黄 光偉

Hydrological drought (HD) characterization with different return periods is essential to appropriately design the best water management practices. In particular, characterizing the interactive relations of discharge, drought, and return periods using a novel triple diagram can deepen the interpretation of regional droughts, which have not been adequately considered, especially in semi-arid areas. Considering the critical role of HD in water exploitation and management in Iran, this study was therefore conducted to analyze the HD in different return periods in rivers of the Ardabil Province (area = 17,953 km2). To this end, the streamflow drought index (SDI) was computed using DrinC software at 1-, 3-, and 6-month time scales for 25 hydrometric stations during 1981–2014. Then, the drought severity was evaluated by CumFreq software in different return periods (2, 5, 10, 25, 50, and 100 years). Finally, the relationship between discharge, SDI, and return periods was analyzed using triple diagram models. The results revealed that the drought events had mild (−1 ≤ SDI < 0) and moderate (−1.5 ≤ SDI < −1) severity for most study stations in the study area. The mean values of SDI in the 1-, 3-, and 6-month time scales were 1.08, 0.80, and 0.55, respectively. At all study time scales, the drought severity in both rivers with low and high flows increased with increasing return periods. In such a way, the maximum drought severity has been found for rivers with high flow at a 100-year return period. The current results can be considered a screening tool for the distinctive conservation and directive management of watershed resources.

It is a well-accepted notion that women are more vulnerable to natural disasters than men, especially in developing countries. However, in developed countries, how women’s empowerment by economic and social development has reduced the gender gap in vulnerability remains insufficiently answered. As Japan passed its golden age, moving into an aging society, a study on how the gender difference in flood vulnerability has evolved can contribute to a better understanding of the types and causes of vulnerability, leading to better flood risk management in a new social context. Following this thinking, the present study conducted a longitudinal analysis using representative flooding cases in Japan over a period of forty years. It found that the women’s fatality rate increased with age much faster than men’s in the 1980s but reversed in a recent major flood disaster. It also revealed that most flood disaster victims were elderly in recent years. These findings suggest that the flood vulnerability at present is more driven by age-related physical ability decline, much less relevant to gender. Based on the results, it proposed a new framework for assessing flood vulnerability in an aging society. Such outcomes can help with the better formulation of flood management policies and probing into solutions.

An effective flood warning system is crucial for successful flood management. Flood warning systems have been developed in many countries across the world. However, scientific literature on flood warning systems has been mainly focused on technical capacity building, and the effectiveness of warning systems in mobilizing evacuation was much understudied. Japan is a country with a long history of fighting against flood disasters; the evaluation of its practices in providing flood warnings and the effectiveness are certainly important for further flood research development in Japan, and sharing the experience and lessons with the rest of the world will contribute to flood damage reduction on a global scale. Following this line of thinking, this article is intended to present a clear and concise picture of the current flood warning system in Japan, which has been poorly documented up until now. It is also aimed at providing a performance assessment for the flood warning system through case study approach and the use of Strengths, Weaknesses, Opportunities, and Threats (SWOT) model. Through analyses, the pros and cons of the current flood warning system in Japan are highlighted, and the directions for further development and refinement are explained.

The occurrence and intensity of climatic and hydrologic extreme events, as indicators of climate change, are increasing in most parts of arid and semi-arid regions, including Ardabil province, Iran. Recent studies have revealed the need for the multidimensional assessment of flood disasters in this area. Consequently, this present study was conducted to provide comprehensive information on the flood vulnerability of 26 watersheds in Ardabil province. Here, six components, including meteorological, hydrological, physical-environmental, social, economic, and countermeasures, were computed at a watershed scale based on 19 different criteria. Finally, the flood vulnerability index (FVI) for each watershed was calculated. The results revealed the need for different management approaches for flood hotspots based on the vulnerability to the six components studied. The integrated FVI showed that 46.97%, 33.63%, 18.10%, 1.20%, and 0.10% of the province have very high, high, medium, low, and very low flood vulnerability, respectively. The spatial mapping also revealed that all study areas were under flood stress, except small parts in central, east, and north. The preliminary version of the flood vulnerability atlas is presented, which estimates the flood disaster risk throughout the province. In addition, the developed regional framework in this study also allows for more comprehensive and extensive dataset analysis.

