Hydropower Development Research Articles

Estimated capital costs of fish exclusion technologies for hydropower facilities

Hydropower is a reliable source of renewable energy, and its future expansion is likely to be in the form of either smaller new stream development (NSD) projects or powering existing non-powered dams. Thresholds for entrainment risk to fish and the requirements for fish exclusion at hydropower facilities often differ depending on the species involved, the characteristics of the facility, and the goals of stakeholders, but little quantitative information is present within the literature regarding the specific costs of fish exclusion measures. Cost data associated with protection, mitigation, and enhancement (PM&E) measures related to positive barrier screening were identified using keyword searches of an existing environmental mitigation cost data set and manual extraction from regulatory licensing documents available in the Federal Energy Regulatory Commission (FERC) eLibrary. This approach yielded a total of 50 p.m.&E mitigation measures with estimated capital construction costs pertaining to positive barrier screens and represented <10% of the 171 total FERC project dockets available in the data set. These data were highly skewed toward conventional relicensing projects, as <7% were associated with NSD projects. Results indicate highly variable costs are associated with fish screening, with flow-normalized costs one to two orders of magnitude higher for screening with the highest exclusion capability (≤0.09 in. spacing) compared with coarser screening (1–2 in.). These data provide an initial baseline for estimating exclusion costs for hydropower development and may help developers consider options for more fish-friendly generation technologies, though gaps remain relating to a lack of data, particularly for NSD projects.

Tunnels as Temples of 'New Green India': Dominant Narratives of Himalayan Dam Building

The dramatic unfolding of the Joshimath crisis in Uttarakhand, India, has brought the world’s attention once again to the Himalaya. The contribution of a 520-megawatt hydropower dam to land subsidence is squarely in the spotlight. River valleys with bumper-to-bumper hydropower dam building, especially in the North Western Himalaya, in the past decade and a half or so, have witnessed frequent slope de-stabilisation, landslides and seepages. Unlike the visible dispossession of rural—often adivasi and dalit— populations in reservoir based dam affected areas, even establishing and ‘scientifically’ correlating cascading hazards with human impacts of the ‘invisible’ activity of run-of-the-river dams in the relatively sparsely populated regions of the Himalaya, has been an uphill battle for impacted mountain people. This article examines the conflict around hydropower development in Himachal Pradesh to understand the trajectory of State policy, dominant narratives and responses of affected communities. Tracing the history of such contestation in the 180 MW Bajoli Holi hydropower project in Chamba’s tribal belt Bharmour, we illustrate the complicity of project proponents, regulatory institutions, political actors, scientists and the judiciary in transferring the project’s risks to local inhabitants and the environment. The burden of building fresh evidence, staking claims and posing counter-narratives lies unfairly with the dispossessed as they struggle for safety and survival.

Indigenous legal expertise, sacred rivers, and hydropower development projects in Third Pole country Nepal

While Indigenous expertise, values and knowledge systems have become a buzzword in academic and policy debates about climate change, sustainable development, and the protection of ecosystems, this research note turns the lens to Indigenous legal expertise used by Indigenous lawyers in Nepal in the defence of Indigenous peoples’ rights regarding the construction of dams and transmission line projects. Drawing on preliminary insights of legal anthropological research in Nepal, the research note intends to add an additional analytical lens to the emerging concept of cultural expertise of Indigenous knowledge embedded in Indigenous human-water-life ontologies.

Analysis of hydro-abrasive erosion in a high-head Pelton turbine injector using a Eulerian-Lagrangian approach

High-head hydropower plants deploy Pelton turbines to harness energy; however, turbine components face severe abrasive erosion due to suspended sediments. The erosion of the Pelton injector leads to the degradation of the jet quality, reducing the turbine efficiency considerably. Recently, the erosion of an internal servomotor design of the injector has been studied numerically; however, the cavitation-erosion synergy was not explored. This study serves as the extension of the literature with an analysis of the hydro-abrasive erosion and inception of cavitation in an injector with an external servomotor of a high-head hydropower plant (HPP). A Eulerian-Lagrangian approach is used to study the effects of sediment properties and flow parameters on hydro-abrasive erosion; whereas, the Schnerr-Sauer model is used to analyze the inception of cavitation. Interestingly, an increase in particle size from 40 microns to 200 microns resulted in a 95.7% reduction in needle erosion; but, led to a two-fold increase in nozzle erosion. For an increase in the plant head from 200 m to 820 m, the increase in erosion rate of the nozzle and the needle is 4.36 and 1.4 times, respectively. Moreover, the possibility of cavitation in the Pelton injector also increases with an increase in the head of the HPP leading the injector to higher susceptibility to the synergic effect of cavitation and hydro-abrasive erosion. This study attempts to assist the hydropower development in high-head regions with a risk of high sediment flow and manage the existing plants efficiently.

