Analysis of rainfall and temperature time series to detect long-term climatic trends and variability over semi-arid Botswana

Arid and semi-arid environments have been identified with locations prone to impacts of climate variability and change. Investigating long-term trends is one way of tracing climate change impacts. This study investigates variability through annual and seasonal meteorological time series. Possible inhomogeneities and years of intervention are analysed using four absolute homogeneity tests. Trends in the climatic variables were determined using Mann–Kendall and Sen’s Slope estimator statistics. Association of El Niño Southern Oscillation (ENSO) with local climate is also investigated through multivariate analysis. Results from the study show that rainfall time series are fully homogeneous with 78.6 and 50% of the stations for maximum and minimum temperature, respectively, showing homogeneity. Trends also indicate a general decrease of 5.8, 7.4 and 18.1% in annual, summer and winter rainfall, respectively. Warming trends are observed in annual and winter temperature at 0.3 and 1.5% for maximum temperature and 1.7 and 6.5% for minimum temperature, respectively. Rainfall reported a positive correlation with Southern Oscillation Index (SOI) and at the same time negative association with Sea Surface Temperatures (SSTs). Strong relationships between SSTs and maximum temperature are observed during the El Niño and La Niña years. These study findings could facilitate planning and management of agricultural and water resources in Botswana.     

Analysis of seasonal and annual rainfall trends for Ranchi district,Jharkhand, India

The aim of this study was to investigate temporal variation in seasonal and annual rainfall trend over Ranchi district of Jharkhand, India for the period (1901–2014: 113 years). Mean monthly rainfall data series were used to determine the significance and magnitude of the trend using non-parametric Mann–Kendall and Sen’s slope estimator. The analysis showed a significant decreased in rainfall during annual, winter and southwest monsoon rainfall while increased in pre-monsoon and post-monsoon rainfall over the Ranchi district. A positive trend is detected in pre-monsoon and post-monsoon rainfall data series while annual, winter and southwest monsoon rainfall showed a negative trend. The maximum decrease in rainfall was found for monsoon (? 1.348 mm year^?1) and minimum (? 0.098 mm year^?1) during winter rainfall. The trend of post-monsoon rainfall was found upward (0.068 mm year^?1). The positive and negative trends of annual and seasonal rainfall were found statistically non-significant except monsoon rainfall at 5% level of significance. Rainfall variability pattern was calculated using coefficient of variation CV, %. Post-monsoon rainfall showed the maximum value of CV (70.80%), whereas annual rainfall exhibited the minimum value of CV (17.09%), respectively. In general, high variation of CV was found which showed that the entire region is very vulnerable to droughts and floods.     

The chaotic time series of Indian monsoon rainfall and its prediction

The time series of Indian summer monsoon rainfall for the period 1871–1989 has been analysed using the method of deterministic chaos. It is found that a strange attractor underlies the time series implying the existence of a prediction function. This function has been approximated by a second-degree polynomial, involving the rainfalls of the past seven years and the coefficients have been estimated by least squares fit. The interannual variations of actual and computed rainfalls have been presented for a comparative study.     

Fluoride contamination of groundwater and its seasonal variability in parts of Purulia district,West Bengal,India

The contamination of aquifers by fluoride and arsenic is a major cause of concern in several parts of India. A study has thus been conducted to evaluate the extent and severity of fluoride contamination and also its seasonal variability. Two blocks (Purulia-1 and Purulia-2) were considered for this purpose. Twenty groundwater samples (in each season) were collected from tube wells during the pre-monsoon and post-monsoon seasons. In addition to fluoride, groundwater samples were also analyzed for major cations, anions, and other trace elements. The concentration of fluoride shows significant seasonal variation and ranges between 0.94–2.52 and 0.25–1.43 mg/l during the pre-monsoon and post-monsoon seasons, respectively. In pre-monsoon season, more than 40% of the water samples show fluoride concentrations higher than the WHO limit. However, during the post-monsoon season, none of the groundwater sample shows fluoride concentrations higher than the WHO limit. Lesser concentration during the post-monsoon season is attributed to the dilution effect by the percolating rainwater, which has also been reflected in the form of a decrease in concentrations of other elements. The petrographic studies of the rock samples collected from the study area show that the rocks are mainly composed of plagioclase, orthoclase, and quartz with abundant biotite. The weathering and dissolution of biotite plays an important role in controlling the fluoride concentrations in the groundwater of the study area.     

