Analysis of current trends in climate parameters,river discharge and glaciers in the Aksu River basin (Central Asia)

Abstract

Climate variability and change play a crucial role in the vulnerable system of the Aksu River basin located in Kyrgyzstan and northwest China, providing precious water resources for the intense oasis agriculture of the Xinjiang Province (China). Ubiquitous warming and increase in precipitation (in the lower part of the basin) have been detected. Glaciers in the region are retreating. Seasonal trends in river discharge show an increase. A clear link could be demonstrated between daily temperature and lagged river discharge at two headwater stations in summer. However, the correlation breaks over short periods in the end of summer or beginning of autumn at the Xiehela station, when the high (over 95th percentile) flow peaks caused by the glacier lake outburst floods of the Merzbacher Lake occur. This feature is a challenge for the climate impact assessment in the region, as these regular outbursts have to be represented in the projections for the future as well.

Editor D. Koutsoyiannis     

Quantitative evaluation of the rainfall influence on streamflow in an inland mountainous river basin within Central Asia

Stable isotopes of water have been widely used in understanding the hydrological functions of alpine inland catchments. This study identifies dominant runoff generation mechanisms based on isotopic data (δ¹⁸O and δ²H) of 487 rainwater and river-water samples from three tributaries in the Tarim River Basin in China for the period May–September 2013. The isotope hydrograph separation results provide a comprehensive overview of the rainfall influence on hydrological processes. Stream water and groundwater have varied responses to different intensities of rainfall events. Only a small proportion of rainfall is directly transported to the stream during such events. An inconsistent temporal trend of event water contribution is observed in the three catchments. The average fractional contributions of rainfall for the Tizinafu, Kumalak and Huangshuigou rivers are 10.3% (±1.1%), 9.7% (±2.9%) and 8.7% (±2.4%), respectively.     

Effect of sub-cloud evaporation on precipitation in the Tianshan Mountains (Central Asia) under the influence of global warming

It is crucial for accurately describing the precipitation patterns and their underlying mechanisms to optimise the hydro-climatic model parameters and improve the accuracy of precipitation forecasting. Based on 212 precipitation samples collected during August 2015 to July 2016 in the mid-mountain region of the Manasi River Basin in the northern slope of the Tianshan Mountains, we estimated the effect of sub-cloud evaporation on precipitation, analysed the factors that influence the sub-cloud evaporation, and modelled the response of sub-cloud evaporation to global warming. The mean remaining raindrop mass fraction after evaporation (f ) in this region is 94.39%. The mean deviation between d-excess (Δd ) of ground precipitation and raindrops under cloud is −4.22‰. The intensity of sub-cloud evaporation is the highest in summer. There is a significant positive correlation between f and Δd (0.72‰/%). The relative humidity and diameter of raindrops were observed to have a direct influence on the intensity of sub-cloud evaporation. The temperature was observed to influence the intensity of sub-cloud evaporation indirectly by influencing the relative humidity and diameter of raindrops. Global warming will increase the intensity of sub-cloud evaporation in the Tianshan Mountains, especially for small precipitation events.     

Chemical equilibria of thermal waters for the application of geothermometers from the Guanzhong basin, China

In this study, representative samples from thermal wells and springs were chemically analyzed and geothermometers were used to calculate the deep temperatures of geothermal reservoirs on the basis of water–mineral equilibrium. In some cases, however, the chemical components are not in equilibrium with the minerals in the reservoir. Therefore, log(Q/K) diagrams are used to study the chemical equilibrium for the minerals that are likely to participate. The Na–K–Mg triangular diagram is also applied to evaluate the equilibrium of water with reservoir rocks. Standard curves at the reference temperatures are prepared to reveal which type of silica geothermometer is appropriate for the specified condition. This study shows that water samples from geothermal wells W9 and W12 are in equilibrium with the selective minerals, and chalcedony may control the fluid–silica equilibrium. It is estimated that there is an exploitable low-temperature reservoir with possible temperatures of 80–90°C in the Guanzhong basin.     

Isotopic composition of waters from the Danakil depression (Ethiopia)

During two expeditions in the Danakil depression (Ethiopia), water samples were collected from: (a) hot springs in Dallol, Salt Plain, in the north of the depression; (b) cold and hot springs around Lake Giulietti; and c) Lake Giulietti.The isotopic results indicate: the water from Dallol hot springs is enriched in¹⁸O by isotopic exchange with the rocks as has been observed in many other geothermal areas of the world; b) the isotopic composition of the Lake Giulietti water changes with depth, probably as a consequence of a seasonal stratification; c) the springs in the Lake Giulietti region contain waters which result from the mixing of local meteoric water with a brine, or with lake waters.     

