How important is the selection of computational analysis method to the accuracy of rainwater tank behaviour modelling?

As the concept of sustainable urban water management is incorporated into the practice of urban water resource managers, actions, such as the utilization of roof runoff via rainwater tanks, which have multiple benefits, are increasingly being built into urban water systems. Modelling tools are frequently used to predict the yield from rainwater tanks and to estimate the storage capacity required to achieve a given potable supply reduction level, with these estimates used in both urban water resources policy development and engineering design. Therefore, it is important that the accuracy of commonly used models is understood. This paper investigates the impact of computational time step, computational operating rule, initial storage level, and the length of simulation period on the accuracy of the storage–yield–reliability relationship calculated using a simple rainwater tank behaviour model. Four time steps (ranging from 6 min to 24 h), two operational rules (supply before spillage and supply after spillage), two initial storage level states (empty and full), and three simulation periods (50 years, 10 years and 1 year) were applied to a wide range of rainwater tank system configurations and three different locations in Australia. It was found that the supply‐after‐spillage computational operating rule is preferable, while the ratio of the average demand volume in a single computational time step divided by the storage capacity (ΔD/S) can be used to assess whether a given combination of demand, storage, inflow, and computational time step will provide long‐term yield estimates that are within ± 5% of the values produced by a simulation that used a 50‐year time series of climate, 6‐min time step, and a supply‐after‐spillage operational rule (50‐6‐YAS). Copyright © 2007 John Wiley & Sons, Ltd.     

An analytical approach to ascertain saturation‐excess versus infiltration‐excess overland flow in urban and reference landscapes

Uncontrolled overland flow drives flooding, erosion, and contaminant transport, with the severity of these outcomes often amplified in urban areas. In pervious media such as urban soils, overland flow is initiated via either infiltration‐excess (where precipitation rate exceeds infiltration capacity) or saturation‐excess (when precipitation volume exceeds soil profile storage) mechanisms. These processes call for different management strategies, making it important for municipalities to discern between them. In this study, we derived a generalized one‐dimensional model that distinguishes between infiltration‐excess overland flow (IEOF) and saturation‐excess overland flow (SEOF) using Green–Ampt infiltration concepts. Next, we applied this model to estimate overland flow generation from pervious areas in 11 U.S. cities. We used rainfall forcing that represented low‐ and high‐intensity events and compared responses among measured urban versus predevelopment reference soil hydraulic properties. The derivation showed that the propensity for IEOF versus SEOF is related to the equivalence between two nondimensional ratios: (a) precipitation rate to depth‐weighted hydraulic conductivity and (b) depth of soil profile restrictive layer to soil capillary potential. Across all cities, reference soil profiles were associated with greater IEOF for the high‐intensity set of storms, and urbanized soil profiles tended towards production of SEOF during the lower intensity set of storms. Urban soils produced more cumulative overland flow as a fraction of cumulative precipitation than did reference soils, particularly under conditions associated with SEOF. These results will assist cities in identifying the type and extent of interventions needed to manage storm water produced from pervious areas.     

Dead level contours and infiltration pits for risk mitigation in smallholder cropping systems of southern Zimbabwe

The persistent droughts, dry spells, and chronic food insecurity in semi-arid areas necessitate the introduction of more robust rainwater harvesting and soil water management technologies. The study reported here was conducted to assess the influence of dead level contours and infiltration pits on in-field soil water dynamics over two growing seasons. A transect consisting of six access tubes, spaced at 5 m interval, was established across each dead level contour with or without an infiltration pit before the onset of the rains. Two access tubes were installed upslope of the contour while four tubes were installed on the downslope side. Dead level contours with infiltration pits captured more rainwater than dead level contours only resulting in more lateral soil water movement. Significant lateral soil water movement was detected at 3 m downslope following rainfall events of 60–70 mm/day. The 0.2–0.6 m soil layer benefited more from the lateral soil water movement at all the farms. Our results suggest that dead level contours have to be constructed at 3–8 m spacing for crops to benefit from the captured rainwater. It is probably worth exploring strip cropping of food and fodder crops on the downslope of the dead level contours and infiltration pits using the current design of these between-field structures. With the advent of in situ rainwater harvesting techniques included in some conservation agriculture practices it will benefit smallholder cropping systems in semi-arid areas if these between-field structures are promoted concurrently with other sustainable land management systems such as conservation agriculture.     