流域降雨径流时间序列的混沌识别及其预测研究进展

混沌和随机在本质上是两种不同的特征,对这两种特征的描述方法各不相同,确定流域降雨径流时间序列的混沌性和随机性是对其进行模拟和预测的重要基础。近10多年来,许多学者相继开展了流域降雨径流时间序列的混沌识别及其预测研究。着重回顾其中最为重要的相空间重构、混沌识别和混沌预测方法,对将混沌理论应用于降雨径流时间序列的限制条件(序列的数据量大小和数据噪声)也进行了探讨。     

Identification of trends in rainfall,rainy days and 24 h maximum rainfall over subtropical Assam in Northeast India

Trends in rainfall, rainy days and 24 h maximum rainfall are investigated using the Mann-Kendall non-parametric test at twenty-four sites of subtropical Assam located in the northeastern region of India. The trends are statistically confirmed by both the parametric and non-parametric methods and the magnitudes of significant trends are obtained through the linear regression test. In Assam, the average monsoon rainfall (rainy days) during the monsoon months of June to September is about 1606 mm (70), which accounts for about 70% (64%) of the annual rainfall (rainy days). On monthly time scales, sixteen and seventeen sites (twenty-one sites each) witnessed decreasing trends in the total rainfall (rainy days), out of which one and three trends (seven trends each) were found to be statistically significant in June and July, respectively. On the other hand, seventeen sites witnessed increasing trends in rainfall in the month of September, but none were statistically significant. In December (February), eighteen (twenty-two) sites witnessed decreasing (increasing) trends in total rainfall, out of which five (three) trends were statistically significant. For the rainy days during the months of November to January, twenty-two or more sites witnessed decreasing trends in Assam, but for nine (November), twelve (January) and eighteen (December) sites, these trends were statistically significant. These observed changes in rainfall, although most time series are not convincing as they show predominantly no significance, along with the well-reported climatic warming in monsoon and post-monsoon seasons may have implications for human health and water resources management over bio-diversity rich Northeast India.     

Nitrate contamination in groundwater of Sopore town and its environs,Kashmir, India

An attempt has been made in this research work to evaluate the concentration of nitrate in groundwater and its management in Apple town and its environs. Groundwater pollution has been reported in many aquifers because of high concentration of nitrate in ground water, which is the result of excessive use of fertilizers to cropland. Systematic sampling was done, with a view to understand the source of nitrate concentration in the study area. Fifteen sample sites were selected and the samples were taken for a baseline study to understand the geochemistry of the study area and to assess its physicochemical characteristics. The water quality parameters were investigated for summer (May, 2007) and winter (December, 2007) seasons and were compared with the standard values given by ICMR / WHO. The hydrochemical data of 15 samples indicates that the concentration of almost all parameters fall within the permissible limits except nitrate. Linear Trend Analysis on seasonal and annual basis clearly depicted that nitrate pollution in the study area is increasing significantly. About 85% of samples during summer season and 67% of the samples during winter season were showing a high concentration of nitrate, exceeding permissible limit of WHO (50 mg/l), which is due to the use of nitrogenous fertilizers in the study area. Appropriate methods for improving the water quality and its management in the affected areas have been suggested.     

