Large Watershed Scale Research Articles

Effect of Long-Term Wastewater Irrigation on Potential Denitrification and Denitrifying Communities in Soils at the Watershed Scale

Wastewater irrigation mitigates the problem of water shortage but leads to the potential accumulation of pollutants and causes corresponding changes in denitrifying communities and denitrification, hence the potential ecological risk of long-term wastewater irrigation should not be overlooked. We investigated the relative contributions of different environmental factors to the abundance and diversity of denitrifying communities harboring nirK, nirS, and nosZ genes and the relative importance of these biotic and abiotic variables in potential denitrification activity (PDA) in soils with wastewater irrigation for around 25 years at a large watershed scale. Results showed that soil physicochemical properties, pollutants, including heavy metals and PAHs, and vegetation are the major factor groups influencing the abundance and structure of the three denitrifying communities and PDA. NirK-, nirS-, or nosZ-harboring denitrifiers responded in different manners to environmental changes, and were mainly influenced by substrate concentration, carbon source, or pollutants, respectively. The structure of the three denitrifying communities was more relevant to the environmental changes than their abundance. Conversely, the abundance, rather than diversity, was correlated with PDA. Pollutants and vegetation could affect PDA by both direct and indirect paths through soil physicochemical properties including pH, carbon and nitrogen sources, or through the abundance of denitrifying functional genes. The abundance of denitrifying functional genes is a valuable index that integrates potential activity and various environmental factors, and is therefore a good predictor of denitrification in the presence of environmental changes.

Long-term variation (1960–2003) and causal factors of non-point-source nitrogen and phosphorus in the upper reach of the Yangtze River

The knowledge of long-term variation and causal factors of non-point source (NPS) pollution in large-scale watersheds is helpful in the development of water quality control programs. In this study, the Improved Export Coefficient Model and the Revised Universal Soil Loss Equation were combined to estimate the temporal and spatial variations (1960–2003) of NPS pollution in the upper reach of the Yangtze River (URYR). Two change points for NPS pollution were successfully detected. In the URYR, the dissolved nitrogen (DN) and dissolved phosphorus (DP) increased before 2000 and decreased after 2000, whereas the inflection points from increase to decline were around 1980 for the adsorbed N (AN) and adsorbed P (AP). The results also indicated that the dissolved pollutants were mainly contributed by the anthropogenic factors, while the adsorbed pollutants were primarily exported by the natural factors. By comparing the load intensities from each source, it revealed that for the dissolved pollutants, the major source of the high load intensity transferred from urban land to dry land after 1980. Simultaneously, the high load intensity areas of the adsorbed pollutants transferred from forest to orchard around 1980, which was mainly attributed to the increasing fertilizer application. These results may be useful for planning and management of the URYR and other large-scale watersheds.

Assessment OF SURFACE WATER QUALITY at Large Watershed Scale: Land‐Use, Anthropogenic, and Administrative Impacts

AbstractUnderstanding the impacts that influence water quality is critical to the development of best management practices at the large watershed scale. This study describes the spatiotemporal variation in surface water quality and identifies their main impact in the Haihe River basin, China. Multivariate statistical techniques are applied to analyze the similarities among the sampling sites and to identify the main pollution sources in surface water. Results show that: (1) the basin can be clustered into two regions, water quality being better in the mountainous vs. plain regions; (2) water quality improves due to implementation of a strict state policy on environmental pollution control, prodded by the hosting of the Olympic games in the cities of Beijing and Tianjin; and (3) agricultural and residential land uses as well as livestock‐breeding are the main sources affecting water quality in the mountainous regions, whereas rural waste discharge — including domestic waste sewage, human and animal feces, and solid waste — significantly influences water quality in the plain regions. The waste discharge of industrial factories may be a significant source of water pollution in the plain regions. Results indicate that the environmental management from pollution sinks and sources, long‐lasting legal framework, and adequate economic incentives should be improved to optimize the large‐scale watershed management under the background of the rapid development of countries like China.

