def WI_statewide_eqn(Qm, A, Qr, Q90):
    """Regression equation of Gebert and others (2007, 2011)
    for estimating average annual baseflow from a field measurement of streamflow
    during low-flow conditions.

    Parameters
    ----------
    Qm : float or 1-D array of floats
        Measured streamflow.
    A : float or 1-D array of floats
        Drainage area in watershed upstream of where Qm was taken.
    Qr : float or 1-D array of floats
        Recorded flow at index station when Qm was taken.
    Q90 : float or 1-D array of floats
        Q90 flow at index station.

    Returns
    -------
    Qb : float or 1-D array of floats, of length equal to input arrays
        Estimated average annual baseflow at point where Qm was taken.
    Bf : float or 1-D array of floats, of length equal to input arrays
        Baseflow factor. see Gebert and others (2007, 2011).

    Notes
    -----
    Gebert, W.A., Radloff, M.J., Considine, E.J., and Kennedy, J.L., 2007,
    Use of streamflow data to estimate base flow/ground-water recharge for Wisconsin:
    Journal of the American Water Resources Association,
    v. 43, no. 1, p. 220-236, http://dx.doi.org/10.1111/j.1752-1688.2007.00018.x

    Gebert, W.A., Walker, J.F., and Kennedy, J.L., 2011,
    Estimating 1970-99 average annual groundwater recharge in Wisconsin using streamflow data:
    U.S. Geological Survey Open-File Report 2009-1210, 14 p., plus appendixes,
    available at http://pubs.usgs.gov/ofr/2009/1210/.
    """
    Bf = (Qm / A) * (Q90 / Qr)
    Qb = 0.907 * A**1.02 * Bf**0.52
    return Qb.copy(), Bf.copy()