Increase In Annual Streamflow Research Articles

Assessment of land use/ land cover change derived catchment hydrologic response: An integrated parsimonious hydrological modeling and alteration analysis based approach

Land use/land cover (LULC) change, often a consequence of natural or anthropogenic drivers, plays a decisive role in governing global catchment dynamics, and subsequent impact on regional hydrology. Insight into the complex relationship between the drivers of LULC change and catchment hydrology is of utmost importance to decision makers. Contemplating the dynamic rainfall-runoff response of the Indian catchments, this study proposes an integrated modeling-based approach to identify the drivers and relative contribution to catchment hydrology. The proposed approach was evaluated in the tropical climate Nagavali River Basin (NRB) (9512 km2) of India. The Soil and Water Assessment Tool (SWAT) hydrological model, which uses daily-scale rainfall, temperature, wind speed, relative humidity, solar radiation, and streamflow information was integrated with the Indicators of Hydrologic Alteration (IHA) technique to characterize the plausible changes in the flow regime of the NRB. Subsequently, the Partial Least Squares Regression (PLSR) based modeling analysis was performed to quantify the relative contribution of individual LULC components on the catchment water balance. The outcomes of the study revealed that forest land has been significantly converted to agricultural land (45–59%) across the NRB resulting in mean annual streamflow increase of 3.57 m3/s during the monsoon season. The affinity between land use class and streamflow revealed that barren land (CN = 83–87) exhibits the maximum positive response to streamflow followed by the built-up land (CN = 89–91) and fallow land (CN = 88–93). The period 1985–1995 experienced an increased ET scenario (911–1050 mm), while the recent period (2005–2020) experienced reduced ET scenario owing to conversion of forest to agricultural land. Certainly, the study endorses adopting the developed methodology for understanding the complex land use and catchment-scale hydrologic interactions across global-scales for early watershed management planning.

Long-term effects of land-use change on water resources in urbanizing watersheds

The changes in energy balance resulting from land-use change may significantly affect the amount and timing of water loss to the atmosphere as evapotranspiration (ET). Also, these will impact water fluxes in the watershed system, influencing runoff rate, flow volume, intensity, and frequency of floods. During the past century, land-use change in the SuAsCo (Sudbury-Assabet and Concord) watershed has altered basin hydrology, sediment, and nutrient load that is detrimental to water resources in SuAsCo. This study uses an integrated physically-based model Hydrological Simulation Program-FORTRAN (HSPF), along with Land Transformation Model (LTM), to assess predicted temporal and spatial changes in water, nutrient, and sediment yields for future land-use scenarios of 2035, 2065, and 2100. Results showed that a 75% increase in effective impervious area and a 50% decrease in forest area in 2100 (from 2005 baseline levels) are projected to cause a 3% increase in annual streamflow and a 69% increase in total yearly mean surface runoff. The average annual total suspended solid (TSS) yield at the watershed outlet is estimated to increase by 54% in 2100. An increase of 12% and 13% concentrations of average annual total phosphorus (TP) and total nitrogen (TN) are predicted by 2100 due to urban expansion and increased runoff volume. This integrated modeling approach will inform watershed managers and landowners about critical areas of the SuAsCo watershed to apply best management practices (BMPs) to mitigate the effects of land-use land cover (LULC) change.

Retirement of US fossil fuel-fired power plants will increase water availability

Nearly two-thirds of fossil fuel-fired electricity generation capacity in the United States is expected to reach its typical end of life by 2035. While the closure of fossil fuel-fired power plants will help advance decarbonization goals, the cessation of water use for fossil fuel-fired power plant cooling - the largest water user in the US - will also impact the nation’s water resources. We assess when, where, and how much water will be made available upon the expected retirement of the nation’s nearly one thousand fossil fuel-fired power plants by combining a lifespan-based model of fossil fuel-fired generator retirements for the US fossil fuel-fired electricity generation fleet with a national-scale hydrologic model. We show that annual water withdrawals and consumption of fossil fuel-fired power generators will be significantly curtailed (85 % and 68 % reduction, respectively) by 2035 if these generators follow their typical retirement timeline. Most rivers with fossil fuel-fired power plants diverting and/or discharging water will have a net increase in annual streamflow after plant retirement (maximum decrease of 2 %, maximum increase of 57 % by 2050), with the most pronounced increases occurring in the summer months. The retirement of fossil fuel-fired power plants will lead to a large relative change (>5%) in streamflow at least one month per year by 2050 in 31 subbasins. The retirement of power generators was shown to produce noticeable streamflow impacts up to hundreds of kilometers downstream. By the retirement of the last US fossil fuel-fired power generator, 2.6 billion m3 of water that was once consumed by these power plants could be made available for other uses. In addition to the global benefits of reduced greenhouse gas emissions, the notable increases in streamflow and water availability in many US rivers due to the retirement of fossil fuel-fired power plants could benefit local water users and ecosystems.

