Gan River Basin Research Articles

Flood risk transfer analysis based on the “Source-Sink” theory and its impact on ecological environment: A case study of the Poyang Lake Basin, China

Driven by climate change, the frequent occurrence of regional destructive floods poses a grave threat to socio-economic systems and ecological environments. Previous flood risk studies have disregarded risk transfer within a region, resulting in inadequate flood risk assessment and ineffective disaster prevention and mitigation outcomes. Therefore, this study introduced the “Source-Sink” theory into flood disaster field to constructing flood risk transfer model. Flood risk assessment and transfer was conducted in the Poyang Lake Basin, China, where the impacts of the initial and transfer statuses on ecosystem service values were quantified. The results showed that the flood risk in the Poyang Lake Basin was relatively low, with high spatial distribution characteristics in the central-north areas but low in the surrounding areas. High-risk zones were mainly distributed southwest of the Poyang Lake. The lower-risk zones exhibited a contiguous distribution and were surrounded by higher-risk zones. Following the completion of the flood risk transfer, high-risk zones increased significantly; but there were a few zones where the risk was transferred to other zones, thereby lowering their risks. Flood risk transfer occurs primarily in low- and medium-risk zones, with high-risk zones being the most important growth targets. The change in risk transfer was most evident in the area surrounding Poyang Lake, while that in the Upper Gan River Basin was lower and less sensitive to the transfer effect. Accounting for flood disaster risk, the ecosystem service values of the Poyang Lake Basin decreased by 8.18 %, with the most significant impacts observed in the surrounding environment and southwest Poyang Lake. After the completion of the flood risk transfer, the ecosystem service value in the Poyang Lake Basin declined by 24.66 %. This study provides a reference point for flood risk management and sustainable regional development that account for risk transfer.

Transport dynamics of watershed discharged diffuse phosphorus pollution load to the lake in middle of Yangtze River Basin

Diffuse pollution, including that in the lower and middle reaches of the Yangtze River, is the primary source of pollution in several agricultural watersheds globally. As the largest river basin in China, the Yangtze River Basin has suffered from total phosphorus (TP) pollution in the past decade owing to diffuse pollution and aquatic ecology destruction, especially in the midstream tributaries and mid-lower reaches of the lakes. However, the transport dynamics of diffuse pollutants, such as phosphorus (P) from land to water bodies have not been well evaluated, which is of great significance for quantifying nutrient loss and its impact on water bodies. In this study, diffuse pollution estimation with remote sensing (DPeRS) model coupled with Soil and Water Assessment Tools (SWAT) was utilized to simulate the transport dynamics of P, investigate the spatial heterogeneity and P sources in the Poyang Lake Basin. Additionally, the P transport mechanism from land to water and the migration process in water bodies were considered to investigate the impact of each loss unit on the water body and evaluate the load generated by diverse pollution types. The estimated diffuse TP loss was 6016 t P·yr−1, and the load to inflow rivers and to Poyang Lake were 11,619 and 9812 t P·yr−1, respectively. Gan River Basin (51.09%) contributed most TP to Poyang Lake among five inflow rivers, while waterfront area demonstrated the highest TP load per unit area with 0.057 t km−2·yr−1. Our study also identified P sources in the sub-basins and emphasized agricultural diffuse sources, especially planting, as the most significant factor contributing to TP pollution. Additionally, to improve the aquatic environment and water ecological conditions, further nutrient management should be applied using a comprehensive approach that encompasses the entire process, from source transportation to the water body.

