Summer Floods Research Articles

What made the June 2013 flood in Germany an exceptional event? A hydro-meteorological evaluation

Abstract. The summer flood of 2013 set a new record for large-scale floods in Germany for at least the last 60 years. In this paper we analyse the key hydro-meteorological factors using extreme value statistics as well as aggregated severity indices. For the long-term classification of the recent flood we draw comparisons to a set of past large-scale flood events in Germany, notably the high-impact summer floods from August 2002 and July 1954. Our analysis shows that the combination of extreme initial wetness at the national scale – caused by a pronounced precipitation anomaly in the month of May 2013 – and strong, but not extraordinary event precipitation were the key drivers for this exceptional flood event. This provides additional insights into the importance of catchment wetness for high return period floods on a large scale. The database compiled and the methodological developments provide a consistent framework for the rapid evaluation of future floods.

Categorization of Floods in the Opava River Basine

The paper summarizes our knowledge of the flood regime of the Opava river basin between 1960 and 2010. Emphasis is placed on the categorization of the individual components of the causes of flooding and the development of floods. Analogies were sought among floods based on their causal symptoms and the characteristics of the runoff response. Summer and winter categories of flood waves have been delineated via statistical methods, which characterize common features of floods by cluster analysis and similarity index. Flood episodes have been divided into nine groups (four types of winter- and five types of summer floods) based on the spatial and time distribution of rainfall, which is caused by specific atmospheric circulation and thus influences the development and formation of the flow waves.

丹江口水库洪水资源调控技术研究

丹江口水库既是汉江中下游地区的控制性防洪工程，又是南水北调中线工程的水源地，承担着防洪、供水、发电、航运等重要功能。本文把资料系列延长至2014年并进行设计洪水复核，开展汛期分期、运行水位动态控制和提前蓄水研究。结果表明：在不降低防洪标准的前提下，利用1~5 d预见期信息，夏汛期(6月21日至8月20日)和秋汛期(9月1日到10月10日)的运行水位分别在160.0~162.9 m和163.5~ 165.7 m区间浮动，年均可增加蓄水量31.6~49.98亿m³，或增加发电量9.96~100.21 M kW•h；汛末提前蓄水时间为9月15日，蓄水水位上限值为166 m，与原设计方案相比，水库蓄满年份从4年增加到12年，年均多蓄水8.98亿m³。 The Danjiangkou Reservoir is both a key flood control project for the middle and lower reaches of the Han River and water source of the South-to-North Water Diversion Project in China. It is a multi-purpose reservoir, including flood control, water supply, hydropower generation, navigation, etc. The hydrological data series were extended to 2014 and the design flood values were rechecked. The flood seasonal identification, dynamic control of water levels during flood season and early refill of reservoir were studied. Results show that with 1 - 5 d forecasting information, dynamic control bounds of water level during summer flood season (Jun. 21 - Aug. 20) and autumn flood season (Sep. 1 - Oct. 10) are 160.0 - 162.9 m and 163.5 - 165.7 m respectively without decreasing flood protection standards, which can increase 3.16 - 4.998 billion m³ storage water or 9.96 - 100.21 MkW•h hydropower generation annually. It is also shown that reservoir’s early refill starts on Sep. 15 with the maximum water level limited to 166 m during September; the full storage rate can increase from 4 years to 12 years, and the storage water increases 0.898 billion m³ annually.