Update On A Long-term Winter Operational Cloud Seeding Program In Central/Southern Utah

North American Weather Consultants, Inc. (NAWC) has conducted operational winter cloud seeding programs in the mountainous areas of Central and Southern Utah since 1974. Beginning in 1988, seeding has also been conducted in three additional mountainous target areas within the State. The goal of these programs has been to enhance winter snowpack accumulation in the target areas, which now include most of the mountainous areas of the State. Studies have demonstrated that a large majority of the annual runoff in Utah streams and rivers is derived from melting snowpack, which explains the focus on wintertime seeding (within the November – April period). Augmented water supplies are typically used for irrigated agriculture or municipal water supplies. Programs are typically funded at the county level with cost sharing grants from the Utah Division of Water Resources (UDWR) and the three Lower Colorado River Basin States of Arizona, California, and Nevada, since 2007. An earlier WMA paper (Griffith et al. 2009) provided a summary of seeding operations for the water years of 1974 through 2007 for the four target areas. This paper is focused on the Central and Southern Utah program which is both the largest target area and the longest running program in the state. It covers all but three water years from 1974 through 2021 and is one of the three or four longest operational winter cloud seeding programs that have been conducted in the United States. The target area encompasses several mountain ranges in Central and Southern Utah. NAWC has defined the target area boundaries as those locations that are above 7,000 feet MSL. This is a large area of approximately10,000 square miles. Cloud seeding is accomplished using networks of ground-based, manually operated silver iodide nuclei generators located in valley or foothill locations upwind of the intended target mountain barriers. As such, these programs are classified as orographic winter cloud seeding programs. Orographic winter cloud seeding programs are typically categorized as those with the highest level of scientific support based upon capability statements of such organizations as the American Meteorological Society and the Weather Modification Association. NAWC historical target/control evaluations of this program indicate an average increase in December-March target area precipitation of 12% or an average increase in precipitation of 1.3”. These results were significant at the 0.06 level from a one-tailed Student’s t-test. The UDWR has conducted periodic studies to estimate the increases in annual streamflow resulting from the estimated increases in April 1st snow water content produced by this seeding program. The most recent study (UDWR 2018) indicated an estimated average annual streamflow increase of about 84,000 acre-feet for the Central and Southern Utah target area. Factoring in the cost of conducting this program resulted in an estimate of the average cost of the augmented runoff to be $2.02 per acre-foot.

Evaluation of Streamflow under Climate Change in the Zambezi River Basin of Southern Africa

The Zambezi River basin is the fourth largest basin in Africa and the largest in southern Africa, comprising 5% of the total area of the continent. The basin is extremely vulnerable to climate change effects due to its highly variable climate. The purpose of this study was to evaluate the impact of climate change on streamflow in one of the sub-basins, the Kabombo basin. The multi- global climate model projections were used as input to the Soil Water Assessment Tool (SWAT) hydrological model for simulation of streamflow under RCP 4.5 and RCP 8.5 climate scenarios. The model predicted an annual streamflow increase of 85% and 6% for high uncertainty and strong consensus, respectively, under RCP 8.5. The model predicted a slightly reduced annual streamflow of less than 3% under RCP 4.5. The majority of simulations indicated that intra-annual and inter-annual streamflow variability will increase in the future for RCP 8.5 while it will reduce for the RCP 4.5 scenario. The predicted high and moderate rise in streamflow for RCP 8.5 suggests the need for adaptation plans and mitigation strategies. In contrast, the streamflow predicted for RCP 4.5 indicates that there may be a need to review the current management strategies of the water resources in the basin.