Detecting Changes in Impervious Surfaces Using Multi-Sensor Satellite Imagery and Machine Learning Methodology in a Metropolitan Area

This study utilizes multi-sensor satellite images and machine learning methodology to analyze urban impervious surfaces, with a particular focus on Nanchang, Jiangxi Province, China. The results indicate that combining multiple optical satellite images (Landsat-8, CBERS-04) with a Synthetic Aperture Radar (SAR) image (Sentinel-1) enhances detection accuracy. The overall accuracy (OA) and kappa coefficients increased from 84.3% to 88.3% and from 89.21% to 92.55%, respectively, compared to the exclusive use of the Landsat-8 image. Notably, the Random Forest algorithm, with its unique dual-random sampling technique for fusing multi-sensor satellite data, outperforms other machine learning methods like Artificial Neural Networks (ANNs), Support Vector Machines (SVMs), Classification and Regression Trees (CARTs), Maximum Likelihood Classification (Max-Likelihood), and Minimum Distance Classification (Min-Distance) in impervious surface extraction efficiency. With additional satellite images from 2015, 2017, and 2020, the impervious surface changes are tracked in the Nanchang metropolitan region. From 2015 to 2021, they record a notable increase in impervious surfaces, signaling a quickened urban expansion. This study observes several impervious surface growth patterns, such as a tendency to concentrate near rivers, and larger areas in the east of Nanchang. While the expansion was mainly southward from 2015 to 2021, by 2021, the growth began spreading northward around the Gan River basin.

The response of non-point source pollution to land use change and risk assessment based on model simulation and grey water footprint theory in an agricultural river basin of Yangtze River, China

Non-point source (NPS) pollution has gradually become the main source of water environmental pollution with the rapid economic development during the recent decades, especially for the economically developed Yangtze River Basin of China. Due to rapid urbanization, the pressure of the water environment in the Poyang Lake basin (PYLB) has been increasing. In this study, the spatial and temporal variations of NPS pollution loads including total nitrogen (TN) and total phosphorus (TP) in the PYLB during the period 2003–2012 were firstly investigated by using the SWAT; then the changes in NPS pollution loads under different land use types were identified by using the SWAT, land use transition matrix, statistical analysis and scenario analysis methods; finally, the NPS pollution risk assessment were achieved by means of the grey water footprint theory. The results showed that the NPS pollution loads in the PYLB were concentrated from April to June with a large inter-annual variability. The Gan River basin contributed the largest proportion of pollutants entering into the Poyang lake while the Xiu River basin produced the smallest pollution loads. Under the background of the policy of “Grain for Green Project” since 2002, the areas of cultivated land, grassland and bare land decreased during the period 2000–2010, while those of forest land and settlement increased. As the main source of NPS pollution, the area of cultivated land has decreased, while the unit load intensity under cultivated land has significantly increased. By calculating the annual GWF of TN and TP loads and their corresponding WPL, which all showed an upward trend. The results obtained in this study have practical significance for reducing the NPS pollution loads in the PYLB and controlling the environmental pollution in the Yangtze River.

The severity of heat and cold waves amplified by high relative humidity in humid subtropical basins: a case study in the Gan River Basin, China

High relative humidity (RH) and temperature extremes can occur simultaneously and persist for periods of time, resulting in serious harm to human health, especially in humid regions. Here, in the case of the Gan River Basin, we used air temperature and RH from the observed and ERA5 reanalysis datasets to construct the apparent temperature and investigate the characteristics of heat and cold waves. Heat waves showed the increasing trends from 1961 to 2018 (particularly from 1997 to 2018), whereas during the same period, cold waves showed the significant decreasing trends. In general, ERA5 reasonably reflected the spatiotemporal characteristics of heat and cold waves, and the ability to simulate cold waves was slightly greater than that of heat waves. The amplifying effect of high RH on heat waves was significantly greater than on cold waves. The increasing rates of heat waves in ERA5 at the mild, moderate, and severe grades were slightly greater than the observations. Cold waves at various grades showed significant downward trends, and the decreasing rates of cold waves in the observations were slightly greater than those in ERA5. Using an analysis of the return period (occurrence probability), traditional univariate risk assessment methods based on maximum or minimum temperature may substantially underestimate the risk of extreme events, such as the 2014 heat wave and the 1969 cold wave, because the effects of RH were ignored.

