1:1.3.2 Hourly Air Temperature

Air temperature data are usually provided in the form of daily maximum and minimum temperature. A reasonable approximation for converting these to hourly temperatures is to assume a sinusoidal interpolation function between the minimum and maximum daily temperatures. The maximum daily temperature is assumed to occur at 1500 hours and the minimum daily temperature at 300 hours (Campbell, 1985). The temperature for the hour is then calculated with the equation:

$T_{hr} = \overline T_{av} + \frac{T_{mx}-T_{mn}}2 cos(0.2618 (hr-15))$ 1:1.3.1

where $T_{hr}$ is the air temperature during hour $hr$ of the day ($\degree C$), $\overline T_{av}$ is the average temperature on the day ($\degree C$), $T_{mx}$ is the daily maximum temperature ($\degree C$), and $T_{mn}$ is the daily minimum temperature ($\degree C$).

Table 1:1-6: SWAT+ input variables that pertain to hourly air temperature.

Definition	Source Name	Input Name	Input File
$T_{mx}$: Daily maximum temperature ($\degree C$)	max temp	tmpmax	.tmp
$T_{mn}$: Daily minimum temperature ($\degree C$)	min temp	tmpmin	.tmp