Impacts of climate and land-use changes on the migration of non-point source nitrogen and phosphorus during rainfall-runoff in the Jialing River Watershed, China

Summary The loss of nitrogen and phosphorus via non-point source (NPS) pollution in the Jialing River Watershed has become the main pollution sources of river waters in the Three Gorges reservoir area in the past decades, while climatic conditions and human activities directly affect changes of rainfall-runoff and land use types which are closely related to NPS pollution. This study is to assess the impact of climate change on hydrological behavior considering future land-use types and rural residential area and their propagation to NPS pollution loads. An integrated pollution load model composed of regional climate, the Semi-distributed Land Use based Runoff Processes (SLURPs) hydrological model and the improved export coefficient approach within a single framework was explored and developed to assess impacts of climate and land-use changes on NPS pollution load. Climate data for the Special Report on Emissions Scenarios (SRESs) future scenario B2 from Met Office Hadley center were generated and used as the input data for the runoff and NPS load evaluation of the Jialing River Watershed and the Markov process was used to forecast changes of land use types, respectively. Simulations of present and future regional NPS pollution from land use, livestock and poultry breeding, and agricultural population over the Jialing River Watershed were performed to investigate the potential impacts of global climate change on river water quality using the established model. Results demonstrate that: (1) Annual pollution load would obviously change due to variations of runoff and livestock and poultry breeding, the largest growth months in one year for total nitrogen (TN) and total phosphorus (TP) load are both in June, which is in accordance with changes of rainfall amount. (2) The impacts of global climate change on pollution load are relatively greater when compared to the impacts of future livestock and poultry breeding increase or agricultural population reduction; the effects from runoff increment leads to approximately 28.6% and 22.5% increases of TN and TP pollution load, respectively. And (3) the impacts of land-use change have shown insignificant effect due to soil conservation measures, whereas the impacts of rural residential area account for great proportion changes, of which about 5% of its increases are contributed to the increase of livestock and poultry breeding; but the biggest contribution rate is still from the output of different land use types. These data will be useful and valuable in evaluating potential NPS pollution load for the control of watershed pollution in the future and understanding its migration and transformation in a large-scale watershed where meteorological and underlying surface data are mutative.

Small-scale watershed extended method for non-point source pollution estimation in part of the Three Gorges Reservoir Region

Non-point source (NPS) pollution has been increasingly recognized as a major contributor to the declining quality of aquatic environment in recent years. Because of the data shortage, the non-point source loads estimation in the large-scale watershed is always difficult in most developing countries. In this study, small-scale watershed extended method (SWEM) was introduced with a case study in the middle part of Three Gorges Reservoir Region (TGRR). Small-scale watershed extended method is the method which uses physical-based models in some small typical catchments of the targeted large watershed, and then the parameters obtained from those small catchments are extended to the surrounding area until the non-point source pollution loads in the entire watershed or region are obtained. The selected small catchments should have sufficient data. Here, the middle part of the Three Gorges Reservoir Region, about 12,500 km2, was chosen as the targeted region for the case study. In this region, considering the data availability, Xiaojiang River was screened as a typical watershed and was simulated with Soil and Water Assessment Tool model through accurate parameter calibration and validation. And then the parameter group obtained in Xiaojiang River Watershed was extended to the entire study area to quantify the total non-point source pollution loads. After which, the spatio-temporal characteristics of the non-point source pollution in the middle part of the Three Gorges Reservoir Region were analyzed, as well as the pollution from each tributary and different under layer surface conditions. The small-scale watershed extended method provides a practical approach for non-point source pollution loads estimation in the large-scale watershed or region.

