Precipitation

PRECIPITATION - is probably the process that is intuitively most obvious. We deal with precipitation in our everyday life when we decide whether we might need an umbrella when going out for the day. The amount of precipitation is what we are concerned with when building a hydrologic model. It is also important to know in what form (liquid or solid - rain or snow) the precipitation will arrive.

Precipitation is recorded by most of the metheorologic stations in mm/day or inches/day. A sample data sheet for precipitation registered at Baltimore Washington Airport, MD in 1996 looks like this:

0.0T stands for traces, which means that the precipitation was recorded at levels below measurment accuracy. To convert inches to meters - the unit that we use in our model - we need to multiply the data by 0.0254. In many cases you can find metheorologic data for your area at the National Climatic Data Center (NCDC). For example, going to this site you can choose Maryland and find the station at Baltimore Washington Airport and then generate a graphic for the table shown above:

You can then download the data in numeric format to use in your model. Data for temperature, wind, humidity are also available from that web page. Temperature is important for us to decide whether precipitation that comes is rain or snow. See the SNOW/ICE model to describe this process.

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