Water Balance Processes Research Articles

Multi-scale evapotranspiration of summer maize and the controlling meteorological factors in north China

Evapotranspiration (ET) scale effect influences the understanding of water and energy balance processes at different scales. However, there are fewer studies about the relationships between multi-scale ET and the controlling meteorological factors. In this study, the variations in leaf and plant transpiration and farmland ET of summer maize were systematically analyzed using three-successive-year data from an irrigation experiment station in north China, and the meteorological factors affecting ET at different scales were analyzed based on multivariate regression. The main findings include (1) the transpiration rate (Tr) and stomatal conductance (gs) of sun and shade leaves reduced with the reduction of photosynthetically active radiation (PAR), and the Tr and gs in shade leaves were about half of sun leaves. When the differences in PAR were smaller, leaf Tr and gs at lower part of canopy were slightly lower than those at middle and upper parts of canopy. (2) The sap flow rate (plant transpiration) of summer maize was related to the net radiation but lagged 1h. (3) Diurnal variation in latent heat flux (λET) of summer maize was similar to that in net radiation but lagged slightly. λET, sensible heat flux and ground heat flux accounted for 66.9–70.7, 23.4–26.1 and 4.0–9.2% of net radiation over the whole growing period, respectively. The Bowen ratio ranged from 0.33 to 0.37 over the whole growing period, and peaked at around 10:00 a.m. (4) Leaf transpiration and farmland ET can be characterized by net radiation, air temperature, vapor pressure deficit and wind speed, but plant transpiration cannot be well characterized by them, possibly due to the change of stored water in the stalk.

Drying of Porous Media

Drying of porous media is part of our daily experience, yet this common process is central to many environmental and engineering applications ranging from soil evaporation affecting hydrological water balance and climatic processes, to the drying of food and building materials, and driving plant life through transpiration. Drying rates from porous media may exhibit complex dynamics reflecting internal transport mechanisms and motion of phase change fronts that determine rates of drying and critically affect surface energy partitioning. These interactions and resulting drying dynamics present a challenge to the prediction of drying rates and interplay among mass and energy exchange even for fixed boundary conditions.

Limiting factors for nomadic pastoralism in Mongolian steppe: A hydrologic perspective

In this study, limiting factors for continuing nomadic pastoralism in steppe areas were studied based on a hydrologic perspective. Two small watersheds in central Mongolia were selected for an assessment of water balance and hydrologic processes. We determined that the majority of annual precipitation, ∼88–96 mm, was lost by evaporation (82%) while only a small proportion went to groundwater discharge, surface runoff, and groundwater consumption by nomadic activities. The soil column was found to absorb large fluctuations in precipitation although its connection to groundwater was very weak. Groundwater recharge was, therefore, very small and occurred only rarely during heavy rainfall events in valley bottoms. However, current water storage in shallow groundwater was determined to be quite sufficient for continuing nomadic pastoralism when compared to the drinking water requirements of livestock. The main limiting factors identified were a temporal lack of feed to animals due to a loss of aboveground biomass resulting from soil moisture shortages during drought conditions, and a decline in the number and maintenance level of the traditional well network that, due to access to shallow groundwater, has allowed herders to migrate to areas with better conditions in remote Mongolian steppe.

Ecohydrologic role of solar radiation on landscape evolution

AbstractSolar radiation has a clear signature on the spatial organization of ecohydrologic fluxes, vegetation patterns and dynamics, and landscape morphology in semiarid ecosystems. Existing landscape evolution models (LEMs) do not explicitly consider spatially explicit solar radiation as model forcing. Here, we improve an existing LEM to represent coupled processes of energy, water, and sediment balance for semiarid fluvial catchments. To ground model predictions, a study site is selected in central New Mexico where hillslope aspect has a marked influence on vegetation patterns and landscape morphology. Model predictions are corroborated using limited field observations in central NM and other locations with similar conditions. We design a set of comparative LEM simulations to investigate the role of spatially explicit solar radiation on landscape ecohydro‐geomorphic development under different uplift scenarios. Aspect‐control and network‐control are identified as the two main drivers of soil moisture and vegetation organization on the landscape. Landscape‐scale and long‐term implications of these short‐term ecohdrologic patterns emerged in modeled landscapes. As north facing slopes (NFS) get steeper by continuing uplift they support erosion‐resistant denser vegetation cover which leads to further slope steepening until erosion and uplift attains a dynamic equilibrium. Conversely, on south facing slopes (SFS), as slopes grow with uplift, increased solar radiation exposure with slope supports sparser biomass and shallower slopes. At the landscape scale, these differential erosion processes lead to asymmetric development of catchment forms, consistent with regional observations. Understanding of ecohydrogeomorphic evolution will improve to assess the impacts of past and future climates on landscape response and morphology.

