Note that the law doesn't stipulate how you have to assess your takeoff performance
And you can't if you're not taking off from the paved, level, dry runway typically specified on the chart.
djpil in an earlier post provided information on how to factor the take off distance for runways that were not as described on the chart, but I'm not aware of any OFFICIAL document giving our newly minted 172 PPL guidance, or anybody else for that matter.
In a previous life used to operate out of wheat paddocks with standing stubble. Sure extends the run.
FB, you raise a good point about temperature. In summer the aircraft gauge could get up to 60C from heat soak if it had been standing for a period of time. No other source of info. Prop wash after start used to bring it back.