The flood disasters caused a great loss of life and property in Yangtze River Basin during June-July of 2016. Meiyu became one of the main causes of flood disasters due to its high frequency, long duration and high intensity. In this study, chronology of extreme Meiyu events since 1736 was derived from Chinese historical documents and the observational data. Furthermore, and the long-term variation characteristics of extreme Meiyu events and relationships between extreme Meiyu and El Niño events were analyzed. The general circulation patterns were diagnosed to explain how El Niño influenced extreme Meiyu. The results show that there were 44 extreme Meiyu events (including 21 mega-Meiyu events) from 1736 to 2016. The most frequent occurrences of extreme Meiyu events were detected during 1901-1920 and 1991-2000. There were 21 mega-Meiyu events over the past 300 years, whose intensities were similar to that in 2016. Closely corresponding relationships was found between extreme Meiyu events and El Niño in this period. For example, 37 of total 44 extreme Meiyu events occurred in the El Niño episodes or their following years, and 16 of total 21 mega-Meiyu events occurred in the El Niño episodes. In the El Niño years, the meridional circulations were intensified over the mid-latitudes. The water vapor transported westerly and northerly to the mainland of China. A great amount of water vapor from south intersected with the cold air from high latitudes in the mid-lower reaches of the Yangtze River, which led to continuous precipitation. Moreover, in the El Niño following years, there was a steady subtropical high system at low latitudes. The transportation path of vapor was northerly, and then the vapor fluxes increased in Yangtze River Basin. It tends to cause extreme Meiyu events under this circulation background.
Based on the simulation of 1 000-year control experiment by the Community Earth System Model (CESM) with constant pre-industrial external forcing, 212 El Niño events and 226 La Niña events were identified according to the monthly SST (Sea Surface Temperature) of Nino3.4 region. Furthermore, the spatial pattern of May to September precipitation in eastern China in the El Niño (La Niña) episodes and their following years were illustrated. The relationship between the ENSO episodes and the floods/droughts of four regions including North China, Jianghuai, Jiangnan and South China in eastern China were analyzed. The results show that during the El Niño episodes, precipitation decreases by 2%-10% (with respect to the mean value of the whole 1 000 years) in North China and South China from May to September, and precipitation slightly increases by 0-2% in the Yangtze River Basin. In the following year of El Niño, precipitation in Jiangnan region turns to increase by 2%-10%, but precipitation in North China is still in decreasing conditions. During the La Niña episodes, precipitation in North China increases by 2%-10%. In the following year of La Niña, precipitation in Jianghuai decreases obviously by 2%-5%. The stronger El Niño (La Niña) events lead to more intense precipitation changing, and the percentages of precipitation anomalies increase. In the year when El Niño hasn’t vanished and La Niña starts to develop, the probability of flooding in the Jiangnan region might be more than twice as that in normal years. This finding provides background of abnormal climate for understanding the 2016 extreme flood in Yangtze River, and thoroughly reveals the influence of inter-annual internal variability in climate system on the changes of precipitation’s spatial patterns and regional flood/drought.
The differences of oceanic and atmospheric circulation anomalies between 2015 and 2016 are analyzed and their impacts on summer precipitation in China are investigated in this paper by using the monthly precipitation data of 160 stations in China and NCEP/NCAR monthly data. The results show that the distributions of summer precipitation anomalies are obviously different in 2015 and 2016. The summer precipitation anomalies are less over North China, but more over South China in 2015. Compared with 2015, the summer precipitations in 2016 increase obviously, especially in northern China, forming a longitudinal rain belt. The abnormal sea surface temperature (SST) in 2015 is corresponding to the development year of El Niño, warm phase of basin-wide SSTA variation in the tropical Indian Ocean (IOBW) and positive phase of Tropical Indian Ocean Dipole (TIOD), while the SST in 2016 shows the ending year of El Niño, warm phase of IOBW and negative phase of TIOD. In 2015, the western Pacific subtropical high is stronger and more southward than normal under the effect of SST anomalies in the tropical Indian-Pacific Ocean. It combined with active cold airs and southward westerly jet axis and thus resulted in the less precipitation over northern China and more precipitation over southern China. In 2016, El Niño decay and negative TIOD led the subtropical high northward, and the battery charge caused by warm IOBW led subtropical high stronger. The northward and stronger subtropical high met with weak cold air and northward westerly jet axis, which caused more precipitation in the middle and lower reaches of Yangtze River and the region north to it.
