Current changes in water resources in Lena River basin

The effect of climate on the present-day formation conditions of the regimes of annual and base runoff in Eastern Siberia rivers and changes in those regimes are studied. The significant climate warming in Eastern Siberia in recent decades is shown to be accompanied by not only an increase in air temperature and some increase in precipitation, but also by a considerable changes in the annual and seasonal values of river and groundwater runoff. Hydrometeorological data are used to analyze variations in the mean annual and mean base runoff over the entire observation period divided into subperiods of 1940–1969 and 1970–2005. Plots, diagrams, and tables are constructed for the most representative gauges. The zoning of the territory by the runoff formation conditions was carried out and new estimates were derived for total water resources and natural groundwater resources for 1970–2005 with the construction of maps in ArcMap program.     

Temporal trends of hydro‐climatic variables and runoff response to climatic variability and vegetation changes in the Yiluo River basin,China

The Yiluo River is the largest tributary for the middle and lower reaches of the Yellow River below Sanmenxia Dam. Changes of the hydrological processes in the Yiluo River basin, influenced by the climatic variability and human activities, can directly affect ecological integrity in the lower reach of the Yellow River. Understanding the impact of the climatic variability and human activities on the hydrological processes in the Yiluo River basin is especially important to maintain the ecosystem integrity and sustain the society development in the lower reach of the Yellow River basin. In this study, the temporal trends of annual precipitation, air temperature, reference evapotranspiration (ET₀) and runoff during 1961–2000 in the Yiluo River basin were explored by the Mann‐Kendall method (M‐K method), Yamamoto method and linear fitted model. The impacts of the climatic variability and vegetation changes on the annual runoff were discussed by the empirical model and simple water balance model and their contribution to change of annual runoff have been estimated. Results indicated that (i) significant upwards trend for air temperature and significant downwards trend both for precipitation and ET₀ were detected by the M‐K method at 95% confidence level. And the consistent trends were obtained by the linear fitted model; (ii) the abrupt change started from 1987 detected by the M‐K method and Yamamoto method, and so the annual runoff during 1961–2000 was divided into two periods: baseline period (1961–1986) and changeable period (1987–2000); and (iii) the vegetation changes were the main cause for change of annual runoff from baseline period to changeable period, and climatic variability contributed a little to the change of annual runoff of the Yiluo River. Copyright © 2009 John Wiley & Sons, Ltd.     

Effects of climate change on thermal properties of lakes and reservoirs, and possible implications

Meteorologic-driven processes exert large and diverse impacts on lakes’ internal heating, cooling, and mixing. Thus, continued global warming and climate change will affect lakes’ thermal properties, dynamics, and ecosystem. The impact of climate change on Lake Tahoe (in the states of California and Nevada in the United States) is investigated here, as a case study of climate change effects on the physical processes occurring within a lake. In the Tahoe basin, air temperature data show upward trends and streamflow trends indicate earlier snowmelt. Precipitation in the basin is shifting from snow to rain, and the frequency of intense rainfall events is increasing. In-lake water temperature records of the past 38 years (1970–2007) show that Lake Tahoe is warming at an average rate of 0.013°C/year. The future trends of weather variables, such as air temperature, precipitation, longwave radiation, downward shortwave radiation, and wind speed are estimated from predictions of three General Circulation Models (GCMs) for the period 2001–2100. Future trends of weather variables of each GCM are found to be different to those of the other GCMs. A series of simulation years into the future (2000–2040) is established using streamflows and associated loadings, and meteorologic data sets for the period 1994–2004. Future simulation years and trends of weather variables are selected so that: (1) future simulated warming trend would be consistent with the observed warming trend (0.013°C/year); and (2) future mixing pattern frequency would closely match with the historical mixing pattern frequency. Results of 40-year simulations show that the lake continues to become warmer and more stable, and mixing is reduced. Continued warming in the Tahoe has important implications for efforts towards managing biodiversity and maintaining clarity of the lake.     