Inter-annual variability of summer monsoon rainfall over Orissa (India) in relation to cyclonic disturbances

The summer monsoon rainfall over Orissa, a state on the eastern coast of India, is more significantly related than Indian summer monsoon rainfall (ISMR) to the cyclonic disturbances developing over the Bay of Bengal. Orissa experiences floods and droughts very often due to variation in the characteristics of these disturbances. Hence, an attempt was made to find out the inter-annual variability in the rainfall over Orissa and the frequencies of different categories of cyclonic disturbances affecting Orissa during monsoon season (June–September). For this purpose, different statistical characteristics, such as mean, coefficient of variation, trends and periodicities in the rainfall and the frequencies of different categories of cyclonic disturbances affecting Orissa, were analysed from 100 years (1901–2000) of data. The basic objective of the study was to find out the contribution of inter-annual variability in the frequency of cyclonic disturbances to the inter-annual variability of monsoon rainfall over Orissa. The relationship between summer monsoon rainfall over Orissa and the frequency of cyclonic disturbances affecting Orissa shows temporal variation. The correlation between them has significantly decreased since the 1950s. The variation in their relationship is mainly due to the variation in the frequency of cyclonic disturbances affecting Orissa. The variability of both rainfall and total cyclonic disturbances has been above normal since the 1960s, leading to more floods and droughts over Orissa during recent years. The inter-annual variability of seasonal rainfall over Orissa and the frequency of cyclonic disturbances affecting Orissa during monsoon season show a quasi-biennial oscillation period of 2–2.8 years. There is least impact of El Nino southern oscillation (ENSO) on inter-annual variability of both the seasonal rainfall over Orissa and the frequencies of monsoon depressions/total cyclonic disturbances affecting Orissa.     

Nitrate pollution and its distribution in the groundwater of Srikakulam district, Andhra Pradesh, India

The complex depositional pattern of clay and sand in most of the areas controlled the vertical and lateral movement of nitrate in groundwater. The variation of nitrate concentration at different groundwater levels and the lateral distribution of nitrate in the groundwater at two sites indicated the filtration of nitrate by clayey formations. A rural agricultural district located in the Vamsadhara river basin, India was selected for studying the lateral and vertical distribution of nitrate in the groundwater and the association of nitrate with other chemical constituents. The nitrate concentrations in the groundwater are observed to vary between below detectable limit and 450 mg NO₃/L. The sources for nitrate are mainly point sources (poultry farms, cattleshed and leakages from septic tanks) and non-point sources (nitrogenous fertilisers). The nitrate concentrations are increased after fertiliser applications. However, very high concentrations of nitrate are derived from animal wastes. Relatively better correlations between nitrate and potassium are observed (R = 0.74 to 0.82). The better relationship between these two chemical constituents in the groundwater may be due to the release of potassium and nitrate from both point and non-point sources. The nitrate and potassium concentrations are high in the groundwater from clayey formations.     

Identifying trends in groundwater quality using residence time indicators: an example from the Permian aquifer of Dumfries, Scotland

The Permian sandstone and breccia aquifer of Dumfries has an important role in supplying water to the principal town in southwest Scotland. The area comprises mainly pastoral farmland with some industry and fish farming. Ongoing development of the aquifer has revealed the existence of complex groundwater flow through fractures and increasing nitrate concentrations. To further investigate these issues, the age and quality of groundwater throughout the aquifer has now been assessed using standard hydrogeochemical techniques together with CFCs and SF₆ as residence time indicators. The aquifer consists of sandstone- and breccia-dominated units: the Locharbriggs Sandstone in the east and the Doweel Breccia in the west. Groundwater throughout the aquifer is of Ca–Mg–HCO₃ type and moderately mineralised; pH is near neutral. The observed groundwater chemistry is the product of maritime rainfall modified by the dissolution of carbonate material in the breccia, sandstone and surficial deposits. CFC and SF₆ concentrations are interpreted on the basis of mixing between older (>50 years) and recent (1990s) components. Although there is generally a higher proportion of older water within the Locharbriggs Sandstone compared to the Doweel Breccia, stable isotope evidence suggests that the older water component in the interbedded sandstones of the breccia is of much greater antiquity, possibly containing an element of palaeowater. Concentrations of nitrate across the aquifer can be directly related to the amount of recent recharge. Modern groundwater contains approximately 9 mg l^–1 NO₃-N and pre-1950s groundwater has approximately 2 mg l^–1 NO₃-N. Nitrate concentrations measured at individual boreholes are explained by the relative proportions of modern and pre-1950s groundwater. If current practices continue, the concentrations of nitrate measured across the Dumfries Basin will rise as the proportion of pre-1950s groundwater diminishes.

