Read hourly weather data from met files

[byzheng]

In the experiments of controlled environments, the weather data are generally recorded in sub-daily interval (e.g. hourly). As the variation of climate in the CE, the daily variation of temperature is not similar as open environments and not always equals to the target temperature. See an example below.

It would be useful if we can read the hourly temperature for thermal time and any other functions. I conduct a simple analysis to illustrate one of the problem I noticed.

The thermal time are calculated using two methods for an experiment in CE using cardinal temperature in wheat, i.e. x: 0, 26, 37 and y: 0, 26, 0

• hourly: use hourly temperature to calculate the thermal time and them sum up by daily. This method is similar as 3 hourly method in APSIM with 24 points instead of 8 point.
• daily: calculate the daily minimum and maximum temperatures using min and max functions from records in the daily temperature, then calculate the daily thermal time using 3 hourly method in APSIM.

The difference of thermal time between daily and hourly methods are ranged from -2 to 2 degree days. The thermal times from daily method are higher than the ones from hourly method in this case. The accumulative difference could be up to 130 degree days during one season.

PS: There might be other methods to convert hourly into daily temperatures used by APSIM. Happy to learn and test them.

[zur003]

Hourly data would also be very useful for erosion modelling, as daily average values generally don't provide good estimates of the short-term intensity of rainfall or wind.