Simulated runoff responses to land use in the middle and upstream reaches of Taoerhe River basin,Northeast China,in wet,average and dry years

Study on runoff variations and responses can lay a foundation for flood control, water allocation and integrated river basin management. This study applied the Soil and Water Assessment Tool model to simulate the effects of land use on annual and monthly runoff in the Middle and Upstream Reaches of Taoerhe River basin, Northeast China, under the wet, average and dry climate conditions through scenario analysis. The results showed that from the early 1970s to 2000, land use change with an increase in farmland (17.0%) and decreases in forest (10.6%), grassland (4.6%) and water body (3.1%) caused increases in annual and monthly runoff. This effect was more distinct in the wet season or in the wet year, suggesting that land use change from the early 1970s to 2000 may increase the flood potential in the wet season. Increases in precipitation and air temperature from the average to wet year led to annual and monthly (March and from June to December) runoff increases, while a decrease in precipitation and an increase in air temperature from the average to dry year induced decreases in annual and monthly (all months except March) runoff, and moreover, these effects were more remarkable in the wet season than those in the dry season. Due to the integrated effects of changing land use and climate conditions, the annual runoff increased (decreased) by 70.1 mm (25.2 mm) or 197.4% (71.0%) from the average to wet (dry) year. In conclusion, climate conditions, especially precipitation, played an important role in runoff variations while land use change was secondary over the study area, and furthermore, the effects of changes in land use and/or climate conditions on monthly runoff were larger in the wet season. Copyright © 2012 John Wiley & Sons, Ltd.     

Estimation of future precipitation change in the Yangtze River basin by using statistical downscaling method

In this study, the applicability of the statistical downscaling model (SDSM) in downscaling precipitation in the Yangtze River basin, China was investigated. The investigation includes the calibration of the SDSM model by using large-scale atmospheric variables encompassing NCEP/NCAR reanalysis data, the validation of the model using independent period of the NCEP/NCAR reanalysis data and the general circulation model (GCM) outputs of scenarios A2 and B2 of the HadCM3 model, and the prediction of the future regional precipitation scenarios. Selected as climate variables for downscaling were measured daily precipitation data (1961–2000) from 136 weather stations in the Yangtze River basin. The results showed that: (1) there existed good relationship between the observed and simulated precipitation during the calibration period of 1961–1990 as well as the validation period of 1991–2000. And the results of simulated monthly and seasonal precipitation were better than that of daily. The average R ² values between the simulated and observed monthly and seasonal precipitation for the validation period were 0.78 and 0.91 respectively for the whole basin, which showed that the SDSM had a good applicability on simulating precipitation in the Yangtze River basin. (2) Under both scenarios A2 and B2, during the prediction period of 2010–2099, the change of annual mean precipitation in the Yangtze River basin would present a trend of deficit precipitation in 2020s; insignificant changes in the 2050s; and a surplus of precipitation in the 2080s as compared to the mean values of the base period. The annual mean precipitation would increase by about 15.29% under scenario A2 and increase by about 5.33% under scenario B2 in the 2080s. The winter and autumn might be the more distinct seasons with more predicted changes of precipitation than in other seasons. And (3) there would be distinctive spatial distribution differences for the change of annual mean precipitation in the river basin, but the most of Yangtze River basin would be dominated by the increasing trend.     

Precipitation variation in the northeastern Tibetan Plateau recorded by the tree rings since 850 AD and its relevance to the Northern Hemisphere temperature

With their high resolution and reliability, tree rings play a very important role in global climate change study. The long tree-ring chronology is considered as one of the most important information sources to study the climatic change in the past several thousands years. In recent years, the tree-ring researches in China have made great progress, and the temperature and precipita- tion in some areas were reconstructed[1-20] which on- tributed to the global change studies in China. Due to the…     

Multiscale variability of streamflow changes in the Pearl River basin,China

The Pearl River basin bears the heavy responsibility for the water supply for the neighboring cities such as Macau, Hong Kong and others. Therefore, effective water resource management is crucial for sustainable use of water resource. However, good knowledge of changing properties of streamflow changes is the first step into the effective water resource management. With this in mind, stability and variability of streamflow changes in the Pearl River basin is thoroughly analyzed based on monthly streamflow data covering last half century using Mann–Kendall trend test and scanning t- and F-test techniques. The results indicate: (1) significant increasing monthly streamflow is observed mainly in January–April, June and October–December. Monthly streamflow during May–September is in not significant changes. Besides, stations characterized by significant monthly streamflow changes are located in the middle and the lower Pearl River basin; (2) changing points of monthly streamflow series are detected mainly during mid-1960s, early 1970s, mid-1970s, early 1980s and early 1990s and these periods are roughly in good agreement with those of annual, winter and summer precipitation across the Pearl River basin, implying tremendous influences of precipitation changes on streamflow variations; (3) abrupt behaviors tend to be ambiguous from the upper to the lower Pearl River basin, which should be due to enhancing combined effects of abrupt changes of precipitation. The streamflow comes to be lower stability in recent decades. However, high stability of streamflow changes are observed at hydrological stations in the lower Pearl River basin. The results of this study will be of great scientific and practical merits in terms of effective water resource management in the Pearl River basin under the influences of climate changes and human activities.     

