Spatio-temporal Variation Characteristics of Extreme Climate Events and Their Teleconnections to Large-scale Ocean-atmospheric Circulation Patterns in Huaihe River Basin,China During 1959–2019

Huaihe River Basin(HRB) is located in China’s north-south climatic transition zone,which is very sensitive to global climate change.Based on the daily maximum temperature,minimum temperature,and precipitation data of 40 meteorological stations and nine monthly large-scale ocean-atmospheric circulation indices data during 1959–2019,we present an assessment of the spatial and temporal variations of extreme temperature and precipitation events in the HRB using nine extreme climate indices,and analyze the teleconnection relationship between extreme climate indices and large-scale ocean-atmospheric circulation indices.The results show that warm extreme indices show a significant(P < 0.05) increasing trend,while cold extreme indices(except for cold spell duration) and diurnal temperature range(DTR) show a significant decreasing trend.Furthermore,all extreme temperature indices show significant mutations during 1959-2019.Spatially,a stronger warming trend occurs in eastern HRB than western HRB,while maximum 5-d precipitation(Rx5day) and rainstorm days(R25) show an increasing trend in the southern,central,and northwestern regions of HRB.Arctic oscillation(AO),Atlantic multidecadal oscillation(AMO),and East Atlantic/Western Russia(EA/WR) have a stronger correlation with extreme climate indices compared to other circulation indices.AO and AMO(EA/WR) exhibit a significant(P < 0.05) negative(positive)correlation with frost days and diurnal temperature range.Extreme warm events are strongly correlated with the variability of AMO and EA/WR in most parts of HRB,while extreme cold events are closely related to the variability of AO and AMO in eastern HRB.In contrast,AMO,AO,and EA/WR show limited impacts on extreme precipitation events in most parts of HRB.

Assessing the Seasonal Predictability of Summer Precipitation over the Huaihe River Basin with Multiple APCC Models

Seasonal rainfall predictability over the Huaihe River basin is evaluated in this paper on the basis of 23-year(1981-2003) retrospective forecasts by 10 climate models from the Asia-Pacific Economic Cooperation(APEC) Climate Center(APCC) multi-model ensemble(MME) prediction system.It is found that the summer rainfall variance in this basin is largely internal,which leads to lower rainfall predictability for most individual climate models.By dividing the 10 models into three categories according to their sea surface temperature(SST) boundary conditions including observed,predicted,and persistent SSTs,the MME deterministic predictive skill of summer rainfall over Huaihe River basin is investigated.It is shown that the MME is effective for increasing the current seasonal forecast skill.Further analysis shows that the MME averaged over predicted SST models has the highest rainfall prediction skill,which is closely related to model's capability in reproducing the observed dominant modes of the summer rainfall anomalies in Huaihe River basin.This result can be further ascribed to the fact that the predicted SST MME is the most effective model ensemble for capturing the relationship between the summer rainfall anomalies over Huaihe River basin and the SST anomalies(SSTAs) in equatorial oceans.

The Analysis on the Temporal and Spatial Variation of Strong Precipitation Caused Flood and Agricultural Disaster Loss in Huaihe River Basin of Anhui Province during Meiyu Period of 2007

[Objective] The research aimed to analyze temporal and spatial variation of strong precipitation caused flood and agricultural disaster loss in Huaihe River basin of Anhui Province during Meiyu period of 2007.[Method] On the basis of rainfalls of each station in Huaihe River basin of Anhui,rainfall data during Meiyu period of 2007 and flood disaster data in the same period,the temporal and spatial distribution characteristics of strong precipitation caused flood during Meiyu period of 2007 and its harm on agriculture were analyzed.The variation rule,distribution characteristics of strong precipitation during Meiyu period in Huaihe River basin of Anhui and its relationship with agricultural disaster loss were discussed.[Result] During Meiyu period of 2007 in Huaihe River basin of Anhui,the rainstorm was more,and the rainfall was large.The precipitation variation showed 'three-peak' trend.Rainfall in Huaihe River basin during Meiyu period of 2007 was greatly more than that homochronously in Yangtze River basin.The rain area over 400.0 mm during Meiyu period mainly located in Huaihe River basin,and the rain area over 600.0 mm mainly located from area along Huaihe River to central Huaibei.The rainfall during Meiyu period gradually decreased toward south and north by the north bank of Huaihe River as the symmetry axis.The rainfall in area along Huaihe River showed wavy distribution in east-west direction.The flood disaster loss index and disaster area of crops in Huaihe River basin of Anhui both increased as rainfall in Meiyu period.[Conclusion] The research provided theoretical basis for flood prevention,disaster reduction and agricultural flood-avoiding development in Huaihe River basin.