The Current State of Modeling

Today’s groundwater modeling tools are characterized by power, capability, and sophistication that was unthinkable even a few years ago. Boundary conditions (lakes, streams, wetlands) have advanced modules that allow more realistic depictions of the natural world. Models can simulate multiple scales conjunctively (Mehl and Hill 2005; Hunt 2006), or combine different formulations of the underlying mathematical governing equations (Haitjema et al. 2010). The unsaturated zone can be rigorously included (Jones and Woodward 2001; Radcliffe and Simůnek 2010), even on a large watershed scale using kinematic wave approximations (Niswonger et al. 2006). The ability to efficiently simulate unsaturated zone flow has been a critical advance to allow models to explicitly simulate groundwater and surface water interactions at the watershed scale (Therrien et al. 2006; Markstrom et al. 2008). At the same time groundwater flow modeling has attained an advanced state, contaminant transport models have continued to grow to provide improved simulation capabilities for complex field conditions. These include simulation of transport processes in highly heterogeneous media based on the dual-domain mass transfer formulation (Zheng et al. 2011), accommodation of a full suite of biogeochemical reactions through fully coupled multicomponent geochemical-transport models (Prommer et al. 2009; Ma et al. 2010; Parkhurst et al. 2010), and consideration of multiphase and multimedia processes (Pruess et al. 2011). Additionally, numerous efforts are ongoing to develop new or improved mathematical formulations that may deal more effectively with non-ideal contaminant transport behaviors arising from strong aquifer heterogeneity (Berkowitz et al. 2002; Zhang and Benson 2008). One example of such heterogeneity by Bianchi et al. (2011) shows decimeter-scale preferential flow paths with a varying degree of connectivity within a small aquifer cube (Figure 1). Groundwater flow and contaminant transport modeling have been greatly facilitated by rapid technological advances on two fronts: (1) the development of compact and large-memory field sensors that have yielded rich datasets for model calibration, (2) the exponential growth in computing power, which has substantially strengthened

Examining individual recession events instead of a data cloud: Using a modified interpretation of dQ/dt–Q streamflow recession in glaciated watersheds to better inform models of low flow

Summary To examine stream recession rates, hydrologists have plotted the rate of change in discharge (dQ/dt) versus the mean discharge (Q). Such plots typically result in a large cloud of data points where the slope of the lower bound of the cloud is often used to infer aquifer hydraulic properties as informed by certain interpretations of the Boussinesq Equation. For seven watersheds in New York State, USA ranging from 100 km2 to 6415 km2, we distinguish data points in the dQ/dt–Q plot belonging to individual recession events instead of looking at the entire data cloud. The recession curve of individual events consistently shifts upward during the summer and late fall (relative to spring and late fall curves) and much of the scatter in the data cloud appears to be due to seasonal variations in recession. We speculate that these seasonal variations in recession rate may be due to variations in watershed evapotranspiration (ET). Additionally, most individual recession events have slopes of approximately two when plotted as log dQ/dt versus log Q. Application of the Boussinesq Equation to watershed-scale recession date predicts slopes shifting from 3 to 3/2 as recession progresses, thus the observed slope of two casts doubt on whether it is appropriate to apply hydraulic aquifer theory to these types of watersheds to infer aquifer properties or predict low flows. As a further validation of the hydrologic information content of individual recession curves, the individual recession curves from time periods with minimal ET (early spring and late fall) were used to establish storage–discharge functions for two of the smaller watersheds. With these storage–discharge functions, a simple hydrologic model could reasonably simulate time series with minimal calibration (Nash–Sutcliffe R2 of 0.71 and 0.67 on log transformed discharge). Overall, this paper suggests that the analysis of individual event recession curves (particularly when compared among watersheds and seasons) can be a valuable tool for gaining insights into hydrological processes at the scale of large watersheds and can justify alternatives to current low flow models.

Enhanced HSPF Model Structure for Chesapeake Bay Watershed Simulation

AbstractFor more than two decades, an HSPF-based watershed model has been used to simulate nutrient and sediment load delivery to the Chesapeake Bay. Over time, the watershed model has increased in complexity commensurate with the management challenges in Chesapeake Bay restoration. The increased complexity poses challenges to the standard application of HSPF for efficient operation of the model in a large-scale watershed, as well as difficulties in incorporating changes in best management practices (BMPs) and land uses over time. In response, the U.S. Environmental Protection Agency’s Chesapeake Bay Program Office developed a software solution that enhances the existing HSPF model structure. The software system, consisting of preprocessors, an external transfer module, and postprocessors, was devised to conveniently generate and update parameter files essential to operations of a large and complex watershed-modeling system and to implement land-use and non-point-source-pollution management changes on any...

