Garden with Insight v1.0 Help: Weather params group
Climate station elevation: Elevation of the climate station at which the current climate data was
collected. The current climate station's elevation is used in the simulation to calculate barometric pressure.
Climate station latitude: Latitude of the climate station at which the current climate data was
collected. The current climate station's latitude is used in the simulation to calculate day length and solar radiation.
Mean daily maximum temperature by month: Longterm monthly averages for daily high
temperatures, corresponding to 'seasonal' daily 'highs' on the weather forecast. Used (with autocorrelation) to generate simulated daily high temperatures. 'Smoothed'
values are interpolated from these values.
Standard deviation of maximum temperature by
month: The standard deviation of the distribution whose mean is the longterm average daily
maximum temperature per month (another parameter). Used to
generate daily maximum temperature with a normal distribution
modified by an autocorrelation matrix.
Mean daily minimum temperature by month: Longterm monthly averages for daily low
temperatures, corresponding to 'seasonal' daily 'lows' on the weather forecast. Used (with autocorrelation)
to generate simulated daily low temperatures. 'Smoothed' values are interpolated from these values.
Standard deviation of minimum temperature by month: The standard deviation of the
distribution whose mean is the longterm average daily minimum temperature per month (another
parameter). Used to generate daily minimum temperature with a normal distribution modified by an
autocorrelation matrix.
Mean total precipitation by month: Longterm monthly averages for the total amount of
precipitation (rain and snow) in each month. Affects longterm monthly averages of daily rainfall.
Standard deviation of daily rainfall by month: The standard deviation of the distribution whose
mean is the longterm average amount of daily rainfall per month (another parameter). Used to generate
daily rainfall using the skewed normal distribution (amount of skew is another monthly parameter).
Skew coefficient for rainfall by month: The long
term monthly amount of skew in the longterm monthly normal distribution of daily rainfall amounts. A
normal distribution is skewed when more than half of its area can be found above or below its mean.
Probability of wet day after dry day by month: The
probability that if yesterday was 'dry' (no rain or snow fell), rain or snow will fall today. Calculated from the number of wet days per month.
Probability of wet day after wet day by month: The probability that if yesterday was 'wet' (rain or
snow fell), rain or snow will fall today. Calculated from the number of wet days per month.
Number of wet days by month: The average number of days on which it rains in each month.
Used to determine the probabilities of a wet day after a wet day and after a dry day, which are used to
determine whether it rains on any particular day.
Mean proportion of rain falls in first half hour by month: The
average proportion of total rainfall for any rainfall event (storm) that occurs during the first halfhour.
This measure of rainfall intensity is used to determine whether the rain falls too fast to infiltrate the soil
(and thus runs off).
Mean daily radiation by month: Longterm monthly averages for daily solar radiation. Used
(with autocorrelation) to generate simulated daily solar radiation
values. 'Smoothed' values are interpolated from these monthly values.
Mean daily relative humidity by month: Longterm monthly averages for daily relative humidity.
Used (with autocorrelation) to generate simulated daily relative humidity values. 'Smoothed' values are
interpolated from these monthly values.
Mean daily wind speed by month: Longterm monthly averages for daily wind speed. Used (with
autocorrelation) to generate simulated daily wind speed values. 'Smoothed' values are interpolated from
these monthly values.
Coefficient for rainfall modified exponential distribution: Coefficient for the modified exponential rainfall
distribution, which is used when monthly standard deviation and skew for rainfall are not available. Ranges from 1.0 to 2.0; the higher the
number the more extreme amounts of rainfall are generated.
EXPK  Parameter used to modify exp rain distribution (1)
The variable EXPK is used to modify the exponential rainfall amount distribution. The modified
exponential distribution is used to generate rainfall amounts if the standard deviation and skew coefficient
are not available. An EXPK value of 1.3 gives satisfactory results in many locations.
Coefficient for wetdry probabilities given the number of wet days: A
parameter used to generate the probability of a wet day after a wet or dry day when only the number of wet
days per month has been input. Ranges from 0.6 to 0.9; a value of 0.75 is typical.
BTA  Coeff. used to est. wetdry prob. given mon. num. wet days (6,4)
The variable BTA is used to estimate wetdry rainfall probabilities if the only information available is the
average monthly number of wet days. Generally the number of wet days is much more readily available
than the wetdry rainfall probabilities. A value of .75 for BTA usually gives satisfactory estimates of the
wetdry probabilities.
Parameter for modified exponential wind speed distribution: Exponent for the
modified exponential wind speed distribution for simulating daily wind speed from monthly longterm averages. Ranges from 0.2 to 0.6 with a value of 0.5 being
reasonable.
UXP  Power Parameter of modified exp. dist of wind speed (1)
The power parameter of the modified, exponential windspeed distribution ranges from about 0.2 to about
0.6. A value of [0.50] usually gives satisfactory estimates of daily wind speed.
Years of maximum halfhour rainfall record: Another parameter describes the average proportion of total rainfall that falls during the first halfhour of storms.
This is the number of years of data used to calculate those means. Used
to calculate rainfall peak rate for runoff.
YWI  Number years of max monthly 0.5 hour rainfall record (1)
The number of years of maximum monthly 0.5h rainfall available can be obtained from the U.S.
Department of Commerce. Values of YWI available in 1982 are shown in Table I.1.
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