Application of a Coupled Land Surface-Hydrological Model to Flood Simulation in the Huaihe River Basin of China

A hydrological simulation in the Huaihe River Basin(HRB) was investigated using two different models: a coupled land surface hydrological model(CLHMS), and a large-scale hydrological model(LSX-HMS). The NCEP-NCAR reanalysis dataset and observed precipitation data were used as meteorological inputs. The simulation results from both models were compared in terms of flood processes forecasting during high flow periods in the summers of 2003 and 2007, and partial high flow periods in 2000. The comparison results showed that the simulated streamflow by CLHMS model agreed well with the observations with Nash-Sutcliffe coefficients larger than 0.76, in both periods of 2000 at Lutaizi and Bengbu stations in the HRB, while the skill of the LSX-HMS model was relatively poor. The simulation results for the high flow periods in 2003 and 2007 suggested that the CLHMS model can simulate both the peak time and intensity of the hydrological processes, while the LSX-HMS model provides a delayed flood peak. These results demonstrated the importance of considering the coupling between the land surface and hydrological module in achieving better predictions for hydrological processes, and CLHMS was proven to be a promising model for future applications in flood simulation and forecasting.

RELATIONSHIPS BETWEEN THE POSITION VARIATION OF THE WEST PACIFIC SUBTROPICAL HIGH AND THE DIABATIC HEATING DURING PERSISTENT INTENSE RAIN EVENTS IN YANGTZE-HUAIHE RIVERS BASIN

By using NCEP/NCAR daily reanalysis data and daily precipitation data of 740 stations in China, relationships between the position variation of the West Pacific subtropical high (WPSH) and the diabatic heating during persistent and intense rains in the Yangtze-Huaihe Rivers basin are studied. The results show that the position variation of WPSH is closely associated with the diabatic heating. There are strong apparent heating sources and moisture sinks in both the basin (to the north of WPSH) and the north of Bay of Bengal (to the west of WPSH) during persistent and intense rain events. In the basin, Q 1z begins to increase 3 days ahead of intense rainfall, maximizes 2 days later and then reduces gradually, but it changes little after precipitation ends, thus preventing the WPSH from moving northward. In the north of Bay of Bengal, 2 days ahead of strong rainfall over the basin, Q 1z starts to increase and peaks 1 day after the rain occurs, leading to the westward extension of WPSH. Afterwards, Q 1z begins declining and the WPSH makes its eastward retreat accordingly. Based on the complete vertical vorticity equation, in mid-troposphere, the vertical variation of heating in the basin is favorable to the increase of cyclonic vorticity north of WPSH, which counteracts the northward movement of WPSH and favors the persistence of rainbands over the basin. The vertical variation of heating in the north of Bay of Bengal is in favor of the increase of anti-cyclonic vorticity to the west of WPSH, which induces the westward extension of WPSH.

Possible connection between anomalous activity of Scandinavian Atmospheric Teleconnection Pattern and winter snowfall in the Yangtze-Huaihe River Basin of China

利用中国地面气候资料日值数据集(V3.0)逐日气象资料研究了我国江淮冬季降雪的时空变化及其与斯堪的纳维亚遥相关型(SCAND)的可能联系。结果表明:江淮冬季降雪表现出空间一致的年际变化,SCAND与江淮地区冬季降雪异常关系密切。江淮冬季降雪偏多通常对于SCAND正位相,500hPa阻塞高压、东亚大槽加强,有利于冷空气活动增强,江淮地区垂直运动增强,水汽输送增强;降雪偏少则对应SCAND负位相。研究结果有助于深入理解江淮冬季降雪异常的相关机理。

Analysis on the Climate Characteristics of Rainstorm Weather over Huaihe River Basin and Its Influence on Agriculture Production

By the daily precipitation data at 18 meteorological stations of Huaihe River basin in recent 50 years,the temporal-spatial distribution features of the rainstorm over Huaihe River basin during 1958- 2007 and its influence on agriculture production were analyzed. The results showed that the interannual change magnitudes of the rainstorm days and rainstorm amount from 1958 to 2007 were fierce. Especially in the late 1990 s,rainstorm days and rainstorm amount increased obviously. As a result of interannual variability of East Asian summer monsoon and East Asian circulation system,rainstorm had significant quasi-2-year periodic oscillation in summer. Because of water vapor and terrain,rainstorm mainly concentrated in the southwest over the Huaihe River basin,but was less in the north.