Exploring a novel reservoir drawdown operation framework for boosting synergies of hydropower generation and drought defense

The seasonal operation of drought-limited water level (DLWL) can efficiently boost the synergies of hydropower production and drought defense. This study proposes a seasonal DLWL operation framework for mimicking reservoir drawdown operation to improve hydropower output and mitigate drought risk. Firstly, three statistical analysis methods were used to divide the drought season into three segments. And then, the simulation model of seasonal DLWL operation was configured to evaluate the effect of reservoir drawdown operation on risk and benefits. Lastly, the combined distance-based assessment method was employed to identify the best scheme of seasonal DLWL operation. The Three Gorges Reservoir sited in the Yangtze River of China constitutes the case study. The results suggested that the proposed framework could facilitate reservoir drawdown operation to achieve 2346.95 million kW·h (7.0% improvement) in annual hydroelectricity production and 3.3% improvement in annual utilization efficiency of water resources, while could reduce 22.2% in drought risk during the dry year, compared with the annual DLWL operation scheme. This study not only can provide scientific and technical support for reservoir drawdown operation benefiting synergies of hydropower generation and drought defense but also can suggest policymakers with various favorable strategies to experience potential risks and benefits of seasonal DLWL operation in the interest of sustainable hydropower development.

A Large Ensemble Global Dataset for Climate Impact Assessments

We present a self-consistent, large ensemble, high-resolution global dataset of long‐term future climate, which accounts for the uncertainty in climate system response to anthropogenic emissions of greenhouse gases and in geographical patterns of climate change. The dataset is developed by applying an integrated spatial disaggregation (SD) − bias-correction (BC) method to climate projections from the MIT Integrated Global System Model (IGSM). Four emission scenarios are considered that represent energy and environmental policies and commitments of potential future pathways, namely, Reference, Paris Forever, Paris 2 °C and Paris 1.5 °C. The dataset contains nine key meteorological variables on a monthly scale from 2021 to 2100 at a spatial resolution of 0.5°x 0.5°, including precipitation, air temperature (mean, minimum and maximum), near-surface wind speed, shortwave and longwave radiation, specific humidity, and relative humidity. We demonstrate the dataset’s ability to represent climate-change responses across various regions of the globe. This dataset can be used to support regional-scale climate-related impact assessments of risk across different applications that include hydropower, water resources, ecosystem, agriculture, and sustainable development.

Quantifying the variation of Scaly-sided merganser’ population and their divergent response to changes in hydrological connectivity of rivers in a high-latitude water tower

The Scaly-sided Merganser (SSME) is a globally endangered waterbird species, primarily inhabiting rivers. In recognition of its precarious status, it was added to the International Union for Conservation of Nature’s (IUCN) Red List of Threatened Species in 2002. The SSME is highly sensitive to ecological environmental changes driven by changes in hydrological connectivity, particularly within riverine habitats. Changbai Mountain, a high-latitude water tower in the Northeast Asia, is considered one of the most optimal breeding grounds for the SSME worldwide. Its extensive water system and dense primary forest create an environment particularly well-suited for this species. Over the past 40 years, rivers within Changbai Mountain have experienced phases of hydropower development and ecological restoration. These activities have dramatically altered the hydrological connectivity of the area. However, the response of SSME to these changes in aquatic ecology, driven by shifts in hydrological connectivity, remains uncertain. We employed the AutoRegressive Integrated Moving Average (ARIMA) model to analyze changes in the population size of the SSME. Furthermore, the GeoDetector model was used to understand the impact of ecological changes on the maximum population size (MPS) and distribution of SSME in the context of alterations in hydrological connectivity. Our findings reveal that the restoration of hydrological connectivity, a method of ecological restoration, exerts a bidirectional influence on both the distribution and the MPS of SSME. Our findings can be summarized as follows. Firstly, there was a general trend of increase in both the distribution points and population size of the SSME. Secondly, the contribution of driving factors to the MPS of SSME was ranked in the following order: temperature > Connectivity Status Index (CSI) > river width > fish abundance > river depth > velocity > altitude > forest type. Thirdly, the impacts on the distribution and MPS of SSME were not due to a single factor, but rather a complex interplay of multiple factors. Finally, the construction of small hydropower stations significantly disrupted the hydrological connectivity of rivers, thereby altering the natural habitat of the SSME. The reduction in fish population, resulting from the loss of hydrological connectivity, adversely affected the MPS. Conversely, an increase in water temperature due to loss of hydrological connectivity positively impacted the MPS. However, these effects displayed heterogeneity across different rivers. Our study suggests that the construction of gravel dams may be a suitable approach in certain sections of the river, with a recommended height limit of 1.5 m. This research provides valuable insights for managers, offering a sustainable foundation for future energy planning and ecological restoration efforts.