DYNAMIKA STŘEVlÍKOVITÝCH (Carabidae) LUŽNÍHO LESA JIŽNÍ MORAVY

During the years 1993–2001 the monitoring of the soil surface invertebrates was carried out in the flood- plain forest in the Ranšpurk National Nature Reserve (Southern Moravia). The dynamics of carabid beetles is described in detail in this paper. A total of 8 529 individuals belonging to 67 carabid species was collected. The most abundant species were Pterostichus niger (Schaller, 1783), Nebria brevicollis (Fabricius, 1792), Carabus ullrichi Germar, 1824, Carabus violaceus Linnaeus, 1758, Abax carinatus (Duftschmid, 1812), Patrobus atrorufus (Stroem, 1768), Pterostichus melanarius (Illiger, 1798), Carabus granulatus Linnaeus, 1758, Poecilus cupreus (Linnaeus, 1758), Bembidion mannerheimi C. R. Sahlberg, 1827 and Epaphius secalis (Paykull, 1790). During the years 1993–1996 the species composi- tion indicated especially the drainage of the locality. In July 1997, a disastrous flood affected all groups of invertebrates, including the carabids. The abundance of hygrophilous species increased extremely during the years after the flood. The summer flood showed that the submersion of the soil surface had higher impact on carabid taxocenoses than flooding by system of canals.

Flood seasonality in Greece and its comparison to seasonal distribution of flooding in selected areas across southern Europe

AbstractThis paper examines flood seasonality in Greece and its 13 regions by studying a catalogue of 553 events between 1880 and 2010. Findings are compared with the conclusions of similar analyses in selected areas across southern Europe. Results show that flooding in Greece presents strong seasonality as 46.6% of the total events occur during autumn and mostly during November (20.6%). Examination of smaller geographical entities shows different seasonality patterns between eastern, western, southern, and northern parts of Greece. Comparison with findings in Spain, Italy, and Cyprus show that summer floods are far more frequent in the northern parts of these countries. On the contrary, winter floods present higher percentages in the south. A significant shift in seasonality was identified between the western and southeastern Mediterranean Region. Results provide new knowledge for flood prevention planning by improving the current understanding of flood seasonality across the region.

Environmental variation as a key process of co‐existence in flood‐meadows

AbstractQuestionHow does the species composition and functional structure of flood‐meadows change over time during a period with strong variations in flooding frequency and height?LocationFlood‐meadows at the northern Upper Rhine, Germany.MethodsFrom 1998 to 2004 annually, and again in 2008, species composition and above‐ground biomass were studied in 46 permanent plots located along a flooding gradient ranging from frequently flooded Magnocaricion to rarely flooded Arrhenaterion meadows. The plots were situated in the functional floodplain (natural) and in the fossil floodplain on the land side of high winter levees (anthropogenic altered). Temporal variation of the functional structure was analysed based on community‐weighted mean traits.ResultsProductivity and functional structure varied markedly over the study period and between the functional and fossil floodplain. During the study period two contrasting extreme events occurred: a summer flood in 1999 and a drought period after 2003. After the flood in 1999, species composition and functional structure of the studied flood‐meadows shifted towards the species composition of wetter sites. Flooding reduced species richness in the functional floodplain, but not in the fossil floodplain.ConclusionsFlood‐meadows in the Upper Rhine fully recover from extreme disturbance events within a time frame of less than 10 yr. Environmental fluctuations and disturbances, enabling the co‐existence of species with contrasting ecological requirements are a key factor for the preservation of plant biodiversity in flood‐meadows.

The Copula Function-Based Probability Characteristics Analysis on Seasonal Drought & Flood Combination Events on the North China Plain

