Increase In Streamflow Research Articles

Forests as ‘sponges’ and ‘pumps’: Assessing the impact of deforestation on dry-season flows across the tropics

Forests act as ‘pumps’ through their evapotranspiration (Etot) and as ‘sponges’ by enhancing soil infiltration capacity and moisture retention. Tropical deforestation and poor post-forest land management generally result in lower Etot, but also reduce infiltration. Strongly diminished infiltration is typically accompanied by enhanced overland flow and can cause reduced groundwater recharge and baseflows. A grid-based land surface hydrological model (W3RA–LUM) was tailored to incorporate the trade-offs between the ‘pump’ and ‘sponge’ effects to investigate where deforestation can be expected to have the greatest impacts on dry-season flows. Streamflow sensitivity analyses for scenarios with or without full forest cover and/or good versus poor surface infiltration were performed for: (i) selected tropical catchments with documented changes in streamflow after deforestation; and (ii) the tropics at large (23.5°N to 35°S, to include important seasonal montane forests). The catchment sensitivity analyses showed that W3A–LUM captured the streamflow response to imposed deforestation and changes in surface conditions reasonably well. For the tropics as a whole, an increase in mean annual streamflow of 18% was obtained for forest conversion (to pasture) only, versus 26% after an additional imposed reduction in surface infiltration. Much of the inferred flow increases concerned water-limited regions. A reduction in dry-season flows was predicted for nearly one-fifth of all grid cells (despite lower Etot after forest conversion) after impaired infiltration, marking potential 'hot spots' of hydrological change after deforestation and reduced infiltration due to surface degradation. The affected grid cells shared the following key characteristics: (i) strong seasonality; (ii) high infiltration capacity under forested conditions; (iii) sufficient wet-season precipitation to recharge deep soil- and groundwater stores; (iv) sufficient soil water storage under forested conditions to ‘carry over’ infiltrated wet-season rainfall into the subsequent dry season; and (v) slow groundwater recession maintaining baseflow throughout the dry season.Our results demonstrate that forest removal in highly seasonal tropical catchments, whilst typically increasing mean annual water yield, can indeed decrease dry-season flows, depending on pre- and post-forest removal surface conditions and groundwater response times.

Spatio-temporal changes and their relationship in water resources and agricultural disasters across China

ABSTRACTChanges in monthly streamflow and the potential influences and feedbacks of agricultural activities are investigated. Significant decreases in streamflow are observed in northern China, including the Yellow, Huaihe and Haihe river basins, while in southern China streamflow increases significantly in the Yangtze, Pearl and South river basins. This spatial pattern of changes in streamflow indicates that the imbalance in water resources between northern (dry) and southern (wet) China has increased during past decades. On the one hand, available water resources are a controlling factor determining the expansion of irrigated land and the structure of crop plantation (i.e. rice, wheat, corn or bean); on the other hand, crop planting structure and effective irrigated areas are important determinants of changes in streamflow. The increasing effective irrigation and rice planting areas in northern China may increase water withdrawal from rivers, causing subsequent decreases in streamflow, while in southeastern China, decreasing effective irrigation areas enhance the increases in streamflow.

Missing in action: possible effects of water recovery on stream and river flows in the Murray–Darling Basin, Australia

ABSTRACTWe use published water balance data from irrigated cropping to show that water entitlements acquired for environmental purposes through water infrastructure subsidies in the Murray–Darling Basin, Australia, have resulted in smaller increases in net stream and river flows than is estimated by the Australian Government, and may even have reduced net stream and river flows. Two key policy implications arising from our results are: (1) subsidies to improve irrigation efficiency so as to increase stream and river flows must employ water accounting so that the effects on return flows are known and the volume of water extracted for irrigation is adjusted to achieve desired stream and river flows; and (2) if the net increases in stream and river flows in the MDB are much less than estimated by the Australian Government, water infrastructure subsidies to increase irrigation efficiency may have compromised the delivery of key objects of the Water Act (2007).

