Does warm weather increase the chances of an upset stomach?
In warmer weather, organic material tends to “go off” more quickly, due to more rapid bacterial and fungal proliferation. (e.g. bread goes mouldy more quickly in summer). This means that in warm weather dogs are more likely to pick up semi-rotten decaying material which is more likely to upset their digestive system. It’s also likely that dogs socialise more in warmer weather (owners take their dogs for walks more often) and this will lead to quicker spread of viral infections through the dog population.
For both these reasons, vets often see a spike in gastro-intestinal upsets in dogs during spells of warmer weather.