Evaluation of water resource management in Salt Lake City,West Bengal,India

The tenets of sustainable development are often ignored by growing cities in developing countries. Salt Lake City, located on the eastern fringes of Kolkata, despite being a planned township, has failed to manage its water resources in a sustainable way. Results from the study show that the water supplied at the households is hard in nature, saline, and replete with dissolved solids. The problem is further aggravated due to over-extraction of groundwater resources, resulting in an intense fall of the groundwater level in the area. This paper attempts to suggest measures for sustainable water resource management, with particular emphasis on rainwater harvesting.     

Airports and Environment: Proposal of Wastewater Reclamation at São Paulo International Airport

One way to reduce water consumption in urban areas is by using alternative sources of supply that can be provided by collecting rainwater and reusing wastewater for less restricted purposes. Thus, this study evaluated the characteristics of effluents produced by the wastewater treatment plant (WWTP) of São Paulo International Airport (SPIA), Brazil, in order to reuse it in non‐potable situations. The results achieved, indicated high efficiency in the biological system utilized by SPIA. The removal rates is equal to or >90% for most of the parameters analyzed, among them, fluoride, salinity, nitrite, nitrate, ammonium nitrogen, total nitrogen, phosphorus, sedimentable solids, turbidity, conductivity, apparent color, chemical oxygen demand, biochemical oxygen demand, total organic carbon, fecal coliforms, and oils and greases. Despite the final effluents were good enough to be launched in the local streams, they shall be submitted to a complementary treatment in order to fit some quality parameters to be reused for specific demands (landscape irrigation, toilet flushing, vehicle washing, fire fighting, and dust control).     

Restoration of wadi aquifers by artificial recharge with treated waste water

Fresh water resources within the Kingdom of Saudi Arabia are a rare and precious commodity that must be managed within a context of integrated water management. Wadi aquifers contain a high percentage of the naturally occurring fresh groundwater in the Kingdom. This resource is currently overused and has become depleted or contaminated at many locations. One resource that could be used to restore or enhance the fresh water resources within wadi aquifers is treated municipal waste water (reclaimed water). Each year about 80 percent of the country's treated municipal waste water is discharged to waste without any beneficial use. These discharges not only represent a lost water resource, but also create a number of adverse environmental impacts, such as damage to sensitive nearshore marine environments and creation of high-salinity interior surface water areas. An investigation of the hydrogeology of wadi aquifers in Saudi Arabia revealed that these aquifers can be used to develop aquifer recharge and recovery (ARR) systems that will be able to treat the impaired-quality water, store it until needed, and allow recovery of the water for transmittal to areas in demand. Full-engineered ARR systems can be designed at high capacities within wadi aquifer systems that can operate in concert with the natural role of wadis, while providing the required functions of additional treatment, storage and recovery of reclaimed water, while reducing the need to develop additional, energy-intensive desalination to meet new water supply demands.     

Dynamic attribution of global water demand to surface water and groundwater resources: Effects of abstractions and return flows on river discharges

As human water demand is increasing worldwide, pressure on available water resources grows and their sustainable exploitation is at risk. To mimic changes in exploitation intensity and the connecting feedbacks between surface water and groundwater systems, a dynamic attribution of demand to water resources is necessary. However, current global-scale hydrological models lack the ability to do so. This study explores the dynamic attribution of water demand to simulated water availability. It accounts for essential feedbacks, such as return flows of unconsumed water and riverbed infiltration. Results show that abstractions and feedbacks strongly affect water allocation over time, particularly in irrigated areas. Also residence time of water is affected, as shown by changes in low flow magnitude, frequency, and timing. The dynamic representation of abstractions and feedbacks makes the model a suitable tool for assessing spatial and temporal impacts of changing global water demand on hydrology and water resources.     

