But it doesn't change the URL based on the year, it just updates the tables on the webpage. So what's going on behind the scenes? You can click anywhere on the page and "View page source" to find out. Here's the part that's important.
This is the drop-down list, which exists in a PHP form object. The form sends an API post request when the user hits the "Go" button. Since there is a name associated with this form, newYear, we can pass along that variable right in the URL to get back the years we want.