Analysis of Causes and Seasonal Prediction of the Severe Floods in Yangtze／Huaihe Basins during Summer 1991

The present paper shows that a seasonal prediction for the large scale flooding and waterlogging of the mid-lower Yangtze/ Huaihe River basins in the summer of 1991 made successfully in early April 1991.The seasonal forecasting method and some predictors are also introduced and analyzed herein. Because the extra extent of the abnormally early onset of the plum rain period in 1991 was unexpected,great efforts have been made to find out the causes of this abnormality. These causes are mainly associated with the large scale warming of SST surrounding the south and east part of Asia during the preceding winter,while the ENSO-like pattern of SSTA occurred in the North Pacific.In addition,the possible influence of strong solar proton events is analyzed.In order to improve the seasonal pre4iction the usage of the predicted SOl in following spring/summer is also introduced.The author believes thatthe regional climate anomaly can be correctly predicted for one season ahead only on the basis of physical understanding of the interactions of many preceding factors.

Hydrological Processes in the Huaihe River Basin, China： Seasonal Variations, Causes and Implications

Understanding streamflow changes in terms of trends and periodicities and relevant causes is the first step into scientific management of water resources in a changing environment. In this study, monthly streamflow variations were analyzed using Modified Mann-Kendall(MM-K) trend test and Continuous Wavelet Transform(CWT) methods at 9 hydrological stations in the Huaihe River Basin. It was found that: 1) streamflow mainly occurs during May to September, accounting for 70.4% of the annual total streamflowamount with Cv values between 0.16–0.85 and extremum ratio values between 1.70–23.90; 2) decreased streamflow can be observed in the Huaihe River Basin and significant decreased streamflow can be detected during April and May, which should be the results of precipitation change and increased irrigation demand; 3) significant periods of 2–4 yr were detected during the 1960 s, the 1980 s and the 2000 s. Different periods were found at stations concentrated within certain regions implying periods of streamflow were caused by different influencing factors for specific regions; 4) Pacific Decadal Oscillation(PDO) has the most significant impacts on monthly streamflow mainly during June. Besides, Southern Oscillation Index(SOI), North Atlantic Oscillation(NAO) and the Ni?o3.4 Sea Surface Temperature(Ni?o3.4) have impacts on monthly streamflow with three months lags, and was less significant in time lag of six months. Identification of critical climatic factors having impacts on streamflow changes can help to predict monthly streamflow changes using climatic factors as explanatory variables. These findings were well corroborated by results concerning impacts of El Nino-Southern Oscillation(ENSO) regimes on precipitation events across the Huaihe River Basin. The results of this study can provide theoretical background for basin-scale management of water resources and agricultural irrigation.

Effect and Risk Assessment of Animal Manure Pollution on Huaihe River Basin, China

Currently the deteriorated water quality for Huaihe River Basin(HRB) in China was still serious because of the negative influence multiple pollution sources including animal manure. However, little attention was paid to the potential risk of animal manure for farmland and water quality of HRB. This study was quantified and forecasted animal manure risk and its spatiotemporal variations in HRB from 2008 to 2018, through pollution discharge coefficient method and pollution load calculation, combined with kriging interpolation method of ArcGIS technology, based on statistics principle. All the data were originated from livestock and poultry breeding in HRB from 2008 to 2018. The future risk of farmland and water environment in HRB was further forecasted. The results indicated that the livestock and poultry manure has become a key pollution source causing a negative influence on farmland and water quality owing to a large amount of animal manure production without efficient recycle utilization. The chemical oxygen demand(COD) and total nitrogen(TN) discharge of animal manure in HRB almost accounted for 17.00% and 39.00% of the whole COD and TN discharge in China. The diffusion concentration of TN and TP in those regions of Shangqiu, Zhoukou, Heze, Zhumadian, Luohe, Jining, Xuchang,Kaifeng, Taian and Zhengzhou of HRB has exceeded the threshold value 10.00 mg/L of TN and 0.08 mg/L of TP, causing water eutrophication and cancer villages. The assessment of farmland and water quality risk revealed that Zhumadian, Zhoukou, Shangqiu, Taian, Jining, Heze, Linyi and Rizhao belonged to high risk areas in HRB, which were still obtained high farmland and water quality risk index in 2030. The results provided insight into an important significance of sustainable balance of livestock and poultry development and ecosystem in HRB.

