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ABSTRACT In this study, an analysis of hourly air temperatures in four groups of 32 stations from the UK highland (5 stations), UK lowland (4 stations), Italian highland (11 stations), and Italian lowland (12 stations) at different altitudes was carried out  over the period from 2002 to 2021. The study aimed to examine the trends of each hour of the day during this period, over different averaging time windows (10‐day, 30‐day, and 60‐day). The trends were computed using the Mann–Kendall trend test and Sen's slope estimator. The similarity of trends within and across the groups of stations was assessed using the hierarchical clustering with dynamic time warping technique. An additional analysis was conducted to show the correlation of trends among the group of stations using the correlation distance matrix. Hierarchical clustering and distance correlation analysis show trend similarities and correlations, also indicating dissimilarities among different groups. Using 30‐day averages, significant warming trends in specific months at the Italian stations are evident, especially in February, July, August, and December. The UK highland stations did not show statistically significant trends, but clear pattern similarities were found within the groups, especially in certain months. The ultimate goal of this article is to provide insights into temperature dynamics and climate change characteristics on regional and diurnal scales. [ABSTRACT FROM AUTHOR]

River ecosystems in Central Asia face significant stress from environmental changes and pollution. This study assesses temporal and spatial variations in water quality parameters within the Zarafshan River Basin using retrospective data and field measurements. Water quality indicators, including electrical conductivity (EC), total suspended solids (TSS), ammonium nitrogen (N‐NH4), nitrite nitrogen (N‐NO2), nitrate nitrogen (N‐NO3), temperature (T), chemical oxygen demand (COD), dissolved oxygen (DO), and discharge, were analyzed using the Pearson's correlation coefficient and ANOVA, with the Mann–Kendall (MK) test detecting trends over time. Obtained results indicate significant seasonal effects with elevated TSS during summer, increasing sediment load and changing aquatic habitats. The strong inverse correlation (–0.89) between DO and N‐NH4 signifies ecological challenges particularly in low DO concentrations during summer (3.25 mg L–1). Long‐term analysis identifies Navoiazot chemical factory as a major pollution hotspot. Spatial analyses based on extended sampling have revealed the Siab and Dargom canals and Samarkand City as major pollution sources of elevated N‐NO2 and COD, respectively. Trends at various gauging stations (MK‐test) show increasing EC (τ = 0.72) and N‐NH4 (τ = 0.46) levels, with decreasing TSS, N‐NO3, T, and COD levels over time. Recommendations include targeted measures to reduce pollution at the Navoiazot factory and downstream, introducing sustainable agriculture practices, increasing public awareness for environmental conservation, and improving urban wastewater treatment to meet water quality requirements for different users. [ABSTRACT FROM AUTHOR]

Non‐stationarity in heavy rainfall time series is often apparent in the form of trends because of long‐term climate changes. We have built non‐stationary (NS) models for annual maximum daily (AMP1) and 2‐day precipitation (AMP2) data observed between 1984 and 2020 years by 71 stations and between 1960 and 2020 by eight stations over Thailand. The generalized extreme value (GEV) models are used. Totally, 16 time‐dependent functions of the location and scale parameters of the GEV model are considered. On each station, a model is selected by using Bayesian and Akaike information criteria among these candidates. The return levels corresponding to some years are calculated and predicted for the future. The stations with the highest return levels are Trad, Samui, and Narathiwat, for both AMP1 and AMP2 data. We found some evidence of increasing (decreasing) trends in maximum precipitation for 22 (10) stations in Thailand, based on NS GEV models. [ABSTRACT FROM AUTHOR]

This study investigated the water quality variation spanning 30 years (1986–2017) in 16 catchments of Hong Kong against different urbanization indices, namely, built area fraction; population; and product of population and built area fraction. Pearson correlations of three different periods of time (1988–1990, 1998–2000, and 2015–2017) indicated that water quality trends were dependent on the urbanization index. Total solids, nitrite‐nitrogen, total phosphorus, electrical conductivity, dissolved oxygen, and flow rate had significant deteriorative trends (Pearson r > 0.5 and p < 0.05) with population and product of built area and population. Results also interpreted that built area fraction and product of built area and population were the worst and best indices that represented urbanization and/or its impacts, respectively. Mann‐Kendall test for the entire 30 year period showed that water quality had improved with time with respect to certain water quality parameters (e.g., dissolved oxygen, ammoniacal nitrogen and total suspended solids). The results portrayed that although the urbanization of catchments had increased with time, the river water quality with respect to many parameters showed signs of improvement and the legislative measures implemented seemed to be effective in controlling pollution. [ABSTRACT FROM AUTHOR]

