Continental River Basins Research Articles

Suitable oasis scale in a typical continental river basin in an arid region of China: A case study of the Manas River Basin

An oasis is defined here as an efficient eco-geographical landscape that allows flourishing vegetation or human settlement due to a stable water supply in an arid region. The water resource is the major limiting factor impacting the oasis scale in arid regions. For discussion of the suitable scale of an oasis supported by a specific quantity of water resource, the Manas River Basin, a typical continental river basin in the arid region of China, was taken as the study object. Based on the remote sensing images and socio-economic data, the stability and suitable scale of oasis in 1976, 1987, 1998, 2010, and 2020 were analyzed using an oasis water-heat balance model. The results indicated that (1) the respective stability index (H0) of 1976, 1987, 1998, and 2010 was 0.10, 0.15, 0.40, and 0.38, respectively, changing from an unstable level into a metastable level. (2) Under the guarantee of natural oasis ecosystem stability, the suitable scales of natural oasis in 1976, 1987, 1998, and 2010 were 697.2–1045.7 km2, 942.2–1413.3 km2, 2042.0–3063.0 km2, and 1428.2–2142.3 km2, respectively. The suitable scales of the total oases were 3681.3–4030.3 km2, 5259.1–5730.2 km2, 7654.5–8675.5 km2, and 8130.3–8844.4 km2, respectively. (3) If the artificial oasis scale remained unchanged from 2010, the suitable scale of the natural oasis in the Manas River Basin in 2020 would be 1695.8–2543.8 km2, and the suitable scale of the total oases would be 8398–9246 km2. With a reasonable proportion between natural and artificial oases, the suitable scales of each would be 3400.3–5100.5 km2 and 2266.9–3400.4 km2. This paper not only provides data for reasonable oasis planning of the Manas River Basin, but also provides a new direction for studies on the suitable scale of oases in arid regions.

Effects of Land‐Use and Land‐Cover Change on Evapotranspiration and Water Yield in China During 1900‐20001

Abstract: China has experienced a rapid land‐use/cover change (LUCC) during the 20th Century, and this process is expected to continue in the future. How LUCC has affected water resources across China, however, remains uncertain due to the complexity of LUCC‐water interactions. In this study, we used an integrated Dynamic Land Ecosystem Model (DLEM) in conjunction with spatial data of LUCC to estimate the LUCC effects on the magnitude, spatial and temporal variations of evapotranspiration (ET), runoff, and water yield across China. Through comparisons of DLEM results with other model simulations, field observations, and river discharge data, we found that DLEM model can adequately catch the spatial and seasonal patterns of hydrological processes. Our simulation results demonstrate that LUCC led to substantial changes in ET, runoff, and water yield in most of the China’s river basins during the 20th Century. The temporal and spatial patterns varied significantly across China. The largest change occurred during the second half century when almost all of the river basins had a decreasing trend in ET and an increasing trend in water yield and runoff, in contrast to the inclinations of ET and declinations of water yield in major river basins, such as Pearl river basin, Yangtze river basin, and Yellow river basin during the first half century. The increased water yield and runoff indicated alleviated water deficiency in China in the late 20th Century, but the increased peak flow might make the runoff difficult to be held by reservoirs. The continuously increasing ET and decreasing water yield in Continental river basin, Southwest river basin, and Songhua and Liaohe river basin implied regional water deficiency. Our study in China indicates that deforestation averagely increased ET by 138 mm/year but decreased water yield by the same amount and that reforestation averagely decreased ET by 422 mm/year since most of deforested land was converted to paddy land or irrigated cropland. In China, cropland‐related land transformation is the dominant anthropogenic force affecting water resources during the 20th Century. On national average, cropland expansion was estimated to increase ET by 182 mm/year while cropland abandonment decreased ET by 379 mm/year. Our simulation results indicate that urban sprawl generally decreased ET and increased water yield. Cropland managements (fertilization and irrigation) significantly increased ET by 98 mm/year. To better understand LUCC effects on China’s water resources, it is needed to take into account the interactions of LUCC with other environmental changes such as climate and atmospheric composition.

