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A Simple Model for Runoff Predictability
Roman Olson,Axel Timmermann,June-Yi Lee,Soon-Il An 한국기상학회 2021 한국기상학회 학술대회 논문집 Vol.2021 No.10
Recent work has identified potential multi-year predictability in soil moisture (Chikamoto et al., 2015). Whether this long-term predictability translates into an extended predictability of runoff still remains an open question. To address this question we develop a physically-based zero-dimensional stochastic runoff model. The model extends previous work of Dolgonosov and Korchagin (2007) by including a runoff-generating soil moisture threshold. We consider several assumptions on the input rainfall noise. We analyze the applicability of analytical solutions for the stationary probability density function (pdf) and for the waiting time for runoff under different assumptions. Out results suggest that knowing soil moisture provides important information on the waiting time for runoff. In addition, we fit the simple model to the daily NCEP1 reanalysis output on a near-global scale, and analyze the fitted model performance. Over many tropical regions, the model reproduces the simulated runoff in NCEP1 reasonably well. More detailed analysis over a single gridpoint illustrates that the model, despite its simplicity, is able to capture some key features of the runoff time series and pdfs of a more complex model. Our model exhibits runoff predictability of up to two months in advance. Our results suggest that there is an optimal predictability “window” in the transition zone between runoff-generating and dry conditions. Our model can serve as a “null hypothesis” model reference against more complex models for runoff predictability.
Projected Heat Wave Characteristics over the Korean Peninsula During the Twenty-First Century
신종수,Roman Olson,안순일 한국기상학회 2018 Asia-Pacific Journal of Atmospheric Sciences Vol.54 No.1
Climate change is expected to increase temperatures globally, and consequently more frequent, longer, and hotter heat waves are likely to occur. Ambiguity in defining heat waves appropriately makes it difficult to compare changes in heat wave events over time. This study provides a quantitative definition of a heat wave and makes probabilistic heat wave projections for the Korean Peninsula under two global warming scenarios. Changes to heat waves under global warming are investigated using the representative concentration pathway 4.5 (RCP4.5) and 8.5 (RCP8.5) experiments from 30 coupled models participating in phase five of the Coupled Model Inter-comparison Project. Probabilistic climate projections from multi-model ensembles have been constructed using both simple and weighted averaging. Results from both methods are similar and show that heat waves will be more intense, frequent, and longer lasting. These trends are more apparent under the RCP8.5 scenario as compared to the RCP4.5 scenario. Under the RCP8.5 scenario, typical heat waves are projected to become stronger than any heat wave experienced in the recent measurement record. Furthermore, under this scenario, it cannot be ruled out that Korea will experience heat wave conditions spanning almost an entire summer before the end of the 21st century.