Urban water systems under climate stress: An isotopic perspective from Berlin,Germany

Large urban areas are typically characterized by a mosaic of different land uses, with contrasting mixes of impermeable and permeable surfaces that alter “green” and “blue” water flux partitioning. Understanding water partitioning in such heterogeneous environments is challenging but crucial for maintaining a sustainable water management during future challenges of increasing urbanization and climate warming. Stable isotopes in water have outstanding potential to trace the partitioning of rainfall along different flow paths and identify surface water sources. While isotope studies are an established method in many experimental catchments, surprisingly few studies have been conducted in urban environments. Here, we performed synoptic sampling of isotopes in precipitation, surface water and groundwater across the complex city landscape of Berlin, Germany, for a large -scale overview of the spatio-temporal dynamics of urban water cycling. By integrating stable isotopes of water with other hydrogeochemical tracers we were able to identify contributions of groundwater, surface runoff during storm events and effluent discharge on streams with variable degrees of urbanization. We could also assess the influence of summer evaporation on the larger Spree and Havel rivers and local wetlands during the exceptionally warm and dry summers of 2018 and 2019. Our results demonstrate that using stable isotopes and hydrogeochemical data in urban areas has great potential to improve our understanding of water partitioning in complex, anthropogenically-affected landscapes. This can help to address research priorities needed to tackle future challenges in cities, including the deterioration of water quality and increasing water scarcity driven by climate warming, by improving the understanding of time-variant rainfall-runoff behaviour of urban streams, incorporating field data into ecohydrological models, and better quantifying urban evapotranspiration and groundwater recharge.     

Algal Cultivation for Treating Wastewater in African Developing Countries: A Review

The tremendous increase in human population and rapid decline in freshwater resources have necessitated the development of innovative and sustainable wastewater treatment methods. Africa as a developing continent is currently backing on sustainable solutions to tackle impending water resource crisis brought forward by wastewater‐induced environmental pollution and climate change. Microalgae‐based wastewater treatment systems represent an emerging technology that is capable of meeting the new demand for improved wastewater treatment and climate change mitigation strategies in an environmentally friendly manner. This review critically looks at the opportunities of Africa in harnessing and exploiting the potential of microalgae for the treatment of various wastewaters based on their capacity to recycle nutrients and for concurrent production of valuable biomass and several useful metabolites. Wastewaters, if improperly/completely untreated and discharged, simultaneously pollute freshwater sources and present significant health and environmental risks. Nutrients in wastewater can be utilized and recovered in the form of marketable biomass and products when integrated with the cultivation of microalgae. Several valuable bioproducts can be generated from wastewater‐grown microalgal biomass including biofuels, biofertilizers, animal feed, and various bioactive compounds. This biorefinery approach would most certainly improve wastewater treatment process economics, enhancing the technical feasibility of algae‐based wastewater remediation in African countries.     

Aquifer Storage and Recovery Using Saline Aquifers: Hydrogeological Controls and Opportunities

Aquifer storage and recovery (ASR) is a valuable tool for managing variations in the supply and demand of freshwater, but system performance is highly dependent upon system-specific hydrogeological conditions including the salinity of the storage-zone native groundwater. ASR systems using storage zones containing saline (>10,000 mg/L of total dissolved solids) groundwater tend to have relatively low recovery efficiencies (REs). However, the drawbacks of low REs may be offset by lesser treatment requirements and may be of secondary importance where the stored water (e.g., excess reclaimed, surface, and storm waters) would otherwise go to waste and pose disposal costs. Density-dependent, solute-transport modeling results demonstrate that the RE of ASR systems using a saline storage zone is most strongly controlled by parameters controlling free convection (e.g., horizontal hydraulic conductivity) and mixing of recharged and native groundwater (e.g., dispersivity and aquifer heterogeneity). Preferred storage zone conditions are moderate hydraulic conductivities (5 to 20 m/d), low degrees of aquifer heterogeneity, and primary porosity-dominated siliclastic and limestones lithologies with effective porosities greater than 5%. Where hydrogeological conditions are less favorable, operational options are available to improve RE, such as preferential recovery from the top of the storage zone. Injection of large volumes of excess water currently not needed into saline aquifers could create valuable water resources that could be tapped in the future during times of greater need.     