Drought & flood events, especially the drought & flood combination events (DFCEs) on the North China Plain (NCP), known as an important grain production region in China, constitute a serious threat to China’s food security. Studies on DFCEs in this region are of great significance for the rational allocation of water resources and the formulation of integrated response strategy for droughts and floods. In this study, L-moments theory and bivariate copula method were used to evaluate the probability characteristics of seasonal DFCEs (continuous drought, continuous flood, and alternation between drought and flood) on the NCP, based on the daily precipitation data (1960–2012) at 19 meteorological stations. Results indicate the following: (1) On the NCP, the precipitation in summer accounts for 56.45%–72.02% of mean annual precipitation, and the precipitation in autumn and spring come second. The winter precipitation is the smallest (less than 4%); (2) The best-fit distribution for precipitation anomaly percentages in spring, summer and autumn are Generalized Normal (GNO), Generalized Logistic (GLO) and Pearson III (P-III) in sub-region I, respectively. While in sub-region II, they are respectively the P-III, P-III and Generalized Extreme-Value (GEV); (3) Compared with the Gumbel copula and Clayton copula, Frank copula is more suitable for spring-summer and summer-autumn precipitation anomaly percentage sequences on the NCP; (4) On the time scale, continuous drought respectively dominate in spring-summer DFCEs and in summer-autumn DFCEs on the NCP. Summer-autumn DFCEs prevail in sub-region I with the average probability value 0.34, while spring-summer DFCEs dominate in sub-region II, of which average probability value is 0.42; (5) On the spatial scale, most areas where the probability of continuous drought in spring-summer and spring drought & summer flood is relatively high are located in the northwest, northeast, and coastal parts of sub-region II; all the events with high probability of continuous drought in summer-autumn and summer flood & autumn drought occurred at the central part in the northwest of sub-region II.

Geographies of UK flooding in 2013/4

Between December 2013 and February 2014, an extreme storm surge, a series of intense storms, and the cumulative effects of heavy and persistent rainfall caused widespread flooding throughout the UK, prompting renewed public and scientific debates on who, or what, might be to blame. The public divided fairly evenly into two diametrically opposed groups, the first blaming the government (who initially responded by trying to shift blame to their expert advisors), attributing the mounting flood losses and prolonged misery to lack of investment in flood defences and river dredging. The second group blamed farmers for over‐intensive agriculture in upstream catchments, inappropriate development in floodplains, and poor judgement on the part of the victims in choosing to live, work or farm in areas vulnerable to inundation. The floods resulted from a protracted sequence of deep, Atlantic depressions that followed a more southerly track than usual due to the position and configuration of the planetary jet stream. This prompted a second, no less polarised, scientific debate concerning whether the meteorological characteristics of the floods provided evidence that climate change has started to influence not only the probability of UK flooding, but also its nature, spatial distribution and duration. Both debates are intrinsically geographical, and this commentary sets out how understanding the geographies of flooding can help frame and inform them. This is addressed through consideration of these geographies, characterised as physical, rural, urban, social, economic and political. While an individual event (or even a sequence clustered of floods) cannot alone prove anything, the winter floods reinforce the conclusions of the Government's Flood Foresight study, which was commissioned in response to the 2000 (Millennium) Floods and updated following nationwide floods in summer 2007.

Evaluating Abiotic Influences on Soil Salinity of Inland Managed Wetlands and Agricultural Croplands in a Semi-Arid Environment

Agriculture and moist-soil management are important management techniques used on wildlife refuges to provide adequate energy for migrant waterbirds. In semi-arid systems, the accumulation of soluble salts throughout the soil profile can limit total production of wetland plants and agronomic crops and thus jeopardize meeting waterbird energy needs. This study evaluates the effect of distinct hydrologic regimes associated with moist-soil management and agricultural production on salt accumulation in a semi-arid floodplain. We hypothesized that the frequency of flooding and quantity of floodwater in a moist-soil management hydroperiod results in a less saline soil profile compared to profiles under traditional agricultural management. Findings showed that agricultural croplands differed (p-value < 0.001, df = 9) in quantities of total soluble salts (TSS) compared to moist-soil impoundments and contained greater concentrations (TSS range = 1,160–1,750 (mg kg-1)) at depth greater than 55 cm below the surface of the profile, while moist-soil impoundments contained lower concentrations (TSS range = 307–531 (mg kg-1)) at the same depths. Increased salts in agricultural may be attributed to the lack of leaching afforded by smaller summer irrigations while larger periodic flooding events in winter and summer flood irrigations in moist-soil impoundments may serve as leaching events.