Quantifying Co-Benefits and Trade-Offs between Forest Ecosystem Services in the Gan River Basin of South China

Forest ecosystem services are intrinsically linked. We design a spatially explicit approach to quantify and analyze the co-benefits and trade-offs between the main forest ecosystem services. Our goal is to develop criteria for forest management that include ecosystem service interactions. Chinese fir and pine plantations provide the largest portion of the overall ecosystem services currently provided. They are volume stock and water yield service hotspots, but these have negative effects on soil retention and carbon storage, causing environmental problems. The natural forests (broad-leaf and bamboo forests) are carbon storage and volume stock hotspots and show the lowest erosion modulus. Thus, their protection, combined with expanding the plantation area under forest management should be considered in order to increase ecosystem service synergies. In contrast, an increased area of broad-leaf plantations reduces water yield service due to their lower water production capacity, in comparison with plantations of fast-growing species. Our study shows that the inclusion of ecosystem services as part of forest management could provide opportunities for optimal allocation of forest resources and sustainable utilization. Management based only on economically beneficial ecosystem services can be detrimental to the forest ecosystem and can cause environmental problems.

Dam Construction Impacts Fish Biodiversity in a Subtropical River Network, China

Dams and diversions are a primary threat to freshwater fish biodiversity, including the loss of species and restructuring of communities, often resulting in taxonomic homogenization (increased similarity) over time. Mitigating these impacts requires a strong scientific understanding of both patterns and drivers of fish diversity. Here, we test whether different components of fish biodiversity have changed in response to major dam construction, and whether these patterns are predictable as a function of key environmental factors in the Gan River Basin, China. The results showed that total and native species alpha diversity have declined from the historical period (pre-dam) to the current period (post-dam). A total of 29 native species are lost, while 6 alien species were gained over time. We found evidence for fish faunal homogenization in the Gan River Basin, with a slight (1%) increase in taxonomic similarity among river basins from the historical period to the current period. Additionally, we revealed significant associations between drainage length, drainage area, and average air temperature, and alpha and beta fish diversity. This study provides new insight into the patterns and drivers of fish biodiversity change in the broader Yangtze River Basin and helps inform management efforts seeking to slow, and even reverse, current trajectories of biodiversity change.

Population Exposure to Compound Droughts and Heatwaves in the Observations and ERA5 Reanalysis Data in the Gan River Basin, China

The frequency, duration, and magnitude of heatwaves and droughts are expected to increase in a warming climate, which can have profound impacts on the environment, society, and public health, and these may be severely affected specifically by compound droughts and heatwaves (CDHWs). On the basis of daily maximum temperature data and the one-month standardized precipitation evapotranspiration index (SPEI) from 1961 to 2018, the Gan River Basin (GRB) was taken as a case here to construct CDHW identification indicators and quantify the population exposure to CDHWs. We found that ERA5 reanalysis data performed well in overall simulating temperature, precipitation, one-month SPEI, heatwaves, and CDHWs in the GRB from 1961 to 2018. CDHWs during the period from 1997 to 2018 were slightly higher than that in 1961–1997. CDHWs were more likely to occur in the southern parts of the basin due to the relatively high values of drought–heatwave dependence indices. Atmospheric circulation analysis of the 2003 CDHW in the GRB showed a relatively long-lasting anomalous high pressure and anticyclonic circulation system, accompanied by the positive convective inhibition and surface net solar radiation anomalies. These circulating background fields eventually led to the exceptional 2003 CDHW occurrence in the GRB. The population exposure to CDHWs basically increased, especially for the moderate CDHWs in ERA5. The change in total exposure was mainly due to climate change. Compared with the period from 1989 to 1998, the contributions of the population change effect in 2009–2018 gradually increased with the increase in the CDHW magnitude both in the observations and ERA5 reanalysis data.