Quantifying the impacts of decadal landuse change on the water balance components using soil and water assessment tool in Ghaggar river basin

The landuse and landcover change is considered as one of the most vital components of the global environmental change responsible for influencing the quantity, seasonal patterns and durations of the water flow within basins around the world. The aim of this study is to assess the impacts of changes in landuse landcover on the various hydrological components for Ghaggar river basin for a period of 1985–2015 using Soil and Water Assessment Tool model. The landuse landcover maps have been prepared using various Landsat satellite images for the year 1985, 1995, 2005 and 2015.The fixing changing method has been employed to quantify the impacts of landuse changes on hydrological components by changing the landuse maps of different year and keeping rest of the inputs same. The correlation and Partial Least square regression are used to examine the impacts of change in landuse on the hydrological components. The results unveiled that the increase in agriculture and built-up area and decrease in area of evergreen, deciduous and mixed forest. During the period 1985–2015 there is increase in annual stream flow (0.20%), wet season streamflow (1.55%), surface runoff (12.23%) and water yield (0.22%) on the contrary there is decrease in dry season streamflow (2.1%), Evapotranspiration (0.08%), groundwater flow (8.62%), Percolation (8.02%) and lateral flow (3.92%) owing to changes in landuse landcover. There is an urgent need to adopt soil and water conservation practices in the area to avert these deleterious effects of landuse landcover changes.

ANALYSIS OF LAND USE / LAND COVER AND CLIMATE IMPACTS ON KANGIMI STREAMFLOW AND SEDIMENT YIELD: KANGIMI CATCHMENT, KADUNA NIGERIA

The Kangimi reservoir is an important dam augmenting water supply and recreational activities in and around the Kangimi Watershed in Kaduna, Nigeria. However, the impending hydrological effect of land use / land cover (LULC) dynamics in relation to agricultural expansion has not been established. This study determines the LULC dynamics on hydrological parameters (streamflow and sediment yield) using the ArcGIS 10.2 interfaced with ArcSWAT 2009 and detailed LULC maps (1975, 2000 and 2013). The catchment was delineated into ten subbasins, and 39 hydrological response units (HRUs) were created according to multiple HRU development. Kangimi hydrology was simulated for three different LULC types. The model was verified through calibration and validation to determine its performance; the values were determined to be (R2=0.92, NS=0.93) for calibration and (R2=0.82, NS=0.86) for validation, respectively. The hydrological response was considered based on three conditions (climate of 1979-2014 & 1975 LULC, the climate of 1979-2014 & 2000 LULC, and climate of 1979-2014 & 2013 LULC). Model results for the Kangimi catchment confirm that agricultural growth and bare surface increase led to an increase in annual streamflow and sediment yield. Thehydrology streamflow increased 28.23% (from 345.2 m3/s to 387.37 m3/s) as well as 33.31% (from 60.03 to 90.02 t/ha) of sediment yield due to LULC and climate dynamics. The results confirm the prominence of incorporating physical hydrologic models through the use of GIS for estimating catchment characteristics and the relative effect of LULC dynamics on hydrologic response. A well-parameterized model can be equally used to estimate the impact of LULC dynamics on water quality, pesticide loading, nutrients and land management practice.Keywords: Hydrological parameters, Climate changes, SWAT, GIS

Feasibility/Design Study for a Cloud Seeding Program in the Yadkin River Basin, North Carolina

North American Weather Consultants (NAWC) was contracted by Cube Hydro Partners, LLC with headquarters in Bethesda, Maryland, to conduct a cloud seeding feasibility/design study for the Yadkin River Basin located in North Carolina. This study was prepared in conformance with American Society of Civil Engineer’s Guidelines and Standards. The goal of the program would be to augment precipitation over the Yadkin River Basin to increase streamflow into a series of Cube Hydro reservoirs along the Yadkin River. This increased streamflow would then be used to generate additional hydropower (clean energy) from facilities installed on project dams. NAWC compiled a site-specific climatology for this Basin. Both ground-based and airborne seeding was considered, but only airborne seeding was recommended due to the lack of significant topographic features in the Basin and the rather high average height of the -5° C level in potentially “seedable” storms (630 mb), as well as other meteorological factors. Regression equations relating precipitation to streamflow suggest that seeding only during the cool season produces streamflow increases not only during the cool season, but would also have a residual effect that increases streamflow throughout the remainder of the year. Overall, cool-season seeding is likely to have about 1.4 times as much impact on total streamflow as warm-season seeding (assuming the same increase percentage-wise in precipitation), with the cool season increase more evenly distributed throughout the year in terms of the resultant streamflow. Therefore, only a cool season program was recommended. Detailed examination of a 3-year cool season storm climatology in the Yadkin Basin suggest that aircraft-based cloud seeding during the cool season could enhance precipitation by 4.1%, resulting in an estimated 5.2% increase in annual streamflow (109,200 acre-feet). Cost estimates were prepared for a seasonal program. Once the estimated costs were established, NAWC was able to develop benefit/cost ratio estimates. Using information provided by Cube Hydro, NAWC calculated a potential benefit/cost ratio of 5/1. NAWC concluded that the proposed program was feasible based upon both technical and economic considerations as recommended in the “Guidelines for Cloud Seeding to Augment Precipitation”, Third Edition by the American Society of Civil Engineers (ASCE,2016).