Evapotranspiration from Corn, Soybean, and Prairie Grasses using the METRIC Model

Core Ideas Evapotranspiration of native prairie grasses is marginally higher than that of corn and soybean. Evapotranspiration of recently burned prairie was lower than those of previously burned prairie. Landscape evapotranspiration is likely similar from the changeover of small grains and native prairies to soybean. Land use in the US Upper Midwest has evolved from small grains and prairie systems to corn (Zea mays L.) and soybean [Glycine max (L.) Merr.]. This change has been assumed to cause a dramatic decrease in landscape evapotranspiration (ET) and consequently a large increase in streamflow. This study assessed ET from corn, soybean, and native prairie grasses using the satellite image based surface‐energy balance model named METRIC in west‐central Minnesota. The METRIC model uses properties of satellite images along with daily weather to calculate landscape ET. The land covers analyzed were irrigated and non‐irrigated corn, non‐irrigated soybean, native prairie grasses under different grazing and burn regimes, and wetlands. For 8 June through 22 Oct. 2015, estimated ET followed the trend: wetlands (717 mm) > non‐irrigated corn (662 mm) > irrigated corn (647 mm) > non‐irrigated soybean (554 mm) > previously burned prairie (537 mm) > recently burned prairie (406 mm). For 1 May to 22 Oct. 2015, the estimated ET of wetlands, previously burned and recently burned prairie grasses were 884, 666, and 511 mm, respectively. These model estimates showed that ET of native prairie grasses are similar to slightly higher than that of corn and soybean. Considering soybean also replaced low ET small grains suggests that changes in landscape ET from a changeover of vegetative cover starting in 1940s are likely minimal. This supports our earlier findings that recently increased streamflows in the Upper Midwest are primarily from increased precipitation and not due to land cover changes.

Impacts of Climate Variability and Human Activities on Streamflow in the Wanquan River Basin along the East Coast of Hainan Island, Southern China

Zhao, Y.; Zou, X.; Liu, Q., and Chen, Y., 2019. Impacts of climate variability and human activities on streamflow in the Wanquan River Basin along the east coast of Hainan Island, southern China. Journal of Coastal Research, 35(2), 410–419. Coconut Creek (Florida), ISSN 0749-0208.The influences of climate change and human activities on streamflow change have received significant attention recently. In this study, daily data from seven precipitation gauges and one hydrological station are analyzed to assess the impacts of climate variability and human activities on streamflow over the past 54 years in the Wanquan River Basin (WRB). The Mann-Kendall test and Morlet wavelet method were employed to analyze the streamflow series, and the relative effects of climate change and human activities were empirically determined based on a coupled water and energy budget analysis. The results show that annual streamflow exhibited a statistically insignificant decreasing trend throughout the entire basin at an annual rate of –0.015 × 108 m3/y. Meteorological factors, such as temperature, exhibited significant increases throughout the entire basin. A decreasing trend in precipitation and an increasing trend in potential evapotranspiration were identified in the upstream region, whereas the opposite trends were observed in the downstream region. Moreover, an abrupt change in streamflow at Jiaji station occurred in 1974, exhibiting periodicities of 2 to 4 and 8 to 11 years at a 95% confidence level during the periods of 1965–80 and 1970–75, respectively. Regarding the catchment-averaged water balance, a quantitative analysis revealed that climate change resulted in an increase in streamflow from the 1970s to the 2000s throughout the entire basin, and streamflow increased by 146%, 259%, 473%, and 128% in the 1970s, the 1980s, the 1990s, and 2000–13 relative to streamflow in the 1960s. However, human activities may have decreased streamflow (–46%, –159%, –373%, and –28% in the 1970s, the 1980s, the 1990s, and 2000–13, respectively). Therefore, the relative effect of climate change was greater than that of human activities. Further research is needed to clarify the mechanisms associated with the anthropogenic effects on runoff changes.

Uncertainty Forecasting for Streamflow based on Support Vector Regression Method with Fuzzy Information Granulation

Accurate and comprehensive forecasting of streamflow plays an important role in the uncertainly analysis of the hydrologic system. It is widely accepted that prediction interval (PI) can provide more precise and detailed information than deterministic forecasting when the uncertainty level of streamflow increases. Support vector regression (SVR) is a supervised learning model for classification and regression analysis based on associated learning algorithms. In this paper, fuzzy information granulation (FIG) is combined with SVR model (FIG-SVR) for uncertainty forecasting of streamflow. On behalf of evaluating the performance of the forecasting results, the evaluation metrics of point forecasting and interval prediction results are introduced. The real streamflow data from the Three Gorges in the Yangtze River are used to validate the proposed method based on the proposed method. The results show that the proposed method provides the high-quality point predictand and PIs, and the uncertainly of streamflow can be well handled.

