Their late father David kept records of the rainfall on their farm in Tuatapere since 1958 and they continued to keep the data updated after his death in 2011.
"He apparently began the records before then but never wrote them down.
"Now Eric and I have kept it up," Ms Erskine said.
By keeping track of the rainfall records, their father knew when to shift stock from the back paddock which was close to the Waiau River.
Their Westwood farm had experienced a green drought from December to March.
The grass was green but there was little soil moisture below.
"To find the last dry four-month spell we had on our farm, we had to go back to December 1973 through to March 1974 which Dad recorded as the driest years — and that’s about 50 years ago."
Though they were unsure of the exact year, the siblings recalled a time their father mentioned the weather being so dry he did farm work in his gym shoes.
They would often get calls or messages from agents and people within the neighbourhood for the rainfall level records, Eric Erskine said.
"It actually helps during those wet days when agents or neighbours are needing to know, so that’s why we do what we do."
Ms Erskine would often put up photos of her "rain book" on social media to allow followers to compare the seasons.
"I often make a comment on whether it’s above average or below for the year, so it’s a great talking point, but it is quite interesting what we have here compared to what they have over the Longwoods or up the Otahu Flats."
Weather could be completely different even for farm properties 5km away from each other, she said.
They had recently found old documentation of their farm lease which dated back to July 1915.
It was important to maintain original documentation as well as the rainfall reports of the farm as it was a part of the farm’s history, Ms Erskine said.
"It is something that is going to be here for forever, whereas if people don’t keep those records, they can get lost.
"But I think it is important to hold on to those records because you never know, one of these days you may wish that you actually held on to them," she said.