Simulating the Impact of Climate Change on the Hydrological Regimes of a Sparsely Gauged Mountainous Basin, Northern Pakistan

Projected climate changes for the 21st century may cause great uncertainties on the hydrology of a river basin. This study explored the impacts of climate change on the water balance and hydrological regime of the Jhelum River Basin using the Soil and Water Assessment Tool (SWAT). Two downscaling methods (SDSM, Statistical Downscaling Model and LARS-WG, Long Ashton Research Station Weather Generator), three Global Circulation Models (GCMs), and two representative concentration pathways (RCP4.5 and RCP8.5) for three future periods (2030s, 2050s, and 2090s) were used to assess the climate change impacts on flow regimes. The results exhibited that both downscaling methods suggested an increase in annual streamflow over the river basin. There is generally an increasing trend of winter and autumn discharge, whereas it is complicated for summer and spring to conclude if the trend is increasing or decreasing depending on the downscaling methods. Therefore, the uncertainty associated with the downscaling of climate simulation needs to consider, for the best estimate, the impact of climate change, with its uncertainty, on a particular basin. The study also resulted that water yield and evapotranspiration in the eastern part of the basin (sub-basins at high elevation) would be most affected by climate change. The outcomes of this study would be useful for providing guidance in water management and planning for the river basin under climate change.

Hydrological effects of forest plantation clear-cut on water availability: Consequences for downstream water users

Study RegionSão Paulo State, Brazil. Study FocusThis study assessed the influence of forest plantations on streamflow in a gauged catchment (85 ha), covered with fast-growing Eucalyptus sp. plantations. One strategy for reducing the effects of plantations on streamflow is to reduce the area of a catchment occupied by forest, and in this context, our objectives were to simulate the effects on streamflow of different proportions of forest cover (70%, 50% and 0% of the forest cover). Moreover, we used low-flow indices (Q90 and 7Q10) to examine the effects of such scenarios on water availability for downstream users. New Hydrological InsightsFast-growing forest plantation areas have been expanding globally, with simultaneously increasing concerns about the water consumption of these forests, especially in water-limited regions with consequences for downstream users. Simulations of scenarios with varying forest cover proportions showed an annual streamflow increase of 90% when clear-cutting had removed the forest cover in the catchment. The 100% forest cover scenario produced rates of streamflow below the low flow indices, resulting in less water availability for downstream water users. The reduction in forest cover proportion at the catchment scale promoted an attenuation of water use. Therefore, forest plantation management should adopt management strategies such as regulating the forest cover proportion to minimize the effects on water supply for downstream water users.

Hydrologic responses to climate change using downscaled GCM data on a watershed scale

AbstractThe changing climate has raised significant concerns for water resources, especially on a watershed scale. In this study, the downscaled global circulation model (GCM) products were further bias corrected and evaluated for the period of 1981–2099. Driven by the bias-corrected products, a calibrated Precipitation-Runoff Modeling System (PRMS) model was used to assess long-term hydrologic responses in the Lehman Creek watershed, eastern Nevada. The results of this study show: (1) the Parameter–elevation Regressions on Independent Slopes Model (PRISM) products offer a reliable replacement for limited observations for bias correction using quantile mapping (QM) technique; (2) average increases of 2.3 °C, 2.2 °C, and 35.1 mm in maximum temperature, minimum temperature, and precipitation by the end of century; (3) an annual streamflow increase of 7.6–11.6% with greatest increases in April and greatest decreases in June; (4) 20 days' earlier shift in annual peak flow – as indicated by the date of winter-spring center of volume – by the end of the century. For management of local water resources, this study provides a better understanding of variations in the streamflow rate and timing to a potential climate change in the study area as well as corresponding uncertainties in the estimation processes.