Ecosystem respiration and its components from a Carex meadow of Poyang Lake during the drawdown period

Little is known about the components of ecosystem respiration from a subtropical littoral wetland with dramatic annual inundation dynamics. In this study, we investigated ecosystem respiration and its components in a Poyang lake Carex meadow during the drawdown periods from May 2009 to June 2011. Both ecosystem respiration and its components showed clear temporal variation pattern, with temperature being the dominant control. Ecosystem respiration ranged from 98.01 to 1359.25 mg CO2 m−2 h−1. Shoot and root respiration contributed approximately 36% and 26% to the ecosystem respiration, respectively, whereas microbial respiration accounted for 38% of the ecosystem respiration. The ratio of total soil respiration to ecosystem respiration varied from 0.45 to 0.90, depending on growing season stages. Their Q10 values ranged from 1.72 to 2.51, with the maximum for shoot respiration and the minimum for microbial respiration. In addition, the Q10 values varied with time and among ecosystem respiratory components and hence could not be treated as a constant. None of the respiration measurements was significantly related to soil moisture, suggesting that soil moisture was not a limiting environmental factor for respiratory activity during the drawdown periods in this meadow. The Carex meadow acted as strong carbon sink during the drawdown periods due to double growing seasons, but the previous summer flood duration could substantially alter carbon sink intensity in the following drawdown period. The total carbon sink of the littoral zone of Poyang Lake during drawdown periods was estimated to be 0.17–0.59 Tg C yr−1.

Coastal Research: Estuarine Processes and Submarine Ground Water Discharge

The estuarine and coastal environments of Mauritius are suffering ever-increasing impact from anthropogenic activities and Submarine Groundwater Discharge (SGD) is now recognized as an important pathway between land and sea. As such, this flow may contribute to the biogeochemical and other marine budgets of nutrients in nearshore waters. The stable isotopic composition of submarine waters is also characterized by significant variability and heavy isotope enrichment and used to predict the contribution of fresh terrestrially derived groundwater to SGD (range from a few % to almost 100%) in Flic en Flac lagoon, Mauritius. Sources of input of trace metals (in particular, Pb, Cu and Zn) in Mauritius in recent years include industrial effluents, urban and road runoff, sewage sludge, landfill leachates including scrap metal and solid waste leachates [1-5]. The potential sources of Pb in sediments from upstream to the estuary were from the adjacent motorway and road runoff causing significant quantities to be trapped within the St. Louis River in the Grand River North West catchment area. Pb and Zn were significantly positively correlated in the sediments along St. Louis River indicating a common source for Pb and Zn. Significant negative correlations were also found for both Pb and Zn with dissolved oxygen in summer along St. Louis River which indicated that the presence of anoxic waters influenced the trapping of Zn and Pb in the sediment phase. A phasedown of Pb in petrol was necessary and with the introduction of unleaded petrol and vehicles equipped with catalytic converters, studies on levels of Pd and Pt to provide baseline data need to be done in the near future and integrated in environmental development schemes and effective coastal zone management of small island states [6-9]. The common influential cycling of Pb and Zn was further reinforced as both dissolved Pb and Zn were significantly positively correlated to dissolved phosphate, which suggested a biological role in the cycling of Zn and Pb. The mean concentrations of Zn (204.0 ± 92.3 mg kg1) and Pb (44.5 ± 16.4 mg kg-1) in sediments at Sable Noir, an urban estuary, can be considered below those from contaminated estuarine sediments in industrialized countries. Pb significantly decreased from two consecutive winters 2004/2005 to summer 2005/2006 at Sable Noir at 5% significance level due to flash floods in summer and dilution with cleaner background sediments. Pb was however significantly higher at Sable Noir in winter 2004 compared to winter 2005 and significantly increased from summer 2005 to summer 2006 due to a minor diesel spill in the estuary. Both Pb and Zn were significantly higher at Sable Noir in winter 2004 compared to Flic en Flac in winter 2008. Pb and Zn were also significantly higher at Sable Noir in summer 2005 compared to Flic en Flac in summer 2009. The presence of Cu at Sable Noir can be attributed to road run off, brake linings and urban activity prevailing in the area. The contamination of sediments with Cu in downstream and estuarine sediments was significant showing an increasing trend following flash floods in March 2013 sediments and values indicated that the sources of Cu are traffic and urban related and potentially constitutes a health hazard [10-13].

