Floods and Droughts

Question 1

what does MQ mean?

Answer 1

mean or average flow

Question 2

what does HQ mean?

Answer 2

absolute peak flow (e.g. per year)

Question 3

what does Q90 mean?

Answer 3

discharge that is exceeded at 90% of time (indicator of low flows)

Question 4

what is Q10?

Answer 4

discharge that is exceeded at 10% of time (indicator of high flows)

Question 5

what is a flow duration curve?

Answer 5

plot that shows the percentage of time that flow in a stream is likely to equal or exceed some specified value

Question 6

what does a steep slope on a flow duration curve mean?

Answer 6

high variability

Question 7

what is a hydrologic regime?

Answer 7

characteristic hydrological behavior of a basin by plotting monthly average flows throughout the year

Question 8

what are Monthly Pardé indices?

Answer 8

calculate the hydrologic regime with this equation:

mean flow of a specific month/ mean of all months

Question 9

what is the hydrological definition of a flood?

Answer 9

a rise, usually brief, in the water level in a stream to a peak from which the water level recedes at a slower rate

Question 10

what are the two related indicators of floods?

Answer 10

high water level and peak flow

Question 11

how can floods be expressed in discharge measurements?

Answer 11

maximum daily flow or absolute peak flow

Question 12

what are the main causes of floods?

Answer 12

• 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

Question 13

how are floodplains important ecological systems?

Answer 13

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

Question 14

does forest cover decrease flooding?

Answer 14

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

Question 15

what is a drought?

Answer 15

no universally accepted definition
- condition of insufficient moisture caused typically by a deficit in precipitation over some time period

Question 16

what are the 5 different types of floods?

Answer 16

• 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

Question 17

what are the main causes of droughts?

Answer 17

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)

Question 17

what is the relationship between forest change and drought?

Answer 17

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)