Establishment of a hybrid rainfall-runoff model for use in the Noah LSM

There is an increasing trend to incorporate the basin hydrological model into the traditional land surface model (LSM) to improve the description of hydrological processes in them. For incorporating with the Noah LSM, a new rainfall-runoff model named XXT (the first X stands for Xinanjiang, the second X stands for hybrid, and T stands for TOPMODEL) was developed and presented in this study, based on the soil moisture storage capacity distribution curve (SMSCC), some essential modules of the Xinanjiang model, together with the simple model framework of the TOPMODEL (a topography based hydrological model). The innovation of XXT is that the water table is incorporated into SMSCC and it connects the surface runoff production with base flow production. This improves the description of the dynamically varying saturated areas that produce runoff and also captures the physical underground water level. XXT was tested in a small-scale watershed Youshuijie (946 km2) and a large-scale watershed Yinglouxia (10009 km2) in China. The results show that XXT has better performance against the TOPMODEL and the Xinanjiang model for the two watersheds in both the calibration period and the validation period in terms of the Nash-Sutcliffe efficiency. Moreover, XXT captures the largest peak flow well for both the small- and large-scale watersheds during the validation period, while the TOPMODEL produces significant overestimates or underestimates, so does the Xinanjiang model.

Unraveling the mysteries of the large watershed black box: Implications for the streamflow response to climate and landscape perturbations

Spatial and temporal trends in stream chemistry have been used to provide insights into the scale dependencies of streamflow generation processes in small catchments. However, these scale dependencies have not been thoroughly investigated at large watershed scales (defined as drainage areas greater than 1000 km2). Quantifying these scale dependencies is critical to understanding how large watersheds will respond to future perturbations; e.g., the long‐term streamflow response to climate change and/or changes in land‐cover and land‐use. Here we investigate the spatial and temporal scaling relationships of all dominant streamflow generation processes in a large alpine watershed in the southern Rocky Mountains of Colorado. Observations in the watershed indicate that dominant streamflow processes are spatially and temporally variable. The relative strengths of dominant streamflow mechanisms vary as a function of internal watershed structure (i.e., spatial variability in topographic relief, soil development, groundwater flowpath development, and stream network structure) and external forcing such as timing and character of precipitation. This behavior coupled with previous observations that streamflow from the watershed contained a significant component of basin‐scale groundwater, suggests that similar large watersheds may have internal buffering, at least initially, against rapid change.

Impact of critical source area on AnnAGNPS simulation

The objective of this paper is to study the impact of critical source area (CSA) within an Annualized AGricultural Non-Point Source pollution models (AnnAGNPS) simulation at medium- large watershed scale. The impact of CSA on terrain attributes is examined by comparing six sets of CSA (0.5, 1, 2, 4, 6 and 8 km(2)). The accuracy of AnnAGNPS stimulation on runoff, sediment and nutrient loads on these sets of CSA is further suggested in this paper. The results are as followed: (1) CSA has little effect on watershed area, and terrain altitude. The number of cell and reach decreases with the increase of CSA in power function regression curve. (2) The variation of CSA will lead to the uncertainty of average slope which increase the generalization of land characteristics. At the CSA range of 0.5-1 km(2), there is little impact of CSA on slope. (3) Runoff amount does not vary so much with the variation of CSA whereas soil erosion and total nitrogen (TN) load change prominently. An increase of sediment yield is observed firstly then a decrease following later. There is evident decrease of TN load, especially when CSA is bigger than 6 km(2). Total phosphorus load has little variation with the change of CSA. Results for Dage watershed show that CSA of 1 km(2) is desired to avoid large underestimates of loads. Increasing the CSA beyond this threshold will affect the computed runoff flux but generate prediction errors for nitrogen yields. So the appropriate CSA will control error and make simulation at acceptable level.