Study on Hydrological Functions of Litter Layers in North China

Canopy interception, throughfall, stemflow, and runoff have received considerable attention during the study of water balance and hydrological processes in forested ecosystems. Past research has either neglected or underestimated the role of hydrological functions of litter layers, although some studies have considered the impact of various characteristics of rainfall and litter on litter interception. Based on both simulated rainfall and litter conditions in North China, the effect of litter mass, rainfall intensity and litter type on the maximum water storage capacity of litter (S) and litter interception storage capacity (C) were investigated under five simulated rainfall intensities and four litter masses for two litter types. The results indicated: 1) the S values increased linearly with litter mass, and the S values of broadleaf litter were on average 2.65 times larger than the S values of needle leaf litter; 2) rainfall intensity rather than litter mass determined the maximum interception storage capacity (Cmax); Cmax increased linearly with increasing rainfall intensity; by contrast, the minimum interception storage capacity (Cmin) showed a linear relationship with litter mass, but a poor correlation with rainfall intensity; 3) litter type impacted Cmax and Cmin; the values of Cmax and Cmin for broadleaf litter were larger than those of needle leaf litter, which indicated that broadleaf litter could intercepte and store more water than needle leaf litter; 4) a gap existed between Cmax and Cmin, indicating that litter played a significant role by allowing rainwater to infiltrate or to produce runoff rather than intercepting it and allowing it to evaporate after the rainfall event; 5) Cmin was always less than S at the same litter mass, which should be considered in future interception predictions. Vegetation and precipitation characteristics played important roles in hydrological characteristics.

Rainfall, Soil Water Content, and Groundwater Levels at the Riverlands Nature Reserve (South Africa)

Quantified medium- and long-term hydrological datasets are scarce in South Africa, yet they are essential to gain understanding of natural systems, contribute to ecosystem conservation, and ultimately quantify water balance processes accurately. A hydrological experiment was carried out at Riverlands Nature Reserve (Western Cape, South Africa) in order to quantify the components of the soil water balance at experimental sites occupied by endemic and invasive vegetation. In two separate follow-up projects, five-year time series were collected in three treatments, namely, endemic fynbos vegetation, bare soil, and land invaded by Acacia saligna. Rainfall was recorded daily with a manual rain gauge. Groundwater levels were logged hourly at 14 boreholes. Volumetric soil water contents and soil temperatures were logged hourly at different depths in the soil profile. Groundwater levels and soil water contents responded to rainfall with very clear seasonal trends. The data can be applied in water balance and evapotranspiration studies, unsaturated flux studies, soil temperature profile studies, and rainfall-groundwater level response analysis and for calibrating and validating a wide range of hydrological models.

Estimation of Snowmelt Infiltration into Frozen Ground and Snowmelt Runoff in the Mogot Experimental Watershed in East Siberia

Understanding how spring runoff is generated in East Siberia during the spring thaw is important to predicting river flows. To evaluate the snowmelt runoff generated, a simple runoff model was developed. The model involves processes of water and energy balance within the snowpack and energy balance within soil, snowmelt infiltration into the frozen ground, and surface runoff. The model reproduced inter-seasonal and seasonal variations of snow depth, active layer depth within soil, and snowmelt runoff. Snowmelt infiltration into frozen ground within the upper 20 cm of soil was also reproduced by the model. Thus, we believe the model can simulate snowmelt infiltration and surface runoff in the Mogot experiment watershed. The model suggested that the inter-annual variation in infiltration determined the amount of spring runoff. The amount of infiltration during thaws exceeded the discharge; the range was from 20 to 60 mm and the percentage of infiltration to melt water was 44% to 60%. Therefore, infiltration into the frozen ground strongly determined snowmelt runoff. In addition, ongoing climatic change can increase snowmelt runoff, because of less sublimation loss and snowmelt infiltration into the frozen ground.

