Time Lag Response Research Articles

Distinctive water bodies surrounding lakes: An effective indicator for drought monitoring and assessment

The response mechanisms of surface water to drought and the potential and performance of water body changes in drought monitoring and assessment remain insufficiently elucidated. We take the Poyang Lake Basin, which suffers from drastic water body changes and frequent droughts, as a representative. Through integrating multisource data to extract long-term precise water bodies, we construct standardized water body area/number anomaly indices (SAAI/SNAI). Subsequently, we quantify the correlation and time lag response between SAAI, SNAI and drought. Our findings reveal that overall, water body area and number in the Poyang Lake Basin all exhibit a significant correlation with typical drought indices. Among them, the large water body area has a higher correlation coefficient with drought, making it a more effective indicator for drought monitoring. Water body changes of Poyang Lake surrounding area offer a more precise reflection of drought conditions than other sub-basins and exhibit greater sensitivity to drought. Meanwhile, water body area changes in Poyang Lake surrounding area lag behind meteorological drought by approximately half a month. And the basin’s water body area can typically respond with changes to some prolonged and severe hydrological droughts about 1 to 2 months in advance. We propose an integrated mechanism for drought monitoring and assessment informed by these conclusions and use actual drought events for qualitative validation. The results indicate that it is possible to assess water body drought conditions for the next approximately half month based on current meteorological drought conditions. Also, combining water body area changes with meteorological drought severity can aid in evaluating hydrological drought conditions for the following about 1–2 months. We extend our investigation to explore the universality of these phenomenon across eight shallow lakes globally characterized by significant water fluctuations. The results reveal that the water body changes in most of these lakes exhibit good potential for drought monitoring and assessment, and present a strong consistency with deep soil moisture, allowing for the accurate reflection of deep soil drought conditions. The lag response patterns between water bodies and drought in Dongting Lake, Hongze Lake, and Tonlé Sap Lake—also situated in the monsoon climate zone—are more similar to those observed in Poyang Lake. These distinctive lake water bodies can serve as an innovative indicator for drought monitoring and assessment, providing potential support for endeavors in drought prevention and mitigation.

Long-term trend forecast of chlorophyll-a concentration over eutrophic lakes based on time series decomposition and deep learning algorithm

Long-term trend forecast of chlorophyll-a concentration (Chla) holds significant implications for eutrophication management and pollution control planning on lakes, especially under the background of climate change. However, it is a challenging task due to the mixture of trend, seasonal and residual components in time series and the nonlinear relationships between Chla and the hydro-environmental factors. Here we developed a hybrid approach for long-term trend forecast of Chla in lakes, taking the Lake Taihu as an instantiation case, by the integration of Seasonal and Trend decomposition using Loess (STL), wavelet coherence, and Convolutional Neural Network with Bidirectional Long Short-Term Memory (CNN-BiLSTM). The results showed that long-term trends of Chla and the hydro-environmental factors could be effectively separated from the seasonal and residual terms by STL method, thereby enhancing the characterization of long-term variation. The resonance pattern and time lag between Chla and the hydro-environmental factors in the time-frequency domain were accurately identified by wavelet coherence. Chla responded quickly to variations in TP, but showed a time lag response to variations in WT in Lake Taihu. The forecasting method using multivariate and CNN-BiLSTM largely outperformed the other methods for Lake Taihu with regards to R2, RMSE, IOA and peak capture capability, owning to the combination of CNN for extracting local features and the integration of bidirectional propagation mechanism for the acquisition of higher-level features. The proposed hybrid deep learning approach offers an effective solution for the long-term trend forecast of algal blooms in eutrophic lakes and is capable of addressing the complex attributes of hydro-environmental data.

Assessing the Ecological Quality Status in tropical Indian estuaries: testing the applicability of benthic foraminiferal indices.