Large Shift in Source of Fine Sediment in the Upper Mississippi River

Although sediment is a natural constituent of rivers, excess loading to rivers and streams is a leading cause of impairment and biodiversity loss. Remedial actions require identification of the sources and mechanisms of sediment supply. This task is complicated by the scale and complexity of large watersheds as well as changes in climate and land use that alter the drivers of sediment supply. Previous studies in Lake Pepin, a natural lake on the Mississippi River, indicate that sediment supply to the lake has increased 10-fold over the past 150 years. Herein we combine geochemical fingerprinting and a suite of geomorphic change detection techniques with a sediment mass balance for a tributary watershed to demonstrate that, although the sediment loading remains very large, the dominant source of sediment has shifted from agricultural soil erosion to accelerated erosion of stream banks and bluffs, driven by increased river discharge. Such hydrologic amplification of natural erosion processes calls for a new approach to watershed sediment modeling that explicitly accounts for channel and floodplain dynamics that amplify or dampen landscape processes. Further, this finding illustrates a new challenge in remediating nonpoint sediment pollution and indicates that management efforts must expand from soil erosion to factors contributing to increased water runoff.

Influence of land use on water quality in a tropical landscape: a multi-scale analysis.

There is a pressing need to understand the consequences of human activities, such as land transformations, on watershed ecosystem services. This is a challenging task because different indicators of water quality and yield are expected to vary in their responsiveness to large versus local-scale heterogeneity in land use and land cover (LUC). Here we rely on water quality data collected between 1977 and 2000 from dozens of gauge stations in Puerto Rico together with precipitation data and land cover maps to (1) quantify impacts of spatial heterogeneity in LUC on several water quality indicators; (2) determine the spatial scale at which this heterogeneity influences water quality; and (3) examine how antecedent precipitation modulates these impacts. Our models explained 30-58% of observed variance in water quality metrics. Temporal variation in antecedent precipitation and changes in LUC between measurements periods rather than spatial variation in LUC accounted for the majority of variation in water quality. Urbanization and pasture development generally degraded water quality while agriculture and secondary forest re-growth had mixed impacts. The spatial scale over which LUC influenced water quality differed across indicators. Turbidity and dissolved oxygen (DO) responded to LUC in large-scale watersheds, in-stream nitrogen concentrations to LUC in riparian buffers of large watersheds, and fecal matter content and in-stream phosphorus concentration to LUC at the sub-watershed scale. Stream discharge modulated impacts of LUC on water quality for most of the metrics. Our findings highlight the importance of considering multiple spatial scales for understanding the impacts of human activities on watershed ecosystem services.

Development and application of distributed rainfall-runoff model using MPI technique

A lumped model, in general, is expressed by ordinary differential equations, which does not take into account the spatial variability of processes, input, boundary conditions and watershed geometric characteristics. For this reason, recently distributed run-off models have been developed to represent the variability in physical watershed characteristics such as topography, land use, and rainfall properties. However, the distributed rainfall-runoff model requires a lot of time and effort to generate input data. Also, it takes a lot of time to calculate the discharge using a numerical analysis based on kinematic wave theory in runoff process. Therefore, most river basins that use the distributed model are of limited scales, such as small river basins. Especially, the necessity for an integrated watershed management system has been increasing due to changes in watershed management concepts and discharge calculations for whole river basins, including the upstream and downstream of dams. In this study, a distributed rainfall-runoff model using Message Passing Interface (MPI) technique was developed to decrease the calculation time needed for the application of large scale watersheds. This model, which uses a parallelized based K-water hydrologic & hydraulic Distributed RUnoff Model (K-DRUM), can simulate temporal changes and the spatial distribution of flood discharge by taking into consideration radar grid rainfall and grid based hydrological parameters. The model was applied to the Geum River Basin, which include the Yongdam and Daecheong Dam Watersheds located on the Korean Peninsula. The results were calculated between a single domain and a divided small domain. They were compared to analyze the application effects of the parallelization technique. As a result, a maximum of 10 times the amount of calculation time was saved by using parallelization code rather than a single processor. Also, problems related to the running time and inaccurate settings that typically occurred using the existing trial and error method were solved by applying an auto calibration method in setting initial soil moisture conditions. As the result, the calculation results showed a good agreement with the observed data.

Streamflow generation in a large, alpine watershed in the southern Rocky Mountains of Colorado: Is streamflow generation simply the aggregation of hillslope runoff responses?