Knowledge of landscape fragmentation is known to be important in ecological integrity, hydrological processes, urban planning, sustainable land management, and policymaking. Recent anecdotal studies reveal a need for analytical quantification of landscape fragmentation at different levels. Therefore, the present study was conducted at KoozehTopraghi Watershed, Ardabil Province, Iran, where covers by different land uses/covers, to (a) explore the spatial pattern of landscape fragmentation metrics comprehensively in different scales, (b) distinguish the landscape fragmentation hot spots, and (c) investigate the spatial clustering of landscape fragmentation metrics. The behaviors of 7, 10, and 13 fragmentation metrics concerning three levels of patch, class, and landscape across 36 sub-watersheds were explored using principal component analysis (PCA) and expert elicitation. The Getis-Ord Gi* and local Moran’s I indices were also used to analyze the hot spots and clusters of landscape fragmentation, respectively. The results verified the high degree of spatial variability of the metrics in the three levels of fragmentation analysis. The class-level fragmentation analysis showed that the watershed is characterized by high-fragmented residential land use and low-fragmented dry farming land use. The spatial trend analysis at the landscape level further indicated that sub-watersheds 1, 2, 11, 21, to 26, and 34 to 36, mainly located in lowlands and central parts, allocated better status considering the fragmentation metrics rather than other parts of the watershed. The significant hot spots and high clusters of fragmentation also were distributed in different parts of the watershed in terms of various landscape metrics.

Disaster reduction is one of the most important keys towards sustainable development. Using a number of case studies, the present work was intended to elucidate the need for improved communication between the urban flood management community and the road planning sector for better flood risk management. These cases were classified in three categories: (1) Road tragedy during evacuation, (2) Why some roads are vulnerable to flooding, (3) How to quickly evaluate the potential impact of road construction on surface drainage characteristics. These cases provided strong evidence that insufficient dialogue between water and road sectors may hinder sound flood risk management by recommending wrong flood evacuation routes that are life threatening and neglecting the impact of road construction on the alteration of surface drainage characteristics. These cases were selected purposively but not comprehensively. Based on findings from these case studies, it can be stated that evacuation safety should be improved through better communication between flood risk and road management professionals, which in turn will lead to better road planning.

A water allocation policy that aimed to balance water demand with water availability to ensure sustainability was implemented in an arid region of China over ten years ago. This policy's success was assessed across three dimensions: society, the environment, and the economy. While the assessment was not intended to be comprehensive, it highlighted the best outcomes of the policy intervention while revealing some hidden issues. It was found that although the policy was successful in placing a ceiling on water use in the middle reaches of the Heihe River, the Water User Association, one of the main actors in water policy implementation, was under-recognized, even though it functioned well. Moreover, the economic structural adjustment at the macro level had not led to any significant reduction in water use, the reasons for which were explored.

It is already well known that river regulation influences biota via disrupting the natural flow regime in addition to causing physical barrier for the movement of aquatic life and material. However, studies often looked into various effects in an isolated manner and paid little attention to animal adaptive behaviour. In this work, the influence of river regulation by dam operation on the breeding habitat of the Little Tern was studied from a coast-river continuum perspective. It was found that there was a decade-long time lag between flow regulation and the degradation of coastal habitat in the case investigated. As the coastal habitat degradation became manifested, a habitat use shift occurred from coast to river. On the other hand, the riverine habitat was affected by river regulation both positively and negatively. The positive aspect is the reduction in flooding risk of breeding colony, and the negative effect is the vegetation development on the habitat, which is out of favour by the bird. As a net result, the bird did not abandon the riverine habitat although its physical characteristics may be considered as suboptimal. The findings suggest that species adaptive behaviours should be taken into consideration in assessing environmental impacts caused by human activities such as dam development.