The ecological quality status (EcoQS) of Vellar and Uppanar estuaries (Southeast coast of India) has been monitored monthly, using a combination of foraminiferal (Foram Stress Index: FSI and exp(H'bc) indices and abiotic (Pollution Load Index: PLI, Dissolved Oxygen: DO, and Total Organic Carbon: TOC) parameters. The Uppanar Estuary shows relatively higher values of PLI and TOC and lower DO values than Vellar Estuary. The highest value of TOC and PLI are recorded during the monsoon season. These variations are well mirrored by the change in exp(H'bc) and FSI. The lowest values of exp(H'bc) are observed with the monsoon season and could be ascribed by an overall reduction of salinity, and to the highest level of TOC and PLI in response to enhanced river discharge. The FSI also exhibits great variability with significant higher values in the Vellar Estuary than in the Uppanar Estuary. The EcoQS evaluated by a combination of pollution- (i.e., PLI, TOC and DO) and foraminiferal-based [i.e., FSI and exp(H'bc)] indices are highly consistent (73.4%). The most frequent disagreement among indices is mostly associated to Uppanar Estuary and, particularly, in the inner stations. This difference might be related to a time-lag response of benthic foraminifera in terms of diversity and assemblages' compositions as well as of the pollution indicators in response to enhanced riverine input. This study further supports the application of foraminiferal-based indices in EcoQS assessment in transitional environments including tropical Indian estuaries. It also fills the gap of knowledge by providing a seasonal perspective on the variation of EcoQS based on a monthly-scale sampling.

PERFORMANCE IMPROVEMENT OF TRANSIENT PULSATING FLOW IN ROOT CANAL IRRIGATION AND FLOW MECHANISM ANALYSIS

Inflow conditions dominate the process of root canal irrigation, and the application of pulsating inflow in dentistry is necessary to be explored due to its mass transfer enhancement capability. A prepared root canal model with a 30G side-vented needle is numerically investigated under pulsating inflow with different frequencies and amplitudes. Root canal apical pressure, extending depth, and effective cleaning area are adopted to evaluate the safety, mass transfer capacity, and clean efficiency of the irrigation system. Time-averaged results show that the irrigation performance is improved with pulsating flow maintaining safety. Compared with steady cases, the extending depth and effective cleaning area are increased by up to 43.6% and 11.42%, respectively. Three typical cases with significant improvement are selected for transient analysis. Transient results show that the apical pressure and extending depth have instant response features, while the effective cleaning area has a time-lag response characteristic. It is convinced that the transient characteristic of the system results from the coupling effects of the pulsating effect, instantaneous flow rate, and Coanda effect. The internal flow distribution of root canal system is prompted under the optimal parameters combinations of pulsating conditions, in which mass transfer capacity and clean efficiency are enhanced with guaranteed safety.

Alternative vegetation trajectories through passive habitat rewilding: opposite effects for animal conservation

ContextPassive habitat rewilding after rural abandonment can affect wildlife differently depending on the type of habitats that it generates.ObjectiveEvaluate and compare the effects of two alternative vegetation trajectories that occur through passive habitat rewilding in Mediterranean ecotone areas (crop-scrub and crop-pine forest transitions) on the long-term population dynamics of animal species.MethodsWe used the spur-thighed tortoise (Testudo graeca), a characteristic long-lived species of cultural landscapes, as study species. We applied a spatially explicit and individual-based model (STEPLAND) to simulate the movement and demographic processes in a long-term period, by comparing an “impact scenario” (i.e., historical land-use changes) to a “control scenario” (no land-use changes).ResultsThe two landscape scenarios resulted in different population trends. In the crop-scrub scenarios (control and impact), population densities increased similarly over time. However, the crop-pine forest scenario negatively affected population density throughout the simulation period, and showed a time-lag response of three decades. The extinction risk was 55% with a time-lag response of approximately 110 years.ConclusionsOur study highlights the need to analyse the legacy effects on long-lived ectotherms, using them as a proxy to understand the future effects of dynamic landscapes created by “passive habitat rewilding”. Our results showed how traditional agriculture in Mediterranean ecotone areas may generate “ecotone effects” (i.e. increase in demographical parameters), but also population extinction on long-lived ectotherms. Therefore, we consider it relevant to maintain traditional agricultural areas in Mediterranean landscapes, especially in ecotone areas associated with pine forests (generating mosaics with open habitats).