The performance of rainwater tanks for stormwater retention and water supply at the household scale: an empirical study

Urban stormwater run‐off degrades the ecological condition of streams. The use of rainwater tanks to supplement water supply can reduce the frequency and volume of urban stormwater run‐off that is otherwise conveyed directly to streams via conventional stormwater drainage systems. Few studies, however, have examined the use of tanks in the context of managing flow regimes for stream protection, with most focussed uniquely on their water conservation benefits. We used measured tank water level data to assess the performance of 12 domestic rainwater tanks against the dual criteria of their ability to (i) reduce potable mains water usage and (ii) retain run‐off from rainfall events and thus reduce the volume and frequency of stormwater run‐off. We found that five households relied almost entirely on tank water. Three of the tanks achieved stormwater retention performance approaching that of the same area of pre‐developed land, although nine did not – a consequence of limited demand and small tank capacity. Our results suggest that tank water usage can result in substantial reductions in mains water use, if regular and sufficiently large domestic demands are connected to tanks. In many cases, such demands will also result in the best stormwater retention performance. Our results highlight an opportunity to design tank systems to achieve multiple objectives. Application of similar analyses in different locations will help to optimize tanks for simultaneous water supply and stormwater retention purposes. Copyright © 2014 John Wiley & Sons, Ltd.     

Sustainable sanitation systems for low income urban areas – A case of the city of Bulawayo,Zimbabwe

Lack of basic sanitation systems threaten environmental and human health in low income urban communities. In 2005, the Government of Zimbabwe carried out a cleanup exercise in urban areas involving the destruction of illegal structures which left many people homeless. As a solution to this problem, the government embarked on an extensive housing construction exercise on unserviced land; the ‘Garikai/Hlalani Kuhle’ development programme. The objective of this paper was to investigate the sanitation status in one such area (Cowdray Park Extension, Bulawayo) and determine a sustainable sanitation system for the improved collection of wastewater from the unserviced low income urban area. The study was carried out between October 2010 and February 2011. The sanitation status as well as the residents’ preferences for improved sanitation and the economic set up of the community for the study area was determined through use of questionnaires to the residents. The local authority was then consulted to recommend sanitation facilities and system for the area that met regulatory requirements. A literature study identified sanitation options that were applicable to low income and high density urban areas. The baseline survey found that 61% of the people in the study area lacked sanitation facilities and practiced open defecation. The majority of the residents (70%) preferred ‘flush and discharge’ system sanitation facilities, which was in line with the local council’s requirements. On-site sanitation options were found not to be feasible as per the council regulations and the findings of the literature study, for areas with a high density of houses. Therefore a sewerage system was designed using the conventional sewerage design approach as well as the simplified sewerage design approach in order to determine the collection system that would best meet the needs of the community. In conclusion, the community was in dire need of a sanitation system and a waterborne offsite sanitation system was found to be a feasible option. The simplified sewerage system was found to deliver the same hydraulic benefits for collecting wastewater as the conventional but was 33% cheaper to construct and hence more affordable for the community. It was recommended that stringent environmental monitoring of the sanitation system be put in place to minimise any potential environmental impacts.     

Opportunities and challenges of the Sponge City construction related to urban water issues in China