On the sources of hydrological prediction uncertainty in the Amazon

Abstract. Recent extreme events in the Amazon River basin and the vulnerability of local population motivate the development of hydrological forecast systems using process based models for this region. In this direction, the knowledge of the source of errors in hydrological forecast systems may guide the choice on improving model structure, model forcings or developing data assimilation systems for estimation of initial model states. We evaluate the relative importance of hydrologic initial conditions and model meteorological forcings errors (precipitation) as sources of stream flow forecast uncertainty in the Amazon River basin. We used a hindcast approach that compares Ensemble Streamflow Prediction (ESP) and a reverse Ensemble Streamflow Prediction (reverse-ESP). Simulations were performed using the physically-based and distributed hydrological model MGB-IPH, comprising surface energy and water balance, soil water, river and floodplain hydrodynamics processes. The model was forced using TRMM 3B42 precipitation estimates. Results show that uncertainty on initial conditions plays an important role for discharge predictability, even for large lead times (∼1 to 3 months) on main Amazonian Rivers. Initial conditions of surface waters state variables are the major source of hydrological forecast uncertainty, mainly in rivers with low slope and large floodplains. Initial conditions of groundwater state variables are important, mostly during low flow period and in the southeast part of the Amazon where lithology and the strong rainfall seasonality with a marked dry season may be the explaining factors. Analyses indicate that hydrological forecasts based on a hydrological model forced with historical meteorological data and optimal initial conditions may be feasible. Also, development of data assimilation methods is encouraged for this region.

Quantification of the water balance and hydrogeological processes of groundwater–lake interactions in the Pampa Plain, Argentina

This paper gives an account of the assessment and quantification of the water balance and the hydrogeological processes related to lake–groundwater interaction in the Pampa Plain by using hydrogeochemical, isotopic and flow numerical modeling techniques. La Salada is a permanent shallow lake, with an area of 5.8 km2, located on the SE of Buenos Aires Province. A total of 29 lake water samples and 15 groundwater samples were collected for both hydrochemical analysis and environmental stable isotope determination. Water table depths were measured in wells closed to the lake. Groundwater samples appear grouped on the Local Meteoric Water Line, suggesting a well-mixed system and that rainfall is the main recharge source to the aquifer. Water evaporation process within La Salada is also corroborated by its isotopic composition. The model that best adjusts to La Salada Lake hydrochemical processes includes evaporation from groundwater, calcite precipitation with CO2 release and cationic exchange. The annual water balance terms for the lake basin indicates for each hydrological component the following values: 1.16 E08 m3 rainfall, 8.15 E07 m3 evapotranspiration, 1.90 E06 m3 runoff, 1.55 E07 m3 groundwater recharge, 6.01 E06 m3 groundwater discharge to the lake, 9.54 E06 m3 groundwater discharge to the river, 5.00 E05 m3 urban extraction and 4.90 E06 m3 lake evaporation. Integrated analysis of hydrochemical and isotopic information helped to calibrate the groundwater flow model, to validate the conceptual model and to quantitatively assess the basin water balance.