River runoff decrease in North-Eurasian plains during the Holocene optimum

Three stages were identified in the development of meandering rivers and the formation of floodplains with natural levees in Northern Eurasia: the development of rivers with size larger than that of the modern ones; the development of rivers smaller than the modern ones; and the development of rivers of the present-day morphodynamic type. Small oxbows of the second stage are widespread in the floodplains of lowland rivers in Northern Eurasia. The largest amount of floodplain segments with such oxbows can be seen in the forest zone, mostly in the coniferous forests of northeastern European Russia. The available radiocarbon datings show that river channel were significantly decreasing in size and the steepness of meanders was increasing during the Atlantic period of the Holocene. Data on changes in the size of river channels were used to evaluate the ratios between paleo- and modern discharges and to construct a map of difference between runoff depths in the Holocene optimum and in the present and assess changes in water runoff volume. The discharges in the basins of the Vyatka and middle Irtysh accounted for as little as 40–50% of their current values. North, east, and west from those basins, the ratio of ancient and present-day discharges increases. During the Holocene optimum, water runoff from the northern megaslope of the East European Plain was ∼180 km³/year, which is 30% less than the present runoff from the same drainage area. The annual runoff in Volga basin was ∼134 km³, which is almost half as large as the present value. The runoff in Don and Dnieper basins during the Holocene optimum was 40% less, and that in the Ob and Irtysh basin was 30% less than the present one. If we accept the hypothesis that the Holocene optimum was a climate analogue of global anthropogenic warming of the mid-XXI century, the obtained estimates of the state of water resources in Northern Eurasia acquire great prognostic importance.     

Modelling sand–mud morphodynamics in the Friesche Zeegat

The objective of the study presented in this paper is to investigate the predictive capabilities of a process-based sand–mud model in a quantitative way. This recently developed sand–mud model bridges the gap between noncohesive sand models and cohesive mud models. It explicitly takes into account the interaction between these two sediment fractions and temporal and spatial bed composition changes in the sediment bed [Van Ledden (2002) 5:577–594, Van Ledden et al. (2004a) 24:1–11, Van Ledden et al. (2004b) 54:385–391]. The application of this model to idealized situations has demonstrated a good qualitative agreement between observed and computed bed levels and bed composition developments. However, in real-life situations, a realistic quantitative prediction of the magnitude and timescale of this response is important to assess the short-term and long-term impacts of human interventions and/or natural changes. For this purpose, the Friesche Zeegat in the Wadden Sea (the Netherlands) is used as a reference to hindcast the morphological response in the period 1970–1994. Due to the closure of the Lauwerszee in 1969, the tidal prism of this tidal basin was reduced by about 30%. Significant changes in the bed level and bed composition have occurred in the decades following the closure to adjust to the new hydrodynamic conditions. We modeled the long-term bed level and bed composition development in the Friesche Zeegat in the period 1970–1994 starting with the geometry of 1970 by using a research version of Delft3D, which incorporates the sand–mud formulations proposed by [Van Ledden (2002) 5:577–594].The computed total net deposition in the tidal basin in the period 1970–1994 agrees well with the observations, but the observed decrease of the import rate with time is not predicted. The model predicts net deposition in the deeper parts and at the intertidal area in the basin and net erosion in between, which resembles the observations qualitatively. Furthermore, the computed distribution of sand and mud in the basin of the Friesche Zeegat appears to be realistic. Analysis of the results shows that the absence of the decreasing import rate in the basin is caused by a poor quantitative prediction of the changes in the hypsometry of the basin. Because of this, the computed velocity asymmetry in the main channel tends toward flood dominance, whereas the observations indicate that the system is ebb-dominant in 1992. Although the sand–mud model needs to be further improved and verified, the results presented in this paper indicate that the model can be applied as a first step to estimate the effects of human interventions on the large-scale bed level and bed composition changes in tidal systems with sand and mud.     