Assessing mechanisms of climate change impact on the upland forest water balance of the Willamette River Basin, Oregon

AbstractProjected changes in air temperature, precipitation, and vapor pressure for the Willamette River Basin (Oregon, USA) over the next century will have significant impacts on the river basin water balance, notably on the amount of evapotranspiration (ET). Mechanisms of impact on ET will be both direct and indirect, but there is limited understanding of their absolute and relative magnitudes. Here, we developed a spatially explicit, daily time‐step, modeling infrastructure to simulate the basin‐wide water balance that accounts for meteorological influences, as well as effects mediated by changing vegetation cover type, leaf area, and ecophysiology. Three CMIP5 climate scenarios (Lowclim, Reference, and HighClim) were run for the 2010–2100 period. Besides warmer temperatures, the climate scenarios were characterized by wetter winters and increasing vapor pressure deficits. In the mid‐range Reference scenario, our landscape simulation model (Envision) projected a continuation of forest cover on the uplands but a threefold increase in area burned per year. A decline (12–30%) in basin‐wide mean leaf area index (LAI) in forests was projected in all scenarios. The lower LAIs drove a corresponding decline in ET. In a sensitivity test, the effect of increasing CO2 on stomatal conductance induced a further substantial decrease (11–18%) in basin‐wide mean ET. The net effect of decreases in ET and increases in winter precipitation was an increase in annual streamflow. These results support the inclusion of changes in land cover, land use, LAI, and ecophysiology in efforts to anticipate impacts of climate change on basin‐scale water balances.

Bark Beetles Cause Big Tree Die-Offs, but Streams Flow Steadily

Recent beetle epidemics have driven tree die-offs across North America, and previous studies predicted an increase in annual streamflow would follow—but a new study shows this may not be the case.

Streamflow Trends and Responses to Climate Variability and Land Cover Change in South Dakota

Trends in high, moderate, and low streamflow conditions from United States Geological Survey (USGS) gauging stations were evaluated for a period of 1951–2013 for 18 selected watersheds in South Dakota (SD) using a modified Mann-Kendall test. Rainfall trends from 21 rainfall observation stations located within 20-km of the streamflow gauging stations were also evaluated for the same study period. The concept of elasticity was used to examine sensitivity of streamflow to variation in rainfall and land cover (i.e., grassland) in the study watersheds. Results indicated significant increasing trends in seven of the studied streams (of which five are in the east and two are located in the west), nine with slight increasing trends, and two with decreasing trends for annual streamflow. About half of the streams exhibited significant increasing trends in low and moderate flow conditions compared to high flow conditions. Ten rainfall stations showed slight increasing trends and seven showed decreasing trends for annual rainfall. Streamflow elasticity analysis revealed that streamflow was highly influenced by rainfall across the state (five of eastern streams and seven of western streams). Based on this analysis, a 10% increase in annual rainfall would result in 11%–30% increase in annual streamflow in more than 60% of SD streams. While streamflow appears to be more sensitive to rainfall across the state, high sensitivity of streamflow to rapid decrease in grassland area was detected in two western watersheds. This study provides valuable insight into of the relationship between streamflow, climate, and grassland cover in SD and would support further research and stakeholder decision making about water resources.

Climate change impacts on streamflow and sediment yield in the North of Iran

Climate change will accelerate the hydrological cycle, altering rainfall, and the magnitude and timing of runoff. The purpose of this paper is to assess the impacts of climate change on streamflow and sediment yield from the Gorganroud river basin in the North of Iran. To study the effects of climatic variations, the SWAT model was implemented to simulate the hydrological regime and the SUFI-2 algorithm was used for parameter optimization. The climate change scenarios were constructed using the outcomes of three general circulation models for three emission scenarios. The study results for 2040–2069 showed an increase in annual streamflow of 5.8%, 2.8% and 9.5% and an increase in sediment yield of 47.7%, 44.5% and 35.9% for the A1F1, A2 and B1 emission scenarios, respectively. This implies that the impact of climate change on sediment yield is greater than on streamflow. Monthly variations show that the increase in discharge and sediment yield is more pronounced in wet seasons and the decrease is more pronounced in summer (July–September). The results highlighted the strong impact of climate change and reflected the importance of incorporating such analysis into adaptive management.Editor Z.W. Kundzewicz Associate editor Not assigned

Water quantity implications of regional-scale switchgrass production in the southeastern U.S.

