*4.2. Bias Correction and Downscaling of Future Climate Scenarios*

The future climate projections of the selected climate models needed to be downscaled and corrected for biases, before further use in hydrological model simulation. Therefore, as a first option, all the dynamically downscaled climate projections available for UIB were checked for whether any Regional Climate Model (RCM) projections were available that have dynamically downscaled projections for the already shortlisted GCM at first or second position in the ranking. We found that, for both RCPs, the outputs of at least three (3) CORDEX-SA experiments were based on the GCMs ranked 1st in our study (IPSL-CM5A-MR\_RCA4, MPI-ESM-LR\_RCA4 and NorESM1-M\_RCA4). The GSM CanESM2, which is at 2nd rank for RCP4.5 and at 1st for RCP8.5, has dynamically downscaled projections under CORDEX-SA experiments, CanESM2\_RegCM4-4. The output of one CORDEX-SA experiment (GFDL-ESM2M\_RCA4) was based on GFDL-ESM2M, which is ranked at 2nd position for both the RCPs in our study (Tables 4 and 5).

It was decided to utilize the available dynamically downscaled data for our selected GCMs, ranked at 1st or 2nd positions. Therefore, five CORDEX-SA experiments (Table 6), including IPSL-CM5A-MR\_RCA4, MPI-ESM-LR\_RCA4, NorESM1-M\_RCA4, Can ESM2\_RegCM4-4, and GFDL-ESM2M\_RCA4 were selected for further processing and bias correction. These five GCMs were dynamically downscaled by CORDEX using two different RCMs (RCA4 and RegCM4). Their RCM outputs are at a considerably finer scale (0.44◦) than the source GCMs.



#### *4.3. Projected Changes in Temperature and Precipitation*

The five (5) selected (CORDEX-SA) RCM outputs were further bias-corrected using the "distribution mapping technique" [43] for RCP4.5 and RCP8.5 for two sets of durations, i.e., mid-century (2041–2070) and end-century (2071–2100). Major properties of the downscaled projections are given in Table 7.


**Table 7.** Future precipitation and temperature projections from 5 GCM models, 2 RCPs and 2 periods.

The downscaled projections show changes in temperature ranging from 2.3 ◦C to 6.33 ◦C for RCP4.5 and of 2.92 ◦C to 9.0 ◦C for RCP8.5. The downscaled and bias-corrected precipitation ranges from a minor increase of 2.2% for the drier scenarios to as high as 15.9% for the wet scenarios. Thus, both temperature and precipitation show increases, as do the extremes, since the probabilities of the wet days are projected to decrease, while the precipitation intensities are projected to increase unanimously by both RCPs.

The spatial distribution of the projected future changes for precipitation and temperature across the UIB also show certain distinct trends. Thus, the precipitation (Figure 5) over the mid-century (2041–2070), as well as the late century (2071–2100), reveals for all scenarios a remarkable decrease in the southeastern parts of the basin, but an increase in the northeastern parts. This decrease/increase is particularly intense for the "Dry-Warm" and the "Median" scenarios over the late 21st century.

**Figure 5.** Spatial distribution of projected precipitation change across the UIB over the mid (2014–2070) and the late- (2071–2100) 21st century for 5 models and 2 RCPs. The figure is arranged in a tabular form where the 1st and 2nd column represent projected change in precipitation for RCP 4.5, for the mid-century (2014–2070) and the late-century (2071–2100), respectively, while the 3rd and 4th columns show the projected change in the mid-century and the late-century precipitation for RCP 8.5, respectively. The rows represent the climate models used.

The spatial distribution of the projected changes for in temperature (Figure 6) also shows similarities across all scenarios, with the northern and northwestern parts of the basin exhibiting higher increases, while the eastern and southern parts experience a comparatively smaller temperature increase.

For RCP8.5, the projected temperature changes appear to be very high over the late 21st century and this occurs under all scenarios, especially for the "Warm" scenarios, with an almost uniform spread across the whole UIB. The projected temperature changes range for all RCPs and the two 20th-century periods from a minimum increase of 3.76 ◦C (NorESM1-M\_RCA4, RCP4.5, Period: 2041–2070) to a maximum increase as high as 10.4 ◦C (IPSL-CM5A-MR\_RCA4, RCP8.5 and period: 2071–2100).

**Figure 6.** Similar to Figure 5, but for temperature changes.