In the present study, Amaravati, the proposed city of India is considered to assess the impacts of urbanization on water quality of the Krishna River in the vicinity. Long‐term surface water quality data of various parameters of Krishna River are obtained from Central Water Commission (CWC). Trends of various parameters are analyzed using a modified version of Mann‐Kendall (M‐K) test; bootstrapped M‐K trend test with optional bias corrected pre‐whitening and R programming are used affecting water quality prior to and at the commencement of urbanization. During the onset of urbanization, minimum BOD is decreased from 0.49 to 0.2 mg/L, while the maximum BOD is increased by 67.7%. Dissolved oxygen's (DO) minimum value is decreased by 29.33% while maximum DO value is decreased by 4.47% at the beginning of urbanization. During the process of urbanization, total coliform's minimum count is increased to 330 from 2 MPN/100 ml while the maximum count of total coliforms is increased to 16,000 from 2400 MPN/100 ml. Faecal coilform's minimum count is increased from 2 to 80 MPN/100 ml while maximum count is increased to 16,000 from 800 MPN/100 ml during urbanization. It is found that due to urbanization, pH, DO values exceed the allowable limit. [ABSTRACT FROM AUTHOR]

Long‐term precipitation monitoring plays a vital role in water resource management and disaster prevention and mitigation. This study assesses spatial and temporal trends in seasonal and annual precipitation in Pakistan between 1960 and 2016 at an interannual scale. The Mann–Kendall (MK) test, Sen's slope (SS) estimator, and Sequential Mann–Kendall (SQMK) test were employed to assess trends. Cluster analysis and L‐moment approach were used to identify the homogenous precipitation regions. In general, increasing precipitation trends between 1960 and 2016 were evident. Results indicated increasing precipitation in winter, autumn, summer and annual scale at the rates of 0.20, 2.18, 5.16, and 10.89 mm·decade−1, respectively. In spring, the precipitation trend shows a decreasing trend at −0.67 mm·decade−1. Moreover, a significant decreasing trend occurred in winter in southern Pakistan. The overall increasing trends were more noticeable between 1960 and 1988, compared to the declining precipitation during 1989–2016. SQMK analysis indicates a clear downward trend in most regions during 1989–2016, except in autumn. Annual precipitation has increased topographically except at 500 m and 1,500 m during 1960–2016 with a significant increase of 1.37 mm·decade−1 at elevation <250 m. Results indicate a negative correlation in SS test value with seasonal and annual precipitation with elevation and a positive correlation in winter. The seasonal and annual precipitation trends exhibit increasing and decreasing trends before and after 1990, respectively, in most subregions. The notable finding based on the outcomes of this study is that the whole country observed an increasing trend during 1960–1988, followed by a decreasing trend in during 1989–2016. This decreasing tendency is particularly pronounced between 1985 and 1995, except in autumn. Agriculture production is largely reliant on precipitation in many regions. So, a detailed study of the influence of monsoon trends and large‐scale climatic variability controls over Pakistan is vital for improved water resource management in the context of global warming and rising human activity. The results will help policy makers while establishing and updating water‐related initiatives and regulations. [ABSTRACT FROM AUTHOR]

There is high confidence that climate change has increased the probability of concurrent temperature‐precipitation extremes, changed their spatial‐temporal variations and affected the relationships between drivers of such natural hazards. However, the extent of such changes has been less investigated in Australia. Daily data spanning the period 1889‐2019 (131 years) were extracted from SILO gridded dataset at 700 grid cells (1◦ × 1◦) across Australia to calculate annual and seasonal mean daily maximum temperature (MMT) and total precipitation (TPR). A nonparametric multivariate copula framework was adopted to estimate the return period of compound hot‐dry (CHD) events based on an 'And' hazard scenario (hotter than a threshold 'And' drier than a threshold). CHD extremes were defined as years with joint return periods of longer than 25 years calculated over the period 1889‐2019. Mann‐Kendall nonparametric tests were used to analyse trends in MMT and TPR as well as in the frequency of univariate and CHD extremes. Results showed a general cooling‐wetting trend over 1889‐1989. Significant increasing trends were detected over 1990‐2019 in the frequency and severity of hot extremes across the country while trends in dry extremes were mostly insignificant (and decreasing). A significant increase in the association between temperature and precipitation was identified at various temporal scales. While the frequency of CHD extremes was mostly stable over 1889‐1989, it significantly increased between 1990 and 2019 at 44% of studied grid cells, mostly located in the north, south‐east and southwest. [ABSTRACT FROM AUTHOR]

