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As an indicator of atmospheric evaporating capability over a hypothetical reference surface, reference evapotranspiration (ET_0) is the most important hydrological and meteorological variable to reflect climate change. This is par...
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As an indicator of atmospheric evaporating capability over a hypothetical reference surface, reference evapotranspiration (ET_0) is the most important hydrological and meteorological variable to reflect climate change. This is particularly true for the Yellow River Basin, which faces serious water shortages and is vulnerable to climate change. In this study, the ET_0 at 80 sites during 1957-2008 in the Yellow River Basin was calculated using the Penman-Monteith method with the calibrated Angstrom coefficients. Spatial and seasonal patterns of changes in ET_0 as well as the concerned climatic variables are specially focused on using advanced statistical tests and GIS method. The entire Yellow River Basin is characterized by complicated spatial variability in the change of ET_0. Significant negative trends are mainly distributed in the southeast corner, northern side, and midwest of the Yellow River Basin, while significant increases of ET_0 mainly occur in the middle part and southwest corner of the basin. Still, no coherent spatial patterns in ET_0 trends are seen in any season. The dominance of warming trends in temperature and decreasing trends in wind speed and sunshine duration can be found in the basin. Relative humidity presents insignificant or weak trends at many sites but with a mixed spatial structure of positive and negative trends at both annual and seasonal scales. The combined effects of climatic variables to ET_0 changes and their spatial and seasonal variability are revealed by further analysis of sensitivity of ET_0 to climatic variables and the contribution of climatic variables to ET_0 changes over six homogenous regions identified by a rotated empirical orthogonal function (REOF) clustering method on annual and seasonal scales. The decline of surface wind speed offsets the increasing effect of the temperature increase and is mainly responsible for the ET_0 reduction in the west and north of the Loess Plateau. The reduced sunshine duration is the leading factor for ET_0 decrease in the middle-lower Yellow River Plain, especially during the summer time. The increasing mean temperature plays the most important role in the ET_0 increase in the source area of the Yellow River Basin. Furthermore, regional actual evapotranspiration and ET_0 present complementary behavior, but does not accurately fall in the 1:1 complementary relationship of the Bouchet's hypothesis, especially for the high elevation subregions. In addition, although precipitation changes are the main driving factors for drought variation, increasing ET_0 intensified the drought in middle regions.
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Spatiotemporal changes in climatic extremes in the Yellow River Basin from 1959 to 2008 were investigated on the basis of a suite of 27 climatic indices derived from daily temperature and precipitation data from 75 meteorological ...
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Spatiotemporal changes in climatic extremes in the Yellow River Basin from 1959 to 2008 were investigated on the basis of a suite of 27 climatic indices derived from daily temperature and precipitation data from 75 meteorological stations with the help of the Mann-Kendall test, linear regression method and GIS technique. Furthermore, the changes in the probability distribution of the extreme indices were examined. The results indicate: (1) The whole basin is dominated by significant increase in the frequency of warm days and warm nights, and dominated by significant decrease in the frequency of cold days and cold nights. Although trends in absolute temperature indices show less spatial coherence compared with that in the percentile-based temperature indices, overall increasing trends can be found in Max Tmax (TXx), Min Tmax (TXn), Max Tmin (TNx) and Min Tmin (TNn). (2) Although the spatial patterns and the number of stations with significant changes for threshold and duration temperature indices are also not identical, general positive trends in warm indices (i.e., summer days (SU25), tropical nights (TR20), warm spell duration indicator and growing season length) and negative trends in cold indices (i.e., frost days, ice days and cold spell duration indicator) can be found in the basin. Annual nighttime temperature has increased at a faster rate than that in daytime temperature, leading to obvious decrease in diurnal temperature range. (3) The changes in precipitation indices are much weaker and less spatially coherent compared with these of temperature indices. For all precipitation indices, only few stations are characterized by significantly change in extreme precipitation, and their spatial patterns are always characterized by irregular and insignificant positive and negative changes. However, generally, changes in precipitation extremes present drying trends, although most of the changes are insignificant. (4) Results at seasonal scale show that warming trends occur for all seasons, particularly in winter. Different from that in other three seasons, general positive trends in max 1-day precipitation (RxlDAY) and max 5-day precipitation (Rx5DAY) are found in winter. Analysis of changes in probability distributions of indices for 1959-1983 and 1984-2008 indicate a remarkable shift toward warmer condition and a less pronounced tendency toward drier condition during the past decades. The results can provide beneficial reference to water resource and eco-environment management strategies in the Yellow River Basin for associated policymakers and stakeholders.