Analysis and Zoning of Rainstorm Flood Disaster Risk in Huaihe River Basin

Taking the rainstorm flood disaster of Huaihe River basin as the research object,according to the principles of risk assessment for natural disasters,starting from the fatalness of inducing factors and the vulnerability of hazard bearing body,the weight of each impact factor was calculated by using AHP. By using spatial analysis and statistical function of GIS,the integrated risk chart of rainstorm flood disaster in Huaihe River basin was obtained. The results showed that the high risk areas of rainstorm flood disaster in Huaihe River basin mainly distributed in the southern part of Henan,the central northern part of Anhui and eastern part of Jiangsu Province. Due to higher fatalness of inducing factors in southern Henan,there was high risk in the region. Central Anhui and east Jiangsu were not only high-fatalness zones but also high vulnerability zones of population and economy.

Source apportionment of river water pollution in a typical agricultural city of Anhui Province, eastern China using multivariate statistical techniques with APCS– MLR

The deterioration of the surface water environment has become a serious challenge for water resources management due to increasing anthropogenic disturbance. Water resources protection requires control of potential pollution sources. In this study, 99 water samples were collected from a river in a typical agricultural city of Anhui Province in eastern China, and these samples were analyzed in terms of pH, electrical conductivity, and the concentrations of F-, Cl-, SO42-, Na+, K+, Mg2+, Ca2+, As, Cr, Cu, Zn, and Pb. Cluster analysis, co-occurrence network analysis, and principal component analysis/factor analysis were conducted to qualitatively identify the potential sources of river water pollution in the study area. An absolute principal component score-multiple linear regression receptor model was used to quantitatively evaluate the contribution of each source to water quality parameters. The results showed that all observed water quality indices met the quality criteria specified in the Chinese drinking water standards, except for pH, ρ(F-), ρ(SO42-), and ρ(As). The heat map showed that the frequent recharge of pollutants from the tributaries during the wet season was the main reason for the deterioration of water quality. Five sources of river water pollution were identified, and their contribution ratios in a descending order were as follows: the geogenic process (24%) > agricultural activities (21%) > poultry farming sources (17%) > domestic pollution (9%) > transportation pollution (5%). Therefore, controlling pollution from agricultural activities, strengthening the regulation of livestock farming, and improving the sewage network are the recommended strategies for improving the quality of surface water resources in this area.

Flood and Waterlogging Monitoring over Huaihe River Basin by AMSR-E Data Analysis

In this paper, we investigated the potential of Advanced Microwave Scanning Radiometer for Earth Observation System (AMSR-E) for flood monitoring. The proposed approach was based on the polarized ratio index (PRI), which was computed by using AMSR-E data at 37GHz, vertically and horizontally polarized brightness temperature values and the water surface fraction (WSF) got by using the PRI at 37GHz. Moderate Resolution Imaging Spectrora-diometer (MODIS) data were used to validate the WSF values. The analysis of flood and waterlogging using the WSF map on July 6, 2003 indicates that the use of WSF for flood and waterlogging disaster assessment is feasible. Utilizing the correlation of WSF derived from AMSR-E and water area derived from MODIS, the water area of the Huaihe River Basin were computed by only using AMSR-E data in the summer of 2003, which overcame the influence of cloud on water estimation using MODIS data during flood.

