Journal of Korea Water Resources Association (한국수자원학회논문집)

Korea Water Resources Association (한국수자원학회)
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Quantitative uncertainty analysis for the climate change impact assessment using the uncertainty delta method

기후변화 영향평가에서의 Uncertainty Delta Method를 활용한 정량적 불확실성 분석

  • Lee, Jae-Kyoung (Innovation Center for Engineering Education, Daejin University)
  • 이재경 (대진대학교 공학교육혁신센터)
  • Received : 2018.07.25
  • Accepted : 2018.10.31
  • Published : 2018.11.30
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Abstract

The majority of existing studies for quantifying uncertainties in climate change impact assessments suggest only the uncertainties of each stage, and not the total uncertainty and its propagation in the whole procedure. Therefore, this study has proposed a new method, the Uncertainty Delta Method (UDM), which can quantify uncertainties using the variances of projections (as the UDM is derived from the first-order Taylor series expansion), to allow for a comprehensive quantification of uncertainty at each stage and also to provide the levels of uncertainty propagation, as follows: total uncertainty, the level of uncertainty increase at each stage, and the percentage of uncertainty at each stage. For quantifying uncertainties at each stage as well as the total uncertainty, all the stages - two emission scenarios (ES), three Global Climate Models (GCMs), two downscaling techniques, and two hydrological models - of the climate change assessment for water resources are conducted. The total uncertainty took 5.45, and the ESs had the largest uncertainty (4.45). Additionally, uncertainties are propagated stage by stage because of their gradual increase: 5.45 in total uncertainty consisted of 4.45 in emission scenarios, 0.45 in climate models, 0.27 in downscaling techniques, and 0.28 in hydrological models. These results indicate the projection of future water resources can be very different depending on which emission scenarios are selected. Moreover, using Fractional Uncertainty Method (FUM) by Hawkins and Sutton (2009), the major uncertainty contributor (emission scenario: FUM uncertainty 0.52) matched with the results of UDM. Therefore, the UDM proposed by this study can support comprehension and appropriate analysis of the uncertainty surrounding the climate change impact assessment, and make possible a better understanding of the water resources projection for future climate change.

기존 기후변화 영향평가에서 발생하는 불확실성에 대한 연구들은 전체과정에서 총 불확실성과 그 전파에 대한 것보다 각 단계별 불확실성에 초점을 맞추어 연구가 진행되었다. 따라서 본 연구에서는 first-order Taylor series expansion에 기반하여 전망의 분산을 이용하는 Uncertainty Delta Method (UDM)를 제안하였으며, 이 방법은 각 단계별 불확실성 정량화와 증감정도, 단계별 불확실성 비율, 총 불확실성의 전파 과정 제시가 가능하다. 본 연구에서는 기후변화 영향평가 과정의 단계별 불확실성 정량화와 전파과정 분석을 위해 미래 2030년부터 2059년까지를 대상으로 2개 배출 시나리오, 3개 GCM, 2개 상세화기법, 2개 수문모형을 사용하였다. 결과를 분석하면, UDM을 이용한 총 불확실성은 5.45(배출시나리오: 4.45, 상세화기법: 0.45, 상세화기법: 0.27, 수문모형: 0.28)이며, 배출 시나리오의 불확실성(4.45)이 가장 크게 나타났다. 불확실성은 각 단계를 거칠수록 증가하는 것으로 나타났다. 이러한 결과는 어떠한 배출시나리오를 선정하느냐에 따라 미래 수자원전망이 매우 달라질 수 있음을 의미한다. 다음으로 Hawkins and Sutton (2009)가 제안한 Fractional Uncertainty Method (FUM)을 이용한 기후변화 영향평가 불확실성 분석에서 가장 불확실성이 큰 요인은 배출 시나리오(FUM 불확실성: 0.52)이며, 이 결과는 UDM 결과와 동일하게 나타났다. 따라서 이 연구에서 제안한 UDM은 기후변화 영향평가에서의 불확실성 이해와 적합한 분석 및 미래 기후변화 대비 보다 나은 수자원 전망이 가능하도록 기여할 것으로 판단된다.

Keywords

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Fig. 1. Basic concept of application of the uncertainty delta method (UDM) in the climate change impact assessment

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Fig. 2. The relative importance of each source of uncertainty in climate change impact assessment: (a) Uncertainty changes significantly with region, forecast lead time, and the amount of any temporal meaning applied, (b) Fractional uncertainty in decadal mean surface air temperature prediction for global mean

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Fig. 3. Uncertainty propagation in the climate change impact assessment by employing the UDM

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Fig. 4. Fractional uncertainties of the three sources of uncertainty and total uncertainty in the climate change impac assessment over lead time (2030∼2059)

Table 1. Characteristics of the study basin

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Table 2. Description of emission scenario, GCM, downscaling technique, and hydrological model stages in the climate change impact assessment

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Table 3. Precipitation and streamflow projection results from January 2030 to December 2059(a) Precipitation projection

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Table 4. Uncertainty quantification results for each stage in the climate change impact assessment using the uncertainty delta method (UDM)

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Table 5. Uncertainty quantification of three uncertainty sources in the climate change impact assessment using the fractional uncertainty method (FUM)

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