Floods and Droughts Flashcards
what does MQ mean?
mean or average flow
what does HQ mean?
absolute peak flow (e.g. per year)
what does Q90 mean?
discharge that is exceeded at 90% of time (indicator of low flows)
what is Q10?
discharge that is exceeded at 10% of time (indicator of high flows)
what is a flow duration curve?
plot that shows the percentage of time that flow in a stream is likely to equal or exceed some specified value
what does a steep slope on a flow duration curve mean?
high variability
what is a hydrologic regime?
characteristic hydrological behavior of a basin by plotting monthly average flows throughout the year
what are Monthly Pardé indices?
calculate the hydrologic regime with this equation:
mean flow of a specific month/ mean of all months
what is the hydrological definition of a flood?
a rise, usually brief, in the water level in a stream to a peak from which the water level recedes at a slower rate
what are the two related indicators of floods?
high water level and peak flow
how can floods be expressed in discharge measurements?
maximum daily flow or absolute peak flow
what are the main causes of floods?
- heavy rain or long-lasting rainfall that leads to complete saturation of all soils
- large weather systems
- temporal overlap of single flood waves from individual subbasins
how are floodplains important ecological systems?
they help attenuate flood waves, they are usef for agriculture, they trigger ecological processes and they shape the river channel by flushing out or delivering sediment
does forest cover decrease flooding?
it has been shown that forest cover does reduce local flooding from small storm events in headwater watersheds. however, over a longer time scale, with more extreme rainfall events, and for a larger river catchment, its flood-diminishing effect decreases
** the development on floodplains means that when natural flood events occur, they cause the loss of human life and property
what is a drought?
no universally accepted definition
- condition of insufficient moisture caused typically by a deficit in precipitation over some time period
what are the 5 different types of floods?
- meteorological drought: prolonged period with less than average precipitation
- agricultural drought: deficit in soil moisture affecting crop production
- streamflow drought: deficit in river discharge or surface water storage
- groundwater drought: deficit in groundwater storage
- socioeconomic drought: conflict of water shortage and water management demand
what are the main causes of droughts?
climatic factors (decrease precipitation due to large-scale circulation patterns, increase evaporation due to intensified solar radiation, climate change) + poor land-use practices and water mismanagement (land degradation + desertification)
what is the relationship between forest change and drought?
it is variable, in some cases dry season decreases with the presence of trees, in others, it increases because it increases water infiltration (young forests and plantations, often with water-consuming trees dry up water flow)