Zoning assessment of water environmental supporting capacity for socioeconomic development in the Huaihe River Basin, China

There have been substantial conflicts in the human-water relationship in the Huaihe River Basin （HRB）. To achieve sustainable economic development without degrading the water environment in the HRB, we develop a three-dimensional water environmental sup- porting capacity （WESC） model based on water environmental carrying capacity （WECC）, water environmental pressure （WEP）, and water pollution prevention and control capacity （WPPC）. Geographic information systems spatial analysis with the analytical hierarchy process method and dynamic weighted summation is applied. Several proposals for suitable locations for industry and environmental protection strategies for water were presented. The following results were obtained. （1） The spatial differences in WECC are substantial; areas with high-value WECC zones are mainly located along the main stream of the Huaihe River on the south side. WEP is generally high, with an overall low level of pollution prevention and control in the whole HRB. WPPC and WEP show high spatial overlapping due to the fact that areas with higher environmental pollution usually have high level of economic development, and thus have a strong capacity for pollution control. （2） Overall, WESC is moderate in the HRB. In particular, areas with a high WESC value only account for 56.24% of the HRB in 2010 Distinct differences in WESC also exist between areas located in the south compared with in the north of the basin, and areas alongside the downstream region compared with alongside the upstream and midstream regions. （3） Consequently, according to the guidance for indus- try zoning in the HRB, the areas in the south and alongside the downstream and sub-streams with a low WEP value and high WECC and WPPC, traditional industries should be developed based on strict environmental access and pollution emission standards. While for the areas along the midstream of the HRB and along the whole Yishusi River Basin, which have a high WEP value, industrial restructuring and technological upgrading are suggested. Action should be taken to limit development and protect the environment in the upstream region of the basin which is a key source of drinking water, in the eastern route along the line of the South-toNorth Water Diversion Project, and in the ecologically fragile region alongside the basin. This will ensure good environmental functionality including subsistent provision of clean water, while at the same time satisfying the urgent need to adjust, transform, and upgrade the industrial structure.

Isotopic evidence for the moisture origin and composition of surface runoff in the headwaters of the Heihe River basin

We investigated the moisture origin and contribution of different water sources to surface runoff entering the headwaters of the Heihe River basin on the basis of NECP/NCAR(National Centers for Environmental Prediction/National Center for Atmospheric Research) re-analysis data and variations in the stable hydrogen and oxygen isotope ratios(δ D and δ 18O) of precipitation,spring,river,and melt water. The similar seasonality in precipitation δ 18O at different sites reveals the same moisture origin for water entering the headwaters of the Heihe River basin. The similarity in the seasonality of δ 18O and d-excess for precipitation at Yeniugou and Urumchi,which showed more positive δ 18O and lower d-excess values in summer and more negative δ 18O and higher d-excess values in winter,indicates a dominant effect of westerly air masses in summer and the integrated influence of westerly and polar air masses in winter. Higher d-excess values throughout the year for Yeniugou suggest that in arid inland areas of northwestern China,water is intensively recycled. Temporal changes in δ 18O,δ D,and d-excess reveal distinct contributions of different bodies of water to surface runoff. For example,there were similar trends for δ D,δ 18O,and d-excess of precipitation and river water from June to September,similar δ 18O trends for river and spring water from December to February,and similar trends for precipitation and runoff volumes. However,there were significant differences in δ 18O between melt water and river water in September. Our results show that the recharge of surface runoff by precipitation occurred mainly from June to mid-September,whereas the supply of surface runoff in winter was from base flow(as spring water) ,mostly with a lower runoff amount.

A comparative study of the atmospheric circulations associated with rainy-season floods between the Yangtze and Huaihe River Basins

Here we present the results from the composite analyses of the atmospheric circulations and physical quantity fields associated with rainy-season for the selected floods cases over the Yangtze and Huaihe River basins for the 21 years(1990–2010),using the daily rain gauge measurements taken in the 756 stations throughout China and the NCEP/reanalysis data for the rainyseasons(June–July)from 1990 to 2010.The major differences in the atmospheric circulations and physical quantity fields between the Yangtze and Huaihe River basins are as follows:for flooding years of the Yangtze River Basin,the South Asia high center is located further east than normal,the blocking high over the Urals and the Sea of Okhotsk maintains,and the Meiyu front is situated near 30°N whereas for flooding years of the Huaihe River Basin,the South Asia high center is further west than normal,the atmospheric circulations over the mid and high latitudes in the Northern Hemisphere are of meridional distribution,and the Meiyu front is situated near 33°N.In addition,there are distinct differences in water vapor sources and associated transports between the Yangtze and Huaihe River basins.The water vapor is transported by southwesterly flows from the Bay of Bengal and monsoon flows over the South China Sea for flooding years of the Yangtze River Basin whereas by southeast monsoons from the eastern and southern seas off China and monsoon flows over the South China Sea for flooding years of the Huaihe River Basin.

