Bananas like to grow in temperatures between 26-30 deg C, in high humidity, which means your 45 degrees is a bit much for it, particularly if it's in an unshaded position. They grow best in 'jungle' conditions, meaning with other plants giving some relief and shade from hot midday and afternoon sun. They also don't like being exposed to a lot of wind, so in other words, your plant will do best if its surrounded and slightly shaded by other plants in such a hot climate as yours. If it is in the ground, then a thick mulch (on ground which is already damp) will help, but you do need to provide some shading for it during the hottest part of the day. Obviously, extra watering, possibly misting it with water as often as possible, will help, but that shading is the most essential thing.