Rainfall is time concentric in nature. The spatial and temporal distribution of rainfall is changing over the Earth with recent anthropogenic warming. The study explores various characteristics of annual and seasonal concentration of rainfall across India using the precipitation concentration index (PCI) and its trends during the period of 1986–2015, based on a high‐resolution gauge‐based rainfall data (0.25 × 0.25°), obtained from the India Meteorological Department (IMD). An intercomparison is made with 11 other gridded rainfall datasets to infer whether these datasets can reasonably reproduce the spatiotemporal distribution of PCI and its trends in various homogenous rainfall regions of India or not. These datasets are categorized into gauge‐based (APHRODITE, GPCC, CPC), satellite‐derived (CHIRPS, PERSIANN‐CDR), and reanalysis (JRA‐55, MERRA‐2, NCEP‐2, PGF, ERA‐Interim, ERA‐5). On annual scale, about 8.52, 24.1, and 67.38% of area of India are under moderate, irregular, and strongly irregular rainfall distribution, respectively. Spatial variation of PCI in India is influenced by geographical factors such as latitude, longitude, and elevation. Significant increasing and decreasing trends in annual PCI have been observed in the northeast, eastern, and western coasts of India, respectively. Gridded data intercomparison suggests that the gauge‐based APHRODITE, GPCC, and satellite‐derived CHIRPS datasets better perform in capturing the temporal and spatial variation of PCI across India when compared to the IMD gridded dataset, whereas the ERA‐5 performs better among the reanalysis datasets. However, the rainfall datasets exhibited marked differences with the IMD while estimating the annual and seasonal trend and its magnitude across various regions of India. The JRA‐55 overestimated areas of positive trend and its magnitude on annual and seasonal scale. These findings have practical implications for hydroclimatic studies. [ABSTRACT FROM AUTHOR]

Spatial and temporal rainfall variability analysis at a basin scale is essential to understand water availability for sustainable water resource management. This study investigated the spatial distribution and temporal rainfall trend in the Tekeze river basin using daily rainfall data collected from 43 meteorological stations with records from 1960 to 2019. Coefficient of variation, seasonality index (SI) and trend index were used to evaluate monthly, seasonal and annual rainfall variability in the basin. The non‐parametric Mann‐Kendall's test was used to understand any rainfall trends. Results showed that there is moderate annual rainfall variability in the basin. Rainfall variability is higher in the Tsedey, Bega and Belg than kiremt season. SI results showed that majority of the Tekeze river basin is categorized as seasonal, most of the rain occurring in less than 3 months. Overall, Mann‐Kendall's test result revealed that there is no significant annual rainfall trend in the basin except for four stations. The seasonal rainfall characteristics and short duration of rain in the basin indicate that there is a need to implement water harvesting measures during the wet season for use in the dry periods. [ABSTRACT FROM AUTHOR]

One of the most relevant and debated topics related to the effects of the climate change is whether intense rainfall events have become more frequent over the last decades. It is a crucial aspect, since an increase in the magnitude and frequency of occurrence of heavy rainfall events could result in a dramatic growth of floods and, in turn, human lives losses and economic damages. Because of its central position in the Mediterranean area, Sicily has been often screened with the aim to capture some trends in precipitation, potentially related to climate change. While Mann‐Kendall test has been largely used for the rainfall trend detection, in this work a different procedure is considered. Precipitation trends are here investigated by processing the whole rainfall time‐series, provided by the regional agency SIAS at a 10‐min resolution, through the quantile regression method by aggregating precipitation across a wide spectrum of durations and considering different quantiles. Results show that many rain gauges are characterized by an increasing trend in sub‐hourly precipitation intensity, especially at the highest quantiles, thus suggesting that, from 2002 to 2019, sub‐hourly events have become more intense in most of the island. Moreover, by analysing some spatial patterns, it has been revealed that the south and the east of Sicily are more interested in significant increasing rainfall trends, especially at the 10‐min duration. Finally, the comparison between the two procedures revealed a stronger reliability of the quantile regression in the trend analysis detection, mainly due to the possibility of investigating the temporal variation of the tails of precipitation distribution. [ABSTRACT FROM AUTHOR]