Flash Drought Characteristics by Different Severities in Humid Subtropical Basins: A Case Study in the Gan River Basin, China

AbstractIt is essential to assess flash drought risk based on a reliable flash drought intensity (severity) index incorporating comprehensive information of the rapid decline (“flash”) in soil moisture toward drought conditions and soil moisture thresholds belonging to the “drought” category. In this study, we used the Gan River basin as an example to define a flash drought intensity index that can be calculated for individual time steps (pentads) during a flash drought period over a given grid (or station). The severity of a complete flash drought event is the sum of the intensity values during the flash drought. We explored the spatial and temporal characteristics of flash droughts with different grades based on their respective severities. The results show that decreases in total cloud cover, precipitation, and relative humidity, as well as increases in 500-hPa geopotential height, convective inhibition, temperature, vapor pressure deficit, and wind speed can create favorable conditions for the occurrence of flash droughts. Although flash droughts are relatively frequent in the central and southern parts of the basin, the severity is relatively high in the northern part of the basin due to longer duration. Flash drought severity shows a slightly downward trend due to decreases in frequency, duration, and intensity from 1961 to 2018. Extreme and exceptional flash droughts decrease significantly while moderate and severe flash droughts trend slightly upward. Flash drought severity appears to be more affected by the interaction between duration and intensity as the grade increases from mild to severe. The frequency and duration of flash droughts are higher in July–October. The southern part of the basin is more prone to moderate and severe flash droughts, while the northern parts of the basin are more vulnerable to extreme and exceptional flash droughts due to longer durations and greater severities than other parts. Moderate, severe, extreme, and exceptional flash droughts occurred at approximately 3–6-, 5–15-, 10–50-, and 30–200-yr intervals, respectively, based on the copula analysis.

Impact of rural depopulation and climate change on vegetation, runoff and sediment load in the Gan River basin, China

Abstract Climate change and rural depopulation are changing the ecological and hydrological cycles in China. Data on the normalized difference vegetation index (NDVI), temperature, precipitation, streamflow, sediment and rural population are available for the Gan River basin from 1981 to 2017. We investigated the spatio-temporal variations in climate, human activity and vegetation mainly using the Mann–Kendall test and examined their relationship using the Granger causality test. The results showed that (1) the temperature markedly increased in all seasons; (2) the precipitation increased in summer and winter but decreased in spring and autumn; (3) overall, the NDVI increased markedly during 2005–2017, but showed seasonal differences, with decreases in summer and winter and increases in spring and autumn; (4) the annual sediment transport showed a significant decreasing trend and (5) a large number of the population shifted from rural to urban areas, resulting in a decrease in the rural population between 1998 and 2018. Rural depopulation has brought about farmland abandonment, conversion of farmland to forests, which was the factor driving the recovery of the vegetation and the decrease in sediment. The results of this study can provide support for climate change adaptation and sustainable development.

Multi-Temporal Variabilities of Evapotranspiration Rates and Their Associations with Climate Change and Vegetation Greening in the Gan River Basin, China

Understanding the spatial-temporal dynamics of evapotranspiration in relation to climate change and human activities is crucial for the sustainability of water resources and ecosystem security, especially in regions strongly influenced by human impact. In this study, a process-based evapotranspiration (ET) model in conjunction with the Global Land Surface Satellite (GLASS) LAI dataset was used to characterize the spatial-temporal pattern of evapotranspiration from 1982 to 2016 over the Gan River basin (GRB), the largest sub-basin of the Poyang Lake catchment, China. The results showed that the actual annual ET (ETa) weakly increased with an annual trend of 0.88 mm year−2 from 1982 to 2016 over the GRB, along with a slight decline in annual potential ET (ETp). On an ecosystem scale; however, only the evergreen broadleaved forest and cropland presented a positive ETa trend, while the rest of the ecosystems demonstrated negative trends of ETa. Both correlation analysis and sensitivity analysis revealed a close relationship between ETa inter-annual variability and energy availability. Attribution analysis illustrated that contributions of climate change and vegetation greening on the ETa trend were −0.48 mm year−2 and 1.36 mm year−2, respectively. Climate change had a negative impact on the ETa trend over the GRB. However, the negative effects have been offset by the positive effects of vegetation greening, which mainly resulted from the large-scale revegetation in forestland and agricultural practices in cropland. It is concluded that large-scale afforestation and agricultural management were the main drivers of the long-term evolution of water consumption over the GRB. This study can improve our understanding of the interactive effects of climate change and human activities on the long-term evolution of water cycles.