Spatial and temporal trends in stream chemistry were investigated in a large (1600 km2) alpine watershed in the southern Rocky Mountains of Colorado to help understand mechanisms of streamflow generation. We observed linear increases of concentrations of chemical constituents in streamflow as accumulated drainage area increased along the main channel of Saguache Creek. We tested two conceptual models of streamflow generation against our stream chemistry observations. One model is essentially two‐dimensional and treats streamflow generation at the large watershed scale as the aggregation of runoff responses from individual hillslopes, primarily surface and shallow subsurface flow paths. Alternatively, a fully three‐dimensional conceptual model treats streamflow generation as being controlled by a distribution of large‐scale groundwater flow paths as well as surface and shallow subsurface flow paths. The structure and magnitude of groundwater contributions in streamflow as a function of increasing scale provided a key distinction between these two conceptual models. End‐member mixing analysis and measurements of hydraulic head gradients in streambeds were used to quantify basin‐scale groundwater contributions to streamflow with increasing spatial scale in the Saguache Creek watershed. Our data show that groundwater contributions are important in streamflow generation at all scales and, more importantly, that groundwater contributions to streamflow do increase with increasing watershed scale. These results favor the three‐dimensional conceptual model in which long groundwater flow paths provide a streamflow generation process at large scales that is not operative at smaller scales. This finding indicates that large watersheds may be more than simply the aggregation of hillslopes and small catchments.

A framework for priority non-point source area identification and load estimation integrated with APPI and PLOAD model in Fujiang Watershed, China

Abstract The non-point source (NPS) pollution is difficult to manage and control due to its complicated generation and formation. In large scale watersheds, the priority sources areas (PSAs) identification is an important and necessary process for efficient aquatic environmental management. Here, a framework for the PSAs identification and pollution load estimation in PSAs screened for Best Management Practices (BMPs) is proposed. Fujiang Watershed, a branch of Jialingjiang, the upper reach of Yangtze River, was chosen for evaluation of the method proposed here. The entire Fujiang Watershed was divided into 21 subbasins, after which the Agricultural Pollution Potential Index (APPI) was used to identify the PSAs, and a modified runoff coefficient was introduced to mitigate the impact of the rainfall heterogeneity in the process. Next, the identified PSAs were further divided into 34 subbasins, after which quantification of the pollution load was conducted using the Pollution Load (PLOAD) model. The results indicated that there are five subbasins have much higher NPS pollution load intensities, with an average value of 6.05 t/km2/year for TN and 0.31 t/km2/year for TP. According to the cluster analysis on land use structure, these five subbasins were featured by higher proportion of agricultural land, suggesting a need for better fertilizer application management. The method developed here provided a helpful framework for conducting NPS pollution management in a large watershed.

분포형 강우유출모형 병렬화 처리기법 적용

Distributed Models have relative weak points due to the amount of computer memory and calculation time required for calculating water flow using a numerical analysis based on kinematic wave theory when compared to the conceptual models used so far. Typically, the distributed models have been mainly applied to small basins. It was necessary to decrease the resolution of the grid to make it applicable for large scale watersheds, and because it would take up too much time to calculate using a higher resolution. That has been one of the more difficult factors in applying the model for actual work. In this paper, MPI (Message Passing Interface) technique was applied to solve the problem of calculation time as it is one of the demerits of the distributed model for performing physical and complicated numerical calculations for large scale watersheds. The comparison studies were performed a single domain and a divided small domain in Yongdam Dam watershed in case of typoon `Ewiniar` at 2006. They were compared to analyze the application effects of parallelization technique. As a result, a maximum of 10 times the amount of calculation time was saved but keeping the level of quality for discharge by using parallelization code rather than a single processor.