Collisions with vehicles can be a major threat to wildlife populations, so wildlife mitigation structures, including exclusionary fencing and wildlife crossings, are often constructed. To assess mitigation structure effectiveness, it is useful to compare wildlife road mortalities (WRMs) before, during, and after mitigation structure construction; however, differences in survey methodologies may make comparisons of counts impractical. Location‐based cluster analyses provide a means to assess how WRM spatial patterns have changed over time. We collected WRM data between 2015 and 2019 on State Highway 100 in Texas, USA. Five wildlife crossings and exclusionary fencing were installed in this area between September 2016 and May 2018 for the endangered ocelot (Leopardus pardalis) and other similarly sized mammals. Roads intersecting State Highway 100 were mitigated by gates, wildlife guards, and wing walls. However, these structures may have provided wildlife access to the highway. We combined local hot spot analysis and time series analysis to assess how WRM cluster intensity changed after mitigation structure construction at fine spatial and temporal scales and generalized linear regression to assess how gaps in fencing and land cover were related to WRM cluster intensity in the before, during, and after construction periods. Overall, WRMs/survey day decreased after mitigation structure construction and most hot spots occurred where there were more fence gaps, and, while cluster intensity increased in a few locations, these were not at fence gaps. Cluster intensity of WRMs increased when nearer to fence gaps in naturally vegetated areas, especially forested areas, and decreased nearer to fence gaps in areas with less natural vegetation. We recommend that if fence gaps are necessary in forested areas, less permeable mitigation structures, such as gates, should be used. Local hot spot analysis, coupled with time series and regression techniques, can effectively assess how WRM clustering changes over time. [ABSTRACT FROM AUTHOR]

Extreme cold events ("cold waves") have disastrous impacts on ecosystem and human health. Evidence shows that these events will still occur under current increasing mean temperatures. Little research has been done on extreme cold events, especially in developing countries such as South Africa. These events pose a significant threat due to the low adaptive capacity, urgent development needs and relatively inadequate infrastructure in South Africa. This study presents annual and seasonal, spatial and temporal trend analyses of extreme cold temperature events for the period 1960–2016. We apply the World Meteorological Organisation Commission for Climatology and Indices Expert Team on Sector‐Specific Climate Indices (ET‐SCI) to South Africa for the first time, with comparison to the World Meteorological Organisation Expert Team on Climate Change Detection (ETCCDI) indices previously used in South Africa. The extreme cold indices are calculated using the RClimDex and ClimPACT, respectively. Trends were calculated using the non‐parametric Mann‐Kendall test, Spearman Rank Correlation Coefficient and Sen's slope estimates. A decreasing trend is found for annual cold spell duration and cold wave frequency, at rates of 0.10 days.day−1 and 0.02 events.day−1, respectively. Seasonally, coldest day temperatures increased in autumn, with increases of 0.02°C.day−1 for the period 1960–2016. Regionally, increasing trends in annual cold spell duration days were evident in stations located in the Western Cape, Eastern Cape, North‐West Province, at a rate of 0.03 days.day−1. Increasing trends in cold waves were observed for stations in Northern Cape, Gauteng, KwaZulu‐Natal and the Eastern Cape Province, at a rate of 0.01 events.day−1. These results contribute to the awareness and recognition of the incidence and duration of cold extreme events in South Africa, seeing that studies suggest that anomalously cold events may persist in a warming world. [ABSTRACT FROM AUTHOR]