Intense human activity can quickly change the pattern of the land use/cover, and have a significant impact on the surface parameters and hydrological elements. The middle Yellow River, a typical region of GGP, was used to detect the process and trend of LUCC and identify the impact of GGP on surface parameters and hydrological elements. The results indicated that: 1) Although GGP did not significantly changed the distribution pattern of land use, it changed the speed of land use change and the balance status of land uses. After the implementation of GGP, the bidiredictional change of land use turned to one-way change from farmland to forest and grass. 2) There were significant differences of LUCC among subbasins. Before GGP, the change speed of LUCC in the Fenhe Basin was faster than in other regions, and was in quasi-balance status. In the early period of GGP, the net change speed and total change speed in Helong region and Weihe River Basin was faster than in other regions. However, there was no significant difference of speed in the end period of GGP, and it was in unbalanced status. 3) The GGP had significantly changed the terrestrial parameters and hydrological elements. The GGP implementation resulted in the significant increase of NDVI, LAI and emissivity and decrease of albedo, especially in the Helong region. In addition, the runoff coefficient decreased significantly, while evaporation coefficient increased significantly, especially in the Helong region.
Streamflow changes of the Yellow River Basin are heavily influenced by climate changes and human activities such as construction of water reservoirs, hence significant hydrological alterations and even dry-up events happened. In this case, deep understanding of eco-flow changes as a result of hydrological alterations is of great scientific and practical merits in scientific water management and sustainable exploitation of water resources of the Yellow River Basin. Therefore, this study attempts to quantify eco-flow and ecohydrological processes, and describes changes of streamflow downstream to hydraulic facilities in the Yellow River Basin using integrated ecological evaluation index, Do and DHRAM. Besides, SI and IHA 33 are used to analyze ecological effects of hydrological alterations. The results indicated that: 1) FDC is subject to general decrease due to hydrological alterations, and most streamflow components are lower than 25% FDC. Ecodeficit is evident in this case. 2) Impacts of precipitation on ecoflow indices are generally decreasing from upper to the lower Yellow River Basin while water reservoirs have enhancing influences on ecoflow indices. 3) ecohydrological indices are all in good relations with IHA, showing that ecohydrological variations are closely related to hydrological alterations in the Yellow River Basin. 4) Based on evaluation results with Do and DHRAM, ecological environmental risks caused by hydrological alterations are higher at Huayuankou, Sunkou and Lijin stations, moderate at Toudaoguai and Lanzhou stations and lower at Tangnaihai and Longmen stations. Ecological diversity is in significant decrease from upper to the lower Yellow River Basin. The results of this study shed new light on sustainable exploitation of water resources and ecological health of the Yellow River Basin. Human activities should be adapted to eco-flow changes.
Taking the Urumqi River Basin as a research area, this paper quantitatively analyzed the hydrological response to forest changes in the middle of the Tianshan Mountains. Based on the analysis of runoff change with hydrological and meteorological data (1980-2013), and using SWAT model and habitat limiting factors of spruce distribution, the influence of the change of spruce forest on runoff in different dry years was determined in five different distribution scenarios of spruce. The result shows that: 1) The calibrated SWAT model can simulate the monthly flows well and has high simulation precision, and the most sensitive parameters influencing model was CN2 according to the actual condition of forest land. The R2 and Ens of calibration and validation periods were all higher than 0.85, and the relative errors |Re| were all less than 5%. 2) In the same climate condition, the spruce forest changes in wet year, normal year, dry year showed linear correlation with runoff, 1% increase of spruce forest area resulting in runoff depth reduction of 0.06, 0.05 and 0.04 mm, respectively; and the runoff increased more significantly in wet year and normal year. 3) With the decrease of spruce forest area (the forest land cover reduced from 17.73% to 0%), the difference of the runoff variation coefficient and the fluctuation range between scenarios increased gradually, and the range of the runoff fluctuation can expand 5.1 times. The spruce forest in mountain area can effectively reduce the surface runoff and its fluctuation range. It has important significance for the stability of water resources (the uneven distribution of runoff), the quantitative research of forest water conservation, and the scientific regulation and management of water resources in forest regions.
