# Lake Ontario **URL:** \ **Category:** Factual Questions\ **Created:** [February 16, 2011, 9:25pm UTC](https://boards.straightdope.com/t/lake-ontario/571633 "2011-02-16T21:25:23Z")\ **Posts on this page:** 5\ **Page:** 2
**Author:** ![NinetyWt](https://avatars.discourse-cdn.com/v4/letter/n/cc9497/32.png) [@NinetyWt](https://boards.straightdope.com/u/NinetyWt)\ **Post date:** [February 17, 2011, 9:57pm UTC](https://boards.straightdope.com/t/lake-ontario/571633/21 "2011-02-17T21:57:57Z")
> [@Ludovic](#): > > Does most precipitation that falls on land make it into the stream system? Or could it be that a lot of it evaporates (and a tiny portion otherwise used) before it enters a stream? Depending upon the climate, some can be lost to evaporation and plant uptake, but other things to consider are land use, soil type, and antecedent moisture condition. For example, not much water will run off of dry sand. But water will just sheet off of a paved parking lot or saturated clayey loam. ---
**Author:** ![NinetyWt](https://avatars.discourse-cdn.com/v4/letter/n/cc9497/32.png) [@NinetyWt](https://boards.straightdope.com/u/NinetyWt)\ **Post date:** [February 17, 2011, 10:01pm UTC](https://boards.straightdope.com/t/lake-ontario/571633/22 "2011-02-17T22:01:20Z")
> [@Polycarp](#): > > Relevant facts: The area around the lake averages 32-64 inches annual precipitation. The lake has a surface area of 7,340 square miles. The results need to be in cubic meters/second to match the inflow rates. My figures suggested that annual precipitation on the lake surface is over 90% of the total inflow from the whole watershed, which suggests to me I applied erroneous figures. Anyone want to take a shot at it? I’m under the influence of cough syrup, but I can tell you that 99.99% of the precipitation falling on the lake will count as “runoff”. That is, if you have six inches of rain you will get six inches of runoff, on a lake’s surface. ---
**Author:** ![Sunspace](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/sunspace/32/1250_2.png) [@Sunspace](https://boards.straightdope.com/u/Sunspace)\ **Post date:** [February 17, 2011, 10:22pm UTC](https://boards.straightdope.com/t/lake-ontario/571633/23 "2011-02-17T22:22:23Z")
> [@Polycarp](#): > > Relevant facts: The area around the lake averages 32-64 inches annual precipitation. The lake has a surface area of 7,340 square miles. The results need to be in cubic meters/second to match the inflow rates. My figures suggested that annual precipitation on the lake surface is over 90% of the total inflow from the whole watershed, which suggests to me I applied erroneous figures. Anyone want to take a shot at it? Okay, lessee. (I’ve been doing this kind of stuff all week, so I’m on a roll…) If we take the higher figure of 64 inches per year annual precipitation, that’s 1.63 metres (Wow. More than I thought.) A lake surface area of 7340 square miles is 19.0 x 10[sup]9[/sup] m[sup]2[/sup]. So over the year, the lake directly receives a volume of 1.63 m \* 19.0 x 10[sup]9[/sup] m[sup]2[/sup] = 31.0 x 10[sup]9[/sup] m[sup]3[/sup] of water. But 31.0 x 10[sup]9[/sup] m[sup]3[/sup] per year = only 982 m[sup]3[/sup]/s if you average it out. Which, given the number of sunny days, means that the average rainstorm must put out a lot of water in a little time… ---
**Author:** ![RadicalPi](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/radicalpi/32/9806_2.png) [@RadicalPi](https://boards.straightdope.com/u/RadicalPi)\ **Post date:** [February 17, 2011, 10:27pm UTC](https://boards.straightdope.com/t/lake-ontario/571633/24 "2011-02-17T22:27:36Z")
> [@Polycarp](#): > > Relevant facts: The area around the lake averages 32-64 inches annual precipitation. The lake has a surface area of 7,340 square miles. The results need to be in cubic meters/second to match the inflow rates. My figures suggested that annual precipitation on the lake surface is over 90% of the total inflow from the whole watershed, which suggests to me I applied erroneous figures. Anyone want to take a shot at it? I assume that the whole lake surface gets 48 inches of rain a year. So, we’ll call it 1.22 meters. The area of the lake is 19,011 km[SUP]2[/SUP] or 19,011,000,000 m[SUP]2[/SUP]. So, that means the lake gets 23,178,000,000 m[SUP]3[/SUP] of rain a year, which works out to about 734 m[SUP]3[/SUP]/s or thereabouts. I don’t know how that compares to what you got, but I had fun calculating it, so there’s that. ---
**Author:** ![NinetyWt](https://avatars.discourse-cdn.com/v4/letter/n/cc9497/32.png) [@NinetyWt](https://boards.straightdope.com/u/NinetyWt)\ **Post date:** [February 18, 2011, 3:01am UTC](https://boards.straightdope.com/t/lake-ontario/571633/25 "2011-02-18T03:01:26Z")
> [@Sunspace](#): > > means that the average rainstorm must put out a lot of water in a little time… The amount of rainfall varies over the length (time-wise) of the storm. This will vary depending upon where the rain storm is located (geographically). In the U.S., these distributions have been [standardized](http://www.lmnoeng.com/RainfallMaps/RainfallMaps.htm) for use in hydrologic computer modeling. I’m not familiar with Canadian hydrology but I assume something similar has been developed there. [Previous page](https://boards.straightdope.com/t/lake-ontario/571633.md?page=1)