Expansion of ethanol production has led to regional-scale cultivation of cellulosic biofuel crops, such as switchgrass (Panicum virgatum L.), on agriculturally marginal lands. A range of forest-based solutions are also being evaluated, especially in the southeastern U.S. However, there may be unanticipated environmental consequences, including changes in water export when managing forests to accommodate biofuel demands at a regional scale. We used the Soil Water Assessment Tool (SWAT) to simulate effects of regional-scale conversion of loblolly pine (Pinus taeda L.) plantations to switchgrass biofuel production on stream flow in the ∼5 million ha Tombigbee River Watershed in the southeastern U.S. Greater than 50% of the Tombigbee Watershed is forested, with 20% of the watershed supporting primarily loblolly pine forests. We modified the SWAT model by adding five age classes of loblolly pine trees, to more accurately represent existing forested systems. We found that maximum conversion of loblolly pine to switchgrass, affecting 7% of the watershed, represented an extreme land-use change and resulted in a 4% increase in annual stream flow. The more operationally and economically feasible option of converting young (≤4 yrs) and old (≥16 yrs) loblolly pine stands to switchgrass on <8% slope (2% of the watershed) resulted in a 2% increase in stream flow. Changes in annual stream flow were driven primarily by alterations in evapotranspiration (ET). Seasonal changes in stream flow were attributed to complex interactions among water-balance components of ET, surface flow, and groundwater flow.

应用SWAT模型研究潮河流域土地利用和气候变化对径流的影响

Global warming and intensive changes in land use /cover have posted unprecedented impacts on the watershed hydrology and thus the water security at the global scale. To quantitatively analyze the impacts of land use change and climate variability on the streamflow of Chaohe Watershed located in North China,we calibrated and validated a distributed hydrological model-SWAT by using the multi-site calibration procedure. The effects of land use changes and climate variability on the stream of the watershed were then explored by using scenario analysis approach. Two indices,the p-factor,r-factor as well as efficiency of objective function,were used to assess the calibration / uncertainty performance of the SWAT model at the hydrological stations of Dage,Daiying and Xiahui within the research watershed. Results showed that p-factors in the calibration and validation periods were 0. 70 and 0. 77,0. 87 and 0. 82,0. 92 and 0. 78 respectively for the three stations. The r-factors in the calibration and validation periods were 0. 63 and 0. 90,0. 97 and 0. 79,0. 88 and 0. 92 respectively for the three stations. The objective function of efficiency of SWAT was 0.66,suggesting that the model was capable for simulating runoff responses to changes of land use and climate variability in the watershed. Compared with the baseline period( 1981—1990),land use change caused an annual streamflow reduction of 4.1 mm whereas climate change gave rise to an annual streamflow reduction of 29.7mm in the period from 1991 to 2000. For the period of 2001—2009 land use change reduced runoff by 3.0 mm,whereas climate change decreased runoff for 14.3 mm. When the land use in 1999 was set as the reference,the annual streamflow would increase by 158.2% and 4.1% for the shrub land scenario and the grassland scenario,respectively. Contrarily,the farmland scenario and the woodland scenario could induce 41. 7% and 23. 7% annual streamflow reductions,respectively. The climate variability scenario analysis indicated that a 10% increase in annual precipitation could lead to 23.9% annual streamflow increase and a 12% increase in annual mean air temperature could lead to a 6% reduction in annual streamflow. We,therefore,concluded that the annual streamflow variation was more sensitive to precipitation than to temperature in the region. It is of critical importance to develop explicitly integrated"causeeffect"land use planning and strategies for adaptive land and water management at watershed scale under the global change.