Impacts of land use/land cover change on stream flow and sediment yield of Gojeb watershed, Omo-Gibe basin, Ethiopia

Land use/land cover (LULC) change is an important landscape process capable of altering the fluxes of water, sediment, contaminants and energy. In this study, Soil and Water Assessment Tool (SWAT) model was used to examine the effects of LULC on the hydrological process of Gojeb Watershed in the Omo-Gibe basin. The performance of the model was evaluated through sensitivity, uncertainty analysis, calibration and validation. The LULC change analyses for three periods (1989, 2000 and 2013) were performed using ERDAS Imagine 2014 with a maximum likelihood classifier. The time series LULC changes results were used for estimation of stream flow and sediment yield. The result has shown that during the study period most parts of the forest land were converted into cultivated land with an increase of cultivated land by 14.97% over the study periods which resulted in an increase of stream flow and sediment yield by 8.6 m3/s and 41.07ton/km2 respectively. The Nash sutcliff efficiency (NSE), coefficient of determination (R2) and percent of bias (PBIAS) were used for evaluating the model performance. The model results have shown a good agreement with the observed values with NSE > 0.75, R2 > 0.78, and PBIAS < 0.5 values. Based on the validated sediment yield results of 2013 land use, high potential source of spatial variability of sediment was found at middle and downstream of the watershed. Hence, for the critical sub-watersheds, the design and development of three best management practices (BMPs) were performed. These best management scenarios include: S1 (filter strip), S2 (terrace/ bund) and S3 (reforestation). Based on these scenarios, the findings have shown a sediment yield reductions by 22.9%, 29.4% and 32.3% with the implementation of S1, S2 and S3 respectively. Therefore, based on the findings, implementing S3 is the best management strategy as compared to other options and hence, such intervention should be encouraged at a wider scale for efficient sediment reductions of Gojeb watershed.

Assessment of Streamflow Variability with Upgraded HydroClimatic Conceptual Streamflow Model

HydroClimatic Conceptual Streamflow (HCCS) model is a conceptual model for prediction and future assessment of daily streamflow using climate inputs and time-varying watershed characteristics. However, without denying its useful salient features in a changing climate, applicability of the HCCS model is limited to the basins without any major man-made river structure(s), such as reservoirs. Considering this, the originally proposed HCCS model is upgraded (hereinafter ‘upgraded HCCS model’) to accommodate the human-intervened release from such structures within the basin, if any, and to include routing component through the river channels without using rigorous information from the river channels. The upgraded HCCS model is expected to be useful to assess (i) the effect on the streamflow at downstream due to upstream dam release, and (ii) the long-term modification required in the reservoir/dam operation under a changing climate for ensuring water-availability in downstream. The upgraded HCCS model is applied to three river basins for assessing the future streamflow characteristics. Two of these basins have one each and the third basin has two major man-made river structures within them. Hadley Centre Coupled Model, version 3 (HadCM3) simulated climate variables till 2035 are used as inputs for demonstration. The model predicts an increase in streamflow in future. In general, the upgraded HCCS model can be applied to any tropical river basin having major man-made river structure(s) for daily streamflow prediction as well as assessment of future streamflow variation considering the changing climate and watershed characteristics.

Modeling streamflow sensitivity to climate change in New York City water supply streams using a stochastic weather generator

Study regionThe New York City water supply watersheds Study focusThis study is a modeling analysis on climate change impact on streamflow using a stochastic weather generator (SWG), a hydrologic model, and downscaled future climate scenarios. Streamflow generated using synthetic time series of precipitation and air temperature from a SWG were compared to those simulated from observed historical and projected future weather. New hydrologic insights for the regionSynthetic weather was able to mimic the observed annual streamflow cycle for the six watersheds studied, including the seasonal pattern as well as magnitude and occurrence of extreme hydrologic events. Streamflow simulations using projected climate from 20 global climate models (GCM) for one of the New York City water supply watersheds indicate the potential for changes in the hydrologic regime in this region. The models indicate a shift in the timing of spring melt runoff from a distinct peak in late March and April under historical (1950–2009) conditions towards earlier in the year for mid-century (2041–2060) period. Results indicate that the region may experience an overall increase in mean streamflow in the future due to the combined effect of decreasing spring runoff peak and increasing streamflow during other seasons. More importantly, the magnitude and frequency of extreme hydrological events are projected to increase under future scenarios. These results have implications for future operation and management of the water supply.