Protecting the Last Wild River in Europe from Hydropower Development in Albania: An Environmental Movement Strategy in a Flawed Democracy

In 2014, as anti-hydropower plant protests in Albania intensified, an initiative to protect rivers in the Balkans known as “Save the Blue Heart of Europe” launched the Vjosa River Campaign in Albania to save what is known as the “Last Wild River in Europe.” The Campaign’s main goals consisted of preventing the construction of hydropower plants and turning the Vjosa into Europe’s first “Wild River National Park,” a status that would severely limit future development. But, this Campaign would not be easy. Albania is a highly centralized, fragile democracy with a long history of political oppression and economic struggle whose top-down government is still generally inaccessible to public interest groups or influence. The country relies entirely on hydropower for its electricity production, leading to high uncertainties in energy security, especially in face of increasing periods of drought. The Campaign organizers and activists would have to strategize carefully and creatively to navigate the Albanian political landscape to reach its goals. What did they do? What worked or didn’t work along the way? Finally, would hydropower, considered a renewable energy source with low carbon emissions, enhance the country’s energy security? Or, would hydropower development on the Vjosa just not be worth it as a national and cultural treasure is destroyed alongside local livelihoods related to fisheries, agriculture, and tourism? Upon reading this case study, readers will learn about how environmental campaign organizers and activists mobilize in the face of the complexities of hydropower development in Albania, a struggling democracy.

Optimizing hydropower development using a modified discharge beneath a dam with a controlled inundation at upstream reaches

Optimizing hydropower development using a modified discharge beneath a dam with a controlled inundation at upstream reaches

Economically optimal hydropower development with uncertain climate change

Climate change affects the planning, construction, operation and management of hydropower plants in various ways. Evaluating hydropower generation with nonstationary climate changes is important for planning electric power infrastructure development. For a new hydropower plant with climate change, specifying too large a reservoir may result in excessive investment if the future becomes drier, while too small a reservoir may cause insufficient utilization of hydropower resources. Whether to build a new hydropower station at once or build it dynamically in stages over time is challenged by uncertainty in future conditions. This study proposes a planning method for developing a flexible hydropower construction schedule to adapt to long-term uncertain hydrology with climate changes. Projected uncertain nonstationary hydrology scenarios were developed first, and Bayes’ theorem is used to update the probability of each scenario based on observed hydrologic conditions over time. A profit maximization model integrates stochastic dynamic programming and linear programming for a cascade hydropower system to evaluate hydropower plant expansion and how to build it dynamically with uncertain nonstationary climate conditions. In this, stochastic dynamic programming evaluates and prescribes inter-stage reservoir upgrades and linear programming prescribes inner-stage hydroelectric power generation. The case study of Jinsha cascade hydropower system in China’s Yunnan province illustrates the method. The intensity and trend of climate change effects on streamflow directly affect the optimized results. If streamflow decreases in the future, the best strategy is to build a small reservoir initially, without future changes. If streamflow increases in the future, it is better to build a small reservoir first, and gradually increase capacity according to observed changes in streamflow and economies of scale in capacity construction. If there is no clear trend in streamflow change, it is also better to build a small reservoir at first, then decide whether to expand the reservoir according to future observed changes in streamflow. This method with uncertain nonstationary climate change and upgrading adaptively with observed hydrology usually produced better results than optimization for a deterministic nonstationary hydrology.

