Consequently, for every 4,000 feet above sea level you are receiving about one index unit more of UV radiation. Other factors may cause this number to increase as well. Snow is very reflective in the UV part of the spectrum and can reflect as much as 90 percent. At higher locations, the air has fewer pollutants to absorb the UV radiation. At the beach, the light colored sand and water also reflect UV radiation.
People usually wear less clothing at the beach and spend a lot of time in a horizonal position.
Each factor may increase the area and directness of the UV radiation with respect to your skin. The UV Index forecast is VERY dependant upon the cloudiness forecast. However, there are several factor that modify UV radiation, including haze, pollution, and aerosols. If you are travelling to lower latitudes or to the southern hemisphere, you can call your local forecast office for UV information prior to travelling. Seasonal variability can be quite high.