EQ2- 5.5+6 surpluses + climate change Flashcards
areas susceptible to flooding
small river basins
-saturated soils so less infiltration
-steep slopes increase fast run off
-lots of tributaries so more water available to flood
-over topping/bankful stage = flooding stage
areas susceptible to flooding
urbanised areas
-impermable concrete so cannot infiltrate/perculate
-increase surface run off
-fewer trees to intercept
-drainage systems can overfill- pluvial flooding= no river system but sheer excess of water so drains cannot cope w quanitiy of water
areas susceptible to flooding
river estuaries
-river meets sea risk of coastal flooding
-storm surges
-EG- river thames
areas susceptible to flooding
low lying parts of flood plains
-get them in middle/lower- tributariy water connects to main channels here
-increased discharge in lowerpart of river
meteorological causes of flooding
flash flooding
-floods occur following intense torrential storm
-in uk w/extreme rainfall events in summer months
-intensity of rain exceeds capacity of river to cope w/amount of water
-sept 2016: one caused travel chaos in england as thunderstorms deposited almost half a months worth of rain in some places within hours
meteorological causes of flooding
monsoon rainfall
-a seasonal change in direction of prevailing winds of a world region
-south + south east asia between may+ sept (warm moist air from sw indian ocean blows to india, sri lanka,bangladesh)
-july 2016: heacy MR in phillipines led to flooding landlsides + evacuations in villages just NW of the capital Manila
-in this case a larger than normal low pressure system brought heavier rain than usual
meteorological causes of flooding
mid latitude depressions -low pressure
-this happens when polar front jet stream is meandering steadily in mid latitudes
-each depression brings 2 bands of rain :
1. showers + rain w/ warm front
2. heavier rain w/ cold front
-the ground may be able to absorb some of rainfall but when groundwater + through flow cannot transfer the water quickly it becomes saturated
-so rain turns to runoff + this ups rivers discharge = floods
meteorological causes of flooding
melt water + glacial outbursts
-flooding can occur when snow melts + water cant infiltarte into soil/ground surface
-winter 2013: norfolk police reported flood caused by snowmelt + ice after very mild, wet + windy weather caused rapid thawing
-combination of heavy rain + thaw brought flooding in some places
-red river in dakota usa 2009: record flood leevls due to rise in temp causing SM
jokulhaup
-a type of glacier outburst flood that occurs when dam containing a glacial lake fails
surface water flooding
-floodijng occurs when intense rainfall has insuffecient time to infiltarte teh soil, so flows overland
groundwater flooding
-flooding that occurs after the ground has become saturated from prolonged heavy rainfall
flash flooding defintion
-flood w/ an exceptionally short lag time: often mins or hours
human causes of flood
deforestation
reduce interception+evapotranspiration
-^surface run off-ensures rain reaches river channels faster=more flashy hydrographs
-^rates of erosion (soil)-more sediment in river so less capacity to hold water
-eg nepal+tibet known to be ^ frequency + magnitude of floods in bangladesh from ganges
human causes of flood
urbanisation
-more impermable surface so ^ rate of surface run off into river via urban drainage system
-river lag times shortened by urban drainage systems-aim to transfer water effeciently into water corses so that streets dont flood or have standing wtaer]
-bridges+culkets
human causes of flood
floodplain mismanagment
-alterations at 1 point in drainage basin can cause negative imapcts further downstream
-hard engineering is designed to reduce frequency of floods
-HE- embankments to ^ channel capacity but may simply operate by transferring discharge to unprotected areas or choke points downstream
human causes of flood
flood plain drainage
-common in dveeloped countries to provide land for agriculture+ expend urban areas
-drainage processes reduce natural storage capacity of floodplain, especially where natural wetland r lost
-land may shrink as dries out, get lower+ more susceptible to flooding
climate change
precipitation input
-higher frequency og intense rain events mainly over land areas
-warmer temps more rain is falling as rain rather then snow
-sahel is an exception
climate change
evaporation + evapotranspiration
-lower atmosphere becomes warmer
-ET rates rise resulting in increase in amount of mositure circulating throughout troposphere
climate change
soil moisture
-warmer temps have led to increase drying of land surface in some area w/the effect of an increased incidence + severity of drought
-sahel region has been experincing harsher drought conditions
climate change
run off + stream flow
-a 1degree c rise in temp could increase global run off by 40%
-seasons w highest water demand (summer + fall) are impacted by reduced availability of fresh water
-
climate change
groundwater flow
-surface water levels dry to much it can drop
-so more pressure to extract from aquifers + groundwater flows
climate change
reservoir, lake + wetland storage
-increase evaporation leads to reduced water in these stores
-eg pantel brazil
climate change
permafrost
-stores methane: 21 more times warmer than co2
-changes in phsyical climate at high latitudes, primarily rise in air + ocean temperature are leading to permafrost degrationin northern areas
-impacts groundwater supply
climate change
snow
-the length of snow cover season has decreased; especially in northern hemisphere in last 50-100 years
-snowmelt is easier
climate change
ice
-ice stores in retreat
-glaciers have retreated globally since end of ‘little ice age’
-thinning of glacier due to melting ice has accelerated since 1970s
-this is due to rapid temp rise + changes in precipitation type
climate change
ocean
-in areas of ocean warming an increased evaporation will occur
-there is limited evidence however more cyclones are being generated
-eustatic + isostatic adjustement
Anthropogenic Global Warming
-due to ^ greenhouse gases in atmosphere . could lead to many diff impacts affecting the hydrological cycle:
-if temps rise=period between ENSO cycles (now every 2-3 years) could decrease=affect south usa+australia
-global temo ^=^evaporation=droughts + increasing water scarcity.
-BUT, for some=^ convectional rainnfall + enhanced tropical cyclone/depression intensity=more intense+periodic flooding
CC= reduce inputs, reduce stores but may increase outputs w/in the hydrological cycle:
-Less precipitation
- Less water available in stores
-Reduced size of snow and glacier mass
-Water Table drops (height/ capacity of groundwater store) and Aquifer stores deplete
-High rates of evaporation
-More frequent cyclones and monsoons
storm desmond
uk
2015
- it made an atmospheric river, bringing in moist air from the Caribbean to the British Isles.
- so, rainfall from Desmond was unusually heavy.
- heavy rain n strong winds were caused by an area of low pressure which arrived on Friday from the Atlantic.
- £500m damage
causes of storm desmond
- urbanisation
- thing soils n veg=low interception n heavy grazing
- non porous n igneous rocks= more surface runoff
- number of tributaries
- heavy prolonged rainfall=saturate soils,
- steep sided mountain valleys=faster runoff
impacts storm desmund
- £500mn damage
- 100 bridges damaged
- ## 5000 homes flooded