Water balance of the Salado–Juramento river basin (Argentina)

A lumped water balance model was used to derive a monthly water storage series in the Salado–Juramento southern basin, for the period 1954–1986. The evapotranspiration term was estimated using the Bouchet's complementary relationship. Different evapotranspiration formulas following the concepts of potential evapotranspiration and wet environmental evapotranspiration were used. The regional average groundwater levels and the specific yield were used to tune Bouchet's equation. The extrapolation of the water storage series to a secular period (1901–2002) was achieved using a synthetic annual discharge series. The water storage was deficient for most of the century, i.e. more than 60 years; nevertheless in the last 30 years, the system recovers half of the water previously lost. The singular spectral analysis showed that a significant low‐frequency signal is present in the water storage and precipitation series. The main cause of water storage variability would be given by precipitation, in spite of the vast anthropogenic changes on the basin. Anthropogenic effects would be reflected in the river discharges, where no significant signal is detected before 1970; however, an annual signal is insinuated after that year. The conclusions of this work could be different if we only looked at the 1954–1986 period. The results of that period suggest that the basin is primarily accumulating water instead of being mainly in deficit. Thus, here we demonstrated the importance of the secular analysis to illustrate the complete basin behaviour. Copyright © 2012 John Wiley & Sons, Ltd.     

Denitrification in a hyporheic riparian zone controlled by river regulation in the Seine river basin (France)

The purpose of this paper is to study denitrification and the conditions for its development in a hyporheic zone. The study site is the riparian zone of a former branch of the Seine River, where the river stage is kept almost constant during the year by hydraulic regulation. Hydrological and geochemical surveys were performed by monitoring four wells, ten shorter piezometers and the river over a 15‐month period. The water fluxes originating from the chalky hillsides and the river converge in a zone parallel to the river that acts as a drainage flow path through the floodplain. The riparian zone between this flow path and the river shows an important depletion of nitrate during the summer and autumn period, which cannot be explained by a simple mixing of waters coming from the river and the chalky hillsides. It can be attributed to denitrification as it occurs when oxygen concentration is below 2 mg l^?1, and goes along with a consumption of dissolved organic carbon and a decrease of redox potential. The river completely controls these hydro‐geochemical conditions. It also keeps the wetness of the riparian zone almost constant, which allowed us to isolate the high temperatures in summer and autumn as an important triggering factor for denitrification through its influence on the reaction rate and oxygen deficits. We also found a small isotopic enrichment of nitrate, suggesting that denitrification occurs after diffusion of nitrate through the sediment and riparian zone matrix, which is consistent with the hyporheic functioning of the study site. Copyright © 2008 John Wiley & Sons, Ltd.     

Simulating the surface waters of the Amazon River basin: impacts of new river geomorphic and flow parameterizations

This paper describes the impacts of new river geomorphic and flow parameterizations on the simulated surface waters dynamics of the Amazon River basin. Three major improvements to a hydrologic model are presented: (1) the river flow velocity equation is expanded to be dependent on river sinuosity and friction in addition to gradient forces; (2) equations defining the morphological characteristics of the river, such as river height, width and bankfull volume, are derived from 31 622 measurements of river morphology and applied within the model; (3) 1 km resolution topographic data from the Shuttle Radar Topography Mission (SRTM) are used to provide physically based fractional flooding of grid cells from a statistical representation of sub‐grid‐scale floodplain morphology. The discharge and floodplain inundation of the Amazon River is simulated for the period 1968–1998, validated against observations, and compared with results from a previous version of the model. These modifications result in considerable improvement in the simulations of the hydrological features of the Amazon River system. The major impact is that the average wet‐season flooded area on the Amazon mainstem for the period 1983–1988 is now within 5% of satellite‐derived estimates of flooded area, whereas the previous model overestimates the flooded area by about 80%. The improvements are a consequence of the new empirical river geomorphologic functions and the SRTM topography. The new formulation of the flow velocity equation results in increased river velocity on the mainstem and major tributaries and a better correlation between the mean monthly simulated and observed discharge. Copyright © 2007 John Wiley & Sons, Ltd.     

