EQ2 Revision Cards 5.4 Flashcards
What is a drought?
A drought is an extended period (season, year, several years) of deficient rainfall relative to the statistical multi-year average for a region. 38% of the world has some level of drought
What weather does high and low pressure bring?
low pressure brings clouds and rain, hot air rises and cools, forming clouds
high pressure brings dry weather, and either hot or dry depending on the weather
What weather is found at the ICTZ?
it is a belt of low atmospheric pressure so there is lots of rain due to warm air rising and condensing, therefore forming rain
how does the ICTZ migrate and how does this bring rain?
at the ITCZ the air rises as a result of intense heating by the suns energy; there is also high evaporation, especially from oceans. it therefore causes an alternating wet season (when it arrives) and dry season (when it moves away) in some world regions
why might the ICTZ rains fail?
sometimes the subtropical high pressure zones associated with the descending part of the convection cell block the high humidity, rain bearing masses associated with the ICTZ
meterological drought
the degree of dryness compared to ‘normal’ precipitation
agricultural drought
insufficient water for crops, so they wilt without irrigation
hydrological drought
where drainage basins suffer shortfalls
what happens in an el nino year?
on average every 7 years the warm water in the western pacific is pushed eastwards towards the west coast of South America. Wherever this mass of warm water is there is increased rates of evaporation and precipitation. In contrast areas of cooler water brings drier weather.
what happens in a la Nina year?
a niña occurs when the warm mass of water is pushed even further west than normal which causes drought in Peru and California for example.
how does an increased population lead to drought?
more people need more food. this means that more livestock and crops are needed, both of which take large amounts of water to maintain