Hydrological impact of a reservoir network in the upper Gan River Basin, China

AbstractA few relatively large reservoirs, hundreds of small reservoirs, and numerous farm dams were built in the upper Gan River Basin, China. The operation of such a reservoir network can serve as a significant source of variability in the local hydrological regime and should be included in research to better understand the interaction between multiple hydrological processes and watershed management. In this study, a reservoir network module that included reservoirs of multiple sizes was developed and fully integrated into the coupled land surface and distributed hydrologic model system (CLHMS), for a detailed description of the hydrological impact of a reservoir network. A generalized release scheme was employed to determine the outflow of both large and small reservoirs. The integrated model was then evaluated against observations and reanalysis data, which indicate that the model can reasonably reconstruct the reservoir operation, streamflow, and other hydrological variables. Results quantitatively demonstrate that a reservoir network can result in an increased streamflow in dry seasons, a decreased streamflow in wet seasons, a generally larger groundwater discharge, higher groundwater level, a slightly damper soil condition, and a larger amount of evapotranspiration at the basin level. With the integrated model, it is feasible to achieve more sustainable watershed planning and management.

CMADS-Driven Simulation and Analysis of Reservoir Impacts on the Streamflow with a Simple Statistical Approach

The reservoir operation is a notable source of uncertainty in the natural streamflow and it should be represented in hydrological modelling to quantify the reservoir impact for more effective hydrological forecasting. While many researches focused on the effect of large reservoirs only, this study developed an online reservoir module where the small reservoirs were aggregated into one representative reservoir by employing a statistical approach. The module was then integrated into the coupled Noah Land Surface Model and Hydrologic Model System (Noah LSM-HMS) for a quantitative assessment of the impact of both large and small reservoirs on the streamflow in the upper Gan river basin, China. The Noah LSM-HMS was driven by the China Meteorological Assimilation Driving Datasets for the Soil and Water Assessment Tool (SWAT) model (CMADS) with a very good performance and a Nash-Sutcliffe coefficient of efficiency (NSE) of 0.89, which proved to be more effective than the reanalysis data from the National Centers for Environmental Prediction (NCEP) over China. The simulation results of the integrated model indicate that the proposed reservoir module can acceptably depict the temporal variation in the water storage of both large and small reservoirs. Simulation results indicate that streamflow is increased in dry seasons and decreased in wet seasons, and large and small reservoirs can have equally large effects on the streamflow. With the integration of the reservoir module, the performance of the original model is improved at a significant level of 5%.

Short-term concurrent drought and heatwave frequency with 1.5 and 2.0 °C global warming in humid subtropical basins: a case study in the Gan River Basin, China

Short-term concurrent droughts and heatwaves accompanied by high temperatures and low soil moisture (or low precipitation) may significantly impact ecosystems, societies, and economies although the individual events involved may not themselves represent severe extremes. There is little known about the potential frequency of short-term concurrent droughts and heatwaves in the future. Here, we use the Gan River Basin as a case study area to assess the effects of different warming levels on drought and heatwave concurrences based on the coupled model intercomparison project phase 5 and variable infiltration capacity (VIC) model. The results show that the VIC model has high reliability in the simulation of soil moisture and evapotranspiration compared with other well-recognized datasets in the Gan River Basin. The warming level over the Gan River Basin is close to the global warming level. Under RCP4.5 and RCP8.5 scenarios, the multi-model ensemble medians of concurrent events increased by 0.08–0.4 pentads/decade from 2006 to 2099. The uncertainty of concurrent events encompasses a wider range as global temperature increases. Compared to the reference period (1961–2005), drought and heatwave concurrences have increased by more than 50% in the most parts of the basin under 1.5 or 2.0 °C of global warming; there is a 20% frequency difference of 0.5 °C from 1.5 to 2.0 °C. The substantial pentad increases (at least greater than 50%) existed in historical low-pentad-value areas in a 1.5 or 2.0 °C world, especially pronounced for a 2.0 °C world. The greatest increase in concurrent event pentads came from the 25th percentile values in 1.5 or 2.0 °C scenarios. Climatological median pentads of concurrent droughts and heatwaves appear likely to be 9.6–17.6% more frequent in a 2.0 °C world than a 1.5 °C world with respect to the reference period.