Effects of lateral hydrological processes on photosynthesis and evapotranspiration in a boreal ecosystem

AbstractLandscape‐scale hydrological processes can greatly alter the local‐scale water balance and many ecological processes linked to it. We hypothesized that in humid forest ecosystems, topographically driven lateral subsurface flow (SSF) has significant influence on ecophysiological processes such as gross primary productivity (GPP) and evapotranspiration (ET). To investigate how simplified hydrological conceptualizations influence the simulated ET and GPP in space and time, we conducted a numerical experiment using a spatially explicit hydroecological model, BEPS‐TerrainLab V2.0. We constructed three modelling scenarios: (1) Explicit, where a realistic calculation of SSF was employed considering topographic controls, (2) Implict, where the SSF calculations were based on a bucket‐modelling approach and (3) NoFlow, where the SSF was turned‐off in the model. Statistical analyses of model outputs showed considerable differences among the three scenarios for the simulated GPP and ET. The NoFlow scenario generally underestimated GPP and ET, while the Implicit scenario overestimated them relative to the Explicit scenario, both in time and space. GPP was more sensitive to SSF than ET because of the presence of unique compensatory mechanisms associated with the subcomponents of the total ET. The key mechanisms controlling GPP and ET were manifested through nonlinear changes in stomatal conductance, unique contributions from GPP and ET subcomponents, alterations in rhizosphere wetting patterns and their impacts on upscaling mechanisms and variability in nitrogen dynamics (for GPP). Feedback and interactive relationships between hydrological and ecophysiological processes also exacerbated the biases. Thus, we conclude that ecological models that have simplified hydrological representations could have significant errors in the estimation of GPP and ET. Copyright © 2010 John Wiley & Sons, Ltd.

Ecohydrology of dry regions of the United States: water balance consequences of small precipitation events

AbstractSmall precipitation events (≤5 mm) are a key component of the precipitation regimes of dry regions in the United States. Understanding their importance is useful, but exploring their significance for water balance processes is of utmost consequence for our knowledge about the functioning of ecosystems and their responses to climate change. Our objective was to evaluate the implications of precipitation event size distributions for the partitioning of water loss between evaporation and transpiration and for the number of days with wet soil. We used sites from the Great Plains of the United States to provide long‐term weather data for our simulation analyses. Our simulations varied distributions of precipitation event size and potential evapotranspiration (PET) for two contrasting soils: a sandy loam with low water holding capacity and a silt loam with high water holding capacity. Event size and specifically the numerical importance of the smallest size (0–5 mm) was the most important control on our results. Soil water holding capacity and PET were important modifiers of the responses. The ratio of evaporation to actual evapotranspiration (E/AET) increased as the percentage of small events increased and as PET increased. E/AET was greater for all combinations of event size and PET for the silt loam than for the sandy loam soils. The number of days with wet soil decreased as small events and PET increased. Our results suggest that the number of small events is one of the most important controls on water balance processes in arid and semiarid regions. Copyright © 2011 John Wiley & Sons, Ltd.

An alternative modelling approach to predict emissions of N2O and NO from forest soils

Emissions of N2O from forest soils in Europe are an important source of global greenhouse gas emissions. However, influencing the emission rates by forest management is difficult because the relations and feedbacks between forest and soils are complex. Process-based models covering both vegetation and soil biogeochemical processes are frequently used to analyse emission patterns. Particularly, the simulation of soil C and N turnover processes driving N2O production, consumption and emission from forest soils requires highly specific input data which renders their regional application difficult since at this scale, soil conditions are often not well understood. Therefore, a soil C and N model (DecoNit) has been developed which describes biogeochemical processes with a simplified structure compared to existing carbon/nitrogen models that nevertheless follows the basic physical and chemical laws involved and which allows to simulate N trace gas emissions. The DecoNit model was previously calibrated using an extensive dataset on decomposition rates of incubated plant materials, microbial dynamics and nitrification. The DecoNit model has now been embedded in a modular simulation environment (MoBiLE) where it is combined with soil water balance and forest process sub-modules. Here, we present the evaluation of MoBiLE-DecoNit with emission data of N2O and NO from forest soils of 15 European sites and compare simulation results with a previous study in which a more complex model (PnET-N-DNDC) was used. Evaluation criteria were as follows: (1) precision of modelled annual average emission rates; (2) coherence of modelled and measured annual average and daily emissions; (3) a dynamic representation of emission rates that correspond with the observed variance of fluxes. The results show that MoBiLE-DecoNit captures average annual emission rates more precisely than the more complex model PnET-N-DNDC. Also the structural underestimation of N trace gas fluxes from forest soils was resolved. Moreover, we present evidence that the new modelling approach is also somewhat more adequate for describing inter-daily emission dynamics. The combined MoBiLE-DecoNit is therefore thought to be a promising approach to simulate forest development and greenhouse gas balances on site and regional scales.