Analysis of terrestrial water storage changes from GRACE and GLDAS

Since March 2002, the Gravity Recovery and Climate Experiment (GRACE) has provided first estimates of land water storage variations by monitoring the time‐variable component of Earth's gravity field. Here we characterize spatial‐temporal variations in terrestrial water storage changes (TWSC) from GRACE and compare them to those simulated with the Global Land Data Assimilation System (GLDAS). Additionally, we use GLDAS simulations to infer how TWSC is partitioned into snow, canopy water and soil water components, and to understand how variations in the hydrologic fluxes act to enhance or dissipate the stores. Results quantify the range of GRACE‐derived storage changes during the studied period and place them in the context of seasonal variations in global climate and hydrologic extremes including drought and flood, by impacting land memory processes. The role of the largest continental river basins as major locations for freshwater redistribution is highlighted. GRACE‐based storage changes are in good agreement with those obtained from GLDAS simulations. Analysis of GLDAS‐simulated TWSC illustrates several key characteristics of spatial and temporal land water storage variations. Global averages of TWSC were partitioned nearly equally between soil moisture and snow water equivalent, while zonal averages of TWSC revealed the importance of soil moisture storage at low latitudes and snow storage at high latitudes. Evapotranspiration plays a key role in dissipating globally averaged terrestrial water storage. Latitudinal averages showed how precipitation dominates TWSC variations in the tropics, evapotranspiration is most effective in the midlatitudes, and snowmelt runoff is a key dissipating flux at high latitudes. Results have implications for monitoring water storage response to climate variability and change, and for constraining land model hydrology simulations.

Distributed tank model and GAME reanalysis data applied to the simulation of runoff within the Chao Phraya River Basin, Thailand

AbstractThe tank model is well known as a lumped conceptual hydrological model. In contrast with the large number of physical‐based models developed over the past 30 years, only a few distributed conceptual hydrological models are available. In this study, a high‐resolution distributed tank model is used to simulate river flow within a continental river basin, the Chao Phraya River basin, Thailand, using GEWEX Asian Monsoon Experiment (GAME) Reanalysis data. The model has a spatial resolution of 0·1 by 0·1 degrees and a temporal resolution of 1 h. Four terrain types and ten types of land use are identified in the model, and the model parameters were found to vary with the terrain type and land use. The model parameters were first determined in the 4841 km2 Khwae Noi River basin as a prototype area before being generalized to the entire 160 000 km2 of the Chao Phraya River basin. Simulation results at various sites indicate that the distributed tank model provides a sound approximation of the observed runoff data and is therefore a useful and reliable tool for the runoff simulation in this tropical continental river basin. Our results also indicated that after assimilating observational data, it was possible to use GAME Reanalysis data for such a distributed hydrological simulation. Copyright © 2007 John Wiley & Sons, Ltd.

Teleconnection between the Arctic Oscillation and Hudson Bay river discharge

Rising surface air temperatures in response to anthropogenic forcing are intensifying the global hydrologic cycle. Some of the more dramatic signs of climate change are increasing precipitation, evaporation, and freshwater discharge in continental river basins draining to high‐latitude oceans. At regional scales, however, an acceleration of the hydrologic cycle is not always detected. In contrast to its major Eurasian counterparts, the North American Hudson Bay Basin experienced a 15% decline in river runoff between 1964 and 1994. It is shown that the Arctic Oscillation explains with statistical significance up to 90% of the recent variability in Hudson Bay river discharge. This study reveals the important role of large‐scale atmospheric phenomena such as the Arctic Oscillation in regulating the terrestrial hydrologic budget. The ability of weather and climate models to represent these interannual to decadal scale phenomena governs their predictions of the surface water budget's future state in a changing climate.

RUNOFF ANALYSIS ON THE 1998 FLOOD IN CHINA USING THE GAME RE-ANALYSIS DATA

The objective of this study is to investigate the applicability of re-analysis data in hydrological forecasting. In this study, flood runoff analysis of the historical 1998 floods occurred in Changjiang and Songhuajiang river basins, China has been carried out by using the GAME re-analysis data (version 1.5). For these two continental river basins, distributed hydrological models with spatial resolution 0.5 by 0.5 degree are built by using our distributed modeling system. For each basin, calculated hydrographs are derived at three hydrological stations. They are compared with the observed ones. It is shown that the flood volume and timing of peak discharge are well represented. This shows that GAME re-analysis data is fully applicable. And this also implies the possibility to apply re-analysis data to hydrological forecasting of the continental scale river basins.