Long-term adaptations of a migratory bird (Little Tern Sternula albifrons) to quasi-natural flooding disturbance

Population size of migratory birds responds to various types of environmental factors, which affect different stages of bird population. In the current study, we analyzed a long-term avifauna monitoring database to investigate population changes in the migratory bird Little Tern, Sternula albifrons, with respect to a quasi-natural disturbance, flooding, induced by a regional characteristic climate pattern, the Korean Monsoon (KM), in the Nakdong River Estuary of South Korea. We scrutinized the time-delayed influence by means of wavelet transformation and year-to-year comparison. Little Tern individuals started to grow in April, and reached its maximum generally in May or June, and an abrupt decrease of individual number was observed after KM occurred. Sequential time-series analysis based on wavelet transformation revealed that the changing pattern of the population size of Little Tern in the estuary was linked to the previous year's flooding (a 9- to 10-month delay), which is regarded as the time difference between Little Tern breeding season and previous KM period. Stronger flooding waters during KM season expelled comparably more individuals of Little Tern from the estuary (r2=0.595; p<0.05; n=9), and the more the individuals left, the smaller the bird arrived at the estuary in the next year. Further examination revealed that earlier initiation and longer duration of KM in yeart−1 negatively affected the newly arriving Little Tern individuals in the current year (i.e., yeart; r2=0.809 for impact of KM onset, r2=0.909 for impact of KM duration; n=10, respectively; p<0.005). The Little Tern population gradually increased when summer flooding was not strong in the previous successive years, from which we concluded that the population of the migratory bird Little Tern tends to adapt to quasi-natural disturbance (flooding) to maintain their population size.

Effects of cumulus parameterizations on predictions of summer flood in the Central United States

This study comprehensively evaluates the effects of twelve cumulus parameterization (CUP) schemes on simulations of 1993 and 2008 Central US summer floods using the regional climate-weather research and forecasting model. The CUP schemes have distinct skills in predicting the summer mean pattern, daily rainfall frequency and precipitation diurnal cycle. Most CUP schemes largely underestimate the magnitude of Central US floods, but three schemes including the ensemble cumulus parameterization (ECP), the Grell-3 ensemble cumulus parameterization (G3) and Zhang-McFarlane-Liang cumulus parameterization (ZML) show clear advantages over others in reproducing both floods location and amount. In particular, the ECP scheme with the moisture convergence closure over land and cloud-base vertical velocity closure over oceans not only reduces the wet biases in the G3 and ZML schemes along the US coastal oceans, but also accurately reproduces the Central US daily precipitation variation and frequency distribution. The Grell (GR) scheme shows superiority in reproducing the Central US nocturnal rainfall maxima, but others generally fail. This advantage of GR scheme is primarily due to its closure assumption in which the convection is determined by the tendency of large-scale instability. Future study will attempt to incorporate the large-scale tendency assumption as a trigger function in the ECP scheme to improve its prediction of Central US rainfall diurnal cycle.