Based on calculating grey water footprint in 31 provinces of China’s mainland from 1997 to 2013, we select the population and GDP as indicators, and use the Gini coefficient to study the spatial and structural equilibrium of the grey water footprint of China during 1998-2013 in this paper. The results suggest that: 1) In terms of regional equilibrium, the economic grey water footprint is worse compared with the population grey water footprint, being close to the warning line (0.4) for a long time, and the proportionality of the eastern regions in the economic grey water footprint is relatively low while the proportionality of the western regions in the population grey water footprint is relatively low. 2) In respect to structural equilibrium, the Gini coefficient of economic grey water footprint has been raised to 0.583 0, that is to say, the proportionality has reached the “big gap” range, and the Gini coefficients of both agriculture and industry are fluctuating in the vicinity of 0.4 in these years, and in the meanwhile the equilibrium of the economic grey water footprint of the life declined significantly in recent years. 3) From the marginal effect point of view, the overall equilibrium can be improved by reducing the grey water footprint of the heavily polluted regions in the central and western regions and the agricultural grey water footprint of each province, and the equity of China’s water environment can be promoted effectively. At last, aiming at the specific problems of the grey water footprint balance in China, we put forward suggestions to reduce the grey water footprint and improve the equity of the water environment in China.
The paper, based on relationship between water resources use and socio-economic development, develops the water resources use development path by applying water use data from different economic entities; and applies the established path to assess the water resources use development processes since 1980 for China and its provinces.
The water use development process has a clear path. The path can be explained by water indicators including water use structure, water productivity, domestic water use per capita, water use per GDP, water use per industrial value-added, and population ratio access to clean water supply. These indicators display changes of the economic development of different economic entities from low income, lower middle income and upper middle income to high income. During this development process, the agricultural water use percentage decreases grammatically from more than 90% to about 40%; the domestic water use per capita increases gradually from 80 L/d to 380 L/d; the water use per industrial value-added decreases significantly; the water productivity increases greatly from less than 2 $/m3 to more than 30 $/m3; and it realizes full population coverage of clean water supply.
Although on the same development way with those international economies, there exist biases of some water use development indicators in China since 1980 resulted from the unbalanced social and economic development. More secondary industries and lagged development of urbanization and tertiary industry caused higher industrial water use and lower domestic water use per capita. Therefore, the water use development in China is behind the economic development in general.
The provinces demonstrate significant regional differences. There are more provinces with water use development lagging behind economic development. The water use data in 1993, 2000 and 2011 show that the provinces with water use development lagging behind economic development are suffered from lower water use, lower domestic water use per capita, and/or lower water productivity. Beijing is the only province that the water use development goes ahead the social and economic development all the time. Therefore, the key task for water sector in China is to make the development of water use catch up with the economic development.
The uncertainty of the satellite rainfall products limits their applicability in mountainous areas. This paper evaluates theapplicability of a new rainfall product-Global Precipitation Measurement (GPM) in Tianshan Mountain area based on the meteorological stations data and commonly used precipitation products-TRMM and CMORPH. The data of a total of 167 weather stations from 2014 to 2015 were used to evaluate and compare the accuracies of GPM, TRMM and CMORPH. Root mean square error (RMSE), Correlation coefficient (R), Percent bias (PB) and Classification statistical analysis index (FAR, POD, ETS, BIAS) were used to assess the applicability of GPM. The result shows that: GPM has the higher accuracy than the other two commonly used satellite rainfall products. Specifically: 1) Although three data sets perform well in summer and autumn, GPM has the highest correlation (R≥0.6) and the smallest relative error (PB≈10%) between the observed data, compared to TRMM and CMORPH. 2) Throughout the Tianshan Mountains, GPM shows the lower error range (-55%-55%). 3) In different elevation zones, GPM shows the lower relative error and higher correlation coefficient. 4) Three sets of data all show higher accuracy (POD≈0.58) and lower error rate (FAR≈0.63) when detecting the weak precipitation. The comprehensive statistical analysis of four indexes indicates that GPM performs the best and estimates the precipitation with higher accuracy and lower error.