Environmental and Economic Impacts of Hydropower Plants

The generating of electricity is the primary application of hydroelectric energy. The major components of hydroelectric power plants are dams, rivers, and turbines. Plants use dams to construct reservoirs that store water. The Importance of Hydropower In contrast to wind and solar, hydropower offers dispatch able electricity using low-risk methods. Hydropower is the most dependable and well-established source of clean, renewable energy. The potential energy of the water turbine and generator generates the vast bulk of hydroelectric power. One advantage of hydroelectric power is that it allows you to control the river flow downstream. Every country has difficulties due to how much of the total energy consumption it makes up. Encountered in the development of hydropower are noted. Connected to hydropower plants have the potential to offer additional advantages including flood control, irrigation, and water supply. Furthermore, hydropower is seen as a potential and sustainable source of energy, with a global economic influence.

Seismic Assessment of Underground Structures in the Weak Himalayan Rock Mass for Hydropower Development

This study focuses on the seismic assessment of underground structures in the transition of Higher Himalayan and Lesser Himalayan region of Nepal. Due to fragile geology of the Himalaya, most of the underground structures are constructed in the highly jointed rock mass. Rock mass classification approaches are extensively used for the estimation of supports without seismic consideration. Design of the underground structures like tunnels and cavern seismic effect is rarely considered in the Nepal Himalaya. For the sustainable development of hydropower project tunnel and caverns plays vital role in terms of its stability. Presence of faults, and crushed zone, along the alignment of tunnel, the existing in-situ stress increases beyond its critical level and strength. The long-term seismic behaviour of an underground structure is very essential in weak rock mass. A detailed dynamic analysis of underground response is evaluated using 2D numerical analysis with the geological data, rock mass and fault encountered in hydropower tunnel, through case study. A comparison is then made between the analysis result of the tunnel response with and without seismic consideration.

Mechanisms of Learning and Innovation in Project Performance: Evidence from Chinese Hydropower Industry

Hydropower, a renewable energy resource, underpins China’s economic and social advancement, gaining prominence amidst the country’s energy structure metamorphosis. Enhancing the performance of hydropower development projects is imperative, with the mechanisms of learning and innovation wielding a substantial impact. The extant literature on how learning and innovation affect hydropower project performance remains nebulous, lacking a systematic model to elucidate these impact mechanisms. This investigation melds theoretical analysis with the idiosyncrasies of hydropower project development, forging a theoretical model to decipher the interplay of learning, innovation, and project performance. Employing a mixed-methods approach, we probe the influence of organizational learning orientation and individual learning on participant capabilities, engineering innovation magnitude, and overall project performance. Path analysis divulges that organizational learning orientation catalyzes individual learning, jointly enhancing engineering innovation and project performance directly, although the effect on each participant’s capability necessitates mediation through the engineering innovation level. This pioneering study establishes the links and influence trajectories between learning, innovation, and project performance, systematically delineating them. It fills a scholarly void in exploring learning and innovation mechanisms within hydropower project development, propounding strategies to augment project efficiency and furnishing pragmatic, constructive insights for better engineering practice outputs.

Optimal reservoir operation for transport timescales using an integrated methodology

Dam construction hinders the transport process of water constituents, resulting in various water quality issues in reservoir areas that impede the sustainable development of hydropower. Conventional reservoir operation optimizations to address these issues face challenges in mathematizing multiple water quality objectives and solving high-dimensional computational problems. Taking a comprehensive perspective, we propose a methodology that incorporates the concept of transport timescales into optimal reservoir operation. Firstly, a specific transport timescale is estimated through numerical tracer experiments using a 3D hydrodynamic model. Subsequently, a surrogate model is developed to approximate the hydrodynamic model for computationally efficient estimation. Finally, we employ a non-dominated ranking genetic algorithm, combined with the surrogate model, to search for a Pareto-optimal solution for multiple objectives. As a case study, we selected flushing time as the representation of transport timescales and applied it to Xiangxi Bay (XXB) in the Three Gorges Reservoir, which has experienced serious water quality problems since dam construction. Our results show that under the optimal operation scheme, the average flushing time for the entire XXB is 23.991 d, which represents a 10.9% reduction compared to the practical operation scheme. The reduction rate of flushing time along XXB shows a monotonically increasing trend towards the reservoir mainstream, with a maximum reduction of 90.9%. The proposed methodology provides a heuristic tool that links optimal reservoir operation and the transport process of holistic water constituents for comprehensive water quality management in reservoirs.