Time-Lag Response of Landslide to Reservoir Water Level Fluctuations during the Storage Period: A Case Study of Baihetan Reservoir

Fluctuations in reservoir water levels exert a strong triggering effect on landslides along reservoir banks, constituting a long-term concern in the safe operation of hydroelectric projects and in the prevention and management of geological disasters. While existing research has investigated the impact of periodic water level changes on the deformation of reservoir bank landslides, observation and detection of such deformation are challenging, with noticeable gaps in understanding how these deformations respond to water level changes during the water impoundment period. To address this, our study targets the Baihetan Reservoir, leveraging 567 ascending and descending LiCSAR data and LiCSBAS (the small-baseline subset within LiCSAR) technology to construct a time series of ground deformations in the study area from 2019 to 2023. The TLCC (Time Lag Cross Correlation) model was employed to examine the time-lag response pattern of reservoir bank landslide deformations to reservoir water level changes during the impoundment period. Our findings indicate a clear time-lag response in reservoir bank landslide deformations to water level changes during the impoundment process. The rise in water levels emerged as a primary factor influencing the instability of reservoir bank landslides. During the half-year impoundment period of the Baihetan Reservoir, a time lag of 5–7 days was observed between landslide deformations and increases in water levels, with landslides on the eastern and western banks exhibiting differing time-lag response patterns. Our study illuminates the time-lag effect between water level changes during reservoir impoundment and reservoir bank landslide deformation monitoring. By proposing a quantitative analysis methodology utilizing LiCSBAS technology and the TLCC model, our findings can inform decision-making in the field of disaster prevention and reduction in reservoir engineering.

Real-Time Hybrid Test Control Research Based on Improved Electro-Hydraulic Servo Displacement Algorithm

Real-time hybrid testing (RTH) is a test method for dynamic loading performance evaluation of structures, which is divided into digital simulation and physical testing, but the integration of the two may lead to problems such as time lag, large errors, and slow response time. The electro-hydraulic servo displacement system, as the transmission system of the physical test structure, directly affects the operational performance of RTH. Improving the performance of the electro-hydraulic servo displacement control system has become the key to solving the problem of RTH. In this paper, the FF-PSO-PID algorithm is proposed to control the electro-hydraulic servo system in real-time hybrid testing (RTH), which uses the PSO algorithm to operate the optimized PID parameters and the feed-forward compensation algorithm to compensate the displacement. First, the mathematical model of the electro-hydraulic displacement servo system in RTH is presented and the actual parameters are determined. Then, the objective evaluation function of the PSO algorithm is proposed to optimize the PID parameters in the context of RTH operation, and a displacement feed-forward compensation algorithm is added for theoretical study. To verify the effectiveness of the method, joint simulations were performed in Matlab/Simulink to compare and test FF-PSO-PID, PSO-PID, and conventional PID (PID) under different input signals. The results show that the proposed FF-PSO-PID algorithm effectively improves the accuracy and response speed of the electro-hydraulic servo displacement system and solves the problems of RTH time lag, large error, and slow response.

Time-Lag Effect: River Algal Blooms on Multiple Driving Factors

Compared to the eutrophication of lakes and reservoirs, the mechanism of river algal blooms in a flowing water body are more complicated, and often lead to serious consequence in catchment scale. Due to the simultaneous impact of a variety of environmental pressures, the water ecosystem integrity state often shows a response characteristic of accumulation, complexity and time lag, therefore it is difficult to use conventional hydrodynamic and water quality models to scientifically characterize and analyze. The lower Hanjiang River (HR) is an important influence area of the middle route of the South-to-North Water Diversion Project (SNWDP) in China, continuous river blooms issue has become a major national concern. In this study, a time-lag analysis approach was developed to identify the causes of algal blooms formation and the time-lag response law in the lower HR, including principal component analysis (PCA), grey relation analysis (GRA), and Almon Distributed Lag Model. Results found that, the hydrological regime (ΔH) contributes the most to the river bloom, especially due to the flow hindrance of the Yangtze River (YR) and the water project upstream. It is also found that the algal bloom outbreak in the lower HR is not an immediate response to the driving factors. It has a time lag of about 1 period (10 days) in the response with antecedent driving factors. Finally, we discussed the influence and its responding mechanism of ΔH on the growth of phytoplankton. The research can provide early warning for the prevention and control of algal blooms in the large river system.