Poyang Lake Plain (PLP) is one of the important rice-producing regions in China, characterized by typical single-and double rice cropping systems (RCS), which are particularly suited for remote sensing monitoring. Investigation on the changes of the RCS in the major rice-producing area (MRPA) of the PLP is of great importance in evaluating farmland use intensity, enhancing food provision and ensuring regional grain security. Taking the MRPA as a study area, Landsat TM/ETM+/OLI images in 2005 and 2013 were used to classify the paddy fields and delineate the RCS within critical temporal windows which is defined by local rice calendar, cloud coverage percentage of scenes and precipitation data. Meanwhile, 677 valid questionnaires focusing on the changes of RCS during 2014-2015 were collected across the PLP. The results showed that: 1) The duration from middle September to early October is proved to be the critical time window for the differentiation of RCS in the PLP. There are 484 LandsatTM/ETM+/OLI scenes with cloud coverage less than 10% in the study area, accounting for 20% of the total observations during 1983-2015, in which 27% were acquired in September and October. Moreover, there is less rainfall in this period, only 4% of the annual precipitation. 2) During 2005-2013, the area of paddy field declined by 2.68% while the multiple cropping index of paddy rice increased from 147.7% to 156.7% accordingly. Specifically, the single cropping rice reduced by 1 061.35 km2, and double cropping rice increased by 1 564.45 km2. 3) Spatially, both rice types were distributed across the study area, but the single cropping rice mainly distribute to the north of Ganjiang and Raohe River, while the double cropping rice mainly distribute to the south of Ganjiang and Raohe River. Double-season rice is mostly cultivated in the delta plains of Ganjiang River and Xinjiang River, while single-season rice is generally distributed in the lowland around the Poyang Lake and the periphery area of the cities and towns. 4) About 30% of the interviewed households altered their rice cropping systems, and 14.2% of them changed double seasons to single season. Besides, there was farmland abandonment in about 44.4% counties. The areal ratio of abandoned farmland or occupied farmland in the study area was 4.9%.
The spatial variation of soil properties is a function of spatial scales. The spatial structure of soil properties in special scale can be discovered with single sample density, however, the whole variation could be discovered with multiple sample densities. The study area locates in Zhangjiagang County, which is a part of Yangtze River delta. Soil organic matter (SOM) is one of the important issues in global change research, thus in this paper the top SOM content in fertilized area is studied. Four hundred and thirty one samples were collected as the fundamental data, 11 levels of density or scale were designed with grid centroid sampling method, then classic statistics, semi-variance function, Moran’s I, spatial fractal dimensions and Kriging interpolation were explored to investigate the variation of SOM in spatial structure, randomness and spatial patterns at different sampling densities. The results shows: There is a low influence of sampling density on SOM variation coefficient. The variation coefficients of SOM at 11 sampling densities are among 21.70%-23.12%, which belongs to the moderate variation. With the decrease of the sampling density or the increase of scale unit, the corresponding ratio of nugget/sill falls from 37.52% to 18.70%, fractal dimension falls from 1.838 to 1.714, and the Moran’s I index increases from 0.485 to 0.857, which indicates the components of spatial structure variation is increasing and spatial correlation is gradually enhanced. The content of SOM shows decreasing trend from southwest to northeast. The spatial pattern of SOM content becomes simple with the decrease of sampling density since more and more details in micro-areas are ignored. In general, the model inference accuracy of SOM is reliable and the spatial character is stable when the sampling density is lower than 0.179 sample per km2. In consideration of science and economy, it can be concluded that the density of 0.179 sample per km2 can reflect the spatial randomness and structure of SOM in the study area, and this density can be regarded as the best sampling density. The paper takes sampling densities as cases to reveal the multiple spatial scale characteristics of SOM, and provides a helpful reference for hierarchical analysis of soil properties.
