, or rented from the government.

Resource -anything that we use for survival in the first place and wealth generation in the second. May be natural, economic or human.

Resource management -the control of resources so that they do not become depleted or exhausted.

Respiration - The process in which an organism uses oxygen for its life processes and gives off carbon dioxide.

Resurgence -the reappearance of a river at the surface after it has spent some time running underground. Common on limestone areas where the limestone is underlain by an impermeable rock.

Retailing -sale of goods and services to the public.

Retail park -an out-of-town centre which allows several stores to operate around some shared resources such as car park and restaurants.

Ria -the flooded lower valley of a river caused by a relative rise in sea-level to form a small inlet.

Ribbon lake -long, narrow, shallow lake formed in the bottom of a glacial trough due to a segment of over-deepening and/or blocking by deposits such as terminal moraine.

Richter scale -a measure of the total amount of energy released during an earthquake. Runs from 1 to 10 on a logarithmic scale i.e. each level is ten times stronger than the one below.

Riffle -a bar-shaped deposit on a channel bed, midstream.

Rift valley -a valley created by the subsidence of land between two parallel faults undergoing tensile forces which pull them apart.

Rilling -a series of small channels which form on a slope after heavy rainfall. Each channel may only be a couple of metres wide and half a metre deep, but they can develop into gullies if rainfall events are particularly frequent. Slopes are often put at danger after ploughing.

Rime -very heavy frost created when fog touches surfaces which are below 0˚C

Risk equation – a mathematical representation of the factors involved in calculating risk expressed as ( magnitude or frequency of event x vulnerability / capacity to cope ).

River -an overland flow of water which forms a vital link in the hydrological cycle.

River capacity -the maximum amount of load a river can carry.

River capture -when the headwaters of one river are able to generate headward erosion and then break into another river channel and divert the flow into the new channel.

River cliff -steep slope on the outer bend of a river where erosion allows for undercutting.

River profile -see long profile.

River regime -the variation in discharge over a year.

River terrace -remnants of previous floodplains left higher than the existing river channel by increased erosion due to rejuvenation.

Roche mouton -lit. sheep-like rock. Where a more resistant rock is passed over by a glacier the rock around it is removed more quickly leaving it protruding from the valley floor. The upglacier side is smoothed by abrasion and covered by striations. The downglacier side is rough due to plucking.

Rossby waves -the wave-pattern of flow of the westerly winds which blow in the upper atmosphere. Thought to be the result of diversion of air flow around the Rockies and Andes, they change in both number and amplitude throughout the year. Have a crucial impact on pressure systems in the troposphere and thus on mid-latitude climate.

Rostow model of growth -after W.W. Rostow who identified five stages of development in a national economy:

• traditional society -mainly agricultural with limited, low-tech industry

• pre-conditions for take-off -capital investment in one or two industries along with investment in agriculture to free up labour.

• takeoff -rapid growth in manufacturing, decline in agricultural employment. Development of infrastructure.

• drive to maturity -self-sustained economic growth and prolonged urbanization.

• age of mass-consumption -expansion of service industry and decline in manufacturing.

Rotational movement -slip or slide over a curved path.

Run-off -all water leaving a drainage basin.

Rural -lit. of the countryside.

Rural depopulation -the net movement of people to urban areas.

Rural settlement -small settlements such as hamlets and villages, up to market towns which are tied to the countryside by function. The distinction between rural and urban is increasingly unclear as people increasingly move away from urban areas and into rural settlements.

Rural-urban migration -the movement of people from rural areas to urban areas.