Changing climate in our lifetime: A review

Paik Kyungrock,Woo Yin San 한국수자원학회 2018 한국수자원학회논문집 Vol.51 No.11

지난 수십 년 동안, 변화하는 기후를 이해하기 위해 많은 연구가 있었고, 여러 기후 변량의 변화추세가 발견되었다. 이들 추세를 설명하기는 쉽지 않 고, 때로는 서로 모순적으로 보여지기도 한다. 다양한 기후 변량의 변화추세를 일반적으로 설명하기 위한 가설을 제시하기 위해 많은 시도도 있었다. 어느 정도 지식이 축적된 이 시점에서, 우리 시대에 진행되는 기후 변화에 대해 우리가 알고 있는 것을 되돌아보고 신중히 정리해볼 필요가 있다. 여기서는 기온, 일사량, 풍속, 증발, 강수에 초점을 맞추어 변화하는 기후에 대해 우리가 얻은 지식을 종합적으로 살펴보고자 한다. 온난화, 흐 려짐, 잔잔하기로 대변되는 주요 변화추세 및 증발의 역설, 강수 변동성의 증가를 서울 지점 자료를 예시로 들어 설명한다. 이러한 변화에 대한 이해를 근거로 수문학자와 공학자들에게 네 가지 함의를 제시하려 한다. During the last decades, considerable efforts have been spent for climate studies, in particular to better understand changing climate. In turn, several significant trends in climatic variables have been reported. Explaining such trends is challenging – some of them have been considered contradictory to another. Various hypotheses have also been suggested for general description of changing climate. At this point in time, it would be beneficial to look back and carefully recollect our knowledge about climate change. In this paper, we aim to provide a comprehensive review on our forefront knowledge in this context with focus on the trends in temperature, solar radiation, wind speed, evaporation, and precipitation. Major trends, namely warming, dimming, and stilling, are demonstrated together with evaporation paradox and increasing precipitation variability, using data at Seoul. On the basis of understanding these notions, we suggest four key implications to hydrologists and engineers.

Power-Law Behavior in Geometric Characteristics of Full Binary Trees

Paik, Kyungrock,Kumar, Praveen Springer-Verlag 2011 Journal of statistical physics Vol.142 No.4

수문학과 네트워크 과학

백경록(Kyungrock Paik) 대한토목학회 2009 대한토목학회지 Vol.57 No.6

Hybrid approach to detect water bodies and their flow paths

Kim, JongChun,Paik, Kyungrock 한국방재학회 2015 한국방재학회 학술발표대회논문집 Vol.14 No.-

Detection of water bodies and their flow paths is elemental process of terrain analysis in any application related with surface water. Several algorithms have been proposed for automatic extraction of surface flow paths from Digital Elevation Models (DEMs) (e.g., O’Callaghan and Mark, 1984; Tarboton, 1997; Paik, 2008). While these algorithms have been widely applied, DEMs-based approaches have fundamental limitation in detecting water bodies. To resolve this issue, we propose a hybrid approach that utilizes DEMs and satellite imagery together. These dataset supplement each other’s weakness, providing extra information for better detection of water bodies and flow paths. The proposed approach is tested for the Geum River, showing successfully extraction of flow boundaries and more resonable flow paths within water bodies.

Optimization Approach for 4-D Natural Landscape Evolution

IEEE 2011 IEEE transactions on evolutionary computation Vol.15 No.5

<P>This paper presents a unique optimization method developed for landscape evolution problems. An existing hypothesis of the optimal channel network states that fluvial landscape evolution can be characterized as the procedure that follows minimum total energy expenditure. Previous studies have tested this hypothesis by solving an optimization problem, i.e., finding landscapes that satisfy the minimum total energy expenditure criterion, and showed that such optimized landscapes are similar to natural landscapes in many respects. These studies have approximated a 3-D landscape as a 2-D river network. While this network-based approach has greatly simplified the formulation of the optimization problem, this approximation limits the investigation of features such as longitudinal profiles, since their representation requires the gravitational direction-wise dimension. Here, an alternative technique is devised to fully handle the optimization of 3-D landforms over time. The proposed idea is to break down the time domain and to apply an optimization algorithm sequentially for discrete time steps. For the optimization part, a heuristic algorithm motivated from adaptation strategies of natural systems (here landscape formation) is used. This method is applied to a theoretical landscape with the condition that the balance between tectonic uplift and sediment lost is satisfied. It is found that landscapes of minimum total energy expenditure exhibit the Hack's law and the power-law in the exceedance probability distribution of drainage area, which are the characteristics found in natural river networks. However, they demonstrate no systematic pattern in longitudinal profiles.</P>

Search for the optimality signature of river network development.