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Resumen El acuífero de areniscas y brechas Pérmicas de Dumfries desempeña un papel importante en el abastecimiento a la ciudad principal del Sudoeste de Escocia. El área comprende sobretodo tierras de pastoreo y granjas, junto con algunas industrias y piscifactorías. El desarrollo iniciado en el acuífero ha revelado la existencia de un complicado flujo subterráneo a través de las fracturas y de un aumento progresivo en la concentración de nitrato. Con el fin de profundizar en el conocimiento de estos temas, se ha determinado la edad y calidad de las aguas subterráneas en todo el acuífero por medio de técnicas hidrogeoquímicas estándar y de indicadores del tiempo de residencia como los clorofluorcarbonados (CFCs) y el fluoruro de azufre (SF₆). El acuífero está formado por las areniscas de Locharbriggs, al Este, y las brechas de Doweel, hacia el Oeste. Las aguas subterráneas son de tipo bicarbonatadas cálcico-magnésicas y presentan una mineralización moderada, mientras que el pH es prácticamente neutro. La química de las aguas subterráneas es el resultado del aerosol marino modificado por la disolución de materiales carbonatados en las brechas, areniscas y depósitos superficiales. Las concentraciones de CFCs y SF₆ se interpretan a partir de una mezcla de aguas entre una componente antigua (más de 50 años) y una reciente (de la década de 1990). Aunque en general se da una mayor proporción de aguas antiguas en las areniscas de Locharbriggs que en las Brechas de Doweel, los isótopos estables sugieren que la componente de aguas antiguas en las intercalaciones de areniscas que aparecen en la formación de brechas es mucho más antigua, y que, posiblemente, se trate de paleoaguas. Las concentraciones de nitrato en el acuífero pueden ser relacionadas directamente con la aportación de recarga reciente. Las aguas subterráneas modernas contienen aproximadamente 9 mg l^–1 de nitrato, mientras que las aguas subterráneas anteriores a 1950 tienen unos 2 mg l^–1. Se puede explicar las concentraciones de nitrato en pozos individuales por las proporciones relativas de aguas subterráneas modernas y anteriores a 1950. Si las prácticas actuales continúan, se producirá un aumento de las concentraciones de nitrato en la cuenca de Dumfries debido a la disminución de la proporción de aguas antiguas.

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Résumé L'aquifère des grès et brèches du Permien de Dumfries joue un rôle important dans l'alimentation en eau de la principale ville du sud-ouest de l'Écosse. La région est principalement soumise à de l'élevage pastoral avec quelques industries et des piscicultures. La progression de l'exploitation de cet aquifère a révélé l'existence d'un écoulement souterrain complexe en fractures et des concentrations en nitrate croissantes. Dans le but d'étudier ces deux points plus en détail, l'âge et la qualité de l'eau souterraine dans tout l'aquifère ont été évalués en utilisant des techniques hydrogéochimiques conventionnelles avec les CFC et SF₆ comme marqueurs du temps de séjour. L'aquifère est constitué par des unités dominées par des brèches et des grès: les grès de Locharbriggs à l'est et les brèches de Doweel à l'ouest. L'eau souterraine dans tout l'aquifère a un faciès bicarbonaté calcique et magnésien et est moyennement minéralisée; le pH est proche de la neutralité. Le chimisme observé de l'eau souterraine résulte des apports marins par la pluie modifiés par la dissolution du matériau carbonaté des brèches, des grès et des formations superficielles. Les concentrations en CFC et SF₆ sont interprétées sur la base d'un mélange entre des composantes ancienne (>50 ans) et récente (années 1990). Bien qu'il y ait en général une plus forte proportion d'eau ancienne dans les grès de Locharbriggs que dans la brèche de Doweel, les isotopes stables suggèrent que la composante d'eau ancienne dans les grès interstratifiés des brèches est beaucoup plus ancienne, contenant probablement un élément d'eau fossile. Les concentrations en nitrate dans l'aquifère peuvent être directement reliées au taux de recharge récente. L'eau souterraine moderne contient approximativement 9 mg l^–1 en NO₃-N et l'eau souterraine d'avant 1950 environ 2 mg l^–1 en NO₃-N. Les concentrations en nitrate mesurées dans des forages individuels sont expliquées par des proportions relatives d'eaux souterraines moderne et antérieure à 1950. Si les pratiques actuelles continuent, les concentrations en nitrate mesurées dans le bassin de Dumfries augmenteront alors que la part de l'eau souterraine d'avant 1950 diminuera.