Attempts at flood management during the 20th century resulted in more flood disasters. To gain a better understanding of what went wrong, it is necessary to examine historical evidence, seek ancient wisdom and compare practices of flood management in different countries. This study examines flood management concepts and practices in China and Japan during different periods of time in history and the differences in the two countries' current management of flood retarding basins. It reveals that during the Western Han Dynasty (206 BC-24 AD), China proposed to redirect a river course to gain sufficient flood retarding capacity, and this same concept was realized, either coincidentally or intentionally, during the Edo period of Japan (1603-1868). In modern times, however, the management of flood retarding basins differs fundamentally between China and Japan. In addition, this study investigates the differences in emergency evacuation practices between China and Japan. This is the first study to highlight the link between a Chinese concept and a Japanese practice that are separated by more than 1000 years.

While the current food security is fulfilled in China, the substantial nitrogen fertilizer use has caused many far-reaching environmental problems. Therefore, reforming the fertilizer management is the key toward sustainable agriculture for 1.3 billion people. The present study is intended to test the applicability of a nitrogen fertilizer management approach for corn production developed in U.S. to regions with different climates in China. Through field work, it was found that the so-called Late Season Cornstalk Nitrate Test approach may have to be adapted to dry continental climate and irrigation water conditions, but meanwhile appeared workable under sub-humid warm temperate continental monsoon climate in China. A hypothesis was made to explain the findings and a simple cure was suggested. Moreover, the importance of applying this approach to China was discussed in relation to GHG emission reduction and national fertilizer subsidy policy. Finally, a new fertilizer management scheme was proposed.

It is widely accepted that sustainable development is the development that meets the needs of the present without compromising the ability of future generations to meet their own needs. However, the question of how to apply this principle to flood management remains insufficiently answered. This article outlines a new strategic concept termed as "Flood Sharing" as a means toward sustainable flood management. Contrary to the traditional concept of flood confinement or blocking, the new concept advocates the need to alleviate flood damage by reducing inundation depth via expanding flood inundation areas. It differs from other contemporary thinking such as "make space for water" and "room for the river" in its emphasis on using the urban fabric. Evidence from a case study was presented to support this new concept, and model/data analyses have been conducted to show that it could be realized through the wise use of infrastructure.

Human modification to rivers may induce considerable barriers to sediment movement, whether directly and immediately or otherwise. For example, dams may prevent sediment from moving through the system once constructed. In-channel vegetation is a form of sediment trap, which could be an indirect consequence of human interference with river, and has received considerable attention. However, sediments retained in various landforms may be remobilized by one cause or another. Better understanding of sediment remobilization mechanisms and related time scales are needed for better sediment management. The present study is motivated by the fact that the long-term behavior of sediment trapped by in-channel vegetation is still poorly understood. It focuses on the temporally changing role of in-channel vegetation with its growth in regard to sediment retention in the lower Tenryu River, Japan. It reveals that although in-channel vegetation can trap sediment during growing stage, it could become a source of sediment supply at the decadal time scale, when the vegetation was well established. The mechanism behind is the formation and destruction of forested overhanging bank. The process can be characterized by the time period scale ratio of riparian forest growth to lateral channel migration. The findings can help identify the residence time of sediment stores and subsequently aid in planning to increase fluvial sediment delivery from river to the coast.

The disruption of sediment supply from river to coast by dam development has been a topic of global concern. In Japan, among the top 30 dams in terms of height, 14 dams were constructed prior to 1970 and another 6 dams before 1980. However, the coastline erosion did not surface up as a grievous problem until the 1980s. According to the River Bureau of Japan, the overall erosion rate along the coastline of Japan was 0.72x10(6) m(2)/yr prior to 1980, but sharply increased to 1.6x10(6) m(2)/yr since 1980. Therefore, there was a time lag between the disruption of sediment supply by dam and beach erosion. This paper presents a case study on what may have delayed the response of beach to the effect of dam construction.

Policy impacts have been studied in different contexts. A change in watershed characteristics may be perceived as positive by one sector, but negative by other sectors. It is also likely that an impact is positive for a period of time but may turn to negative thereafter. Thus, studies on policy impacts from a long-term perspective should be pursued. The present study addressed the issue of policy mismatch in a historical context through a case study. By data synthesis and numerical simulations, it was found that the combination of flood control, rice production reduction, and suburbanization policies was the fundamental cause of water quality deterioration in Lake Tega, and the mismatch also led to flood risk polarization in the lake's watershed. © 2011 International Association for Hydro-Environment Engineering and Research.