Storm Shield uses the Significant-Change Location service (not GPS) of iOS Location Services in order to notify you of weather alerts for your current location (for more information on Apple Location Services, click here). This provides a low-power way for apps to get a device's current location without using GPS and still be notified when significant changes occur. This has a minimal effect on battery life. Battery life depends on a variety of factors such as the version of iOS your device uses, the age of your device and its battery, and other apps using your location.
If you turn off your iOS Location Services, Storm Shield will be unable to send you weather alerts for your current location. If you choose to do this, you could always set one of your five saved locations to where you are most often.
If you still choose to turn off iOS Location Services for your device, go to your device’s iOS Settings (Settings > Privacy > Location Services) then scroll through the list of apps on your device to see which apps have permission to access your location, and make your preferred changes for your device or on a per-app basis.