I find the transition from cold to hot or visa versa can initiate bladder spasms. Being cold and shivering can mess with the pelvic floor tightening up as well.
Hot tea in the winter is good...mostly.
Also, during hot weather you are shedding water through your skin to keep cool. I find that I am more active outside as work demands. So, I appreciate it can appear that I leak less but, it is mainly that I drink less for my level of activities.