Climate change impacts on runoff in the Ferghana Valley (Central Asia)

The main freshwater source of arid/semi-arid Central Asia is stored in its high mountain glaciers. Water for the downstream countries is mainly supplied through the Syrdarya River that originates at the confluence of the Naryn and Karadarya rivers in the Ferghana Valley. Runoff generation from glaciers plays a crucial role, although a considerable number of small tributaries supply the river with additional runoff from snowmelt and rain in the mountains surrounding the Ferghana Valley. Observations of rising air temperature and accelerated glacier shrinkage make it most likely that the relative contributions of the smaller tributaries will increase. Hitherto, assessments of climate change effects on the water resource availability have largely neglected the growing importance of the runoff from smaller tributaries. We used a dynamically downscaled A1B SRES scenario for climate change effects for the period 2071–2100 in relation to the reference period of 1971–2000 and a version of the conceptual hydrological Hydrologiska Byråns Vattenavdelning model (HBV-light) to estimate runoff contributions with particular respect to the small tributaries. The simulations showed a 12–42% decrease in summer runoff; and a 44–107% increase in winter-spring runoff. This indicates the hydrological regime is shifting towards a runoff from snowmelt earlier in the year. The study suggests that actions for climate change adaptation should be complemented by land management configured to secure optimal runoff supplement from the smaller catchments.     

Inter-annual variability in snow cover depletion patterns and atmospheric circulation indices in the Upper Irtysh basin,Central Asia

The Irtysh River is the main water resource of Eastern Kazakhstan and its upper basin is severely affected by spring floods each year, primarily as a result of snowmelt. Knowledge of the large-scale processes that influence the timing of these snow-induced floods is currently lacking, but critical for the management of water resources in the area. In this study, we evaluated the variability in winter–spring snow cover in five major sub-basins of the Upper Irtysh basin between 2000 and 2017 as a possible explanatory factor of spring flood events, assessing the time of peak snow cover depletion rate and snow cover disappearance from the moderate-resolution imaging spectroradiometer (MODIS) MOD10A2 data set. We found that on average, peak snow cover retreat occurs between 22 March and 14 April depending on the basin, with large interannual variations but no clear trend over the MODIS period, while our comparative analysis of longer-term snow cover extent from the National Oceanic and Atmospheric Administration Climate Data Record data set suggests a shift to earlier snow cover disappearance since the 1970s. In contrast, the annual peak snow cover depletion rate displays a weak increasing trend over the study period and exceeded 5,900 km²/day in 2017. The timing of snow disappearance in spring shows significant correlations of up to 0.82 for the largest basin with winter indices of the Arctic Oscillation (AO) over the region. The primary driver is the impact of the large-scale pressure anomalies upon the mean spring (MAM) air temperatures and resultant timing of snow cover disappearance, particularly at elevations 500–2,000 m above sea level. This suggests a lagged effect of this atmospheric circulation pattern in spring snow cover retreat. The winter AO index could therefore be incorporated into long-term runoff forecasts for the Irtysh. Our approach is easily transferable to other similar catchments and could support flood management strategies in Kazakhstan and other countries.     

Probabilistic PGA and Arias Intensity maps of Kyrgyzstan (Central Asia)

New probabilistic seismic hazard and Arias Intensity maps have beendeveloped for the territory of the Kyrgyz Republic and bordering regions.Data were mainly taken from the seismic catalogue of Kyrgyzstan and partlyfrom the world seismic catalogue. On the base of seismicity and activetectonics, seismic zones were outlined over the area. For these,Gutenberg-Richter laws were defined using mainly instrumental data, butregarding also historical events. Attenuation of acceleration inside the targetarea could not be determined experimentally since existing strong motiondata are insufficient. Therefore, empirical laws defined for other territories,principally Europe and China, were applied to the present hazardcomputations. Final maps were calculated with the SEISRISKIII programaccording to EUROCODE8 criteria, i.e. for a period of 50 years with90% probability of non-exceedance. For long-term prediction, 100 yearsmaps with 90% probability of non-exceedance have been developed. Theprocedure used for seismic hazard prediction in terms of PGA (PeakGround Acceleration) was also applied to Arias intensities in order to beable to define regional seismogenic landslide hazard maps.     