Landscape patterns of catchment and land-use regulate legacy phosphorus releases in subtropical mixed agricultural and woodland catchments

Landscape composition and configuration determine the exchange of matter and energy among different landscape patches and may affect riverine phosphorus (P) exports derived from watershed legacy sources. However, a lack of understanding of landscape pattern effects on legacy P releases has yielded large uncertainties in mitigating watershed water quality using management practices or landscape planning. This study revealed the significance of legacy effect in the headwater catchments through the time-lag response of the long-term trend of river P exports to the change of net anthropogenic P input (NAPI). By constructing empirical statistical models that incorporated NAPI, hydroclimatic, terrain factors, soil chemical properties, and land use variables, the sources of annual riverine total phosphorus (TP) and dissolved inorganic phosphorus (DIP) exports were divided into current annual NAPI input and legacy sources inputs. The model estimations indicated that the contribution of legacy sources to riverine TP exports was 0.33–1.12 kg ha−1 yr−1 (50.7–82.8%), which was significantly higher than the contribution to DIP exports (0.18–0.49 kg ha−1 yr−1, 42.4–81.4%) in 2012–2017. Redundancy analysis (RDA) and variance partitioning analysis (VPA) methods were used to quantify the relative contribution of landscape patterns, soil P content, and terrain factors to legacy P releases. Results revealed that the relative contribution of the landscape composition and configuration to the total variations of legacy P releases was greater than that of the soil P and terrain factors. For different land use patches, a large area of woodland with a high aggregation degree and a large area of ponds with multiple net structures may significantly alleviate legacy P releases. In contrast, the legacy P releases were significantly positively associated with highly aggregated agricultural, tea plantation, and residential patches. This study provides theoretical support for strategies aiming to control legacy P from the perspective of landscape planning.

The moisture buffering performance of plasters when exposed to simultaneous sinusoidal temperature and RH variations

Wall constructions have the capacity to contribute to the passive regulation of indoor Relative Humidity. This property, referred to as moisture buffering, is linked to the hygroscopicity of materials, which allows materials to store and release moisture from and to the surrounding air, depending on the indoor Relative Humidity levels. Laboratory testing procedures, based on a step-response method, were introduced to quantify moisture buffering. The step response method monitors the change in mass of samples, when subjected to square wave humidity variation and constant temperature. However, those protocol's prescribed testing environmental conditions may not be representative of the materials behaviour in buildings, as the surface of walls is exposed to an indoor environment that changes with respect to the temperature and humidity daily and seasonally. This paper investigates the response of clay and gypsum plasters to quasi sinusoidal and simultaneous humidity and temperature functions. It was experimentally shown that the relative humidity influences the amount of water vapour adsorbed and desorbed by the materials, while temperature impacts the rate and the time lag response of clay and gypsum to the indoor humidity variation. The significance of the investigation is to demonstrate the joint effects of Relative Humidity and temperature on hygroscopic materials and to seek to developing a laboratory test, which can represent the real behaviour of such materials in buildings, which are exposed to sine wave-forms.