Effects of spatial variability on estimation of evapotranspiration in the continental river basin

Water and energy balance models were developed at the local and basin scale by aggregating a HYDRUS Model across scales in a topographic framework. A spatially distributed approach was followed to aggregate the HYDRUS Model to basin scale. The effects of spatial variability on the estimation of evapotranspiration at basin scale are emphatically discussed. In the present work the main emphasis was focused on the estimation of the spatial variability of both evapotranspiration and the calculation of statistical parameters of soil water storage from local scale to basin scale. Our results illustrate that the changes of the local and area-averaged potential evapotranspiration ( ET p), actual evapotranspiration ( ET) show a strong seasonal trend where the mean and standard deviation ( STD) approximately fit the two-harmonics of Fourier series. Moreover, ET p and ET are random variables which follow the normal distribution with mean and deviation changing with season. A sensitivity analysis of the results shows that to a reasonable degree, the incorporated model can be used to determine the relationship between the actual area-averaged evapotranspiration and the main controlling factors for both bare soil and vegetated surfaces.

Predicting the Discharge of Global Rivers

The ability to simulate coupled energy and water fluxes over large continental river basins, in particular streamflow, was largely nonexistent a decade ago. Since then, macroscale hydrological models (MHMs) have been developed, which predict such fluxes at continental and subcontinental scales. Because the runoff formulation in MHMs must be parameterized because of the large spatial scale at which they are implemented, some calibration of model parameters is inevitably necessary. However, calibration is a time-consuming process and quickly becomes infeasible when the modeled area or the number of basins increases. A methodology for model parameter transfer is described that limits the number of basins requiring direct calibration. Parameters initially were estimated for nine large river basins. As a first attempt to transfer parameters, the global land area was grouped by climate zone, and model parameters were transferred within zones. The transferred parameters were then used to simulate the water balance in 17 other continental river basins. Although the parameter transfer approach did not reduce the bias and root-mean-square error (rmse) for each individual basin, in aggregate the transferred parameters reduced the relative (monthly) rmse from 121% to 96% and the mean bias from 41% to 36%. Subsequent direct calibration of all basins further reduced the relative rmse to an average of 70% and the bias to 12%. After transferring the parameters globally, the mean annual global runoff increased 9.4% and evapotranspiration decreased by 5.0% in comparison with an earlier global simulation using uncalibrated parameters. On a continental basis, the changes in runoff and evapotranspiration were much larger. A diagnosis of simulation errors for four basins with particularly poor results showed that most of the error was attributable to bias in the Global Precipitation Climatology Project precipitation products used to drive the MHM.

Hydrologic sensitivity of global rivers to climate change

Climate predictions from four state-of-the-art general circulation models (GCMs) were used to assess the hydrologic sensitivity to climate change of nine large, continental river basins (Amazon, Amur, Mackenzie, Mekong, Mississippi, Severnaya Dvina, Xi, Yellow, Yenisei). The four climate models (HCCPR-CM2, HCCPR-CM3, MPI-ECHAM4, and DOE-PCM3) all predicted transient climate response to changing greenhouse gas concentrations, and incorporated modern land surface parameterizations. Model-predicted monthly average precipitation and temperature changes were downscaled to the river basin level using model increments (transient minus control) to adjust for GCM bias. The variable infiltration capacity (VIC) macroscale hydrological model (MHM) was used to calculate the corresponding changes in hydrologic fluxes (especially streamflow and evapotranspiration) and moisture storages. Hydrologic model simulations were performed for decades centered on 2025 and 2045. In addition, a sensitivity study was performed in which temperature and precipitation were increased independently by 2 °C and 10%, respectively, during each of four seasons. All GCMs predict a warming for all nine basins, with the greatest warming predicted to occur during the winter months in the highest latitudes. Precipitation generally increases, but the monthly precipitation signal varies more between the models than does temperature. The largest changes in the hydrological cycle are predicted for the snow-dominated basins of mid to higher latitudes. This results in part from the greater amount of warming predicted for these regions, but more importantly, because of the important role of snow in the water balance. Because the snow pack integrates the effects of climate change over a period of months, the largest changes occur in early to mid spring when snow melt occurs. The climate change responses are somewhat different for the coldest snow dominated basins than for those with more transitional snow regimes. In the coldest basins, the response to warming is an increase of the spring streamflow peak, whereas for the transitional basins spring runoff decreases. Instead, the transitional basins have large increases in winter streamflows. The hydrological response of most tropical and mid-latitude basins to the warmer and somewhat wetter conditions predicted by the GCMs is a reduction in annual streamflow, although again, considerable disagreement exists among the different GCMs. In contrast, for the high-latitude basins increases in annual flow volume are predicted in most cases.