Detecting river-scale turbidity disturbance after rainfall using NEXt-Generation Weather RADar (NEXRAD) and the Intelligent River

Turbidity of surface water is a major environmental and human health issue in the United States. This study integrated two years (January 1, 2015, to December 31, 2016) of high frequency in situ turbidity and stream flow data with daily Next Generation Radar rainfall data for nine Intelligent River sensors in order to learn about river-scale turbidity dynamics and disturbances after rainfall in the Savannah River, Georgia. Analysis of Intelligent River turbidity data revealed a highly dynamic system. A prevailing spatial pattern of increasing turbidity with decreasing distance from the Atlantic Ocean was evident at any given time during the study period, but the typical distribution of turbidity can be disrupted for days to months. Observed turbidity disturbances are related to periods of increased stream flow and rainfall events. Short-term (one to seven days) turbidity disturbances at river miles 150 or greater appear to be intricately linked to rainfall, but turbidity disturbances after the same rainfall events at river miles 27 and 61 were much less dramatic or not detected at all. These results paint an expectedly complex picture of high-frequency turbidity measurements at nine locations in a large river network. However, these results also highlight the feasibility and novelty of integrating NEXt-Generation Weather RADar (NEXRAD) and in situ sensing for data-driven knowledge discovery in soil and water conservation.

Trends of streamflow under climate change for 26 Brazilian basins

Abstract Changes in the climate system and the hydrologic regime strongly affect all water uses and human activity. The main goal of this study is to evaluate the impact of rainfall pattern change on streamflow for 26 Brazilian basins with hydropower plants. More precisely, the goal is to estimate the trends on average streamflow for the 2011–2100 period. The estimated trends result from the analysis of rainfall obtained from a possible climate scenario, among others. The annual average streamflow for this 90-year period is simulated and compared with records from 83 years of observations (1931–2013). Simulations were carried out using two rainfall-to-streamflow hydrological models: Soil Moisture Accounting Procedure (SMAP) and Stochastic Linear Model (SLM). Results from simulations show important impacts, namely, an increase of streamflow in the southern basins and a decrease in the northern basins. Such changes can lead to disastrous consequences, considering the historical exposure to floods and droughts in the southern and northeast regions, respectively. These findings, in addition to the recent severe drought events that have occurred in such regions, provide awareness of a new cycle of reform to the existing water policies and Brazilian institutional framework, which saw the completion of its first 20 years in 2017.

Water Quality Control Options in Response to Catchment Urbanization: A Scenario Analysis by SWAT

Urbanization poses a challenge to sustainable catchment management worldwide. This study compares streamflows and nutrient loads in the urbanized Torrens catchment in South Australia at present and future urbanization levels, and addresses possible mitigation of urbanization effects by means of the control measures: river bank stabilization, buffer strip expansion, and wetland construction. A scenario analysis by means of the Soil and Water Assessment Tool (SWAT) based on the anticipated urban population density growth in the Torrens catchment over the next 30 years predicted a remarkable increase of streamflow and Total Phosphorous loads but decreased Total Nitrogen loads. In contrast, minor changes of model outputs were predicted under the present urbanization scenario, i.e. urban area expansion on the grassland. Scenarios of three feasible control measures demonstrated best results for expanding buffer zone to sustain stream water quality. The construction of wetlands along the Torrens River resulted in the reduction of catchment runoff, but only slight decreases in TN and TP loads. Overall, the results of this study suggested that combining the three best management practices by the adaptive development of buffer zones, wetlands and stabilized river banks might help to control efficiently the increased run-off and TP loads by the projected urbanization of the River Torrens catchment.

The impacts of climate change on hydrology in a typical glacier region-A case study in Hailuo Creek watershed of Mt. Gongga in China

The glaciers of the Hengduan Mountains play an important role in the hydrology processes of this region. In this study, the HBV Light model, which relies on a degree-day model to simulate glacier melting, was employed to simulate both glacier runoff and total runoff. The daily temperature and precipitation at the Hailuo Creek No. 1 Glacier from 1952 to 2009 were obtained from daily meteorological observed data at the glacier and from six national meteorological stations near the Hailuo Creek Basin. The daily air temperature, precipitation, runoff depth, and monthly potential evaporation in 1995, 1996, and 2002 were used to obtain a set of optimal parameters, and the annual total runoff and glacier runoff of the Hailuo Creek Glacier (1952–2009) were calculated using the HBV Light model. Results showed the average annual runoff in the Hailuo Creek Basin was 2, 114 mm from 1952 to 2009, of which glacial melting accounted for about 1, 078 mm. The river runoff in the Hailuo Creek catchment increased as a result of increased glacier runoff. Glacier runoff accounted for 51.1% of the Hailuo Creek stream flow in 1994 and increased to 72.6% in 2006. About 95% of the increased stream flow derived from the increased glacier runoff.