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First report of Ranikothalia Caudri from Middle Andaman Island, India and its significance

Genus Ranikothalia Caudri is described for the first time from the Upper Palaeocene sediments of Middle Andaman Island. Three species R. sidensis, R. cf. nuttalli, R. cf. tobleri along with one species of Discocyclina are described here. The occurrence of Ranikothalia has great implication in understanding the stratigraphy of the island and in deciphering the palaeogeography of the area. This point to the extension of the Ranikot Sea at least up to Middle Andaman.     

全国地下水质分布及变化特征

以2013—2017年地下水监测站点水质监测数据为基础,统计地下水质监测指标的变化特征,筛查影响地下水质的主要指标,研究地下水质变化规律。选取2013—2017年具备连续监测数据的地下水监测井,对常规20项监测指标进行分析。研究发现:就监测站点水质指标而言,总硬度、铁、锰、“三氮”等超标率均达到了10%及以上,是导致地下水水质恶化的主要指标。总硬度超标集中在华北、东北、西南和西北地区的监测井,超标率在各省市间差别较大。氨氮超标率在各省市地区的监测井中差别较大,超标较为严重的省份是黑龙江、江苏、广东和宁夏。硝酸盐氮超标率年际变化稳定,华北、东北和西北地区的监测井中硝酸盐氮超标较为严重。亚硝酸盐氮超标在华北、东北和西北,以及上海、江苏、湖北、广西和贵州的监测井中较为严重。铁、锰超标主要集中在华北、华东、中南地区的监测井中,东三省、安徽、湖北、四川、宁夏等省份尤其严重。基于地下水监测井统计数据,在全国尺度上对地下水质量进行了综合分析评价,总结出了地下水监测中需要着重关注的指标,如“三氮”总硬度,铁、锰等。     

On the validity of time-predictable model for earthquake generation in north-east India

North-east India is seismically very active and has experienced many widelydistributed shallow, large earthquakes. Earthquake generation model for the region was studied using seismicity data [(1906–1984) prepared by National Geophysical Data Centre (NGDC), Boulder Colorado, USA]. For establishing statistical relations surface wave magnitudes (M _s≥5·5) have been considered. In the region four seismogenic sources have been identified which show the occurrences of atleast three earthquakes of magnitude 5·5≤M _s≤7·5 giving two repeat times. It is observed that the time interval between the two consecutive main shock depends on the preceding main shock magnitude (M _p) and not on the following main shock magnitude (M _f) revealing the validity of time predictable model for the region. Linear relation between logarithm of repeat time (T) and preceding main shock magnitude (M _p) is established in the form of logT=cM _p+a. The values ofc anda are estimated to be 0–36 and 1–23, respectively. The relation may be used for seismic hazard evaluation in the region.     

