Code php function.date

Salut a tous, Aidez moi s'ils vous plais, Voila j'ai un nouveau pc avec wind 7 quand je fait un aperçu de mes codes PHP en web locale j'ai ces messages d'erreur suivant:

Pour mon site JOOMLA
Warning: date() [function.date]: It is not safe to rely on the system's timezone settings.
You are *required* to use the date.timezone setting or the date_default_timezone_set() function. In case you used any of those methods and you are still getting this warning, you most likely misspelled the timezone identifier. We selected 'Europe/London' for '1.0/DST' instead in C:\xampp\htdocs\webfr\installation\installer\helper.php on line 289

Pour autres sites
Warning: date() [function.date]: It is not safe to rely on the system's timezone settings. You are *required* to use the date.timezone setting or the date_default_timezone_set() function. In case you used any of those methods and you are still getting this warning, you most likely misspelled the timezone identifier. We selected 'Europe/Berlin' for 'CEST/2.0/DST' instead in /home/noxblog/public_html/blog/rss.php on line 11

depuis je cherche la solution je trouve pas aidez moi s'ils vous plait

Mercie d'avance.