Are the yellowish discharges that appear when it's hot, and often occur in women, and are described as a thin yellow water that exits with a slight urge, impure (najis) or pure (tahir)?

If these yellow discharges are usual, not expelled with desire, and not menstruation, then ritual cleansing (istinja') from them is obligatory because they are impure. Then ablution (wudu') for prayer is required because they nullify it. As for normal white discharges, they are pure according to the more sound opinion, but they do nullify ablution.