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Irrigation water availability is a main driver which determines cropping patterns for an irrigation area. Irrigation water availability will potentially reduce due to changes in climate and irrigation extraction limits. Cropping p...
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Irrigation water availability is a main driver which determines cropping patterns for an irrigation area. Irrigation water availability will potentially reduce due to changes in climate and irrigation extraction limits. Cropping patterns should be adjusted to meet this challenge. This study presents a new approach for assessing future cropping patterns using GIS in combination with an Irrigation Water Availability Simulation model (IWAS) at irrigation area scale. The IWAS-GIS framework was developed for analysis of cropping pattern options based on the forecast of irrigation water availability in 2030 for the Murrumbidgee Irrigation Area (MIA) which is one of the most important irrigation areas in Australia. Six scenarios considering climatic conditions and the irrigation availabilities were input into the IWAS-GIS framework to simulate cropping pattern changes corresponding to predicted monthly irrigation water availability. Cropping patterns were designed by integration of soil type and irrigation water availability to improve irrigation sustainability. Simulations results indicate that the total irrigated areas will likely decrease with drier climate and less irrigation availability. Rice and pasture areas change significantly when climate and irrigation availability varies. Under the same climate condition, horticulture area increases when irrigation availability decrease. The percentage of lands which are unsuitable for cropping has reduced with the drying climate and shrinking irrigation availability. The IWAS-GIS is simple to implement and provides an easy way for assessing spatial cropping pattern changes based on irrigation water availability. This framework was developed to help irrigators plan cropping patterns corresponding to irrigation water availability. It is flexible to be adopted for similar applications in other irrigation areas.
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As the most excellent indicator for hydrological cycle and a central link to water-balance calculations, the reference evapotranspiration (ET_0) is of increasing importance in assessing the potential impacts of climate change on h...
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As the most excellent indicator for hydrological cycle and a central link to water-balance calculations, the reference evapotranspiration (ET_0) is of increasing importance in assessing the potential impacts of climate change on hydrology and water resources systems since the climate change has been becoming more pronounced. In this study, we conduct an investigation on the spatial and temporal changes in ET_0 of the Haihe River Basin in present and future stages. The ET_0 in the past five decades (1961-2010) are calculated by the Penman-Monteith method with historical climatic variables in 40 sites while the ET_0 estimation for the future period of 2011-2099 is based on the related climatic variables projected by Coupled General Circulation Model (CGCM) multimodel ensemble projections in Phase 3 of the Coupled Model Intercomparison Project (CMIP3) using the Bayesian Model Average (BMA) approach. Results can be summarized for the present and future as follows. (1) No coherent spatial patterns in ETo changes are seen in the whole basin. Half of the stations distributed mainly in the eastern and southeastern plain regions present significant negative trends, while only 3 stations in the western mountainous and plateau basin show significant positive trends. Radiation is mainly responsible for the ET_0 change in the southern and eastern basin, whereas relative humidity and wind speed are the leading factors in the eastern coastal and north parts. (2) BMA ensemble method is competent to produce lower bias in comparison with other common methods in this basin. Future spatiotemporal ET_0 pattern analysis by means of the BMA method based on the ensembles of four CGCMs suggested that although the spatial patterns under three scenarios are different in the forthcoming two decades, generally increasing trends can be found in the 21st century, which is mainly attributed to the significant increasing temperature. In addition, the implication of future ET_0 change in agriculture and local water resources is discussed as an extension of this work. The results can provide beneficial reference and comprehensive information to understand the impact of climate change on the future water balance and improve the regional strategy for water resource and eco-environment management in the Haihe River Basin.
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The present study explores the spatial and temporal changing patterns of the precipitation in the Haihe River basin of North China during 1957-2007 at annual, seasonal and monthly scales. The Mann-Kendall and Sen's T tests are emp...
