Fig 1.
A map of the Philippines showing the coloured climatic type (I-IV) according to the Coronas classification [5–7].
The darker shaded areas on the map highlight the locations of the 24 basins that were included in this study, while the named points represent the basin outlets. The bar plot in the upper left corner represents the ranked total area of each of the 24 basins, while the graph in the lower left corner shows the period of available measured hydrological data used for model calibration for each basin.
Fig 2.
The probability density function (top) and cumulative distribution function (bottom) of the Gumbel distribution [22] (Eqs 2 and 3).
The black and red curves show the effect of an increasing mu, whereas the black and green curves show the effect of an increasing β. An increase in μ is associated with an increase in magnitude, while an increase in β is linked to an increase in the range.
Fig 3.
Water balance for the four different seasons according to the interpolated Eraint dataset is shown in the middle.
The four figures show the water balance for Dec-Feb (top-left), Mar-May (top-right), Jun-Aug (bottom-left) and Sep-Nov (bottom-right). Surrounding this are the plotted model calibration results that compares the measured data series (blue shading) with modelled ones (box-plots). The blue lines represent the median of the measured data series, whereas the blue shaded areas represent the inter-quartile range. R2 and volumetric efficiency (VE) are also presented in each of the plots.
Fig 4.
Yearly average water balance produced by the BCM2, CNCM3 and MPEH5 GCMs for A1B (top row) and A2 (bottom row) scenarios in comparison with the baseline.
A positive number (%) indicates an increase of available water, a negative number indicates a decrease. The (μ1/2) and β of the Gumbel distribution were determined for all basins using Eq 3. An increase or decrease in median streamflow compared to the baseline is displayed with a percentage in the box-plot, while an increase (+) or decrease (-) in variability (β) is also shown in the box-plot.
Fig 5.
For each basin under each scenario, the minimum, median, maximum and upper and lower quintiles were calculated and compared with the baseline scenario.
An increase in streamflow was indicated with a green bar and a decrease with a red bar. The different lengths of the horizontal bars indicate the number of scenarios with an increase or decrease for the dry (left) and wet (right) season.
Fig 6.
The 2 (black, blue), 10 (red, turquoise) and 100 (green, pink) year return flows were calculated for all scenarios in the 24 basins.
An increase or decrease in return flow is expressed as a percentage compared to the baseline scenario. Return flows for the dry period are shown in the white box and return periods of the wet season in the gray box (note the difference in scale). The dots on the right of each plot indicate the GCM and scenario used (refer to the legend).