Evaluation of Downscaled CMIP5 Coupled with VIC Model for Flash Drought Simulation in a Humid Subtropical Basin, China

Abstract Compared to traditional drought events, flash droughts evolve rapidly during short-term extreme atmospheric conditions, with a lasting period of one pentad to several weeks. There are two main categories of flash droughts: the heat wave flash drought (HWFD), which is mainly caused by persistent high temperatures (heat waves), and the precipitation deficit flash drought (PDFD), which is mainly triggered by precipitation deficits. The authors’ previous research focused on the characteristics and causes of flash drought based on meteorological observations and Variable Infiltration Capacity (VIC) model simulations in a humid subtropical basin (Gan River basin, China). In this study, the authors evaluated the downscaled phase 5 of the Coupled Model Intercomparison Project (CMIP5) models’ simulations, coupled with the VIC model (CMIP5–VIC) in reproducing flash droughts in a humid subtropical basin in China. Most downscaled CMIP5–VIC simulations can reproduce the spatial patterns of flash droughts with respect to the benchmarks. The coupled models fail to readily replicate interannual variation (interannual pentad change), but most models can reflect the interannual variability (temporal standard deviation) and long-term average pentads of flash droughts. It is difficult to simultaneously depict both the spatial and temporal features of flash droughts within only one coupled model. The climatological patterns of the best multimodel ensemble mean are close to those of the all-model ensemble mean, but the best multimodel ensemble mean has a minimal bias range and relatively low computational burden.

Quantifying ecosystem service trade-offs for plantation forest management to benefit provisioning and regulating services.

There is increasing interest worldwide regarding managing plantation forests in a manner that maintains or improves timber production, enhances ecosystem services, and promotes long‐term sustainability of forest resources. We selected the Gan River Basin, the largest catchment of Poyang Lake and a region with a typical plantation distribution in South China, as the study region. We evaluated and mapped four important forest ecosystem services, including wood volume, carbon storage, water yield, and soil retention at a 30 × 30 m resolution, then quantified their trade‐offs and synergies at the county and subwatershed scales. We found that the wood volume and carbon storage services, as well as the soil retention and water yield, exhibited synergistic relationships. However, the carbon storage displayed a trade‐off relationship with the water yield. Additionally, we compared the beneficial spatial characteristics among dominant species in the study region. The results showed that the Chinese fir forest and the pine forest exhibited lower overall benefits than natural forests including the broad‐leaved forest and the bamboo forest. To propose a suitable management strategy for the study region, method of spatial cluster analysis was used based on the four eco‐services at the subwatershed scale. The basin was divided into four management groups instead of treating the region as a homogenous management region. Finally, we proposed more specific and diverse management strategies to optimize forest benefits throughout the entire region.

Flash droughts in a typical humid and subtropical basin: A case study in the Gan River Basin, China