Waterlogging is one of the major water issues in most cities of China and directly restricts their urbanization processes. The construction of Sponge City is an effective approach to solving the urban water issues, particularly for the waterlogging. In this study, both the urban issues emerged at the stage of rapid urbanization in China and the demands as well as problems of Sponge City construction related with the water issues were investigated, and the opportunities and challenges for the Sponge City construction in the future were also proposed. It was found that the current stormwater management focused on the construction of gray infrastructures (e.g., drainage network and water tank) based on the fast discharge idea, which was costly and hard to catch up with the rapid expansion of city and its impervious surface, while green infrastructures (e.g., river, lake and wetland) were ignored. Moreover, the current construction of Sponge City was still limited to low impacted development (LID) approach which was concentrated on source control measures without consideration of the critical functions of surrounding landscapes (i.e., mountain, river, wetland, forest, farmland and lake), while application of the integrated urban water system approach and its supported technologies including municipal engineering, urban hydrology, environmental science, social science and ecoscape were relatively weak and needed to be improved. Besides, the lack of special Sponge City plan and demonstration area was also a considerable problem. In this paper, some perspectives on Good Sponge City Construction were proposed such as the point that idea of urban plan and construction should conform to the integral and systematic view of sustainable urban development. Therefore, both the basic theoretical research and the basic infrastructure construction such as monitoring system, drainage facility and demonstration area should be strengthened, meanwhile, the reformation and innovation in the urban water management system and the education system should also be urgently performed. The study was expected to provide a deeper thinking for the current Sponge City construction in China and to give some of suggestions for the future directions to urban plan and construction, as well as urban hydrology discipline.     

Quantitative simulation and verification of upgrade law of sustainable development in Beijing-Tianjin-Hebei urban agglomeration

The natural formation and development of urban agglomerations is a process in which core cities continue to unite their neighboring cities to enhance sustainability for their own sustainable development.The upgrade mechanism of sustainable development urban agglomeration is a nonlinear composite upgrade curve that is a function of time,increasing with the number of cities.In this paper,the sustainable upgrade function curve,upgrade rate,and upgrade speed of urban agglomerations were solved using a geometrical derivation,and the index system for measuring the upgrade capability of sustainable development of urban agglomerations was established.The dynamic change in economic sustainable upgrade capability,social sustainable upgrade capability,environmental sustainable upgrade capability,and comprehensive sustainable upgrade capability of a Beijing-Tianjin-Hebei urban agglomeration from 2000 to 2015 was measured by technique for order preference by similarity to an ideal solution and a grey correlation method,and a comprehensive,intercity unite strength model and a unite threshold calculation method for urban agglomerations were established.The research shows that the economic sustainable upgrade capability,social sustainable upgrade capability,environmental sustainable upgrade capability,and comprehensive sustainable upgrade capability of the Beijing-Tianjin-Hebei urban agglomeration all show a wave-like rising trend.The average annual upgrade speeds during 2000-2015 are,respectively,2.4%.1.67%,1.1%,and 1.74%,with the intercity comprehensive unite strength of urban agglomerations maintaining a general increase;but there is a limit to the joint threshold.From 2000 to 2015,as the core city of the Beijing-Tianjin-Hebei urban agglomeration,Beijing,to enhance its sustainable upgrade capability,jointly developed with Tianjin,Langfang,and Baoding before 2000,Tangshan in 2002,Cangzhou in 2009,Zhangjiakou and Shijiazhuang in 2012,and Chengde in 2014.By 2015,the comprehensive unite strength between Beijing and four cities(Handan,Qinhuangdao,Hengshui,and Xingtai) was still lower than the unite threshold of 6.14.These four cities are relatively far from Beijing,and offer no substantial contribution to the sustainable upgrade capability of Beijing.Through multiple fittings of the upgrade curve using the long-term sequence index of the comprehensive sustainable upgrade capability of Beijing(the core city of the Beijing-Tianjin-Hebei urban agglomeration) from 2000 to 2015,it was found that the simulated curve of the comprehensive sustainable upgrade function of the agglomeration was very similar to the curve of the comprehensive sustainable upgrade capability,which indicates that the simulation results are satisfactory.The future comprehensive sustainable upgrade capability of the agglomeration can be analyzed and predicted by the comprehensive sustainable upgrade function model.This study provides quantitative decision-supporting evidence for promoting the coordinated development of the Beijing-TianjinHebei urban agglomeration and provides theoretical guidance and algorithms for determining the number of cities joined with the sustainable development of national urban agglomerations.     