Separating climate change and human contributions to variations in streamflow and its components using eight time‐trend methods

AbstractSeparating impacts of human activities and climate change on hydrology is essential for watershed and ecosystem management. Many previous studies have focused on the impacts on total streamflow, however, with little attentions paid to its components (i.e., baseflow and surface run‐off). This study distinguished the contributions of climate change and human activities to the variations in streamflow, baseflow, and surface run‐off in the upstream area of the Heihe River Basin, a typical inland river basin in northwest China, by using eight different forms of time‐trend methods. The isolated contributions to streamflow variation were also compared with those obtained by two Budyko‐based approaches. Our results showed that the time‐trend methods consistently estimated positive contributions of climate variability and human activities to the increases in streamflow and its components but with obviously varying magnitudes. With regard to streamflow, the time‐trend method double‐mass‐curve–Wei, with a physical basis, produced a reasonable smaller contribution of human activities than climate changes, inconsistent with the Budyko‐based approaches. However, all the other time‐trend methods led to contrary results. The contributions to baseflow variation diverged more significantly than those to streamflow and surface run‐off, ranging from 24% to 92% for human activities and from 8% to 76% for climate variability. In terms of surface run‐off, most of the time‐trend approaches produced smaller contributions of human activities (ranging from 21% to 49%) than climate change. The uncertainties associated with the various time‐trend approaches and the baseflow separation algorithm were revealed and discussed, along with some recommendations for future work.

Hydrologic impact of aspen harvesting within the subhumid Boreal Plains of Alberta

AbstractThis study examined the hydrological impact of harvesting aspen (Populus tremuloides) within the subhumid Boreal Plains of Alberta, Canada, following clear‐cutting of two stands in successive winters within a small catchment situated in glacial moraine. Impacts were evaluated using a combination of observational data collected from within the harvested catchment and an adjacent reference catchment and numerical simulations conducted with HydroGeoSphere. Sensitivity simulations evaluated the influence of post‐harvest evapotranspiration rates and variability in atmospheric conditions on the range of hydrologic response. Study results indicate that aspen harvesting had limited impact on groundwater levels and streamflows within these hydrologic systems because of the subhumid climate with low frequency of large storms, large soil‐moisture storage capacity of heterogeneous glacial materials, and high evapotranspiration rates of regenerating aspen. Despite an estimated increase in hillslope groundwater levels of up to 3 m, pond and peatland water levels increased by less than 0.3 m and were accompanied by increased streamflows of less than 10 mm. However, predicted increases in groundwater levels and streamflows were sensitive to regenerating aspen evapotranspiration rates, which can be enhanced by appropriate harvesting techniques but may be reduced by climate change. These results are consistent with previous results from within the Boreal Plains but differ from aspen harvesting studies conducted in other settings where appreciable increases in streamflows have been reported. This disparity highlights the need to consider the integrated response of the hydrologic system when evaluating impacts from disturbance and making comparisons between settings.

Evaluating the impacts of climate and land use/land cover (LU/LC) dynamics on the Hydrological Responses of the Upper Blue Nile in the Central Highlands of Ethiopia

This study integrates GIS and SWAT model to evaluate impacts of climate and LU/LC change on watershed hydrological dynamics. To evaluate the impact of a combined and individual climate and LU/LC dynamics on stream flow, series of simulation were computed by changing climate and LU/LC variables. The model was calibrated and validated against observed data. Statistical measures like coefficient of determination and Nash–Sutcliffe were used to evaluate the model and it results in 0.82 and 0.82 for calibration and 0.81 and 0.80 for validation respectively. During the study period, forest and shrub land decreased by 38% and 48% while, settlement and cultivated land increased by 572% and 7% respectively. Mann–Kendall trend test analysis showed a significant trend in maximum and minimum temperature at 5% significant level, whereas there were three no trend cases for rainfall out of four tested cases and one non-significant decreasing trend. The simulated flow showed a very good agreement with the observed flow data with 0.82 and 0.82 for calibration and 0.81 and 0.80 for validation respectively. Simulation result indicted that LU/LC change increased the wet season flow by 14.5% while decreasing by 9.65% in dry season. In wet season the flow increased by 4.5% while decreased by 3.3% in dry season because of change in climate and seasonal variability. The study showed the increase in stream flows can be directly attributed to the expansion of cultivated lands at a cost of the forested vegetation.