Sedimentary records of 2010 and 2011 Warta River seasonal floods in the region of Poznań, Poland

The Warta River near Poznań (West Poland) represents a meandering lowland river modified by hydro-engineering projects. Recently, two large floods occurred during the summer of 2010 and the winter of 2011. Rapid response surveys were conducted to document erosion and sedimentary records of the floods (spatial extent, grain size, composition, grain microtextures). Follow-up studies, which were conducted during the two years after the floods, assessed postdepositional changes in the flood deposits. A thick sand layer formed that ranged from an average of 10–15 cm (summer) to 30–35 cm (winter), building natural levees, side bars and crevasse splays. The sand layers consisted of fine- and medium-grained sands that were well-sorted, fine skewed and sourced from the river channel. The longer but smaller winter flood produced thicker and coarser deposits at different sites compared with the summer flood. An organic-rich mud layer and algal mats, which were short-existing, were also detected on the floodplain. The study proved that the flood record on engineered rivers may be only in the sand bodies near the river channel and their preservation is mainly controlled by their thickness. A single site may not record all floods, as particular events tend to leave deposits in various places.

Seasonal-dependence in the responses of biological communities to flood pulses in warm temperate floodplain lakes: implications for the “alternative stable states” model

In floodplains located in temperate regions, seasonal variations in temperature affect biological communities and these effects may overlap with those of the flood regime. In this study we explored if and how timing (with regard to temperature seasonality) influences the responses of planktonic and free-floating plants communities to floods in a warm temperate floodplain lake and assessed its relevance for determining state shifts. We took samples of zooplankton, phytoplankton, picoplankton, heterotrophic nanoflagellates and free-floating macrophytes at four sites of the lake characterized by the presence-absence of emergent or free-floating macrophytes along a 2-year period with marked hydrological fluctuations associated to river flood dynamics. We performed ANOVA tests to compare the responses of these communities to floods in cold and warm seasons and among sites. Planktonic communities developed high abundances in response to floods that occurred in the cold season, while the growth of free-floating macrophytes was impaired by low winter temperatures. Spring and summer floods favored profuse colonization by free-floating plants and limited the development of planktonic communities. The prolonged absence of floods during warm periods caused environmental conditions that favored Cyanobacteria growth, leading to a “low turbid waters” regime. The occurrence of floods early in the warm season caused phytoplankton dilution and promoted free-floating plant colonization and a shift towards a “high clear waters” state. Zooplankton:phytoplankton biomass ratio was very low during floods in warm seasons, thus zooplankton grazing on phytoplankton seemed to play a minor role in the maintenance of the clear regime.

Diversity and above-ground biomass patterns of vascular flora induced by flooding in the drawdown area of China's Three Gorges Reservoir.

Hydrological alternation can dramatically influence riparian environments and shape riparian vegetation zonation. However, it was difficult to predict the status in the drawdown area of the Three Gorges Reservoir (TGR), because the hydrological regime created by the dam involves both short periods of summer flooding and long-term winter impoundment for half a year. In order to examine the effects of hydrological alternation on plant diversity and biomass in the drawdown area of TGR, twelve sites distributed along the length of the drawdown area of TGR were chosen to explore the lateral pattern of plant diversity and above-ground biomass at the ends of growing seasons in 2009 and 2010. We recorded 175 vascular plant species in 2009 and 127 in 2010, indicating that a significant loss of vascular flora in the drawdown area of TGR resulted from the new hydrological regimes. Cynodon dactylon and Cyperus rotundus had high tolerance to short periods of summer flooding and long-term winter flooding. Almost half of the remnant species were annuals. Species richness, Shannon-Wiener Index and above-ground biomass of vegetation exhibited an increasing pattern along the elevation gradient, being greater at higher elevations subjected to lower submergence stress. Plant diversity, above-ground biomass and species distribution were significantly influenced by the duration of submergence relative to elevation in both summer and previous winter. Several million tonnes of vegetation would be accumulated on the drawdown area of TGR in every summer and some adverse environmental problems may be introduced when it was submerged in winter. We conclude that vascular flora biodiversity in the drawdown area of TGR has dramatically declined after the impoundment to full capacity. The new hydrological condition, characterized by long-term winter flooding and short periods of summer flooding, determined vegetation biodiversity and above-ground biomass patterns along the elevation gradient in the drawdown area.

