year=date('Y') with error_reporting

{?php
declare(strict_types=1);
$year=date("Y");

The code above works fine.
The code below says Strict Standards : date() [[function.date]: It is not safe to rely on the system’s timezone settings. Please use the date.timezone setting, the TZ environment variable or the date_default_timezone_set() function. In case you used any of those methods and you are still getting this warning,

{?php
declare(strict_types=1);
error_reporting(-1);
$year=date("Y");

how can I set the “year” correctly ?

What’s the problem with solving this with tips you got?

Please use the date.timezone setting, the TZ environment variable or the date_default_timezone_set() function

Thank you