Modeling the Water Balance Processes for Understanding the Components of River Discharge in a Non-conservative Watershed

The study was conducted in the Shibetsu watershed, eastern Hokkaido, Japan, to examine the possibility of using the Soil and Water Assessment Tool (SWAT) model in a non-conservative watershed (the surface watersheds are lying on a discontinuous impervious horizon) with external contribution (EXT). After confirming the capability of model simulation, the EXT was estimated to understand the components of river discharge. The EXT is difficult to measure directly and simulate by SWAT due to its subsurface circulation. In this study, the EXT was roughly estimated from the water balance equation using measured data. The average daily flux of EXT (1.38 mm d-1) was assumed as a point-source discharge in SWAT. The simulation of daily streamflow during the calibration and validation periods produced satisfactory results, with R2 values of 0.65 and 0.66, respectively. In addition, the simulated daily baseflow, monthly streamflow, surface runoff, and evapotranspiration (ET) all showed good agreement with the corresponding observations. Our simulation suggested that the EXT assigned as the assumed discharge in SWAT can help us to reasonably simulate the streamflow in the Shibetsu watershed. The EXT was then investigated indirectly by considering the difference between the observed streamflow and simulated streamflow using calibrated SWAT without adding the assumed EXT. The result indicated that the EXT was an important water source in the Shibetsu watershed, accounting for 47% of streamflow during the study period.

Adopting the downward approach in hydrological model development: the Bradford catchment case study

The paper presents the development of a lumped conceptual rainfall-runoff model [Transformation of rainfall to runoff, Variability across timescales and Model parsimonization (TVM)] and a series of tests on various levels of model structure at different time resolutions. It is applied to the Bradford catchment in the United Kingdom. The TVM model is developed with a flexible structure through various relationships in each module that can be modified depending on the study catchments. Adopting the downward approach, parsimonious models are developed to examine at what level of complexity the model is able to capture runoff variability. The approach aims to compromise between parsimonious and complex alternatives in model development. This study shows that model structure requires data at different aggregation levels of timescales depending on its complexity. It reveals that the absence of the infiltration excess strongly affected all models. The analysis shows that the time resolution of hourly downwards must be used for the study catchment. The investigation of model complexity indicates that the combination of the most complicated model structure and timescale of quarter-hourly is adequate to capture the catchment runoff characteristics. The downward approach in the TVM model helps to gain a deeper understanding of water balance and runoff process in the study catchment. The approach could be applicable to other catchments to obtain parsimonious models. Copyright © 2010 John Wiley & Sons, Ltd.

High‐resolution diatom δ18O records, from the last 150 years, reflecting changes in amount of winter precipitation in two sub‐Arctic high‐altitude lakes in the Swedish Scandes

AbstractWaters from high‐altitude alpine lakes are mainly recharged by meteoric water. Because of seasonal variations in precipitation and temperature and relatively short hydraulic residence times, most high‐altitude lakes have lake water isotopic compositions (δ18Olake) that fluctuate due to seasonality in water balance processes. Input from snowmelt, in particular, has a significant role in determining lake water δ18O. Here we compare two high‐resolution δ18Odiatom records from lake sediments in the Swedish Scandes with instrumental data from the last century obtained from nearby meteorological stations. The time period AD 1900–1990 is characterised by an increase in winter precipitation and high winter/summer precipitation ratios and this is recorded in δ18Odiatom as decreasing trends. Lowest δ18Odiatom values and highest amount of winter precipitation are found around AD 1990 when the winter North Atlantic Oscillation index was above +2. We conclude that for the last 150 a the main factor affecting the δ18Odiatom signal in these sub‐Arctic high‐altitude lakes with short residence times has been changes in amount of winter precipitation and that δ18Odiatom derived from high‐altitude lakes in the Swedish Scandes can be used as a winter precipitation proxy. Copyright © 2010 John Wiley & Sons, Ltd.

