If you don't water your lawn all summer, the hot weather will parch the grass until it's brown and withered. To parch is to dry up or wither due to sunlight or heat.
The verb parch is often used in the context of plants and people. Crops will parch during a drought. A patient's skin will parch during an intense fever. If you're a fan of cooking shows, you may hear the word used in a less dire way. A chef may "parch some corn," which basically means she will roast it lightly. Parch can also mean "to make thirsty," as in "After running a marathon in this heat, you'll feel parched."