High-resolution mapping of land use changes in Norwegian hydropower systems

The Transition towards sustainable energy systems requires phasing out fossil fuels. Hydropower is a key source of renewable energy and can contribute to reaching a 100 % low carbon-based energy system. Uncertainty remains about land cover changes due to hydropower deployment with a widespread perception of major losses in the land from inundation and associated habitat loss in the surrounding areas due to improved access and recreational use. Norway has a dominant share of hydropower generation in Europe with knowledge gaps in the associated land cover changes. We conducted one of the first retrospective analyses of land use change associated with hydropower development in Norway during the last 80 years. Using remote sensing data, we performed object-based analysis on sets of aerial images representing land systems before and after hydropower construction. We quantified the change in the land due to development of 40 hydropower schemes representing 24 % of the total Norwegian installed capacity. Our analysis revealed that 88 % of analyzed reservoirs were developed by regulating or expanding natural lakes. Vegetation growth was observed in the surrounding regions of 22 of 40 schemes, while urbanization was limited to only 0.9 % of the total surrounding area, primarily located within 400 m from reservoir's borders. Our findings provide insights into interaction between land use change and hydropower development in Norway. Our work provides a basis for further assessment of relevant environmental impacts and can be used to quantify expected land changes due to an increase in Norway's hydropower with integration into the European energy market.

The state of energy in sub-Saharan Africa and the urgency for small hydropower development

There exist several renewable energy resources within the African continent. Quite a lot of attempts have been made to study these small hydroelectric sites and ways to harness them. Nevertheless, the majority of these potential sites remain undeveloped. Several countries within the African region such as Togo, Tanzania, Kenya, Ghana, and many others continue to experience a cyclical national power crisis, which is mostly attributable to insufficient power output to meet the continuously rising demand. An increase in electricity demand is unavoidable as the nation works to grow its economy, and more electricity generation will be required to power both established and new sectors. Several villages within the sub-Saharan region have lived with no electrical energy access for several decades now. The majority of these nation's current power generation portfolio is made up of a combination of hydro and thermal power plants, and for a while now, any temporary increase in generation has been achieved by the addition of new thermal power plants, even though these fossil fuels are occasionally in short supply. The country enters a constant cycle of power rationing with serious negative effects on industry and homes due to seasonal reductions in water inflows into hydropower facilities and occasionally difficulty obtaining crude oil or natural gas. Potential problems of this energy crisis are the high demand for electricity caused by certain factors its supply challenges and the lack of structural supply of electricity to consumers.it is therefore important for the entire globe particularly the developed countries to alleviate Africa from the high energy demand and poverty as a result of the energy crisis.

Assessing the long-term impact of cascade hydropower development on the inundation patterns of floodplain wetlands

The inundation process of floodplain wetlands plays a crucial role in maintaining the balance of river ecosystems, which are highly sensitive to hydrological alteration. Nevertheless, the specific mechanisms through which these hydrological changes affect the inundation patterns of floodplain wetlands are still unclear. This study aimed to investigate the impact mechanism of cascade hydropower development on the inundation process of floodplain wetlands. Multitemporal remote sensing datasets and long-term hydrometeorological data series were utilized in this study. By employing the water appearance frequency (WAF) index, wetland hydrological stability assessment, and wavelet analysis, the inundation changes in floodplain wetlands and the underlying hydrological driving mechanisms were examined. The results revealed significant alterations in the inundation frequency of floodplain wetlands due to the construction of upstream dams. Specifically, the construction of the Danjiangkou and Wangfuzhou dams led to an increase in the total inundated area of Part A (16.09 km2) and Part B (76.93 km2), respectively. Conversely, the moderate frequency inundation zone in Part C decreased (26.7 km2) after the construction of the Cuijiaying Dam. The typical floodplain wetland 7 shifted from high to low (8.94 km2) stability after the construction of the Cuijiaying Dam. Furthermore, the cascade hydropower dam construction resulted in increased fluctuations in downstream water discharge. This study provides an effective approach to understanding the impact of cascade hydropower dams on the inundation process of floodplain wetlands.