Modeling the Spatially Varying Water Balance Processes in a Semiarid Mountainous Watershed of Idaho1

Stratton, Benjamin T., Venakataramana Sridhar, Molly M. Gribb, James P. McNamara, and Balaji Narasimhan, 2009. Modeling the Spatially Varying Water Balance Processes in a Semiarid Mountainous Watershed of Idaho. Journal of the American Water Resources Association (JAWRA) 45(6):1390‐1408.Abstract: The distributed Soil Water Assessment Tool (SWAT) hydrologic model was applied to a research watershed, the Dry Creek Experimental Watershed, near Boise Idaho to investigate its water balance components both temporally and spatially. Calibrating and validating SWAT is necessary to enable our understanding of the water balance components in this semiarid watershed. Daily streamflow data from four streamflow gages were used for calibration and validation of the model. Monthly estimates of streamflow during the calibration phase by SWAT produced satisfactory results with a Nash Sutcliffe coefficient of model efficiency 0.79. Since it is a continuous simulation model, as opposed to an event‐based model, it demonstrated the limited ability in capturing both streamflow and soil moisture for selected rain‐on‐snow (ROS) events during the validation period between 2005 and 2007. Especially, soil moisture was generally underestimated compared with observations from two monitoring pits. However, our implementation of SWAT showed that seasonal and annual water balance partitioning of precipitation into evapotranspiration, streamflow, soil moisture, and drainage was not only possible but closely followed the trends of a typical semiarid watershed in the intermountain west. This study highlights the necessity for better techniques to precisely identify and drive the model with commonly observed climatic inversion‐related snowmelt or ROS weather events. Estimation of key parameters pertaining to soil (e.g., available water content and saturated hydraulic conductivity), snow (e.g., lapse rates, melting), and vegetation (e.g., leaf area index and maximum canopy index) using additional field observations in the watershed is critical for better prediction.

Modelling the sensitivity of wheat growth and water balance to climate change in Southeast Australia

A simulation study was carried out to assess the potential sensitivity of wheat growth and water balance components to likely climate change scenarios at Wagga Wagga, NSW, Australia. Specific processes considered include crop development, growth rate, grain yield, water use efficiency, evapotranspiration, runoff and deep drainage. Individual impacts of changes in temperature, rainfall and CO2 concentration ([CO2]) and the combined impacts of these three variables were analysed for 2050 ([CO2] = 570 ppm, T +2.3°C, P −7%) and 2070 ([CO2] = 720 ppm, T +3.8°C, P −10%) conditions. Two different rainfall change scenarios (changes in rainfall intensity or rainfall frequency) were used to modify historical rainfall data. The Agricultural Production Systems Simulator (APSIM) was used to simulate the growth and water balance processes for a 117 year period of baseline, 2050 and 2070 climatic conditions. The results showed that wheat yield reduction caused by 1°C increase in temperature and 10% decrease in rainfall could be compensated by a 266 ppm increase in [CO2] assuming no interactions between the individual effects. Temperature increase had little impact on long-term average water balance, while [CO2] increase reduced evapotranspiration and increased deep drainage. Length of the growing season of wheat decreased 22 days in 2050 and 35 days in 2070 conditions as a consequence of 2.3°C and 3.8°C increase in temperature respectively. Yield in 2050 was approximately 1% higher than the simulated baseline yield of 4,462 kg ha − 1, but it was 6% lower in 2070. An early maturing cultivar (Hartog) was more sensitive in terms of yield response to temperature increase, while a mid-maturing cultivar (Janz) was more sensitive to rainfall reduction. Janz could benefit more from increase in CO2 concentration. Rainfall reduction across all rainfall events would have a greater negative impact on wheat yield and WUE than if only smaller rainfall events reduced in magnitude, even given the same total decrease in annual rainfall. The greater the reduction in rainfall, the larger was the difference. The increase in temperature increased the difference of impact between the two rainfall change scenarios while increase in [CO2] reduced the difference.

