Why are stomata more abundant on the lower epidermis?

All surfaces of the leaf have some amount of stomata for regulating gas exchange for photosynthesis. However, the lower epidermis (the underside of the leaf) has more, because it is more often in the shade and so it is cooler, which means evaporation won't take place as much. read more

To avoid huge transpirational losses plant adapt this strategy to have more number of stomata on the lower epidermis, as it receives lesser sunlight and hence lower evaporation of water from this side compared to upper epidermis. read more

If rain falls on a leaf the water could block stomata if they were on the upper epidermis. Water would be less likely to stay on the lower epidermis. Result: stomata on the lower epidermis should work more reliably. read more