Multi-scale variability and trends of precipitation in North China

The issue of water shortage and related eco-environmental degradation in North China is one of the major emerging problems in China. Precipitation is the most key factor for water resources. Based on the historical flood/dryness grade dataset during the period of 1470–2000 obtained from 25 gauging stations in North China, the multi-scale variability and trends are analyzed by means of power spectral and continuous wavelet transform. It is found that the precipitation is characterized by obvious seasonal changes, quasi biennial oscillations, inter-annual 4–7 year component and inter-decadal 19-year periodicity. The MK test results showe that step changes occurred around 1914 and 1964 in the annual precipitation. As for the historical flood/dryness grade time series, it is characterized by 4∼5 year ENSO mode inter-annual oscillation, quasi-10 year inter-decadal variability, quasi-24 year component and 50–80 year centurial periodicity. However, the scales of these variations have decreased significantly since the 1970s. The trend for precipitation change in North China has been negative for last 30 years. Further research shows that North China will continue to become dryer until 2015 and may change to a wetter regime after 2020. These findings should be helpful for future decision-making to ensure sustainable water resource management in North China.     

Climatic Change and the Dynamics of River Runoff into the Arctic Ocean

Time series of the river runoff into the Arctic Ocean over the period 1921–1999 are obtained through generalization of the available detailed hydrologic data on the drainage basin of the Arctic Ocean and estimates of the river runoff from areas in which no hydrometric observations have been made. Trends in the annual and seasonal river runoff from different parts of the basin are analyzed both for the entire period under study and for the last decades, which in the northern hemisphere are characterized by the most intense rise in air temperature. Potential future changes in the runoff of the main rivers of the basin and in the total river runoff into the ocean are discussed.     

Periodic changes of stream flow in the last 40 years in Tarim River Basin,Xinjiang, China

Using the annual runoff series for the last 40 years from the Tarim River Basin, their periodic properties were analysed and their future trends predicted. Runoff data were collected at five hydrological gauging stations in the three main branches of the Tarim River. An extrapolation method and variance analysis were used to identify periods in annual runoff, and a trend superposition model to predict future changes. Results show that, there is a common period of 17 years in annual runoff changes for all three branches, with Hotan River showing an additional period of 10 years. Based on this trend, it is suggested that the annual runoff of the Tarim River should decrease in the period of 2006–2008, but increase in year 2009, and the flow may possibly begin to decrease significantly in year 2010. The long term trend of runoff in Tarim Basin has followed the global prediction of GCMs, i.e. began to increase in accordance with global increase of air temperature and precipitation in 1990. However, it has shown a local feature of uneven changes among the head streams in the same basin, which needs to be further investigated. Copyright © 2008 John Wiley & Sons, Ltd.     

Quantifying changes of effective springshed area and net recharge through recession analysis of spring flow

The average flow of Silver Springs, one of the largest magnitude springs in Central Florida, declined 32% from 2000 to 2012. The average groundwater head in the springshed declined 0.14 m, and the spring pool altitude increased 0.24 m during the same period. This paper presents a novel explanation of the spring flow recession curve for Silver Springs using the Torricelli model, which uses the groundwater head at a sentinel well, the spring pool altitude and the net recharge to groundwater. The effective springshed area and net recharge (defined as recharge minus groundwater pumping and evapotranspiration) were estimated based on the observed recession slopes for spring flow, groundwater head and spring pool altitude. The results indicate that the effective springshed area continuously declined since 1989 and the net recharge declined since the 1970s with a significant drop in 2002. Subsequent to 2002, the net recharge increased modestly but not to the levels prior to the 1990s. The reduction in net recharge was caused by changes in hydroclimatic conditions including precipitation and air temperature, along with groundwater withdrawals, which contributed to the declined spring flow. Copyright © 2016 John Wiley & Sons, Ltd.     