Integrated impact assessment of climate change and hydropower operation on streamflow and inundation in the lower Mekong Basin

Water resources are key to economic development of the Mekong River Basin, but are threatened by climate change and affected by hydropower development. Knowledge of these drivers’ integrated impact on future hydrological alterations is limited, especially with respect to flood inundation in the lower basin. This study assesses streamflow and flood extent alterations by reservoir operations and climate change using the latest climate projections. A distributed hydrologic model is used to generate discharge and flood extent. Our findings indicate substantial changes in seasonal and annual peak discharge due to reservoir operations. Under the future hydropower scenario, the discharge at Kratie will change by + 28% ( − 10%) during the dry (wet) season. While the effects of hydropower operations vary by season, climate change tends to increase river discharge overall. Under the high-emission scenario, the wet seasonal flow at Kratie will increase by + 7% in the near-future (2026–2050), but change by -5% under integrated impact of climate change and reservoir operations. In the far-future, the wet seasonal flow at Kratie under climate change only (integrated impact) will increase by + 33% (+ 19%). Although climate change is the dominant driver of flow alterations, hydropower development is critical for reducing discharge and flood magnitude. Nonparametric statistical testing shows significant changes in the inundated area by up to + 37% during the projected periods.

The effects of simulated hydropower turbine rapid decompression on two Neotropical fish species

Barotrauma is a major cause of injury and mortality of fish as they pass through hydropower turbines. Current understanding of hydropower related barotrauma is biased towards northern temperate and southern subtropical species with single chambered swim bladders, specifically North American and Australian species, respectively. Today, unprecedented hydropower development is taking place in Neotropical regions where many species have complex multi-chambered swim bladder architecture. This study investigated barotrauma in two dual-chambered physostomous Neotropical fish (pacu, Piaractus mesopotamicus, and piracanjuba, Brycon orbignyanus) exposed to rapid (< 1 s) decompression at different Ratios of Pressure Change (RPC), using a hypo-hyperbaric chamber. The incidence and intensity (percentage surface area of organ affected) of injury and physiological and behavioural response (hereafter just response) of each species immediately after decompression was assessed. Twenty-two injury types (e.g. gill haemorrhage and exophthalmia) and eight response categories (e.g. rising to the surface and loss of orientation) were identified and the influence of: 1) species, 2) RPC, and 3) swim bladder rupture on each was quantified. There was considerable interspecific difference with emboli type injuries occurring more frequently in piracanjuba, but injury intensity tending to be higher in pacu. Both swim bladder chambers tended to rupture in piracanjuba but only the anterior chamber in pacu. RPC was positively correlated with response, incidence and intensity of several injury types for both species with some injuries occurring at very low RPC (e.g. 50 % probability of swim bladder rupture at 2.2 and 1.75 for piracanjuba and pacu, respectively). Multiple responses (e.g. loss of orientation) and injuries (e.g. eye haemorrhage) were correlated with swim bladder rupture suggesting gas venting into the body cavity likely causes secondary injury. When directly comparing our results with those available in the published literature, both pacu and piracanjuba appear to be more susceptible to barotrauma than previously studied subtropical and temperate species.

Public attitudes toward hydropower in China: The role of information provision and partisan identification

The development of hydropower projects needs public support. Although China has led the world in hydropower development during the past few decades, little is known about how the Chinese public views existing hydropower projects and future hydropower development plans. Based on an online survey experiment (N = 2971), this study investigates the effects of five types of information provision, including (1) power generation benefit, (2) emission reduction benefit, (3) flood control, navigation and grid benefits, (4) negative environmental impact and (5) involuntary migration impact of hydropower, and partisan identification on public attitudes to China's hydropower policy and most representative hydropower project, the Three Gorges Project. First, information provision about the benefits of power generation has no significant effect on public attitudes to the Three Gorges Project and China's hydropower development plans. Second, information provision about the benefits of emission reduction and flood control, navigation and grid effects can significantly increase public evaluation of the Three Gorges Project, but does not influence public support for abstract hydropower development plans. Third, information provision about the negative impacts on the environment and involuntary migration can significantly decrease public evaluation of the Three Gorges Project and support for hydropower development plans. Finally, Chinese Communist Party members have more positive attitudes to China's hydropower development plans and the Three Gorge Project than the non-members, and they are more responsive to environmental information but less responsive to the migration issue.