4 - precipitation and excess runoff within the water cycle ✅ Flashcards
what causes clouds
air uplift and condensation occurs and clouds form
OROGRAPHIC, FRONTAL and CONVECTION mechanisms create this
what are the effects of deforestation
- increased flood risk
- infiltration rate into the soil is 67x higher under trees compared to grassland
- devastating effects of Cumbria 2009 and Boscastle 2004 were caused by excess overland flow generated on deforested hills
what is the effect of glaciers
- mountain snow fields and glaciers act as natural reservoirs
- they store precipitation from the cool season (when precipitation falls and forms snow packs) until the warm season when most or all snow packs melt and release water into rivers
what is the bergeron findeisen process
- clouds at high altitude ( >0 degrees) have water droplets and ice crystals
- ice crystals grow rapidly at the expense of the water droplets due to rapid flux of water vapour from droplets towards ice crystals
- the ice crystals fracture as they are jostled by fast high altitude air currents.
- hexagonal ice shapes develop with larger surface areas.
- more water vapour condenses around the larger snowflake shapes, accelerating growth further
- eventually hexagonal snowflakes become too large and fall under gravity, warming as they melt to produce rain
what evidence is there for and against the bergeron-findeisen process
FOR::
- in the UK precipitation is often derived from clouds with temperatures below -5 degrees
- cloud seeding with dry ice can successfully generate rainfall
AGAINST::
- however this process cannot explain rainfall formation in the warm tropics
what is the collision process
- super sized condensation nuclei (eg large sea salt particles) provide ‘seeds’ around which water droplets form
- they are larger and heavier than normal sized droplets
- larger droplets fall and collide with smaller droplets by sweeping them in their wake and absorbing them
what evidence is there for the collision process (3)
- Langmuir carried out experimental work to produce the theory
- he argued that higher terminal velocity of large droplets allows them to overtake and absorb many smaller droplets causing rapid fusion and raindrop growth
- unexpected downpours and flash floods in arid areas demonstrate how high numbers of large raindrops can be generated quickly
what physical characteristics contribute to flooding (10)
- vegetation
- soil type
- drainage area
- basin shape
- elevation
- topography, especially the slope of the land
- drainage network patterns
- ponds, lakes, reservoirs, sinks, etc in the basin which prevent or delay runoff from continuing downstream
- prolonged precipitation and intense storms
- snowmelt
what is the main contributor to excess runoff and causes
STORMS and INTENSE RAINFALL
causes are usually frontal rainfall in winter and convectional events in summer
what can hydrographs reveal about the contribution of snowmelt to excess runoff to rivers
large peaks are the melting of snow (but storms can also contribute)
how might climate change impact snow melt in the future (4)
- recent warming of global climate has reduced accumulation and increased ablation (output) levels
- large volumes of summer melt water and a reduction in winter accumulation has led to lower storage levels in global ice cycle sheets and glaciers
- impact on drainage basins across the world is serious - seasonal river levels dropping due to a lack of meltwater from individual mountain glaciers
- hill slope changes occur as individual glaciers melt completely, depositing their encased material as moraines
what are monsoons
a seasonal change in the strongest, or prevailing winds of a region
how do monsoons work
Southeast Asia experiences two monsoon seasons
the first brings in moisture filled clouds from the Indian Ocean
the second brings cooler, dry air from eastern Asia and the Himalayan region
how could future climate change affect monsoon rainfall
- climate change could affect global precipitation patterns considerably:
increase in precipitation from increased evaporation, regular rainfall could reduced - monsoon rainfall is reducing in duration, affects India/China who rely on it for drinking and food growing
- a complete stop of the monsoon rains in central southern china and northern india:
generated by sharp heat gradients in the atmosphere where warm land meets cool ocean, blocking solar energy = aerosols cool coastal atmosphere, sap monsoons strength)
what is a condensation nuclei
condensation results in cloud formation but needs a surface to occur upon
dust and other microscopic solids in the atmosphere act as condensation nuclei