Development and test of the Export Coefficient Model in the Upper Reach of the Yangtze River

Summary The Export Coefficient Model (ECM) has been widely used to estimate non-point source (NPS) pollution loads for its ease of application. The model uses an export coefficient approach to calculate the nitrogen (N) and phosphorus (P) loads delivered annually to a water body as the sum of the individual loads exported from each nutrient source within a catchment. However, without considering the temporal–spatial heterogeneities of precipitation and terrain, application of the ECM in a large-scale watershed is limited. In this study, the ECM was improved by introducing the precipitation impact factor, α, and terrain impact factor, β, which were defined to characterize the nonuniformities of precipitation and terrain, respectively. A method to determine the export coefficients of different land use types was also developed based on the hydrological and water quality data. The model was tested in the Upper Reach of the Yangtze River (URYR), which is the largest river in China. The test results showed that the relative error between simulated dissolved nitrogen (DN, including organic and inorganic nitrogen) and the observed value was effectively reduced when compared to that obtained from the original model (22% vs. 44% in 1990 and 18% vs. 38% in 2003). These findings demonstrate that the improved model could provide more accurate results and may be useful for planning and management of large-scale agricultural watersheds.

Deforestation and conservation in major watersheds of the Brazilian Amazon

SUMMARYConserving natural vegetation cover is of critical importance for maintaining the ecological integrity and hydrological properties of large river basins (more than 100 000 km2). Recent estimates indicate that more than 700 000 km2 of Brazilian Amazon have already been deforested, and to reduce further losses and preserve the important natural and cultural resources in this region, large conservation areas have been created by the Brazilian government. The present study analysed land cover and land use change in the major watersheds of the Brazilian Amazon, in order to evaluate the current balance between deforestation and conservation of natural areas in the region. The results show that watersheds draining the southern part of the basin have suffered the highest deforestation rates, with the largest losses (8.3–20% of total basin area) occurring in the Madeira, Tapajós, Xingu, Araguaia and Tocantins river basins. Most large watersheds already have significant deforestation in their headwaters, which can affect hydrological functions and ecological sustainability. The greatest allocation of land for conservation was encountered in the Trombetas, Xingu and Negro watersheds, where conservation areas occupied 92.5, 56.9 and 50.6% of the total basin, respectively. While extensive areas of the Amazon biome have been deforested, on the scale of large watersheds there is a positive balance between conservation areas and deforestation, and on average the area delimited by conservation areas is more than three times larger than the deforested areas. An analysis by subwatersheds, however, indicates that certain regions have achieved more critical levels of deforestation, in some situations affecting more than 80% of the subwatersheds.

PROMET – Large scale distributed hydrological modelling to study the impact of climate change on the water flows of mountain watersheds

Summary Climate change will change availability, quality and allocation of regional water resources. Appropriate modelling tools should therefore be available to realistically describe reactions of watersheds to climate change and to identify efficient and effective adaptation strategies on the regional scale. The paper presents the hydrologic model PROMET (Processes of Radiation, Mass and Energy Transfer), which was developed within the GLOWA-Danube project as part of the decision support system DANUBIA. PROMET covers the coupled water and energy fluxes of large-scale ( A ∼ 100,000 km 2 ) watersheds. It is fully spatially distributed, raster-based with raster-elements of 1 km 2 area, runs on an hourly time step, strictly conserves mass and energy and is not calibrated using measured discharges. Details on the model concept and the individual model components are given. An application case of PROMET is given for the mountainous Upper-Danube watershed in Central Europe ( A = 77,000 km 2 ). The water resources are intensively utilized for hydropower, agriculture, industry and tourism. The water flows are significantly influenced by man-made structures like reservoirs and water diversions. A 33-years model run covering the period from 1971 to 2003 using the existing meteorological station network as input is used to validate the performance of PROMET against measured stream flow data. Three aspects of the model performance were validated with good to very good results: the annual variation of the water balance of the whole watershed and selected sub-watersheds, the daily runoff for the whole period at selected gauges and the annual flood peaks and low flows (minimum 7-days average). PROMET is used to investigate the impact of climate change on the water cycle of the Upper Danube. A stochastic climate generator is fed with two scenarios of climate development until 2060. One assumes no future temperature change, the other uses the temperature trends of the IPCC-A1B climate change scenario. PROMET is run with both climate data sets. No change in low-flow is detected when no temperature change is assumed. The IPCC-A1B climate scenario results in marked decreases of low-flow at the outlet of the watershed.