Hydrological modeling of a Mongolian River basin under current and changed climate conditions using permafrost conceptualizations

Heerma, Kor (2013) Hydrological modeling of a Mongolian River basin under current and changed climate conditions using permafrost conceptualizations.

Abstract:Water resources are globally under severe pressure, mainly due to population growth, economic development and climate change. The process of permafrost degradation resulting from global warming increases the vulnerability of all climate dependent sectors affecting the economy in high-latitude Asia. The adverse consequences of climate change are likely to disrupt mountain and highland ecosystems in Central Asia. The consequences for downstream agriculture, which relies on water for irrigation, will (very) likely be unfavorable. The same applies to Mongolia, which has a strong need of developing its own infrastructure and water resources in a more efficient way. Mongolia is a country predominated by mountain ranges with a continental climate, which promote occurrence and development of permafrost regions. Since permafrost is a thermal condition, it is potentially sensitive to climate change and human activities. Impacts of climate change coupled with human pressure for water are upsetting the balances in Mongolian river basins and the situation is forecasted to get worse. In this study, a rainfall-runoff model is developed based on the general structure of the HBV model. The model has proven to be applicable in mountainous areas under extreme and cold climate conditions, as is common in Mongolia. The model is able to cover the most important runoff generating processes using a simple and robust structure, and a small number of parameters. The Buyant River basin in Western Mongolia is used as a case study to simulate discharges for the current climate and predict monthly changes under different climate change scenarios. Permafrost conditions are adapted in the conceptual HBV model in this study, resulting in four different permafrost conceptualizations. Two conceptualizations describe the general structure of the HBV model and take permafrost conditions into account by calibrating under non-permafrost conditions. The other two conceptualizations incorporate freezing and melting functions which simulate the storage and melting of ice in the soil. A further distinction is made between the elevation zones (single and multiple) in the mountainous Buyant River basin. Due to lack of meteorological input data, 5 years of calibration and 5 years of validation are used. Results of the calibration are moderate to good for the conceptualizations simulating permafrost conditions all year round, whereas the conceptualization with one elevation zone performs better in the validation period than the conceptualization with multiple elevation zones. The output of four different Global Circulation Models (GCMs) and three different emission scenarios are used to assess the uncertainty in climate change for the Buyant River basin. The delta approach method is used to translate output from GCMs to climate time series for future conditions. The outputs of these 12 climate change scenarios are combined with the most appropriate HBV conceptualization to assess the climate change impacts on the future discharges of the Buyant River. The application of the single elevation zone with permafrost conditions conceptualization indicates that, under the present estimated climate scenarios of global warming for the period 2080-2100, the runoff in the summer will decrease, while the discharge in spring is likely to increase in the Buyant River basin. However, uncertainties in future climate change impacts are rather high as the incongruity between GCMs and emission scenarios and between different GCMs cause distinct runoff projections, the former being the cause for yielding low and the latter for high variability. Whilst the variability in the models and the coarse resolution yield projections that are at best conjecture, future refinement of these models may yield in more accurate and realistic scenarios.
Item Type:Essay (Master)
Royal HaskoningDHV
Faculty:ET: Engineering Technology
Subject:56 civil engineering
Programme:Civil Engineering and Management MSc (60026)
Link to this item:http://purl.utwente.nl/essays/62666
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