Evaluation and Analysis of RegCM3 Simulated Summer Rainfall over the Huaihe River Basin of China

This study evaluates the ability of the Abdus Salam International Center for Theoretical Physics （ICTP） version 3 Regional Climate Model （RegCM3） in simulating the summer rainfall amount and distribution and large-scale circulation over the Huaihe River basin of China. We conducted the simulation for the period of 1982-2001 and the wet year of 2003 to test the ensemble simulation capacity of RegCM3. First, by comparing the simulated rainfall amount and distribution against the observations, it is found that RegCM3 can reproduce the rainfall pattern and its annual variations. In addition, the simulated spatial patterns of 850-hPa wind and specific humidity fields are close to the observations, although the wind speed and humidity values are larger. Finally, the ensemble simulation of RegCM3 for summer 2003 failed to capture the spatial distribution and underestimated the magnitude of the precipitation anomalies, and the reasons are analyzed.

Variations of Meiyu Indicators in the Yangtze-Huaihe River Basin during 1954-2003

To better understand climate variations of Meiyu, some new indicators for theonset and retreat dates, duration, and Meiyu precipitation in the Yangtze-Huaihe River valley areobjectively developed by using observed daily precipitation data from 230 stations in eastern Chinaduring 1954-2003. The rainy season onset and retreat dates in each station can be denned in terms ofthresholds for rainfall intensity and persistence. Then, the onset and retreat dates of the Meiyufor the Yangtze-Huaihe River basin have been determined when more than 40% of stations reach thefirst rainy season thresholds in the study region. Based on the indicators of Meiyu in theYangtze-Huaihe River basin, variations of Meiyu rainfall during 1954-2003 are analyzed. The resultssuggest that Meiyu rainfall in the Yangtze-Huaihe River basin has increased in recent 50 years. Inaddition, interannual and interdecadal variability of Meiyu is also obvious. All the indicatorsdisplay a predominant period of about 3 years.

Spatio-temporal accuracy evaluation of MSWEP daily precipitation over the Huaihe River Basin,China:A comparison study with representative satellite-and reanalysis-based products

Multi-source weighted-ensemble precipitation(MSWEP)is one of the most popular merged global precipitation products with long-term spanning and high spatial resolution.While various studies have acknowledged its ability to accurately estimate precipitation in terms of temporal dynamics,its performance regarding spatial pattern and extreme rainfall is overlooked.To fill this knowledge gap,the daily precipitation of two versions of MSWEP(MSWEP V2.1&V2.2)are compared with that of three representative satellite-and reanalysis-based products,namely the Tropical Rainfall Measuring Mission(TRMM 3B42 V7),the climate prediction center morphing technique satellite-gauge merged product(CMORPH BLD),and the fifth-generation reanalysis product of the European Centre for Medium Range Weather Forecasts(ERA5).The comparison is made according to the dense daily rainfall observations from 539 rain gauges over the Huaihe River Basin in China during 2006–2015.The results show that MSWEP V2.1,MSWEP V2.2 and CMORPH BLD have better performance on temporal accuracy of precipitation estimation,followed by ERA5 and TRMM 3B42V7.MSWEPs yield the most even spatial distribution across the basin since it takes full advantage of the multi datasets.As the weighted-ensemble method is independently carried out on each grid in MSWEPs,the spatial distribution of local precipitation is changed by different source data,which results in that MSWEPs perform worse than CMORPH BLD in terms of the representation of precipitation spatial pattern.In addition,the capability of MSWEPs to describe the spatial structure in the rainy season is lower than that in the dry season.Strong precipitation(≥100 mm/d)events are better represented in TRMM 3B42 V7 products than in MSWEPs.Finally,based on the comparison results,we suggest to improve the merging algorithm of MSWEP by considering the precipitation spatial self-correlation and adjusting the merging weights based on the performance of the source datasets under different precipitation intensities.