Estimation of evapotranspiration, representing a highly sensitive variable to global warming, is often required in water resources and agricultural studies. This study explores the possible effects of climate change on evapotranspiration (ETo) across Iran. The ETo was computed using the Penman‐Monteith Temperature (PMT) method that requires only minimum and maximum temperature (Tmin and Tmax), provided by the NASA Earth Exchange Global Daily Downscaled Projections dataset (NEX‐GDDP) with a 0.25° × 0.25° spatial resolution. Accuracy of the NEX‐GDDP Tmin and Tmax were evaluated against ground truth observations at 41 synoptic weather stations distributed across the country using a set of statistical measures, including the coefficient of determination (R2) and Nash‐Sutcliffe Efficiency (NSE). Similarly, the PMT estimated evapotranspiration based on the NEX‐GDDP Tmin and Tmax (ETo‐GDDP) were statistically evaluated against the ETo computed with observed variables at selected stations (ETo‐obs). Then, at each grid cell, the 45‐years ETo‐GDDP time series was partitioned into three 15‐years subperiods such that the differences between three subperiods were computed and inter‐compared. Furthermore, annual, seasonal, and monthly ETo time series trends of each cell were evaluated using the Mann–Kendall trend test (MK) while the corresponding change rates were estimated using Theil–Sen's slope estimator (TSSE). The results demonstrated a good agreement between ETo‐GDDP and ETo‐obs with R2 greater than 0.8 and NSE greater than 0.7 in 90.2% and 65.8% of the stations, respectively. The maps of differences between the three subperiods showed negligible changes in ETo between 1975–1990 and 1950–1975 subperiods. The spatial patterns of annual and seasonal MK statistics showed a significant increasing trend in most parts of Iran. On seasonal scale, the highest and lowest ETo changes were observed in spring (0.00035–0.0045) and in autumn (0.0005–0.0015), respectively. [ABSTRACT FROM AUTHOR]

Rainfall trend analysis provides useful information for effective planning, and management of water resources, and gives an insight into climate change of a region. This study investigates trends in annual and seasonal rainfall over Sri Lanka using an Innovative Trend Analysis (ITA) and Mann–Kendall (MK) test with Sen's slope estimator. The MK test showed increasing trends in annual rainfall at 24 stations (65%) with five stations showing significant increasing trend. Annual rainfall at 13 locations (35%) showed decreasing trend, but none were significant (p <.05). ITA results for annual rainfall showed increasing trend at 67% stations while 33% stations showed decreasing trend. MK test results for seasonal rainfall indicated increasing trend at 76, 51, 32, and 86% of stations during First Inter‐Monsoon (FIM), Second Inter‐Monsoon (SIM), South West Monsoon (SWM), and North East Monsoon (NEM) seasons, respectively. Seasonal analysis of rainfall trend using ITA method showed increasing trend in 81, 70, 32, and 65% stations during FIM, SIM, SWM, and NEM, respectively. ITA and MK tests exhibited similar trend results for 80% of the stations. Moreover, Spearman's rho correlation coefficient between ITA and MK test trends showed significant (p <.05) positive correlation. In general, eastern, south eastern, north and north central regions of the country showed increasing rainfall trend over the last 31 years (1987–2017) while western, part of north western and central part of the country indicated a decreasing rainfall trend during the same period. [ABSTRACT FROM AUTHOR]

Copyright of World Water Policy is the property of Wiley-Blackwell and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Irrigation & Drainage is the property of Wiley-Blackwell and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

This study uses the daily maximum and minimum temperature data sets of 48 meteorological stations to assess the observed changes in temperature extremes over China–Pakistan Economic Corridor (CPEC) during 1980–2016. The nonparametric Mann–Kendall, Sen's slope estimator, least squares method, and two‐tailed simple t‐test methods were used to assess the trend in nine temperature extreme indices. The results of the study indicated that the trends in annual mean anomalies of cold nights, cold days, and frost days significantly decreased at the rates of −1.09, −1.58, and −1.05 day/decade, respectively. The number of warm nights, warm days, and summer days exhibited significant positive trends at the rates of 1.49, 1.04, and 4.32 day/decade, respectively. In addition, the trends of the warmest day and coldest day also increased significantly at the rates of 0.45 and 0.51 °C/decade, respectively. The trend of diurnal temperature range decreased significantly with −0.35 °C/decade. The spatial distribution of temperature extreme indices indicated that the number of cold nights, cold days, and diurnal temperature range have been decreased, while the trends of warm nights, warm days, summer days, warmest day, and coldest day have been increased over the whole country. Large‐scale atmospheric circulation changes derived from ERA‐Interim reanalysis show that a weak (strong) wind pressure, increasing (decreasing) geopotential height, and rapid warming (cooling) over the northern (southern) region have contributed to the changes in temperature extremes in Pakistan to some extent. With respect to elevation‐dependent warming (EDW), the trends of cold nights, warm days, summer days, warmest day, and diurnal temperature range showed significant positive correlations with increasing elevation. However, the trends of cold days, warm nights, frost days, and coldest day showed significant negative relationships with increasing elevation. The findings of this study will be helpful in the adaptation of climate change and mitigation of climatological disasters in the region. The study recommends that future studies should investigate the natural and anthropogenic drivers of temperature extremes and the possible mechanism of EDW in the CPEC region. Topographic map of the study area with CPEC routes and selected meteorological stations. [ABSTRACT FROM AUTHOR]

