Sem#2 Chap 7 Flashcards
Hazards of Droughts
- Worldwide, drought leads to more fatalities than any other weather phenomenon [Fig 16 -14].
It affects larger areas, over longer timescales, more than all other types of hazardous weather.
Almost every region of the World is adversely impacted by drought at some time or another. [Tables 16-1, 16-2.]
Drought produces complex effects that accumulate slowly and interact with the demand humans and other forms of life place on the water supply.
The impacts of drought are erosion of dry soils by winds, damage to soil productivity as the soil dries and cracks [Fig 16-15], and loss of vegetation.
What is the other name for a drought?
Creeping
Drought is often accompanied by _______
Famine
Can we predict droughts? Physical triggers or initiation mechanisms
No we cannot predict droughts.
However he do know factors that maintain and intensify a drought.
Meteorological/Climatological Drought
refers to an unusually long period during which precipitation is below normal for a particular area.
Agricultural Drought
refers to a period of deficient moisture in the soil layers from which crops and other plants normally draw their water.
Agricultural droughts often precede hydrological drought, since water in the near-surface soil layer is generally the most important for plants
Hydrological Drought
describes an unusual deficiency of groundwater and/or streamflow (ie, water levels are below normal for the area.)
Socio-economic Drought
occurs when the moisture shortage is sufficiently large that it directly affects people.
Direct Effects: Availability/Demand for economic goods or food or water.
Effect may differ depending on how the land was previously used.(Ie for farming or housing)
Palmer Drought Severity Index
Most widely used indices to indicate drought in a region.
Based on a ground water balance that includes the supply of water by precipitation nd stored water, and the depletion of water and temperature dependent evaporation, recharge of subsurface water, and run off.
Standard Precipitation Index
Another index for assessing the intensity of drought.
Measures the deviation of precipitation from the average value for a particular area.
Agricultural Drought Specifics:
*Agricultural drought considers the impacts water supply on plant growth. Dry periods during a summer may not impact plant growth if water is available in the soil.
*A commonly used index for estimating water available for plants (soil-water budget) is the Palmer Drought Index that compares estimates of the soil- water budget to average
conditions.
Meteorological Drought Specifics:
Defining meteorological drought is regionally specific. A common tool is the Standard
Precipitation Index (SPI), which compares precipitation at a site to historical records as
accumulated over a period of time (usually several
months).
Hydrological Drought Specifics:
*Hydrological drought is indicated by dropping water levels in reservoirs, rivers and lakes. Meteorological droughts do not often immediately impact water levels in lakes and streams.
*Hydrological drought is more closely tied to human activities due to the demands that
humans place on water supply.
Meteorological Causes of Droughts:
Read Slide #21 - 23 Lect#7
Meteorological Conditions for Drought: In north America.
- The normal summertime pattern of sea-level pressure contains two dominant features in the middle latitudes of North America:
The subtropical high-pressure centres of the North Atlantic and the North Pacific [Fig 26.2A SHW].
- The subtropical high centres generally weaken (i.e., their pressures decrease) with altitude, and at upper-levels, they yield to the west-to-east circulation pattern of the jetstream.
- The jetstream during the summer, while considerably weaker than during the winter, is typically located north of the subtropical surface highs.
Isobars (new,sorta)
Demonstrates the typical sea level pressure patterns observed. (In July)
A high pressure system has ________
clear skies that allow warming of the lower atmosphere in the core/center of the high pressure.
Read over Fig26.3
Slide 28 -31
Read over Fig 26.4 SHW
that slide and the next
Pro’s and Cons to Irrigation
Pro: Allowed for mass growth of crops
Cons: Can cause droughts.
- also note that hydrological droughts, when grounds water becomes saline, it cannot be used for agriculture anymore.
(Slide 36-37, chap #7)
Meteorological Conditions for Drought EASTERN NORTH
Occurs when a high pressure center inhibits moist air flowing to the East Coast. Can happen in two ways,
Circulation from the large continental high-pressure system generally brings air to the east coast from dry west or north west.
Semi permanent high-pressure cell over the western Atlantic migrates to the south east coast, Called the Bermuda High. Brings a broad southwesterly flow over the east coast.
Slide 39 Look at figure
(Understand it)
Meteorological Conditions for Drought in WESTERN NORTH
The characteristic feature of the weather pattern conducive to drought in the West is a persistent ridge in the jetstream over the West Coast [Fig 26.14 SHW].
When such a ridge is present, the storm track on the western side of the ridge extends fro the eastern Pacific into the Gulf of Alaska.
- Storms more onshore well to the north of the West Coast of the United States and British Columbia.
In addition, an upper-level ridge of the West Coast is generally associated with a surface high-pressure centre to the east of the ridge [Fig 16.14 SHW].
Look at Figure
Slide 41 lect #7