Evaluation of infiltration‐based stormwater management to restore hydrological processes in urban headwater streams

Urbanization threatens headwater stream ecosystems globally. Watershed restoration practices, such as infiltration‐based stormwater management, are implemented to mitigate the detrimental effects of urbanization on aquatic ecosystems. However, their effectiveness for restoring hydrologic processes and watershed storage remains poorly understood. Our study used a comparative hydrology approach to quantify the effects of urban watershed restoration on watershed hydrologic function in headwater streams within the Coastal Plain of Maryland, USA. We selected 11 headwater streams that spanned an urbanization–restoration gradient (4 forested, 4 urban‐degraded, and 3 urban‐degraded) to evaluate changes in watershed hydrologic function from both urbanization and watershed restoration. Discrete discharge and continuous, high‐frequency rainfall‐stage monitoring were conducted in each watershed. These datasets were used to develop 6 hydrologic metrics describing changes in watershed storage, flowpath connectivity, or the resultant stream flow regime. The hydrological effects of urbanization were clearly observed in all metrics, but only 1 of the 3 restored watersheds exhibited partially restored hydrologic function. At this site, a larger minimum runoff threshold was observed relative to the urban‐degraded watersheds, suggesting enhanced infiltration of stormwater runoff within the restoration structure. However, baseflow in the stream draining this watershed remained low compared to the forested reference streams, suggesting that enhanced infiltration of stormwater runoff did not recharge subsurface storage zones contributing to stream baseflow. The highly variable responses among the 3 restored watersheds were likely due to the spatial heterogeneity of urban development, including the level of impervious cover and extent of the storm sewer network. This study yielded important knowledge on how restoration strategies, such as infiltration‐based stormwater management, modulated—or failed to modulate—hydrological processes affected by urbanization, which will help improve the design of future urban watershed management strategies. More broadly, we highlighted a multimetric approach that can be used to monitor the restoration of headwater stream ecosystems in disturbed landscapes.     

Reuse of waste water: impact on water supply planning / Remploi de l'eau résiduaire: influence sur la planification des systèmes de distribution des eaux

Abstract

As the urban population of the world increases and demand on easily developable water supplies are exceeded, cities have recourse to a range of management alternatives to balance municipal water supply and demand. These alternatives range from doing nothing to modifying either the supply or the demand variable in the supply-demand relationship. The reuse or recycling of urban waste water in many circumstances may be an economically attractive and effective management strategy for extending existing supplies of developed water, for providing additional water where no developable supplies exist and for meeting water quality effluent discharge standards. The relationship among municipal, industrial and agricultural water use and the treatment links which may be required to modify the quality of a municipal waste effluent for either recycling or reuse purposes is described. A procedure is described for analysing water reuse alternatives within a framework of regional water supply and waste water disposal planning and management.     

Multi-city sustainable regional urban growth simulation—MSRUGS: a case study along the mid-section of Silk Road of China

Urban growth along the middle section of the ancient silk-road of China (so called West Yellow River Corridor—He-Xi Corridor) has taken a unique path deviating from what is commonly seen in the coastal China. Urban growth here has been driven by historical heritage, transportation connection between East and West China, and mineral exploitation. However, it has been constrained by water shortage and harsh natural environment because this region is located in arid and semi-arid climate zones. This paper attempts to construct a multi-city agent-based model to explore possible trajectories of regional urban growth along the entire He-Xi Corridor under a severe environment risk, over urban growth under an extreme threat of water shortage. In contrast with current ABM approaches, our model will simulate urban growth in a large administrative region consisting of a system of cities. It simultaneously considers the spatial variations of these cities in terms of population size, development history, water resource endowment and sustainable development potential. It also explores potential impacts of exogenous inter-city interactions on future urban growth on the basis of urban gravity model. The algorithmic foundations of three types of agents, developers, conservationists and regional-planners, are discussed. Simulations with regard to three different development scenarios are presented and analyzed.     

