How Often?

Explore probabilities of future rainfall and temperature events based on past seasons.

Rainfall, temperature, radiation, heat sum, risk assessment

HowOften? allows you to explore probabilities of future rainfall and temperature events based on past seasons. It tests for a rainfall or temperature condition (greater than or less than), a specified threshold value in a set number of days for a period of month(s). It is designed for decision-makers who use probabilities of past rainfall and temperature conditions to manage business risk.

It allows decision-makes to answer questions such as:

  • What is the change of a sowing event based on amount of rainfall over 5 days?
  • How often is a heat sum achieved in a set period of time?
  • What is the probability of temperature being below a critical level for germination or flowering?
  • What are the chances of a planting opportunity next month?
  • How often will I get enough rain to fill my soil profile (assuming a certain fallow efficiency)?
  • What are the chances of wet weather during harvest in November?


HowOften? uses long-term rainfall data from SILO, (1949 to present for iOS versions and 1900- 2010 for stand-alone version) a specified variable (rainfall, temperature), a threshold value and a sample period. Long-term rainfall data for HowOften? (stand-alone) are downloaded within the program or accessed from the SILO data drill (


HowOften? presents results as a text answer, as a fire-risk chart and histograms showing time series of events and number of events recorded each year.


HowOften? was first developed by Steve Glanville and David Freebairn of theAgricultural Production Systems Research Unit in 1998 and updated on the iOS Smart Phone software  for Managing Climate Variability Research and Development Program in 2012. The Queensland Department of Science, Industry, Tourism and Innovation (DSITI) maintain the Silo long term climate database. Silo base data is sourced from the Bureau of Meteorology.


Freebairn, D.M. and S.F. Glanville (1998). HOWOFTEN?. A computer program for calculating daily rainfall probabilities. Agricultural Production Systems Research Unit, QDNR -QDPI-CSIRO, Toowoomba, Queensland.