Detecting drought-induced GPP spatiotemporal variabilities with sun-induced chlorophyll fluorescence during the 2009/2010 droughts in China

In the parallel with the climate change, droughts have become one of the major climate extremes that induce losses in the terrestrial gross primary production (GPP). However, studying of the drought effects on GPP is still challenging, partly due to the lack of direct observations of GPP at large scales. Aiming to explore the potential of spaceborne sun-induced chlorophyll fluorescence (SIF) in monitoring vegetation droughts and quantifying the drought-induced GPP variabilities, we evaluated GOME-2 SIF with two state-of-art GPP products (i.e. FLUXCOM GPP and GLASS GPP) and flux tower observed GPP, using 2009 summer drought in Northeast China and 2010 spring drought in Southwest China as study cases. We found that SIF was a quantifying indicator of GPP and successfully characterized the temporal dynamics and spatial extents of GPP anomalies during the drought events, as well as accurately estimating the drought-induced GPP losses. Moreover, SIF (R2 = 0.87) performed better than enhanced vegetation index (R2 = 0.78) in capturing the photosynthesis changes induced by droughts, suggesting SIF was more sensitive to plant physiological changes. The strong positive correlations of SIF with Palmer drought severity index (PDSI) and root-zone soil moisture, further gave confidences on the capacity of SIF in vegetation drought monitoring. SIF had a time lag response to both PDSI and soil moisture, which might be attributable to the plants adaptation mechanisms for the drought occurrence and physiological recovery after water stress. Our study demonstrates that satellite-based SIF can achieve real-time vegetation drought monitoring and the assessment of drought-induced GPP anomalies at large scales, thus providing a unique opportunity to study the impacts of drought on vegetation carbon uptake.

Excessive positive response of model-simulated land net primary production to climate changes over circumboreal forests.

Land carbon cycle components in an Earth system model (ESM) play a crucial role in the projections of forest ecosystem responses to climate/environmental changes. Evaluating models from the viewpoint of observations is essential for an improved understanding of model performance and for identifying uncertainties in their outputs. Herein, we evaluated the land net primary production (NPP) for circumboreal forests simulated with 10 ESMs in Phase 5 of the Coupled Model Intercomparison Project by comparisons with observation-based indexes for forest productivity, namely, the composite version 3G of the normalized difference vegetation index (NDVI3g) and tree-ring width index (RWI). These indexes show similar patterns in response to past climate change over the forests, i.e., a one-year time lag response and smaller positive responses to past climate changes in comparison with the land NPP simulated by the ESMs. The latter showed overly positive responses to past temperature and/or precipitation changes in comparison with the NDVI3g and RWI. These results indicate that ESMs may overestimate the future forest NPP of circumboreal forests (particularly for inland dry regions, such as inner Alaska and Canada, and eastern Siberia, and for hotter, southern regions, such as central Europe) under the expected increases in both average global temperature and precipitation, which are common to all current ESMs.

Evaluating the relationship between drought and vegetation greenness in Chyulu-Amboseli Rangeland, Kenya

Remote sensing techniques have been widely used to monitor moisture-related vegetation conditions. Vegetation vigour response to drought however is complex and has not been adequately studied using satellite sensor data. This paper investigated the time lag response of vegetation to drought in Kenya’s Chyulu-Amboseli ecosystem based on Standardized Precipitation Index (SPI) derived from monthly precipitation data for the period January 2000-October 2016 downloaded from the Climate Hazards group InfraRed Precipitation with Stations and Normalized Difference Vegetation Index (NDVI) computed from Moderate Resolution Imaging Spectro-radiometer (MODIS) pre-processed images downloaded from the University of Natural Resources and Life Sciences (BOKU) database. Statistical analysis showed that drought severity increased over the study period while corresponding vegetation conditions degenerated. Results further revealed that the relationship between drought and vegetation greenness was significant (R2 = 0.6) with 2 months optimal lag. This calls for policy makers and programme managers to integrate the lag effect in measures to cope with drought in the rangelands.Keywords: Drought, Vegetation greenness, Chyulu-Amboseli, Statistical Analysis, Rangeland

Lucy in the sky with ketamine: Psychoactive drugs have potential for a major breakthrough in treating depression.