Relationship between North Pacific Oscillation in May and Drought/Flood in Summer in North China

The relationship between the North Pacific Oscillation( NPO) in May and the summer drought /flood in North China was analysed using the NCEP /NCAR month by month reanalysis data from 1948 to 2011 including sea level pressure,500 hPa geopotential height,specific humidity( 8 layers) and wind field( 8 layers). The North Pacific Oscillation Index( NPOI) which reflects the changes of the sea level pressure in North Pacific was calculated firstly. Then the correlation coefficient between NPOI and Palmer Drought Severity Index( PDSI)which represents the situation of summer drought /flood in North China from 1960 to 2011 was also calculated.The results show that there is a positive correlation between NPO and summer drought /flood in North China.When in positive NPOI years,PDSI in summer is higher than normal,and North China has more summer floods; otherwise,in negative NPOI years,PDSI in summer is lower than normal,and North China has more summer droughts. In order to explain the positive correlation between NPO and summer drought /flood in North China,wind vector field on 850 hPa and geopotential height field on 500 hPa were composite analysed,respectively,and compare the different intensity,area and position of western boundary of Western Pacific Subtropical High( WPSH) when NPO is in different strength( weak and strong). The possible circulation mechanism is that when in positive( negative) NPOI years,on lower layer( 850 hPa wind field),the common action of anti-cyclonic( cyclonic) in Ural Mountains,the cyclone( anti-cyclonic) of Lake Baikal,and the anti-cyclonic( cyclonic) anomaly circulation in West Pacific have strengthened( weakened) the convergence of south-west warm and humid air flows of low layer in North China region. And also,when in positive( negative) NPOI years,500 hPa geopotential height anomaly shows ‘+-+'( ‘-+-') wave train,and WPSH is stronger( weaker) shifting northwest( southeast) than normal years,cold and warm air activities make more( less) rainfall in North China.Vertically intergraded moisture fluxes was calculated,in order to show water transportation of summer drought /flood in North China and study the relationship between NPO in May and sea surface temperature in winter by using composition method. In the difference of vertically intergraded moisture fluxes field in summer,the moisture transport from the Arabian Sea and Bay of Bengal and the West Pacific make North China the positive anomaly of water vapor moisture,so there is more rainfall in North China; In divergence field,the water vapor divergence is negative in North China,so it is moisture sink and there is more rain. And also the Arabian Sea,Bay of Bengal,the south of Indo-China Peninsula to the South China Sea and the Western Pacific are the water vapor divergence centers,which are important vapor source for North China. The SST in winter in Pacific Ocean has forcing role on NPO in May,which influences summer drought /flood in North China.

Estimating Asian terrestrial carbon fluxes from CONTRAIL aircraft and surface CO&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt; observations for the period 2006–2010