Trend analyses of monthly, seasonal and annual rainfall, air temperature, and streamflow were performed using Mann‐Kendall test within the Langat River basin to identify gradual trends and abrupt shifts for 1980 − 2010. Annual rainfall showed an increasing trend in upstream flow, a combination of decreasing and increasing trends in middle stream flow, and a decreasing trend in downstream flow. Monthly rainfall in most months displayed an insignificant increasing trend upstream. Stations with significant increasing trends showed larger trends in summer than those of other seasons. However, they were similar to the trends observed in annual rainfall. Annual minimum air temperature showed a significant decreasing trend upstream and significant increasing trends in the middle stream and downstream areas. Annual maximum air temperature portrayed increasing trends in both upstream and middle stream areas, and a decreasing trend for the downstream area. Both monthly and seasonal maximum air temperatures exhibited an increasing trend midstream, whereas they demonstrated trends of both decreasing and/or increasing temperatures at upstream and downstream areas. Annual streamflow in upper, middle and lower catchment areas exhibited significant increasing trend at the rates of 0.036, 0.023 and 0.001 × 103 m3/y at α = 0.01, respectively. Seasonal streamflow in the upstream, midstream and downstream areas displayed an increasing trend for spring (0.55, 0.33 and 0.013 m3/y respectively) and summer (0.51, 0.37, 0.018 m3/y respectively). The greatest magnitude of increased streamflow occurred in the spring (0.54 m3/y). Significant increasing trends of monthly streamflow were noticed in January and August, but insignificant trends were found in May, September and November at all stations. Annual streamflow records at the outlet of the basin were positively correlated with the annual rainfall variable. This study concludes that the climate of the Langat River basin has been getting wetter and warmer during 1980‐2010. [ABSTRACT FROM AUTHOR]

ABSTRACT: The long‐term trends in temperature over Iran were examined over 34 synoptic stations during a 50 year period (1961–2010) on seasonal and annual time scales. Two methods, a modified version of the Mann–Kendall test by eliminating the effect of all significant autocorrelation co‐efficients and the regional Kendall test, were used in trend identification. The results revealed that the temperature had experienced significant positive trends in autumn, spring and especially summer over the study area. On an annual time scale and in the winter, the highest increasing trends were observed at stations located in the southern and southeastern parts of Iran. For regional analysis of trends, the stations were divided into five clusters based on the K‐means clustering method and the silhouette index. Subsequently, the regional trend of temperature was analysed on seasonal and annual time scales using the regional Kendall test. The results of the regional Kendall test also indicated the rising trends in temperature during the last 50 years throughout the country on both seasonal and annual time scales. After verifying the presence of an increasing trend in the temperature time series, the non‐parametric Pettitt test was used to detect the change points in the annual and seasonal time scales. The results showed that the change point of average temperature began from the summer of 1972 (Sabzevar station) and continued until the summer of 1998 (Zahedan station). The most frequent change point occurrence was between the years 1986 and 1994. [ABSTRACT FROM AUTHOR]

This paper examines changes in rainfall in New South Wales (NSW), Australia using daily rainfall data from 200 rainfall stations covering the period of 1945–2014. The Mann–Kendall test is applied to identify trends in the selected rainfall indices, while the Pettitt change point test is employed to determine the direction and timing of a change point. Van Bell and Hughes homogeneity test is applied to examine homogeneity of the observed trends. It is found that the southern half of NSW is dominated by a negative trend in annual total rainfall, and autumn and spring rainfall. Based on the Pettitt change point test, it is found that annual maximum 24-h rainfall data in NSW is dominated by a negative shift. Based on the Van Belle and Hughes method, it is found that NSW is dominated by non-homogeneous trends in monthly maximum daily rainfall data. Overall, the results do not show any consistent pattern of rainfall trends in NSW. The findings of this study contribute towards the growing body of knowledge on the nature of changes in rainfall based on the latest data in NSW. [ABSTRACT FROM AUTHOR]

