I saw this paper when it was published in 2017 but didn't pay much attention to it at that time. Then Tim Smith posted it to the Sustainable Water Resources website a while ago, alerted his followers, and it seemed a lot more appealing. I enjoyed it and found the modeling approach useful in a complicated basin.
Freund, E.R., K.C. Abbaspour and A. Lehman, Water Resources of the Black Sea Catchment Under Future Climate and Land Use Change Projections, Water 2017, 9(8): 598; doi:10.3390/w9080598
Abstract
As water resources become further stressed due to increasing levels of societal demand, understanding the effect of climate and land use change on various components of the water cycle is of strategic importance. In this study we used a previously developed hydrologic model of the Black Sea Catchment (BSC) to assess the impact of potential climate and land use changes on the fresh water availability. The BSC model was built, calibrated, and validated against observed daily river discharge for the period of 1973–2006 using the Soil and Water Assessment Tool (SWAT) as the modeling tool. We employed the A2 and B2 scenarios of 2017–2050 generated by the Danish Regional Climate Model (HIRHAM), and four potential future land use scenarios based on the Intergovernmental Panel on Climate Change (IPCC)’s special report on emissions scenarios (SRES) storylines, to analyze the impact of climate change and land use change on the water resources of the BSC. The detailed modeling and the ensemble of the scenarios showed that a substantial part of the catchment will likely experience a decrease in freshwater resources by 30 to 50%.
Summary
Combinations of two regional climate scenarios and four regional landuse scenarios were incorporated in the current study to explore the possible future impacts of climate and landuse changes on water resources of the Black Sea Catchment. The landuse scenarios were driven by the IPCC’s special report on emissions scenarios (SRES) corresponding to four marker scenarios that represent different global socio-economic development pathways. The climate scenarios were generated from the Danish Regional Climate Model (RCM) (HIRHAM) for the IPCC’s SRES A2 and B2 scenarios (HS and HB scenarios respectively). On average, the climate scenarios suggested a 5–15% decrease in future long-term average annual precipitation in most parts of the catchment. The decrease in precipitation is more pronounced in the HS scenario. According to the HS climate scenario, the Western part of the catchment (Danube Basin) will experience a decline in precipitation by 25%. As the historic precipitation records are large in this region, this is expected to have a large impact on the water resources of the entire region, and leaves the catchment with a significant net decrease of precipitation. Both scenarios suggest an increase in temperature by up to 2 °C with a west to east gradient. The extent of changes in temperature is more severe in the HS scenario as compared to the HB scenario.
We also quantified the impacts of combined climate and landuse changes on freshwater distribution in the BSC. As suggested by the ensemble of scenarios, on average, the catchment is expected to experience a decrease in its blue water and green water storage resources, while the green water flow (evapotranspiration) increases in some parts of the catchment and decreases in other parts (Figure 7, Figure 8 and Figure 9). In addition, the decrease in fresh water resources in areas with high temporal variability in their water resources component (mainly in low lying countries around the Black Sea, such as Romania and Ukraine and the Russian part of the catchment) increases the vulnerability with regard to fresh water resources in these regions.
In our analysis, climate change had more pronounced effects on water resources, especially blue water, as opposed to the landuse change. To see the detailed effect of landuse change on the water resources component, it is beneficial to look at the water cycle at the HRU level, where the landuses are identical. This will give a true measure of landuse change impacts on water resources. The strength of the current work is the application of combined landuse and climate change scenarios. However, the study neglects the future changes in soil parameters over time, which accompanies changing landuses. Accounting for these changes will increase the confidence in the projected results, and needs to be further investigated.
An additional concern is the use of two regional climate scenarios (HS and HB) in model prediction while pursuing a thorough investigation based on the combined effect of many other Global Climate Models or Regional Climate Models would reflect climate model uncertainties, and hence is recommended. The study however, provides the basis to improve societal capabilities to anticipate and manage water resources both today and in the future climate change environment in the Black Sea Catchment.
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