EMBO Reports (2018) e47118 “It felt like being in a pod […], like a little boat, going along through rooms [that had] white breathing walls.” This is how American standup comedian Neal Brennan described his experience with ketamine, a psychoactive drug also known as Special K in the club scene, in an interview with fellow comedian Joe Rogan. “I just couldn't get over the fact that this was happening in a doctor's office,” he said about taking ketamine as a medication against depression. > One may argue that treating psychologically unstable patients with an addictive drug that has psychedelic side effects is not a good idea. Ketamine was introduced commercially in the United States in 1970 as an anesthetic. At lower doses, it causes dissociations, out‐of‐body experiences, and hallucinations, which explains its career as club drug. But during the past two decades, it has also gained attention as a fast‐acting antidepressant. Its antidepressant effect was first noted by researchers at Yale University in the 1990s, and the effect was reproduced in a larger double‐blind, placebo‐controlled trial at the US National Institute of Mental Health, published in 2006. A number of studies have since shown the effectiveness of ketamine in treating patients with depression, suicidal ideation, and post‐traumatic stress disorder [1]. Researchers have called it the biggest breakthrough in depression research in half a century. Ketamine is not yet approved by regulatory agencies, but is widely used off‐label by private so‐called ketamine clinics. New medications to treat depression are urgently needed. The last significant innovation—Prozac, the first selective serotonin reuptake inhibitor (SSRI)—is now 30 years old, and SSRIs and many me‐too drugs of similar structure and function still dominate the treatment of depression. They are, however, anything but satisfactory. It takes 6–8 weeks for their effect to kick in, and …

Response of Grassland Degradation to Drought at Different Time-Scales in Qinghai Province: Spatio-Temporal Characteristics, Correlation, and Implications

Grassland, as the primary vegetation on the Qinghai-Tibet Plateau, has been increasingly influenced by water availability due to climate change in last decades. Therefore, identifying the evolution of drought becomes crucial to the efficient management of grassland. However, it is not yet well understood as to the quantitative relationship between vegetation variations and drought at different time scales. Taking Qinghai Province as a case, the effects of meteorological drought on vegetation were investigated. Multi-scale Standardized Precipitation Evapotranspiration Index (SPEI) considering evapotranspiration variables was used to indicate drought, and time series Normal Difference Vegetation Index (NDVI) to indicate the vegetation response. The results showed that SPEI values at different time scales reflected a complex dry and wet variation in this region. On a seasonal scale, more droughts occurred in summer and autumn. In general, the NDVI presented a rising trend in the east and southwest part and a decreasing trend in the northwest part of Qinghai Province from 1998 to 2012. Hurst indexes of NDVI revealed that 69.2% of the total vegetation was positively persistent (64.1% of persistent improvement and 5.1% of persistent degradation). Significant correlations were found for most of the SPEI values and the one year lagged NDVI, indicating vegetation made a time-lag response to drought. In addition, one month lagged NDVI made an obvious response to SPEI values at annual and biennial scales. Further analysis showed that all multiscale SPEI values have positive relationships with the NDVI trend and corresponding grassland degradation. The study highlighted the response of vegetation to meteorological drought at different time scales, which is available to predict vegetation change and further help to improve the utilization efficiency of water resources in the study region.

Numerical issues in modeling combustion instability by quasi-1D Euler equations

The present work is devoted to investigation of numerical issues related to combustion instability simulation through a quasi-1D Eulerian solver. The main aspects addressed are the choice of a suitable multispecies model and heat release response function formulation. Experimental data and high fidelity simulation results, available in literature, are reproduced with acceptable approximation. Main features of the flow field at limit cycle are shown. Moreover, a parametric study has been performed on time-lag response function characteristic parameters, leading to important conclusions on the pertinence of each assumption in the frame of a nonlinear tool.

Grassland gross carbon dioxide uptake based on an improved model tree ensemble approach considering human interventions: global estimation and covariation with climate.