Macroscale hydrological modeling using remotely sensed inputs: Application to the Ohio River basin

Predictions of water and energy budgets at the land surface are central to climate simulation and numerical weather prediction, as well as to water resources planning and management. Macroscale hydrological models provide a new tool for simulating surface water and energy balances at the scale of large continental river basins. However, these models are limited by the scarcity of in situ meteorological forcing data. Remote sensing data provide an alternative to in situ data, with observations that are, in some cases, at a higher spatial and temporal resolution than those available from traditional surface sources. Nonetheless, there remain important questions as to whether the accuracy of remotely sensed surface variables is sufficient to serve as forcings for surface hydrological models. This question is addressed through comparison of hydrologic simulations for the Ohio River basin with the variable infiltration capacity (VIC) macroscale hydrology model, using in situ and remotely sensed data. In situ data consist of gridded (at ½ degree latitude‐longitude spatial resolution) precipitation, temperature, and wind, with downward solar and longwave radiation inferred from the diurnal temperature range. Remotely sensed observations include incident solar radiation, air temperature, and vapor pressure deficit inferred from the Geostationary Operational Environmental Satellite (GOES), the advanced very high resolution radiometer (AVHRR) and the TIROS Operational Vertical Sounder (TOVS), respectively. Precipitation, in all cases, is from gridded station data. The modeled streamflows and evapotranspiration rates are quite similar for the two cases. The largest differences in predicted surface hydrology are associated with differences in modeled snow cover accumulation and snowmelt, and result from a warm bias in the remotely sensed temperature data.

Friction and carrying capacity of ball and roller bearings

Although water is the material basis of human being survival and development, it exhibits inhomogeneity in time and space, which makes it difficult to accurately evaluate the supply and consumption relationship of water resources and its carrying capacity in arid regions. An innovative integrated modeling framework was proposed to dynamically evaluate and predict the water balance and water resources carrying capacity in a continental river basin of Northwest China by coupling the Soil and Water Assessment Tool (SWAT), water resources supply and consumption model, Principal Component Analysis (PCA) and Fuzzy Comprehensive Evaluation (FCE). The following results were obtained: i) the integrated methodology between the SWAT distributed hydrological model and the water resources evaluation model is an important tool for predicting the regional water resources carrying capacity, which has dynamic, advanced, comprehensive and systematic features; ii) from 2000 to 2007, the available water resources in the Heihe River Basin were almost all in the state of shortage, although the water shortage rate decreased gradually and changed from 35% in 2006 to −0.49% in 2007, with 2001 exhibiting the most serious drought period (maximum water shortage rate of 62.77%); iii) the water resources carrying capacity in the upper reaches of Heihe River Basin from 2010 to 2015 showed an overall increasing trend; iv) the pressure risk on the water resources carrying capacity in the upper reaches of Heihe River Basin from 2015 to 2025 indicates gradual and specific changes, with good results observed in 2015, moderate results observed in 2020, and relatively poor results observed in 2025; and v) collaborative and sustainable water resources management strategies are recommended from four dimensions, water resources amount, water environment capacity, water spaces and water dynamics. The results may provide insights for guiding the optimal scheme design of water resources allocation in a continental river basin with arid regions.