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The present study explores the spatial and temporal changing patterns of the precipitation in the Haihe River basin of North China during 1957-2007 at annual, seasonal and monthly scales. The Mann-Kendall and Sen's T tests are employed to detect the trends, and the segmented regression is applied to investigate possible change points. Meanwhile, Sen's slope estimator is computed to represent the magnitudes of the temporal trends. The regional precipitation trends are also discussed based on the regional index series of four sub-basins in the basin. Serial correlation of the precipitation series is checked prior to the application of the statistical test to ensure the validity of trend detection. Moreover, moisture flux variations based on the NCEP/NCAR reanalysis dataset are investigated to further reveal the possible causes behind the changes in precipitation. The results show that: (1) Although the directions of annual precipitation trends at all stations are downward, only seven stations have significant trends at the 90% confidence level, and these stations are mainly located in the western and southeastern Haihe River basin. (2) Summer is the only season showing a strong downward trend. For the monthly series, significant decreasing trends are mainly found during July, August and November, while significant increasing trends are mostly observed during May and December. In comparison with the annual series, more intensive changes can be found in the monthly series, which may indicate a shift in the precipitation regime. (3) Most shifts from increasing trends to decreasing trends occurred in May-June, July, August and December series, while opposed shifts mainly occurred in November. Summer is the only season displaying strong shift trends and the change points mostly emerged during the late 1970s to early 1980s. (4) An obvious decrease in moisture flux is observed after 1980 in comparison with the observations before 1980. The results of similar changing patterns between monthly moisture budget and precipitation confirmed that large-scale atmospheric circulation may be responsible for the shift in the annual cycle of precipitation in the Haihe River basin. These findings are expected to contribute to providing more accurate results of regional changing precipitation patterns and understanding the underlying linkages between climate change and alterations of hydrological cycles in the Haihe River basin.
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In this study, the spatial and temporal patterns of trends for reference evapotranspiration (RET) at 34 meteorological stations (between 1957 and 2007) in the Haihe River basin, China, were analyzed using the Mann-Kendall (MK) tes...
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In this study, the spatial and temporal patterns of trends for reference evapotranspiration (RET) at 34 meteorological stations (between 1957 and 2007) in the Haihe River basin, China, were analyzed using the Mann-Kendall (MK) test and the Sen's method. To reveal the possible causes and main driving forces of the changing patterns of RET, the spatial distribution and temporal patterns of trends for four meteorological variables (i.e., temperature, wind speed, relative humidity, and sunshine duration) were examined for each station. In addition, partial relative analysis between RET and meteorological variables and a sensitivity analysis of RET to meteorological variables were conducted. The results show the following: First, the Haihe River basin is dominated by a significant decreasing MK trend in annual RET at > 95% confidence level, which is observed at most stations in the eastern and southern areas of the basin. There are no observed trends or significant increasing MK trends in annual RET in the western plateau. For the intra-annual variability of RET, similar spatial-changing patterns are only observed in summer. Second, there are no obvious trends in RET from the late 1950s to the early 1970s for the whole basin. However, opposite trends of RET in the plateau area are identified after the 1970s in comparison with those in the plain and mountain area of the Haihe River basin. These two trends become significant in the late 1990s. Third, wind speed and sunshine duration are recognized as the two major driving forces for the decreasing trends in RET. Relative humidity is mainly responsible for the increasing trends in the western Haihe River basin during recent decades.
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The estimation of groundwater evapotranspiration (ET) helps evaluate the risk of soil salinisation and the capacity of regional water resources. This paper focused on the effect of discretisation cell size on the output uncertaint...
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The estimation of groundwater evapotranspiration (ET) helps evaluate the risk of soil salinisation and the capacity of regional water resources. This paper focused on the effect of discretisation cell size on the output uncertainty of regional groundwater evapotranspiration modelling. The study area, the Liuyuankou Irrigation System (LIS), was discretised into cell sizes of 100 × 100 m, 200 × 200 m, 500 × 500 m, 1000 × 1000 m, and 2000 × 2000 m. Digital elevation models (DEM) at the lower resolutions were obtained by resampling the 90 m Shuttle Radar Topography Mission (SRTM) DEM using an averaging algorithm. The krigged groundwater table was subtracted from the ground surface elevation to generate the groundwater depth maps for various cell sizes. For each resolution, the groundwater ET was calculated using two ET functions (linear and exponential) for each cell. Lastly, the effects of the cell size on the output of the regional groundwater ET modelling were evaluated. The results showed that lower ET rates were obtained when a coarser cell size was used due to the smothering of the surface elevations and the groundwater depths, regardless of the employed ET functions. From comparisons of the delineated area, the cell numbers, the groundwater depth maps and the simulated groundwater ET rates, a discretisation cell size of 500 m was recommended for the LIS to balance the model's accuracy and computation efficiency in groundwater ET modelling.
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In order to explore the impacts of scale on soil variability, a study in a 120 × 40 m agricultural field was carried out. Spatial variations of soil water content (SWC) and electrical conductivity (EC) were analyzed with all the ...
