Answer :
generally in summer water is mostly go out in the form of sweat etc. but in winter due to the cool temperature the rate of evaporation of water from our body in the form of sweat etc gets decreased. such that the process of going the water from skin becomes slow down. so the water level with waste materials in our body becomes quite high than water present in our body in summer. due to the high amount of water in bladder, more urine is grouted in winter.
In summer season (due to high temperature) , there is a loss in the quantity of water in our body due to the excretion of water in the form of sweat and also due to evaporation. But in winter(due to a relatively low temperature), the rate of evaporation of water decreases and also water is not lost in the form of sweat and there is more quantity of water in our body. Thus, much water from the body, is liberated in the form of Urine.