As opposed to traditional drought events, flash droughts evolve rapidly and are characterized by soil moisture deficits. The general lack of high resolution soil moisture and evapotranspiration data makes identifying flash droughts at short-term scales (pentads or weeks) nearly impossible, particularly at the basin scale. In this study, we investigated the spatial patterns, temporal characteristics, and related mechanisms of flash droughts in a humid and subtropical basin (Gan River Basin) in China. The variable infiltration capacity (VIC) model can accurately reflect hydrological processes in the Gan River Basin at daily and monthly time scales; here, flash droughts were determined based on VIC outputs (soil moisture and evapotranspiration) and meteorological observations (maximum temperature and precipitation) during the growing season (March-October) from 1961 to 2013. We classified flash droughts into two categories (heat wave and precipitation deficit flash droughts) based on the formation mechanisms. Heat wave flash droughts are high temperature driven events, high temperatures (heat waves) cause evapotranspiration to increase and soil moisture to decrease rapidly. The main driver of precipitation deficit flash droughts is precipitation deficits, which cause soilmoisture to drop and in turn cause evapotranspiration anomalies to decrease and temperature to increase. The northern part of the basin is apparently vulnerable to heat wave flash droughts, whereas precipitation deficit flash droughts tend to occur across the central and southern parts of the basin. Precipitation deficit flash droughts are more common than heat wave flash droughts in general. Both types of flash droughts became significantly more frequent from 1997 to 2013. These increases in both types of flash droughts are likely attributable to climate-related variables such as temperature, precipitation, evapotranspiration, and soil moisture during 1997–2013. As evidenced by our investigation of the evolution of the two types of flash droughts and the example of 2003 summer flash drought across the Gan River Basin, flash droughts can evolve into prolonged droughts.

Analysis of dry/wet conditions in the Gan River Basin, China, and their association with large-scale atmospheric circulation

Droughts and floods are natural phenomena that occur when water availability is significantly below or above normal levels over a specific period. In recent years, the Gan River Basin has frequently been threatened by droughts and floods, and it is important to evaluate the characteristics of dry/wet conditions for better water resource management and disaster mitigation in this region. On the basis of precipitation and temperature data for the period 1964–2013 from 40 meteorological stations across the basin, the variability of dry/wet conditions was analyzed using the standardized precipitation evapotranspiration index (SPEI). In addition, the standardized streamflow index (SSI) and large-scale atmospheric circulation patterns calculated from NCEP/NCAR reanalysis data were used to further explore and evaluate temporal variations, spatial patterns, and possible mechanism responsible for the formation of dry/wet conditions in the basin. The results indicated that robust coefficients between monthly SSI and SPEI exist at multiple timescales. The best correlation coefficients were found at timescales of 2–3months, which better reflect the intensity and magnitude of seasonal dry/wet conditions. Application of a 3-month SPEI for the dry (July–September) and wet (April–June) seasons indicated that severe dry/wet episodes were easy to occur in the northern part of the basin. The difference between composites of anomalous dry/wet seasons shows that both a positive height anomaly at 500hPa and a very little water vapor flux influence the basin during the dry season of anomalous years, which can lead to the occurrence of drought events in the basin. However, during the wet season of anomalous years, geopotential height anomalies caused by areas of high pressure in the south (South China Sea) and areas of low pressure in the north (Mongolia), are responsible for the transport of copious amounts of water vapor from both the Bay of Bengal and the South China Sea. Under these conditions, the negative values of water vapor flux divergence dominate the basin and bring abundant precipitation, which often causes calamitous flood events.