The contradiction between urban master planning, land use planning, environmental protection planning greatly affect the stability and longevity of prime farmland. This is not conducive to food security and economic development. Taking Yujiang County, Jiangxi Province as an example, the paper demarcates the prime farmland on the basis of coordinating the relationship of these plannings. The cultivated land around the city whose natural quality is higher than the average level of the study area was classified into prime farmland. For the other cultivated land, a cultivated land quality comprehensive evaluation system was constructed with evaluation indicators including natural quality, the distance to countryside, the distance to city, the distance to traffic trunk line, spatially contiguous and regular degree. A comprehensive evaluation method for basic farmland is proposed. According to the index of prime farmland protection in land use planning, the final area of prime farmland was determined. The result shows that: The final area of designated prime farmland around the city is 4 474.65 hm2, the area of prime farmland designated from other cultivated land is 24 045.13 hm2, and the total area of prime farmland is 28 519.78 hm2, mainly in the river valley and plains in the central regions of Yujiang County. Comparing with the existing prime farmland, the unchanged prime farmlands are the best to be demarcated into prime farmland. The prime farmlands which are transferred into prime farmland not only have better natural quality, location condition and spatial pattern, but also are conducive to the optimization of the city spatial pattern. The farmlands which are transferred out have low regular degree or spatially contiguous, serious pollution or overlap with construction land in urban master planning and land use planning. The method proposed in this paper can not only promote the space convergence about Multi-planning-in-one, but also provide a new idea for the prime farmland delimitation.
The network of high-speed rail (HSR) adds new elements to the tourism industry in China and produces new changes of tourism destinations. Taking Huangshan City as an example, using tourists flow trajectories and related travel attribute data before and after the opening of Beijing-Fuzhou HSR obtained from field research and network retrieval, the impact of Beijing-Fuzhou HSR on the spatial structure of tourist destination district in Huangshan City was analyzed. The result shows :1）After the opening of HSR, the radius of domestic tourist market extended outwardly, and the tourist flows of Fujian, Shandong, Beijing and other cities along the HSR show the “reverse decay” phenomenon. 2）After the opening of HSR, nodes of tourist destination district changed, and the spatial range tourist destination districts extended. Before and after the opening of HSR, the high-frequency node pairs on the whole network are mainly interregional nodes (such as Huangshang - Yangtze River Delta, Huangshan - Jiangxi Province), supplemented with intro-regional node pairs (such as Huangshan - Hefei, Huangshan - Chizhou, Huangshan - Xuancheng). The function of the whole network is less developed, and there is apparent stratification of the network. After the opening of HSR, the core area of whole network changed. The centralized distribution of core nodes changed to decentralized distribution, so the connection between core areas and marginal areas became loose, and the radiation effect of core area became weaker. The degree centrality values of core nodes and important nodes changed greatly, while the betweens centrality values did not change much. The structural hole levels of core nodes are high, showing the prominent function of the nodes. 3) Before and after the opening of HSR, the spatial structure of the tourist destination districts in Huangshan City has the plate pattern, including Huangshan - Yangtze River Delta plate, southern Anhui tourism area plate (Huangshan - Chizhou - Xuancheng), and Huangshan - Jiangxi plate. The spatial development mode of the destination districts gradually changed from “single core - periphery” to “dual core - periphery”, from cluster to dispersion. The research of the impact of HSR on the tourism development in Huangshan City provides a general reference for the tourism development of Huangshan City and the surrounding areas.
Coupling coordination between vegetation and soil is an important symbol of positive succession during gully vegetation restoration processes. Based on the investigation and analysis of vegetation and soil of three different vegetation restoration pattern gullies, a two-level target system with nine vegetation factors and eleven soil factors was conducted, and the weights of factors were determined by analytic hierarchy process (AHP). Furthermore, models of vegetation and soil coupling degree and coupling coordinative degree were constructed. The results showed that vegetation-soil system in gullies with different vegetation restoration patterns were all in the intermediate level of coordination after twenty years of vegetation restoration. The development of vegetation and soil in Robinia pseudoacacia forest gully exhibited a synchronous style. The development of soil in Caragana korshinskii shrubland gully and natural grassland gully lagged behind the development of vegetation. Linear regression analysis showed that there were different environmental factors (vegetation community or soil conditions) impacting on different vegetation properties and soil properties. There are some differences in coupling coordination between vegetation and soil in gullies with different vegetation restoration patterns in the hilly Loess Plateau, which may resulted from the biological characteristics of the dominant species in the plant communities.
