Do I need to flush rewrite rules when creating new user if using custom author rewrite rules?

I am using custom urls for my author pages like this:

http://site.com/author_name

After I create a new user, that author page appears as not found; however, if I update my permalink structure from admin panel, the author page is found.

So, is it necessary to flush rewrite rules after a new user is created? Is there any other way?

From codex, I read that flushing rewrite rules is a very expensive task. So, I would like to avoid this. Is it possible?

EDIT:

add_filter('author_rewrite_rules', 'no_author_base_rewrite_rules');
function no_author_base_rewrite_rules($author_rewrite) { 
    global $wpdb;
    $author_rewrite = array();
    $authors = $wpdb-get_results("SELECT user_nicename AS nicename from $wpdb-users");    
    foreach($authors as $author) {
        $author_rewrite["({$author-nicename})/page/?([0-9]+)/?$"] = 'index.php?author_name=$matches[1]paged=$matches[2]';
        $author_rewrite["({$author-nicename})/?$"] = 'index.php?author_name=$matches[1]';
    }   
    return $author_rewrite;
}

add_filter('author_link', 'no_author_base', 1000, 2);
function no_author_base($link, $author_id) {
    $link_base = trailingslashit(get_option('home'));
    $link = preg_replace("|^{$link_base}author/|", '', $link);
    return $link_base . $link;
}