from datetime import datetime


def get_gldas_start_date(product):
    """
    Get NOAH GLDAS start date.

    Parameters
    ----------
    product : str
        Product name.

    Returns
    -------
    start_date : datetime
        Start date of NOAH GLDAS product.
    """
    dt_dict = {
        "GLDAS_Noah_v20_025": datetime(1948, 1, 1, 3),
        "GLDAS_Noah_v21_025": datetime(2000, 1, 1, 3),
        "GLDAS_Noah_v21_025_EP": datetime(2000, 1, 1, 3),
    }

    return dt_dict[product]