Projection of glacier runoff in Yarkant River basin and Beida River basin,Western China

Potential changes in glacier area, mass balance and runoff in the Yarkant River Basin (YRB) and Beida River Basin (BRB) are projected for the period from 2011 to 2050 employing the modified monthly degree‐day model forced by climate change projection. Future monthly air temperature and precipitation were derived from the simple average of 17, 16 and 17 General Circulation Model (GCM) projections following the A1B, A2 and B1 scenarios, respectively. These data were downscaled to each station employing the Delta method, which computes differences between current and future GCM simulations and adds these changes to observed time series. Model parameters calibrated with observations or results published in the literature between 1961 and 2006 were kept unchanged. Annual glacier runoff in YRB is projected to increase until 2050, and the total runoff over glacier area in 1970 is projected to increase by about 13%–35% during 2011–2050 relative to the average during 1961–2006. Annual glacier runoff and the total runoff over glacier area in 1970 in BRB is projected to increase initially and then to reach a tipping point during 2011–2030. There are prominent increases in summer, but only small increase in May and October of glacier runoff in YRB, and significant increases during late spring and early summer and significant decreases in July and late summer of glacier runoff in BRB. This study highlights the great differences among basins in their response to future climate warming. The specific runoff from areas exposed after glacier retreat relative to 1970 is projected to general increasing, which must be considered when evaluating the potential change of glacier runoff. Copyright © 2011 John Wiley & Sons, Ltd.     

Hydrological effects of climate change,groundwater withdrawal,and land use in a small Korean watershed

The effects of variability in climate and watershed (groundwater withdrawal and land use) on dry‐weather streamflows were investigated using SWAT (Soil and Water Assessment Tool). The equation to predict the total runoff (TR) using climate data was derived from simulation results for 30 years by multiple regression analysis. These may be used to estimate effects of various climate variations (precipitation during the dry period, precipitation during the previous wet period, solar radiation, and maximum temperature). For example, if daily average maximum temperature increases by 3 °C, TR during the dry period will decrease by 27·9%. Similarly, groundwater withdrawals strongly affect streamflow during the dry period. However, land use changes (increasing urbanization) within the forested watershed do not appear to significantly affect TR during the dry period. Finally, a combined equation was derived that describes the relationships between the TR during the dry period and the climate, groundwater withdrawal and urban area proportion in a small monsoon watershed. This equation will be effective to predict the water availability during the dry periods in the future since it is closely related to changes of temperature, precipitation, solar radiation, urban area ratio, and groundwater withdrawal quantity. Copyright © 2007 John Wiley & Sons, Ltd.     

Climate-driven shifts in diatom assemblages recorded in annually laminated sediments of Sacrower See (NE Germany)

Sacrower See is a eutrophic lake with annually laminated sediments extending back to A.D. 1868. Analysis of annual layers revealed multi-decadal periods of distinct diatom assemblages at A.D. 1868–1875, 1876–1940, 1941–1978, and 1979–2000. Detrended correspondence analysis performed on individual seasonal sediment layers showed decadal-scale patterns of turnover in the diatom flora. The spring–summer layers showed higher sample scores until the early 1960s, after which the differences with the autumn–winter layers became smaller. Rates-of-change analysis revealed that the seasonal variability in diatom assemblages was higher than the annual changes. Summer diatom rates of change over the period A.D. 1894–1960 was on average higher than for winter, whereas between the 1960s and 1970s the winter rates of change became higher than the summer ones. Redundancy Analyses showed that seasonal temperatures and wind strength were significant explanatory variables for diatom assemblages in both annual and seasonal layers. These results suggest that meteorological changes indirectly affected diatom assemblages via the mixing regime of the lake. A comparison of the diatom rates of change with the amplitude of inter-annual climate change shows a statistically significant correlation for the spring-summer layers in the period of A.D. 1963–2000, showing that the sensitivity of diatom assemblages to meteorological changes has varied over the past century, with a stronger effect on diatoms registered during the past 40 years.     

