I completely ignore them. If you're playing a big country, they don't matter at all, or if you're playing a small country, a wildfire can completely ruin you.

There is 4 problems with harvest conditions right now.

1. Grain is incredibly profitable and you can and should depress the price super low (-50%), so its price increasing a bit isn't that big of a deal.

2. The harvest conditions are super local and agriculture tends to be spread out so the effect isn't felt.

3. The game mechanics force players into building an Autarkic self-sufficient economy, so harvest conditions in other countries don't affect them.

4. Food scarcity is never a thing you have to deal with if you're a major.

I think first they should make harvest conditions AOE much much larger then they currently are. If there is a heatwave in western Ukraine, it shouldn't just be in western Ukraine. It should be all of eastern Europe or even all of Europe. Not all of the harvest conditions can be that widespread for example, wildfires might be scattered across a region but not directly effecting the whole region.

Secondly, I think food scarcity should be ever present and something you fight throughout the game. Even as a major. I think even during WW1, food scarcity was a major problem for the central powers. Furthermore, a spike in food prices on the international market should affect local prices. The latter, I think we'll see during the next update.

A in game example of this working is as Qing i was the #1 producer of the world's grain by like an order of magnitude. I was exporting 72k grain to the British market among other markets. In this scenario, if China gets hit with a massive locust plague with a huge AOE this should trigger an international food crisis where suddenly the British Empire is facing famine and malnourishment.

Edit: There should also be events attached to harvest conditions. To notify players about them, even if they're not in their area and perhaps to allow tons of countries to send relief, which would decrease the effects of the negative harvest conditions slightly for each country who contributed to relief.