Adding a link with nid in Global: results summary in Views
Because the header uses the default Drupal PHP interpreter, Views variables aren't available there like they are in the arg php code. You can get them by doing something like this:

&lt;?php
global $current_view;
print $current_view-&gt;args[0];
?&gt;


Update: If you want to use PHP in views header, you can go to configure header, select "Global: Text area" and have to change text format to PHP code; you have to first install the PHP filter module.

Also if you use Global: Text area with PHP filter enabled this should work:

&lt;a href="%/events"&gt;@total&lt;/a&gt;