Filtering a WP_Query meta_query by numeric values isn’t working

Try an array of arrays in your meta query.

$args = Array(
    'post_type'         => 'event',
    'posts_per_page'    => -1,
    'meta_key'          => 'event_date',
    'orderby'           => 'meta_value_num',
    'order'             => 'ASC',
    'meta_query'        => array(
         array(
                'key'       => 'event_date',
                'compare'   => '>=',
                'value'     => intval(strtotime(date('Y-m-d'))),
                'type'      => 'numeric'
         )
    ),
);

$query = new WP_Query( $args );