Assessing the Importance of Potholes in the Canadian Prairie Region under Future Climate Change Scenarios

The Prairie Pothole Region (PPR) of Canada contains millions of small isolated wetlands and is unique to North America. The goods and services of these isolated wetlands are highly sensitive to variations in precipitation and temperature. We evaluated the flood proofing of isolated wetlands (pothole wetlands) under various climate change scenarios in the Upper Assiniboine River Basin (UARB) at Kamsack, a headwater catchment of the Lake of the Prairies in the Canadian portion of the PPR. A modified version of the Soil Water Assessment Tool (SWAT) model was utilized to simulate projected streamflow under the potential impacts of climate change, along with changes to the distribution of pothole wetlands. Significant increases in winter streamflow (~200%) and decreases (~11%) in summer flow, driven by changes in future climates, were simulated. Simulated changes in streamflow resulting from pothole removal were between 55% for winter and 15% for summer, suggesting that climate will be the primary driver in the future hydrologic regime of the study region. This research serves as an important guide to the various stakeholder organizations involved in quantifying the aggregate impacts of pothole wetlands in the hydrology of the Canadian Prairie Region.

Contrasting streamflow regimes induced by melting glaciers across the Tien Shan \u2013 Pamir \u2013 North Karakoram

The glacierized Tien Shan – Pamir – Karakoram mountain complex supplies water to about 42 million people. Yet, the knowledge about future glacial runoff in response to future climate is limited. Here, we address this issue using a hydrological model, that includes the three components of glacial runoff: ice melt, snowmelt and the runoff of rainfall over ice. The model is forced by climate projections of the CMIP5 models. We find that the three components exhibit different long-term trajectories, sometimes opposite in sign to the long-term trend in glacier impacts. For the eastern slope basins, streamflow is projected to increase by 28% (ranging from 9 to 44%, from climate model variation (CMV)) by the late 21st century, under the representative concentration pathway, RCP8.5. Ice melt contributes 39% (25 to 65%, CMV) of the total streamflow increase. However, streamflow from the western slopes is projected to decrease by 5% (−24 to 16%, CMV), due to the smaller contribution of ice melt, less precipitation and higher evapotranspiration. Increasing water supply from the eastern slopes suggests more water availability for currently degraded downstream ecosystems in the Xinjiang province of China, while the likely decreasing streamflow in Central Asian rivers on the western slopes indicates new regulations will be needed.

Analyzing Changes in the Flow Regime of the Yangtze River Using the Eco-Flow Metrics and IHA Metrics

Changes in the flow regime of the Yangtze River were investigated using an efficient framework that combined the eco-flow metrics (ecosurplus and ecodeficit) and Indicators of Hydrologic Alteration (IHA) metrics. A distributed hydrological model was used to simulate the natural flow regime and quantitatively separate the impacts of reservoir operation and climate variation on flow regime changes. The results showed that the flow regime changed significantly between the pre-dam and post-dam periods in the main channel and major tributaries. Autumn streamflow significantly decreased in the main channel and in the tributaries of the upper Yangtze River, as a result of a precipitation decrease and reservoir water storage. The release of water from reservoirs to support flood regulation resulted in a significant increase in winter streamflow in the main channel and in the Minjiang, Wujiang, and Hanjiang tributaries. Reservoir operation and climate variation caused a significant reduction in low flow pulse duration in the middle reach of the Yangtze River. Reservoir operation also led to an increase in the frequency of low flow pulses, an increase in the frequency of flow variation and a decrease in the rate of rising flow in most of the tributaries. An earlier annual minimum flow date was detected in the middle and lower reaches of the Yangtze River due to reservoir operation. This study provides a methodology that can be implemented to assess flow regime changes caused by dam construction in other large catchments.

Economics of Water Recovery in the Murray-Darling Basin, Australia

We review recent water reforms and the consequences of water recovery intended to increase stream flows in the Murray-Darling Basin (MDB), Australia. The MDB provides a natural experiment of water recovery for the environment that includes ( a) the voluntary buy-back of water rights from willing sellers and ( b) the subsidization of irrigation infrastructure. We find that ( a) the actual increase in the volumes of water in terms of stream flows is much less than claimed by the Australian government; ( b) subsidies to increase irrigation efficiency have reduced stream and groundwater return flows; ( c) buy-backs are much more cost effective than subsidies; ( d) many of the gains from water recovery have accrued as private benefits to irrigators; and ( e) more than a decade after water recovery began, there is no observable basin-wide relationship between volumes of water recovered and flows at the mouth of the River Murray.