Ecological water quality analysis of the Guayas river basin (Ecuador) based on macroinvertebrates indices

The Guayas river basin is one of the major watersheds in Ecuador, where increasing human activities are affecting water quality and related ecosystem services. The aims of this study were (1) to assess the ecological water quality based on macroinvertebrate indices and (2) to determine the major environmental variables affecting these macroinvertebrate indices. To do so, we performed an integrated water quality assessment at 120 locations within the river basin. Biological and physical–chemical data were collected to analyze the water quality. Two biotic indices were calculated to assess the water quality with an ecological approach: the Biological Monitoring Working Party Colombia (BMWP-Col) and the Neotropical Low-land Stream Multimetric Index (NLSMI). Both the BMWP-Col and NLSMI indicated good water quality at the (upstream) forested locations, lower water quality for sites situated at arable land and bad water quality at residential areas. Both indices gave relevant assessment outcomes and can be considered valuable for supporting the local water management. A correspondence analysis (CA) applied on both indices suggested that flow velocity, chlorophyll concentration, conductivity, land use, sludge layer and sediment type were the major environmental variables determining the ecological water quality. We also suggested that nutrient and pesticide measurements are important to study water quality in the area where intensive agriculture activities take place. The nutrient levels detected in agricultural areas were relatively low and illustrated that the types of crops and the current cultivation methods were not leading to eutrophication. The applied methods and results of this study can be used to support the future water management of the Guayas river basin and similar basins situated in the tropics.     

Impacts of climate change on the discharge and glacier mass balance of the different glacierized watersheds in the Tianshan Mountains,Central Asia

The Tianshan Mountains represent an important water source for the arid and semi‐arid regions of Central Asia. The discharge and glacier mass balance (GMB) in the Tianshan Mountains are sensitive to changes in climate. In this study, the changes in temperature, precipitation, and discharge of six glacierized watersheds of Tianshan Mountains were explored using non‐parametric tests and wavelet transforms during 1957–2004. On the basis of the statistical mechanics and maximum entropy principle model, the GMB at the watershed scale were reconstructed for the study period. The discharge and GMB responses to climate change were examined in different watersheds. The results showed that regional climate warming was obvious, especially after 1996. The warming trend increased gradually from east to west, and the increase in temperature was greater on the north slope than on the south slope. The changing trends in precipitation increased from eastern region to central region, and then, the trend decreased in the western region, although the value was higher than that in the eastern region. The discharge presented significant periods of 2.7–5.4 years and increased from east to west. Significant periodicity indicated that the discharge in the different watersheds exhibited obviously different patterns. The GMB losses were larger in south and east than in north. The large glaciers had more stable interannual variations in discharge, and large fluctuations in discharge will be observed as the glacier areas shrink. Precipitation was the dominant factor for discharge during the study period, although the influence of increasing temperatures on hydrological regimes should not be neglected in the long term. Systematic differences in discharge and the GMB in glacierized watersheds in response to climate change are apparent in the Tianshan Mountains.     

Dispersion of naturally occurring ions in groundwater from various rock types in a portion of the San Pedro river basin, Arizona

The groundwater in an alluvial basin in southern Arizona was analyzed for concentrations of Ca⁺⁺, Mg⁺⁺, Na⁺, and Cl⁻, ions.

The variety of rock types in the area, plus the undisturbed state of the groundwater basin, make comparative rock mineralization-groundwater ionization interpretations possible. Ionic dispersion in groundwater eminating from source areas composed of differing rock types is plotted as isogram maps. These isolated areas of differing mineral composition each exhibit a unique ionic contribution to groundwater. The ion concentrations in groundwater were then used as naturally occurring tracers to determine source areas of recharge and to delineate subsurface barriers to the normal basin flow net. Ion dispersion plots reveal the carbonates of the Dragoon Mountains to be a major contributor of Ca⁺⁺ and Mg⁺⁺ to the deep alluvial portion of the basin. Cl⁻ dispersion patterns show the granitic intrusives of the Tombstone Hills produce a barrier effect in the normal flow pattern of the basin as well as being a contributor of Cl⁻ to groundwater.     

中国渤海湾盆地上地壳岩石成分模型(英文)

许多地震属性,比如地震的纵横波速度,泊松比,声波阻抗,都能用来区分不同的岩石类型,利用拉梅阻抗作为进一步的约束来代替声波阻抗能更好的降低结果的非唯一性。我们用这种方法构建了渤海湾地区一条剖面的岩石成分模型。我们简要介绍了区分岩石类型的地震参数,重点在于不同的参数组合对于分辨岩石类型的敏感性。为了与室温常压条件下测得的有代表性的岩石的地震波速度和密度进行对比,我们首先需要做温度和压力的校正。接着,我们需要用已知资料和实验测得的各种岩石样品做对比,来确定研究区的岩石类型。我们收集了渤中凹陷一条剖面的纵波速度资料。该剖面10km深范围内的属于同种岩石类型的不同岩石最终通过地震波速度、泊松比、密度、声波阻抗、以及拉梅阻抗综合约束。     