Grassland ecosystems act as a crucial role in the global carbon cycle and provide vital ecosystem services for many species. However, these low-productivity and water-limited ecosystems are sensitive and vulnerable to climate perturbations and human intervention, the latter of which is often not considered due to lack of spatial information regarding the grassland management. Here by the application of a model tree ensemble (MTE-GRASS) trained on local eddy covariance data and using as predictors gridded climate and management intensity field (grazing and cutting), we first provide an estimate of global grassland gross primary production (GPP). GPP from our study compares well (modeling efficiency NSE=0.85 spatial; NSE between 0.69 and 0.94 interannual) with that from flux measurement. Global grassland GPP was on average 11±0.31 PgCyr-1 and exhibited significantly increasing trend at both annual and seasonal scales, with an annual increase of 0.023 Pg C (0.2%) from 1982 to 2011. Meanwhile, we found that at both annual and seasonal scale, the trend (except for northern summer) and interannual variability of the GPP are primarily driven by arid/semiarid ecosystems, the latter of which is due to the larger variation in precipitation. Grasslands in arid/semiarid regions have a stronger (33gCm-2 yr-1 /100mm) and faster (0- to 1-month time lag) response to precipitation than those in other regions. Although globally spatial gradients (71%) and interannual changes (51%) in GPP were mainly driven by precipitation, where most regions with arid/semiarid climate zone, temperature and radiation together shared half of GPP variability, which is mainly distributed in the high-latitude or cold regions. Our findings and the results of other studies suggest the overwhelming importance of arid/semiarid regions as a control on grassland ecosystems carbon cycle. Similarly, under the projected future climate change, grassland ecosystems in these regions will be potentially greatly influenced.

Recharge Estimation of Hard Rock Aquifers under Sahelian Climate Conditions Using Water Table Fluctuation: Case Study of Tougou Catchment, Burkina Faso

This study aims to characterize water table fluctuations and estimate groundwater recharge in the Tougou catchment located in the Sahel zone of Burkina Faso. Water table fluctuation and groundwater budget approaches are developed on an experimental site equipped with observation wells. The trends of water fluctuations in the different layers of the weathering profile are similar. There is a time-lag response of groundwater recharge to the daily precipitation occurrences. The interaction between the upper (clayey alteration) and lower (transition zone-fractured schist complex) parts of the weathering profile shows that generally the hydraulic head in the upper part is higher than that of the lower part due to difference in drainage porosity. The latter varies at the catchment scale between 0.006 and 0.009 and is inversely proportional to the saturated thickness of the clayey alteration layer. The groundwater recharge is annually estimated between 36 and 49 mm, which correspond to 6% and 9% of mean annual rainfall in the catchment. Annual evapotranspiration was estimated to be about 223 to 443 mm.

Reduced winter runoff in a mountainous permafrost region in the northern Tibetan Plateau

The degradation of mountain permafrost under climate warming may alter the runoff regime of high mountainous catchments. In this study, we evaluated the influence of permafrost on the hydrological regime using hydrological signals in the Yeniugou Basin located in a mountainous permafrost region in the Qilian Mountains of the northern Tibetan Plateau (TP). The effect of permafrost degradation on the hydrological response was assessed based on 28years of runoff and meteorological data. The results indicated that the investigated region exhibited a large increase in annual surface ground temperature from 1979 to 2006, with almost unchanged precipitation and evaporation potential. The winter runoff levels exhibited a significant decreasing linear trend, whereas the annual runoff and runoff in other seasons did not show any distinct linear trends. According to a comprehensive analysis of the relationships between winter runoff and meteorological factors, the ratio of maximum (Qmax) and minimum (Qmin) discharge, the recession coefficient and baseflow separation, and the reduced winter runoff were significantly correlated with thawing of permafrost. However, due to a time-lag response of climate forcing to permafrost thawing, some of these changes are undetectable over a short period. This study provides preliminary data on cold region hydrology and its response to climate change.

Dynamics of one-prey two-predator system with square root functional response and time lag

Animals grouping together is one of the most interesting phenomena in population dynamics and different functional responses as a result of prey–predator forming groups have been considered by many authors in their models. In the present paper we have considered a model for one prey and two competing predator populations with time lag and square root functional response on account of herd formation by prey. It is shown that due to the inclusion of another competing predator, the underlying system without delay becomes more stable and limit cycles do not occur naturally. However, after considering the effect of time lag in the basic system, limit cycles appear in the case of all equilibrium points when delay time crosses some critical value. From the numerical simulation, it is observed that the length of delay is minimum when only prey population survives and it is maximum when all the populations coexist.