Thermal influence of urban groundwater recharge from stormwater infiltration basins

Groundwater warming below cities has become a major environmental issue; but the effect of distinct local anthropogenic sources of heat on urban groundwater temperature distributions is still poorly documented. Our study addressed the local effect of stormwater infiltration on the thermal regime of urban groundwater by examining differences in water temperature beneath stormwater infiltration basins (SIB) and reference sites fed exclusively by direct infiltration of rainwater at the land surface. Stormwater infiltration dramatically increased the thermal amplitude of groundwater at event and season scales. Temperature variation at the scale of rainfall events reached 3 °C and was controlled by the interaction between runoff amount and difference in temperature between stormwater and groundwater. The annual amplitude of groundwater temperature was on average nine times higher below SIB (range: 0·9–8·6 °C) than at reference sites (range: 0–1·2 °C) and increased with catchment area of SIB. Elevated summer temperature of infiltrating stormwater (up to 21 °C) decreased oxygen solubility and stimulated microbial respiration in the soil and vadose zone, thereby lowering dissolved oxygen (DO) concentration in groundwater. The net effect of infiltration on average groundwater temperature depended upon the seasonal distribution of rainfall: groundwater below large SIB warmed up (+0·4 °C) when rainfall occurred predominantly during warm seasons. The thermal effect of stormwater infiltration strongly attenuated with increasing depth below the groundwater table indicating advective heat transport was restricted to the uppermost layers of groundwater. Moreover, excessive groundwater temperature variation at event and season scales can be attenuated by reducing the size of catchment areas drained by SIB and by promoting source control drainage systems. Copyright © 2009 John Wiley & Sons, Ltd.     

Assessing urban flood and drought risks under climate change,China

Risk analysis of urban flood and drought can provide useful guidance for urban rainwater management. Based on an analysis of urban climate characteristics in 2,264 Chinese cities from 1958 to 2017, this study evaluated urban flood and drought risks. The results demonstrated that the annual average values of precipitation, aridity index, frequency and intensity of extreme precipitation and extreme drought events differed significantly in these cities. The values of the above six climatic indicators in the cities ranged from 9.29–2639.30 mm, 0.47–54.73, 1.08–8.79 time, 7.82–107.25 mm, 0.76–2.99 time, and 10.30–131.19 days, respectively. The geographical patterns of urban precipitation, aridity index, intensity and frequency of extreme precipitation and drought events in China fit well to the Hu‐Huanyong Line that was created in 1940s to identify the pattern of population distribution. Extreme precipitation in most cities has upward trends, except for those around the Hu‐Huanyong Line. The extreme drought events had upward trends in the cities east of the Hu‐Huanyong Line, but there were downward trends in the cities west of the line. The risk assessment indicated that 3.80% cities were facing serious flood and 6.01% cities were facing serious drought risks, which are located in the coast of southern China and northwestern China, respectively, and other 90.19% cities were facing different types of drought and flood risks in terms of their intensity and frequency.     

Sustainable groundwater management in Kinmen Island

Kinmen county is located in the southwest of Fujen province, China. It comprises Kinmen, Leiyu and other small islands. Its total area is around 150 km². Kinmen is the largest island, and 95% of the population resides there. The average annual precipitation is 1072 mm. Rainfall is concentrated in a 5 month period from mid‐April to mid‐September. Water resources are limited relative to demand. Eastern Kinmen utilizes surface water, whereas western Kinmen uses groundwater. Moreover, the Kinmen sorghum liquor is brewed using the native groundwater in the west of the island. MODFLOW‐96 was used to simulate the groundwater distribution and determine the annual amount of infiltration, pumping, and boundary inflow and outflow. Additionally, a groundwater management index was adopted to evaluate the status of groundwater level change, thus allowing local government officials to adjust the pumping scheme dynamically. To achieve a sustainable groundwater supply in Kinmen, an integrated groundwater extraction plan was proposed. This plan includes enhancing the infiltration by using treated wastewater from the east of the island, monitoring the groundwater level change, adjusting the groundwater pumping scheme, and constructing seawater desalination plants. If the hostile confrontation between Taiwan and mainland China is resolved, then the water supply through an undersea pipeline from Sharmen, China, to Kinmen can be another potential source of water for Kinmen in the future. Copyright © 2006 John Wiley & Sons, Ltd.