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:

Thr=Tav+TmxTmn2cos(0.2618(hr15))T_{hr} = \overline T_{av} + \frac{T_{mx}-T_{mn}}2 cos(0.2618 (hr-15)) 1:1.3.1

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

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

Definition
Source Name
Input Name
Input File

TmxT_{mx}: Daily maximum temperature (°C\degree C)

max temp

tmpmax

TmnT_{mn}: Daily minimum temperature (°C\degree C)

min temp

tmpmin

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