Published by the American Physical Society through 2012 Physical review. E, Statistical, nonlinear, and so Vol.86 No.4

<P>Whether the evolution of natural river networks pursues a certain optimal state has been a most intriguing and fundamental question. There have been many optimality hypotheses proposed but it has yet to be proved which of these best serves as a quantitative signature of river network development. Here, this fundamental question is investigated for the five hypotheses of 'minimum total energy expenditure,' 'minimum total energy dissipation rate,' 'minimum total stream power,' 'minimum global energy expenditure rate,' and 'minimum topological energy.' Using simple example landscapes, I examined whether any of these hypotheses pursues both the treelike river network formation and the concave stream longitudinal profile, the two characteristic patterns of natural landscapes. It is found that none of these hypotheses captures both patterns under the steady-state condition where the balance between tectonic uplift and sediment loss is satisfied. These findings are further verified through simulations of landscapes that satisfy given optimality criteria using an optimization method.</P>

Reconstructing daily evapotranspiration data from multi-annual water budget using insolation and precipitation presence

Springer-Verlag 2016 Environmental earth sciences Vol.75 No.12

<P>This paper presents a simple method for reconstructing daily catchment-wide evapotranspiration (ET) where only two kinds of daily data are available, i.e., catchment-wide precipitation and streamflow at the outlet. Here, multi-annual ET of a catchment obtained from water budget is decomposed into daily values considering two daily factors of insolation at the top of atmosphere (r factor) and precipitation presence (h factor). Precipitation presence is adopted as a surrogate of humidity which is related to two effects of (1) atmospheric transmittance of insolation and (2) moisture diffusion near surface. It is hypothesized that daily humidity condition is described with precipitation presence of the day, the previous day, and the following day. On the basis of this idea, eight possible scenarios are proposed for humidity condition. This paper reports h values analyzed from long-term data of observed pan evaporation and precipitation for five stations in Korea. h values show significant difference between eight scenarios, implying that the proposed scheme is effective in distinguishing various atmospheric conditions in a simple manner. There exists a varying degree of seasonal and spatial variability in h. Such variability is geo-physiographically explained through analysis of other meteorological data such as relative humidity, cloud cover, sunshine duration, surface solar radiation, and wind speed. The proposed methodology is applied for reconstructing daily ET of a real catchment in Korea. Calculated daily ET values well agree with observed pan evaporation data. The proposed method is also well compared with the Priestley-Taylor method, where the latter requires daily air temperature. The proposed method successfully captures sudden daily ET fluctuations in accordance with precipitation presence which is hardly captured by the Priestley-Taylor method. Further, the reconstructed data nicely follow the trend of LandFlux-EVAL dataset.</P>

NEW FINDINGS ON RIVER NETWORK ORGANIZATION: LAW OF EIGENAREA AND RELATIONSHIPS AMONG HORTONIAN SCALING RATIOS

YANG, SOOHYUN,PAIK, KYUNGROCK WORLD SCIENTIFIC PUBLISHING COMPANY 2017 FRACTALS -LONDON- Vol.25 No.3

<P>Horton’s laws have long served as fundamental principles for fractal organization of a drainage basin. Scaling ratios of stream number, length, area, and side tributary have been proposed but the definitions of these basic variables are inconsistent. The concept of eigenarea can be utilized to resolve this issue. Here, we investigated the relationships among Hortonian scaling ratios using the concept of eigenarea. We found that the eigenarea ratio, likewise other scaling ratios, is invariant within a stream network, the law of eigenarea. We analytically revealed that the eigenarea ratio is equivalent to the stream length ratio. Our examination implies that Horton’s original two ratios of stream number and length can represent most Hortonian scaling ratios except Tokunaga ratio.</P>

Optimal sampling network for monitoring the representative water quality of an entire reservoir on the basis of information theory

Lee, Changhyoun,Paik, Kyungrock,Lee, Yosang IWA Publishing 2014 Journal of water and climate change Vol.5 No.2

<P>This study presents a method for optimal selection of sampling stations for representative and effective water quality monitoring of a reservoir on the basis of information theory. We adopt an objective function used for the design of other hydrological monitoring networks such as rain gauge networks. Unlike rain gauges, in which only a single variable of rainfall is of interest, water quality monitoring stations measure multiple water quality variables. To consider this nature, a new concept of multi-variate weighted total information is proposed. This allows us to consider the relative importance between multiple water quality variables in the design of water quality monitoring networks. The proposed methodology is applied to Lake Yongdam, South Korea, where water quality has been extensively observed at several points. The optimal combination of sampling sites selected with the proposed method is found to show little redundancy in comparison with a previous independent study that presents statistical analysis of the same dataset. Further, the water quality data averaged over all stations are very close to those averaged over the selected sites only, implying that the optimal combination of sampling sites is representative of all sites.</P>

Small profile concavity of a fine-bed alluvial channel

Byun, Jongmin,Paik, Kyungrock Geological Society of America 2017 Geology Vol.45 No.7

<P>Although most natural streams have concave-upward longitudinal profiles, there are conflicting perspectives about whether an alluvial channel is less concave than a bedrock channel. Alluvial channels can be classified as coarse-bed and fine-bed channels, depending on the bed grain size. Both are transport limited, but the threshold of motion differs greatly. Whereas a coarse-bed alluvial channel can be claimed to be as concave as a bedrock channel, we claim that a fine-bed channel is distinguishably less concave. We derive the concavity index of a fine-bed alluvial channel using the power-law relationships emergent at a steady-state river network. For known ranges of the scaling parameters, our formulation informs a range of concavity index as 0.07 +/- 0.09 for a fine-bed alluvial channel. Our analyses of previous laboratory experiments and real fine-bed alluvial channels in the midwestern U.S. and northern Europe also support our conclusions, i.e., small profile concavity of steady-state fine-bed alluvial channels.</P>