Hydrological behaviour of grasslands of the Sandhills of Nebraska: water and energy‐balance assessment from measurements, treatments, and modelling

AbstractUnderstanding energy and water balance processes in the Sandhills is crucial to assess the land–atmosphere feedback effects. The Sandhills located in western Nebraska covers a vast grassland ecosystem with limited variability in vegetation and soil. However, the combined effect of topography, land cover, and micrometeorology by subjecting the land surface to various disturbances and treatments is rarely studied. The NOAH Land Surface Model (LSM) was used to estimate net radiation, latent, sensible, and ground heat (GH) fluxes as well as water balance components for two growing seasons between 2005 and 2006 in various plots at the Grasslands Destabilization Experimental (GDEX) site where these plots were subjected to four different treatments and located at two topographical locations, namely high and low positions. The simulated results of net radiation and GH fluxes correlated well with measurements. While the amount of precipitation received was between 900 and 1000 mm for both seasons, on a daily and sub‐daily time scale the partitioning of net radiation into latent, sensible, and GH fluxes showed high variability across the plots, primarily driven by vegetation and soil moisture. Total evapotranspiration and soil moisture averages suggested the influence of vegetation and the timing of precipitation also in controlling various land surface processes in the Sandhills. This study provides a framework for using the LSM to quantify the feedback effects and emphasizes the importance of microtopography and land treatments in the model environment. Copyright © 2009 John Wiley & Sons, Ltd.

Some scientific problems facing research on hydrological processes in an inland river basin

The challenge is put forward to scientific hydrology by the advancement of water sciences; that is, how should we carry out a multidisciplinary, integrated and cooperative research on hydrological processes in the basin, regional and global scales, in order to better understand the role water plays in the changes of the natural resources and environment of the earth, and to understand the hydrosphere and its interactions with the atmosphere, lithosphere and biosphere. How the changes and transformation of the components of the water cycle and water balance occur in an inland river basin has yet to be understood. We also need to understand what the interactions of water cycle, ecosystems and environment are, and what the responses and feedback of the changes to global change and to human activities are. The water cycle in an inland river basin characterizes the runoff generation region of the mountains upstream, the artificial oases region of water resources exploitation and utilization midstream and the natural desert oases region of runoff dissipating downstream. The mountain hydrological processes are discussed from water cycle, energy balance, water balance and ecological processes. The interactions of water and vegetation are discussed in relation to ecohydrology, and the hydrological processes in the ground water-soil-vegetation layer are discussed from the concept of the critical zone newly put forward abroad. The basic frame is put forward to carry out the field measurement, experiment and studies of hydrological processes in a typical inland river basin.

Surface‐coupled three‐dimensional geothermal model for study of permafrost geothermal regime in a building environment

In many Canadian northern communities the stability of building foundation systems relies on the strength of the underlying permafrost. Building deterioration owing to the loss of this strength or stability would profoundly affect the economies and well‐being of the surrounding communities. Although studies of permafrost geothermal regime in natural conditions have been conducted for a long time, studies of ground temperature and its spatial pattern and trend in a building environment are limited. The need for the study is more pressing with the projection of climate warming. Detailed information about the pattern and trend of ground temperature and active layer thickness dynamics under climate warming is essential for examination of potential permafrost degradation, as well as its impacts on buildings that are built on/in it. To quantify geothermal responses, and then permafrost degradation, to climatic change in different locations underneath a building, a surface‐coupled three‐dimensional geothermal model was developed. The model is physical process–based and couples heat and water processes at ground surface and subsurface with simulation of incoming solar radiation and precipitation distributions surrounding and underneath a building by accounting for the effect of the building's dimensions and orientation on the energy and water balance processes at the ground surface. This paper describes the theoretical basis upon which the model is built, the specific factors, and processes considered to represent the permafrost environment surrounding and below buildings, as well as the testing of the model with two different data sets and a theoretical model.