Abstract. Current estimates of the terrestrial carbon fluxes in Asia show large uncertainties particularly in the boreal and mid-latitudes and in China. In this paper, we present an updated carbon flux estimate for Asia ("Asia" refers to lands as far west as the Urals and is divided into boreal Eurasia, temperate Eurasia and tropical Asia based on TransCom regions) by introducing aircraft CO2 measurements from the CONTRAIL (Comprehensive Observation Network for Trace gases by Airline) program into an inversion modeling system based on the CarbonTracker framework. We estimated the averaged annual total Asian terrestrial land CO2 sink was about −1.56 Pg C yr−1 over the period 2006–2010, which offsets about one-third of the fossil fuel emission from Asia (+4.15 Pg C yr−1). The uncertainty of the terrestrial uptake estimate was derived from a set of sensitivity tests and ranged from −1.07 to −1.80 Pg C yr−1, comparable to the formal Gaussian error of ±1.18 Pg C yr−1 (1-sigma). The largest sink was found in forests, predominantly in coniferous forests (−0.64 ± 0.70 Pg C yr−1) and mixed forests (−0.14 ± 0.27 Pg C yr−1); and the second and third large carbon sinks were found in grass/shrub lands and croplands, accounting for −0.44 ± 0.48 Pg C yr−1 and −0.20 ± 0.48 Pg C yr−1, respectively. The carbon fluxes per ecosystem type have large a priori Gaussian uncertainties, and the reduction of uncertainty based on assimilation of sparse observations over Asia is modest (8.7–25.5%) for most individual ecosystems. The ecosystem flux adjustments follow the detailed a priori spatial patterns by design, which further increases the reliance on the a priori biosphere exchange model. The peak-to-peak amplitude of inter-annual variability (IAV) was 0.57 Pg C yr−1 ranging from −1.71 Pg C yr−1 to −2.28 Pg C yr−1. The IAV analysis reveals that the Asian CO2 sink was sensitive to climate variations, with the lowest uptake in 2010 concurrent with a summer flood and autumn drought and the largest CO2 sink in 2009 owing to favorable temperature and plentiful precipitation conditions. We also found the inclusion of the CONTRAIL data in the inversion modeling system reduced the uncertainty by 11% over the whole Asian region, with a large reduction in the southeast of boreal Eurasia, southeast of temperate Eurasia and most tropical Asian areas.

Spatio-temporal variation of sediment transport in the Selenga River Basin, Mongolia and Russia

Many Asian rivers have been intensively used to boost economic growth, resulting in sudden and drastic changes in sediment transport patterns. However, a few rivers are still undisturbed. The present paper considers the unregulated Selenga River and its basin, located in Russia and Mongolia. The river contributes to 50 % of the total inflow to Lake Baikal. Pending scientific challenges include the quantification of sediment loads and erosion–deposition patterns along the Selenga River system, the understanding of suspended particulate matter composition and the importance of peak flow events for total sediment discharge and heavy metal transport. Field data and hydraulic modeling converge on showing that peak flow events during spring and summer contribute to the main part (70–80 %) of the annual sediment and pollution loads in upstream parts of the basin. The Selenga River carries mostly silt and sand. The average particle size differs by a factor of four between summer floods and base flow periods. The low amount of particulate organic matter (ranging between 1 and 16 % in the studied rivers) is consistent with the significant role of sediments originating from mining areas and in-channel sources. The bed load transport in the downstream part of the river basin is high (up to 50 % of the total transport), and channel storage plays an important role in the total sediment transport to Lake Baikal. Reported statistically significant multi-decadal declines in sediment fluxes in the downstream Selenga River can be attributed to the abandonment of cultivated lands and (most likely) to changing hydroclimatic factors.

Changes in runoff and eco-flow in the Dongjiang River of the Pearl River Basin, China

The Dongjiang River, one of the tributaries of the Pearl River, serves as the critical water source for Guangdong Province and the District of Hong Kong in China. In this study, the change trend and change points of flow at three main gaging stations in the Dongjiang River were analyzed using the nonparametric Mann-Kendall test and Pettitt-Mann-Whitney change-point statistics. Flow regime changes in the Dongjiang River were quantified by using both the Indicators of Hydrologic Alteration (IHA) parameters and eco-statistics, such as ecosurplus and ecodeficit. It was found that the change trend for annual median flow in the Dongjiang River increased over the past 60 years, with the major change occurring sometime between 1970 and 1974. IHA analyses showed that the magnitude of monthly flow decreased during the flood period, but increased greatly during the dry period. The median date of the one-day minimum flow moved ahead, and the duration of low pulse for the Dongjiang River was reduced significantly because of reservoir construction and operations. The IHA-based Dundee Hydrological Regime Alteration Method analysis indicated that all three stations have experienced a moderate risk of impact since 1974. The eco-statistical analyses showed that the majority of the flows appeared to be ecosurplus at all three locations after 1974, while flows with less than 30%, or higher exceedance probability, had ecodeficit in the summer flood period due to heavy reservoir operations.