# Shared Flashcard Set

## Details

2GEOG landscapes and water
Water Balance
11
Geography
04/05/2010

Term
 watershed scale
Definition
 the scale at which we consider water blanance
Term
 what is a watershed (aka drainage basin or catchment)?
Definition
 the entire area that drains to a point along a river   any precipitation that falls in the watershed potentially can flow out in a river   any precipitation that falls outside the watershed does not contribute to streamflow within the watershed   there are an infinate number of watersheds that can be identified along any river   any point along the river can be chosen as the outlet to the watershed, and the watershed above that point identified
Term
 what is a divide?
Definition
 a boundary between watersheds
Term
 what is the water balance equation for any watershed?
Definition
 inputs = outputs + change in storage   P = Q+ET+ΔS   or precipitation = runoff + evapotranspiration + change in storage
Term
 what does ΔS refer to?
Definition
 the change in storage   any additions or removals of water from soil water or groundwater
Term
 what is a tipping bucket gague?
Definition
 the most common type of rain gague
Term
 what is the potential ET (PET)
Definition
 used to get an estimate of the possible ET   the amount of water that could be evaporated or transpired from a surface if the water were available   calculated from the air temperature, humidity, and wind speed - all of which are commonly measured at meteorological stations
Term
 what is teh actual ET (AET)?
Definition
 the amount of ET that actually occurs, and will always be less than PET because ET can't happen no matter how hot, dry, or windy the day is if there is no water in the ground to evaporate
Term
 what are the water balance components for one watershed over the course of a year?
Definition
 monthly totals of precipitation (P), potential evapotranspiration (PET), and soil water storage (S), are plotted along with AET and the runnoff (Q).   the AET and S are computed from the measured P and Q and the PET calculated from weather data
Term
 what is drought?
Definition
 a deficiency of precipitation over an extended period of time   ex: a season or more   we lable a period of lower precipitation drought when it affects some activity, group, or ecosystem   how long the precipitation deficiency must go on or how severe the deficiency must be to be labled a drought depends on the region and the system effected   no single standard quantitative measure that defines a drought
Term
 what is the Palmer Drought Severity Index (PDSI)?
Definition
 a commonly used index to asess drought   computed with a formula from temperature and rainfall info for a region   normal conditions have a PDSI of 0 while whet conditions score positive values (up to 6) and dry conditions score negative values (down to -6)   the more negative the PDSI, the more severe the drought   the strength of the PDSI is that it is standardized to local climate
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