Effect of intraband variability on stable isotope and density time series obtained from banded corals

Density, δ¹⁸O and δ¹³C were measured along two tracks, one close to the central growth axis and the other, ∼20ℴ off the axis, in a coral (Porites lutea) collected from the Stanley Reef, Central Great Barrier Reef, Australia. The δ¹⁸O variations in the coral are well correlated with sea surface temperature changes. The common variances between the two tracks were about 60% in the δ¹⁸O, δ{13}C, and the skeletal density variations. Part of the noise (40%) could be due to the difficulty of sampling exactly time contemporaneous parts of each band along the two tracks and part of it could be due to genuine intraband variability. In spite of the intraband variability, the time series obtained from the two tracks are similar, indicating that the dominant causative factor for the isotopic variations is external, i.e., the environmental conditions that prevail during the growth of the coral; density band formation does not appear to be directly controlled by the sea surface temperature.     

Using time series analysis to assess tidal effect on coastal groundwater level in Southern Laizhou Bay,China

Sea water intrusion is an environmental problem cause by the irrational exploitation of coastal groundwater resources and has attracted the attention of many coastal countries. In this study, we used time series monitoring data of groundwater levels and tidal waves to analyze the influence of tide flow on groundwater dynamics in the southern Laizhou Bay. The auto-correlation and cross-correlation coefficients between groundwater level and tidal wave level were calculated specifically to measure the boundary conditions along the coastline. In addition, spectrum analysis was employed to assess the periodicity and hysteresis of various tide and groundwater level fluctuations. The results of time series analysis show that groundwater level fluctuation is noticeably influenced by tides, but the influence is limited to a certain distance and cannot reach the saltwater-freshwater interface in the southern Laizhou Bay. There are three main periodic components of groundwater level in tidal effect range (i.e. 23.804 h, 12.500 h and 12.046 h), the pattern of which is the same as the tides. The affected groundwater level fluctuations lag behind the tides. The dynamic analysis of groundwater indicates that the coastal aquifer has a hydraulic connection with seawater but not in a direct way. Owing to the existence of the groundwater mound between the salty groundwater (brine) and fresh groundwater, the maximum influencing distance of the tide on the groundwater is 8.85 km. Considering that the fresh-saline groundwater interface is about 30 km away from the coastline, modern seawater has a limited contribution to sea-salt water intrusion in Laizhou Bay. The results of this study are expected to provide a reference for the study on sea water intrusion.     

我国北疆地区1961—2017年冻融指数的变化趋势

利用我国北疆地区49个主要气象站1961-2017年的逐日平均气温观测值计算了年冻融指数,并分析其变化趋势及分布特征。结果表明：北疆地区冻结指数出现明显的下降趋势,下降速率为51.6℃·d·（10a）^-1。冻结指数的范围在509~2 304.9℃·d之间,平均值为1 240℃·d。北疆地区融化指数出现明显上升趋势,上升速率为73.9℃·d·（10a）^-1。融化指数的范围在526.4~4 531.1℃·d之间,平均值为3 516℃·d。冻结指数表现出在经纬度和海拔较低的准噶尔盆地和伊宁地区较小,在海拔高的高山地区如阿尔泰山和天山山脉较大;融化指数与之相反。北疆地区冻结指数受经纬度及海拔的综合影响,融化指数则主要受海拔影响;年平均气温和冻融指数有非常强的线性关系。     

New system for the assessment of annual groundwater recharge from rainfall in the United Arab Emirates

In this study, the first groundwater recharge map for United Arab Emirates (UAE) was developed using the recharge potential and water table fluctuation methods. Recharge potential estimates were made using information about infiltration rate, soil type, ground slope, geological and hydrogeological factors, and the availability of rainfall harvesting infrastructure and were validated by measurements of water table rise in alluvial aquifers in wadis. Based on this information, the total recharge in the UAE is estimated to be about 133 million cubic meters per year (MCM/year). Annual recharge rates are calculated to vary between 1 and 28% of precipitation in the different regions of UAE depending on several natural and manmade parameters including, among others, recharge enhancing infrastructure. Estimates from the two methods are 98% in agreement; which suggests that the recharge potential method is suitable for estimating aquifer’s recharge in UAE and arid regions. The water table fluctuation method was found to be more suitable for assessing recharge through gravel plains and wadis in mountainous areas.