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In order to explore the impacts of scale on soil variability, a study in a 120 × 40 m agricultural field was carried out. Spatial variations of soil water content (SWC) and electrical conductivity (EC) were analyzed with all the data measured under 5 × 5 m sampling grid. Then, resampling technique was employed with changing sampling extents and spacing, and spatial variation of each scenario was also determined. The results showed that SWC and EC presented weak or moderate spatial variability, and showed apparent mosaic pattern at the field scale. For all data sets the number of measurement (n = 207) effectively collected was much higher, making the field mean soil moisture and salt content data set very accurate. All the spatial indices measured increased with various degrees with increasing extent. However, spacing did not affect coefficient of variation and had inconsistent effects on the geo-statistics parameters, such as the nugget, sill and the correlation length for SWC data and EC data.
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Climatic variability and human activities are the two primary factors that affect basin hydrology, and thus quantification of their effects is of great importance for water resources management and sustainable development at a cat...
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Climatic variability and human activities are the two primary factors that affect basin hydrology, and thus quantification of their effects is of great importance for water resources management and sustainable development at a catchment scale. In this study, the writers investigated the long-term trends and abrupt changes in hydroclimatic variables, including precipitation, potential evapotranspiration (PET), and runoff, from 1957-2000 in the Hutuo River Basin by the nonparametric Mann-Kendall test and the precipitation-runoff double cumulative curve method. A two-parameter hydrological model and linear regression method were employed to separate and quantify the effects of climatic variability and human activities on runoff. The results are the following: (1) significant downward trends for annual precipitation and annual runoff were detected by the Mann-Kendall test at a 99% confidence level, (2) a change in the gradient of precipitation-runoff double cumulative curves and an abrupt change in runoff series can both be found in 1979, indicating that the relationship between precipitation and runoff has changed; as a result, the annual runoff from 1957-2000 can be divided into two periods termed the baseline (1957-1979) and human-induced (1980-2000) periods, and (3) the climate variability was the primary cause for the decrease in annual runoff from the baseline to the human-induced period, despite certain effects of human activities on the change with respect to annual runoff.
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Purpose With widely applied water-saving irrigation techniques, the transformation and availabilities of copper (Cu) as both a micronutrient and a toxic metal are changed. However, little information is available on the binding fo...
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Purpose With widely applied water-saving irrigation techniques, the transformation and availabilities of copper (Cu) as both a micronutrient and a toxic metal are changed. However, little information is available on the binding forms, bioavailability, and fate of Cu in paddy fields with different irrigation management. Thus, we investigated the effects of irrigation management on the binding forms and the fate of Cu in a non-polluted paddy soil. Materials and methods Field experiments were conducted in 2011 on non-polluted rice fields in Kunshan, East China. Non-flooding controlled irrigation (NFI) was applied in three replications, with flooding irrigation as a control. Samples of soil, soil solution, irrigation water, and rice plants were collected. Fresh soil samples were digested using the modified European Community Bureau of Reference sequential extraction procedure and the dried crop samples digested at 160 ℃ using concentrated HNO_3. Cu contents in irrigation water, soil solution, extraction for different binding fractions, and the digested solutions were measured using inductively coupled plasma optical emission spectrometry. Leaching loss of Cu was calculated based on the Cu contents in 47- to 54-cm soil solutions and deep percolation rates, which were calculated using the field water balance principle. Results and discussion NFI led to multiple dry-wet cycles and high soil redox potential in surface soil. The dry-wet cycles in NFI soil resulted in higher Cu contents in acid-extractable and oxidizable forms and lower Cu in residual form. High decomposition and mineralization rates of soil organic matter caused by the dry-wet cycles partially accounted for the increased Cu in acid-extractable form in NFI soils. The frequently high contents of Cu in reducible form in NFI fields might be due to the enhanced transformation of Fe and Mn oxides. As a result, Cu uptakes in NFI fields increased by 8.1 %. Meanwhile, Cu inputs by irrigation and loss by leaching in NFI fields were reduced by 47.6 and 46.6 %. Conclusions NFI enhanced the transformation of Cu from residual to oxidizable and acid-extractable forms. The oxidizable form plays a more important role than the reducible form in determining the transformation of Cu from the immobile to the mobile forms in NFI soils. NFI helps improve availability and decreases leaching loss of Cu as a micronutrient in a non-polluted paddy soil, but leads to a high concentration of Cu in rice.
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