水文变异条件下鄱阳湖流域生态流量研究

PDF HTML阅读 XML下载 导出引用 引用提醒 水文变异条件下鄱阳湖流域的生态流量 DOI: 10.5846/stxb201404080664 作者: 作者单位: 中山大学 水资源与环境系,江西师范大学 鄱阳湖湿地与流域研究教育部重点实验室,中山大学 水资源与环境系,中山大学 水资源与环境系,中山大学 水资源与环境系 作者简介: 通讯作者: 中图分类号: 基金项目: 鄱阳湖湿地与流域研究教育部重点实验室(江西师范大学)主任开放基金资助项目(ZK2013006); 安徽省高校引进"领军人才"专项项目 Evaluation of ecological flow with considerations of hydrological alterations in the Poyang Lake basin Author: Affiliation: Department of Water Resources and Environment,Sun Yat-sen University,Department of Water Resources and Environment,Sun Yat-sen University,,, Fund Project: 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:受气候变化和人类活动综合影响,鄱阳湖流域水文状况发生变异。河流生态系统适应了变异前的水文状况,变异后势必会影响当地生态系统。基于此,采用8种变异检测方法对水文变异进行综合诊断,阐明水文变异原因。在此基础上,采用15种概率分布函数分别拟合5站各月变异前日流量序列,最终确定5站点各月最优分布函数及所对应的概率密度最大处的流量,即得河道内生态流量。研究表明:(1)抚河于1962年发生弱变异,赣江、修河于1968年发生中变异,信江、饶河于1991年发生弱变异;(2)变异后,赣江、信江、饶河、修河生态需水满足率平均上升11%,抚河生态需水满足率下降32%;(3)水文变异增加提高生态需水满足率,水利工程建设降低年均生态需水满足率、提高干季生态需水满足率。高森林覆盖率提高干季生态需水满足率,对年均生态需水满足率影响不明显。研究结果为鄱阳湖流域水资源管理及区域水资源规划与配置提供重要科学依据。 Abstract:Fluvial hydrological processes within the Poyang Lake basin are significantly altered under the influence of human activities and climate changes. Poyang Lake is the largest freshwater lake and plays an important role in conservation of biological diversity and also in flood mitigation in the Yangtze River basin. In this case, ecological instream streamflow is also altered and the ecological environment is potentially affected under the influences of altered hydrological processes. With consideration of hydrological alterations, re-evaluation of ecological instream streamflow will be of great scientific and practical merit in terms of water resource management and conservation of ecological environment. We use the Hurst coefficient method to preliminary analyze the degree of alterations in five major tributaries of the Poyang lake basin. Then we use eight mutation testing methods to comprehensively investigate change points. We use 15 kinds of probability distribution functions to fit respectively daily flow for each month before occurrence of the hydrological alterations. Finally, the monthly optimal distribution functions and corresponding streamflow with the largest probability are determined and computed, and accepted as the ecological instream streamflow. Results indicate that: (1) main causes behind the hydrological alterations of the Gan, Xin, Rao and Xiu Rivers are the climate changes such as the precipitation changes observed in this study. However, the Hu River is mainly affected by human activities; (2) due to large amounts of water diversion irrigation system, hydrological processes in the Hu River were significantly altered after 1962. The hydrological alterations of the Gan and Xiu Rivers occurred in 1968. The East Asian Summer Monsoon led to anincrease of precipitation during the mid-1960s; The Xin, Rao Rivers were dominated by significant hydrological alterations in 1991. Increase of precipitation in the early 1990s is the main cause behind this hydrological alterations that occurred in the 1960s;(3) The increase of forest coverage and the construction of water conservancy are expected to improve the satisfaction rate of the ecological water requirement in the dry season. The satisfactory rate of ecological water requirement in the dry season is higher than that in the wet season in the Rao, Gan, and Xiu Rivers. However, the Fu and Xin Rivers do not follow this trend. The forestation and increased vegetation coverage can greatly alter the spatiotemporal distribution of water or runoff and can significantly increase the runoff during the dry seasons. Woodland has an important influence on the changes of runoff. Due to the large forest coverage, the ecological instream flow is greatly satisfied during dry seasons in the Rao River when compared to the other four rivers. A difference is found in the Gan River in terms of water requirements of ecological instream flow between wet and dry seasons. The number of reservoirs in the Gan River basin is high when compared to the other four tributaries of the Poyang Lake basin that were considered in this study. Forest coverage in the Xiu River basin accounts for 64.4% of the total area, which is ranked the second largest in the Poyang Lake. However, the difference between wet and dry seasons is small. The quantity and scale of the reservoir in the Xiu River basin falls far behind others. Therefore, the regulation activities of the reservoirs in Xiu River basin is not evident than other river basins. On the contrary, the satisfactory rate of ecological water requirements for the dry season is below that for the wet season in the Fu and Gan River. The rate of forest coverage in those two basins is far less than in other basins. The ability to regulate the forest is limited. These results will provide an important scientific basis for the planning and management of water resources within the Poyang Lake basin under a changing environment. 参考文献 相似文献 引证文献

赣江流域底泥中有机氯农药残留特征及空间分布

赣江流域底泥中有机氯农药残留特征及空间分布