Effects of climate change on annual streamflow using climate elasticity in Poyang Lake Basin, China

Hydrological processes depend directly on climate conditions [e.g., precipitation, potential evapotranspiration (PE)] based on the water balance. This paper examines streamflow datasets at four hydrological stations and meteorological observations at 79 weather stations to reveal the streamflow changes and underlying drivers in four typical watersheds (Meigang, Saitang, Gaosha, and Xiashan) within Poyang Lake Basin from 1961 to 2000. Most of the less than 90th percentile of daily streamflow in each watershed increases significantly at different rates. As an important indicator of the seasonal changes in the streamflow, CT (the timing of the mass center of the streamflow) in each watershed shows a negligible change. The annual streamflow in each watershed increases at different rates, with a statistically significant trend (at the 5 % level) of 9.87 and 7.72 mm year−1, respectively, in Meigang and Gaosha watersheds. Given the existence of interactions between precipitation and PE, the original climate elasticity of streamflow can not reflect the relationship of streamflow with precipitation and PE effectively. We modify this method and find the modified climate elasticity to be more accurate and reasonable using the correlation analysis. The analyses from the modified climate elasticity in the four watersheds show that a 10 % increase (decrease) in precipitation will increase (decrease) the annual streamflow by 14.1–16.3 %, while a 10 % increase (decrease) in PE will decrease (increase) the annual streamflow by −10.2 to −2.1 %. In addition, the modified climate elasticity is applied to estimate the contribution of annual precipitation and PE to the increasing annual streamflow in each watershed over the past 40 years. Our result suggests that the percentage attribution of the increasing precipitation is more than 59 % and the decreasing in PE is less than 41 %, indicating that the increasing precipitation is the major driving factor for the annual streamflow increase for each watershed.

Streamflow Response to Climate Change in the Brahmani River Basin, India

Climate change can significantly affect the water resources availability by resulting changes in hydrological cycle. Hydrologic models are usually used to predict the impacts of landuse and climate changes and to evaluate the management strategies. In this study, impacts of climate change on streamflow of the Brahmani River basin were assessed using Precipitation Runoff Modeling System (PRMS) run under the platform of Modular Modeling System (MMS). The plausible hypothetical scenarios of rainfall and temperature changes were used to assess the sensitivity of streamflow to changed climatic condition. The PRMS model was calibrated and validated for the study area. Model performance was evaluated by using joint plots of daily and monthly observed and simulated runoff hydrographs and different statistical indicators. Daily observed and simulated hydrographs showed a reasonable agreement for calibration as well as validation periods. The modeling efficiency (E) varied in the range of 0.69 to 0.93 and 0.85 to 0.95 for the calibration and validation periods, respectively. Simulation studies with temperature rise of 2 and 4°C indicated 6 and 11% decrease in annual streamflow, respectively. However, there is about 62% increase in annual streamflow under the combined effect of 4°C temperature rise and 30% rainfall increase (T4P30). The results of the scenario analysis showed that the basin is more sensitive to changes in rainfall as compared to changes in temperature.

Catchment hydrological responses to forest harvest amount and spatial pattern

Forest harvest effects on streamflow generation have been well described experimentally, but a clear understanding of process‐level hydrological controls can be difficult to ascertain from data alone. We apply a new model, Visualizing Ecosystems for Land Management Assessments (VELMA), to elucidate how hillslope and catchment‐scale processes control stream discharge in a small Pacific Northwest catchment. VELMA is a spatially distributed ecohydrology model that links hydrological and biogeochemical processes within watersheds. The study site is WS10 of the H.J. Andrews LTER, a 10 ha forested catchment clearcut in 1975. Simulated and observed daily streamflow are in good agreement for both the pre‐ (1969–1974) and postharvest (1975–2008) periods (Nash‐Sutcliffe efficiency = 0.807 and 0.819, respectively). One hundred scenarios, where harvest amounts ranged from 2% to 100% were conducted. Results show that (1) for the case of a 100% clearcut, stream discharge initially increased by ∼29% or 345 mm but returned to preclearcut levels within 50 years, and (2) annual streamflow increased at a near linear rate of 3.5 mm year−1 for each percent of catchment harvested, irrespective of location. Thereafter, to assess the impact of harvest location on stream discharge, 20 harvest scenarios were simulated, where harvest amount was fixed at 20% but harvest location varied. Results show that the streamflow response is strongly sensitive to harvest distance from the stream channel. Specifically, a 20% clearcut area near the catchment divide resulted in an average annual streamflow increase of 53 mm, whereas a 20% clearcut near the stream resulted in an average annual streamflow increase of 92 mm.