Why do we feel thirsty in hot weather?

Hot weather triggers your hyphothalamus and skin. You be become flushed (blood rushes to the surfaces of your skin) this helps the body to prevent over heating. Also, the body perspires, heat is lost through water, because it has a high heat capacity. Water is being lost in order to prevent over heating, but water is an important functional component of the body. The hypothalamus then triggers the cognitive part of your mind to be "thirsty".

Because in hot weather we sweat to try and keep cool, but the only problem is the sweat may be cooling you down, but it is making you lose fluid from your body. So you feel thirsty because the sweating has made you lose water, so you need to hydrate yourself. :)

Hope this helps!

Its physics. We need energy to function, our one of our energy fuels is water. When its hot our body needs to maintain a certain temperature, so it cools itself up by transpiring. However, when we lose water, our body is also asking for us to give it back. That is why we get thirsty.