Factors influencing the removal of fine non-cohesive sediment by vortex settling basin at small river abstraction works

Diverted sediment causes a wide range of problems at small diversion works.The difference in water levels between low flows and floods,low investment capital and presence of cohesive sediment and fine non-cohesive sediment coupled with a requirement for a high level of supply assurance makes the design of such hydraulic structures complex.Vortex settling basins(VSBs)offer a promising alternative to conventional settling structures or hydro-cyclones.In the current study,parameters affecting the trapping of particles>75 mm were numerically investigated using ANSYS Fluent and were validated by physical modeling.It was established that the inlet velocity needs to be maintained at 0.26 m/s,the underflow to inflow ratio should be between 0.05 and 0.10,the cylinder height to cylinder diameter ratio should be greater than 0.5,and the positioning of the inlet pipe to cylinder height ratio should be greater than 0.7,with a cone of slope ratio of 2:1(V:H)and the cylinder diameter to inlet diameter ratio should be 8.2.These parameters form the basic design guidelines for VSB use at small diversion works(<100 L/s duty capacity).     

Verification of short-term runoff forecasts for a small Philippine basin (Marikina)

Storm runoff from the Marikina River Basin frequently causes flood events in the Philippine capital region Metro Manila. This paper presents and evaluates a system to predict short-term runoff from the upper part of that basin (380 km²). It was designed as a possible component of an operational warning system yet to be installed. For the purpose of forecast verification, hindcasts of streamflow were generated for a period of 15 months with a time-continuous, conceptual hydrological model. The latter was fed with real-time observations of rainfall. Both ground observations and weather radar data were tested as rainfall forcings. The radar-based precipitation estimates clearly outperformed the raingauge-based estimates in the hydrological verification. Nevertheless, the quality of the deterministic short-term runoff forecasts was found to be limited. For the radar-based predictions, the reduction of variance for lead times of 1, 2 and 3 hours was 0.61, 0.62 and 0.54, respectively, with reference to a “no-forecast” scenario, i.e. persistence. The probability of detection for major increases in streamflow was typically less than 0.5. Given the significance of flood events in the Marikina Basin, more effort needs to be put into the reduction of forecast errors and the quantification of remaining uncertainties.     

Characteristics of strong ground motion data recorded in the Gubbio sedimentary basin (Central Italy)

Various authors, analysing the set of accelerograms recorded at Gubbio Piana (GBP) (central Italy), have demonstrated that strong amplification occurs at this accelerometric station, which is installed within an alluvial basin. In particular, Ambraseys et al. [(2005a), Bull Earthq Eng 3:1–53; (2005b), Bull Earth Eng 3:55–73] observed that the strong motion peaks at GBP greatly exceed the median values predicted by the attenuation relationships they derived for Europe. In this work, we analyse and discuss some characteristics of the ground motion recorded at the GBP station. We show that the ground motion parameters, such as peak-ground acceleration and peak-ground velocity, are strongly influenced by the presence of locally induced surface waves that produce both a lengthening of the significant shaking duration and an increase in the peak values with respect to a nearby bedrock site. The basin-induced surface waves are observed in the three components of motion and their effects on the peak values are particularly evident in the vertical component. In the frequency domain, the energy of the surface waves is mostly restricted to the frequency band 0.4–0.8 Hz for both the horizontal and vertical components. The horizontal and vertical Fourier amplitudes are also very similar, and this indicates that the H/V spectral ratio technique is not applicable to describing the site response due to the propagation of seismic wave in a complex 2D/3D geological structure. Finally, a preliminary polarization analysis shows that the directions of polarization, as well as the degree of elliptical polarization, exhibit a strong variability with time, that may be related to a complex propagation of Love and Rayleigh waves within the basin.     

New data on the geology and age of the Koreyskaya River area (south Sikhote-Alin)

Abstract The geological structure of the Koreyskaya River area exhibits a complex combination of turbidite—olistostrome deposits making up a matrix and synsedimentary tectonic enclosures represented by allochthons of formations different in age and genesis. Three tectono-stratigraphic units can be distinguished, that have been combined into a single section by accretion. New data on radiolarians have been used to date the tectonic enclosures and matrix. Abundant Mesozoic radiolarians (from Triassic to Late Jurassic) and also Late Permian radiolarians were found in cherty and siliceous mudstone olistoliths and cherty allochthons.