Surface/groundwater interactions in the Bani and Nakambe rivers,tributaries of the Niger and Volta basins,West Africa

Abstract

The upper Niger and Volta rivers exhibit a great and highly contrasting variability of inter-annual runoff. The Bani River, the largest tributary to the Niger River in Mali, shows a dramatic decrease in runoff after the 1970s, with the result that many boreholes in the region have dried up since the drought began. In contrast, the Nakambe River (Upper Volta basin, in Burkina Faso) shows an increase in runoff for the same period, leading to unexpected flood peaks that damaged infrastructures. The contribution that the groundwater and its variability make to surface runoff variability is assessed in this study by comparing the data of the national groundwater monitoring networks of Mali and Burkina Faso to surface runoff. Several variables are compared at the basin scale: the date of the maximum level of the water table, the annual rainfall, discharge, low flows and depletion coefficients. Variability in the low flows of the Bani River is well correlated to a decrease in the water table. Since 1970, the greater decrease in runoff in comparison to the rainfall decrease is due to a reduction in the baseflow, related to the cumulated rainfall deficit. Concerning the Nakambe River, the runoff increase is not supported by a water table increase, but is due to the increase in runoff coefficient related to land degradation.     

Application of a land surface model for simulating rainfall streamflow hydrograph: 2. Comparison with hydrological models

Rainfall runoff hydrographs for 12 river basins ∼10³ km² in area, simulated using land surface model SWAP, are compared with analogous hydrographs obtained using hydrological models that took part in the International Model Parameter Estimation Experiment project and demonstrated the best results. All models were calibrated against data on daily river runoff from each basin over a 20-year period (1960–1979). Optimized model parameters were used to simulate runoff hydrographs for the following 19 years (1980–1998). The comparison of the modeled hydrographs for 12 basins in different calculational periods demonstrated that the SWAP model can simulate river runoff with an accuracy comparable with that of hydrological models.     

The impact of climate change on groundwater recharge and runoff in a humid,equatorial catchment: sensitivity of projections to rainfall intensity

Abstract

Projected warming in equatorial Africa, accompanied by greater evaporation and more frequent heavy precipitation events, may have substantial but uncertain impacts on terrestrial hydrology. Quantitative analyses of climate change impacts on catchment hydrology require high-resolution (<50 km) climate data provided by regional climate models (RCMs). We apply validated precipitation and temperature data from the RCM PRECIS (Providing Regional Climates for Impact Studies) to a semi-distributed soil moisture balance model (SMBM) in order to quantify the impacts of climate change on groundwater recharge and runoff in a medium-sized catchment (2098 km²) in the humid tropics of southwestern Uganda. The SMBM explicitly accounts for changes in soil moisture, and partitions effective precipitation into groundwater recharge and runoff. Under the A2 emissions scenario (2070–2100), climate projections from PRECIS feature not only rises in catchment precipitation and modelled potential evapotranspiration by 14% and 53%, respectively, but also increases in rainfall intensity. We show that the common application of the historical rainfall distribution using delta factors to the SMBM grossly underestimates groundwater recharge (i.e. 55% decrease relative to the baseline period of 1961–1990). By transforming the rainfall distribution to account for changes in rainfall intensity, we project increases in recharge and runoff of 53% and 137%, respectively, relative to the baseline period.     

Precipitation,temperature and runoff analysis from 1950 to 2002 in the Yangtze basin,China / Analyse des précipitations,températures et débits de 1950 à 2002 dans le bassin du Yangtze,en Chine

Abstract

Abstract Monthly precipitation and temperature trends of 51 stations in the Yangtze basin from 1950–2002 were analysed and interpolated. The Mann-Kendall trend test was applied to examine the monthly precipitation and temperature data. Significant positive and negative trends at the 90, 95 and 99% significance levels were detected. The monthly mean temperature, precipitation, summer precipitation and monthly mean runoff at Yichang, Hankou and Datong stations were analysed. The results indicate that spatial distribution of precipitation and temperature trends is different. The middle and lower Yangtze basin is dominated by upward precipitation trend but by somewhat downward temperature trend; while downward precipitation trend and upward temperature trend occur in the upper Yangtze basin. This is because increasing precipitation leads to increasing cloud coverage and, hence, results in decreasing ground surface temperature. Average monthly precipitation and temperature analysis for the upper, middle and lower Yangtze basin, respectively, further corroborate this viewpoint. Analysis of precipitation trend for these three regions and of runoff trends for the Yichang, Hankou and Datong stations indicated that runoff trends respond well to the precipitation trends. Historical flood trend analysis also shows that floods in the middle and lower Yangtze basin are in upward trend. The above findings indicate that the middle and lower Yangtze basin is likely to face more serious flood disasters. The research results help in further understanding the influence of climatic changes on floods in the Yangtze basin, providing scientific background for the flood control activities in large catchments in Asia.