Discussion#
This chapter provides an analysis of the results obtained in the previous chapter. Section 4.1 discusses the uncertainties of the hydrological model PCR-GlobWB. Section 4.2 compares the results obtained in Chapter 3 to other researches. Lastly, Section 4.3 discusses future research directions.
Uncertainties of PCR-GlobWB#
This research relies on a hydrological model rather than direct measurements, introducing
potential for uncertainties in the results. These uncertainties arise from various factors, including
input data, spatial scales and model structure.
The input data consists out of a parameter set and a forcing dataset. For example, the ERA5 datasets may contain errors in observed data or missing data, which could account for some extreme outliers. Similar concerns apply to the CMIP6 dataset, as inaccuracies and unavailable data can be the origin of uncertainties in the simulations. Additionally, the spatial scales of the datasets differ. ERA5 and CMIP6 operate on grids of varying resolution. The coarser the resolution of CMIP6, especially after rescaling to align with ERA5, can temper the precision of the results and potentially affecting their accuracy.
The structure of the model can also be a source of uncertainties. The model incorporates many hydrological components, and not all of which vary over time. For instance, as mentioned in Section 2.2, the irrigation factor in PCR-GlobWB is constant over time. In reality, this factor fluctuates. Therefore, it is a static representation and it likely influences the simulation outcomes.
The results of groundwater recharge simulation, presented Sections 3.1 and 3.2, possibly contain an uncertainty. The low groundwater recharge values suggest potential issues with either the model, the input data, or the interpretation of the simulated outputs. These values are near zero, and indicate an absence of groundwater recharge, which is inconsistent with reality. This suggests that the model’s outcome or the quality of the data may be flawed. It is important to acknowledge the model that is simulating future climate scenarios is not an exact reflection of reality.
Comparing the Results with Other Researches#
To evaluate the results of this research it is compared to a report of the USGS, researching the same region with comparable future climate scenarios. The United States Geological Survey published a report in 2020, containing research on the trends in recent historical and projected climate data from 2020 to 2100 for the Colorado River basin. The projected climate data evaluated 97 Coupled Model Intercomparison Project phase 5 (CMIP5) projections and all Representative Concentration Pathways (RCP) from year 1951 to 2099. In this research, it is expected that the lower Colorado River basin will experience a slight decrease in precipitation, and an increase in temperature. The projected groundwater infiltration decreases rapidly, compared to the historical data.
These findings align with the results generated by the PCR-GlobWB model, which similarly predict a decline in groundwater recharge under more extreme future climate scenarios. The alignment of these results reinforces the reliability of the PCR-GlobWB model.
Future Research#
To achieve more reliable and accurate outcomes in hydrological modelling, several factors are in need of further investigation. One approach is to apply and compare multiple hydrological models. By incorporating a range of models, researchers can identify similarities and differences in the outcomes, improving the accuracy of the results.
Additionally, more focus on important hydrological factors could enhance the reliability. For example, analysing how temperature changes with each climate scenario, analysing shifts in precipitation patterns and evaluating changes in discharge. Understanding the hydrological cycle in more detail can give more insight into the effect on groundwater recharge.
As mentioned in Section 2.5, this study simplified the groundwater flow by assuming it occurs in a single direction. While this simplifies the results, it does not accurately reflect reality. The groundwater flow is often a multiple directions and is influenced by several factors. Incorporating the realistic groundwater flow would yield more accurate groundwater recharge results.
Lastly, to obtain the future climate simulations, three SSPs (SSP1-2.6, SSP2-4.5 and SSP5-8.5) were used. However, CMIP6 contains many more scenarios. Therefore, in future research, evaluating more scenarios can lead to a higher reliability.