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BIO220H1 (238)
Lecture 20

Lecture 20 Notes

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University of Toronto St. George
James Thomson

Lecture 20 Hydrological Cycles Slide 39Drier as you go west Farming in NA was fuelled by people seeking good opportunities lot of land available in the west but those dreams were shattered by the fact that things get drier as you go westMigration coincided with drought when rainy years stopped wetdry there was widespread failure of farms people realized those areas are not suitable for dryland agriculture What do you do about this Change your agriculture or change the weatherPeople didnt give up growing crops they tried to bring in irrigation waters so they could take water from somewhere and put it on the fields Slide 40Ecosystem cycling of waterWater behaves like an element due to its high stability HO bonds are strongOceanswhere most of the water isPrecipitation taken by plants and transpired by leaves can also evaporate from rocks or exposed surfacesoSome of it could drain down into aquifers or underground water tables Slide 41Although we have a lot of water most of it is salty and in the oceans and immaterial to the productivity for terrestrial plants and animals which can be achieved by fresh waterLakes and rivers have freshwater but thats only a small amount on the surfaceMore freshwater as groundwaterhard to get requires drilling wellsThere is a small amount in the atmosphere at any given time Slide 42We have cycles where evaporation tends to be highest around equator High pressure zones around 30 degrees N and S where its dryThe precipitation that the world gets is very patchy on a latitudinal and longitudinal basisOverall the land surfaces in the world have more water coming in than they have evaporating off but in some places this ratio is switched and those are the dry placesRechargeenough rainwater filtering down the layers of the soil to be adding water to the underground storage Dischargepumping out water from wells faster than its being restored
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