ABSTRACT: This study examines the spatial and temporal surface (10 m) wind speed trend characteristics of Brazil during 1980–2014 using two in situ and three climate reanalysis datasets. Nonparametric regression is used to understand how mean seasonal and annual wind speeds change over space and time across Brazil. Overall temporal linear trends show that station and reanalysis products exhibit varying seasonal and annual wind speed trends. A geographic examination displays statistically significant (P < 0.05) positive (negative) mean wind speed trends for equatorial (southeastern and central) Brazil. Quantile regression is performed to interpret how wind speed changed across different percentiles. Results show that the largest positive and negative spatial wind speed trends occur for the upper percentiles (75 and 95%). The spatial and temporal trends and correlations described could be interconnected to possible changes developing with the location of Intertropical Convergence Zone and South Atlantic Anticyclone over the study region. Results have implications for optimizing renewable wind energy production and development across Brazil. [ABSTRACT FROM AUTHOR]

Fluvial flood events have substantial impacts on humans, both socially and economically, as well as on ecosystems (e.g., hydroecology and pollutant transport). Concurrent with climate change, the seasonality of flooding in cold environments is expected to shift from a snowmelt-dominated to a rainfall-dominated flow regime. This would have profound impacts on water management strategies, that is, flood risk mitigation, drinking water supply, and hydro power. In addition, cold climate hydrological systems exhibit complex interactions with catchment properties and large-scale climate fluctuations making the manifestation of changes difficult to detect and predict. Understanding a possible change in flood seasonality and defining related key drivers therefore is essential to mitigate risk and to keep management strategies viable under a changing climate. This study explores changes in flood seasonality across near-natural catchments in Scandinavia using circular statistics and trend tests. Results indicate strong seasonality in flooding for snowmelt-dominated catchments with a single peak occurring in spring and early summer (March through June), whereas flood peaks are more equally distributed throughout the year for catchments located close to the Atlantic coast and in the south of the study area. Flood seasonality has changed over the past century seen as decreasing trends in summer maximum daily flows and increasing winter and spring maximum daily flows with 5-35% of the catchments showing significant changes at the 5% significance level. Seasonal mean daily flows corroborate those findings with higher percentages (5-60%) of the catchments showing statistically significant changes. Alterations in annual flood occurrence also point towards a shift in flow regime from snowmelt-dominated to rainfall-dominated with consistent changes towards earlier timing of the flood peak (significant for 25% of the catchments). Regionally consistent patterns suggest a first-order climate control as well as a local second-order catchment control, which causes inter-seasonal variability in the streamflow response. [ABSTRACT FROM AUTHOR]

ABSTRACT The objectives of this study were to investigate the trend in annual precipitation, sunshine duration, wind speed ( u2), and annual and monthly minimum temperature ( Tmin), maximum temperature ( Tmax), and relative humidity ( RH) and the adaptation strategies for the Senegal River Basin. Annual precipitation, Tmin, Tmax, RH, sunshine duration, and u2 for the period of 1950-2000 recorded at St-Louis, Bakel, Dagana, Fanaye, Podor, and Matam have been analysed using the Mann-Kendall test and Sen's slope estimator. Annual precipitation varied with location from 900 mm registered in 1967 at Bakel to 32 mm obtained at Dagana in 1986. A significant decreasing trend ( p < 0.001) in precipitation was observed at Podor, Dagana, Matam, Bakel, and St-Louis. A non-significant decreasing trend in annual precipitation was observed at Fanaye Dieri. There was a significant increasing trend ( p < 0.001) in Tmax and Tmin at all locations. Sunshine duration had a significant decreasing trend at Podor, Matam, and St-Louis at the rate of 0.27, 0.28, and 0.35 h decade−1, respectively. RH and u2 have differences in their trends, with the first one showing a strong and significant decrease and u2 with less significance in their trends. The trend analysis in the climate variables revealed a change in climate that necessitates some specific actions for resources management sustainability and conservation. [ABSTRACT FROM AUTHOR]

ABSTRACT Trend analysis of precipitation and drought will play a significant role in the future development and sustainable management of water resources. It is the main purpose of this paper to analyse meteorological droughts and trends. The variability of the standardized precipitation index ( SPI) was investigated at 1, 3, 6, 9, 12 and 24 monthly intervals. The trends of 1, 3, 6, 9, 12 and 24 monthly SPI results were analysed by applying linear regression and the Mann- Kendall and Spearman's rho tests at the 5% significance level. The linear slopes of the trends were calculated with a technique proposed by Sen. Meteorological data from eight meteorological stations in the Aegean region of Turkey were used for the period 1960-2013. The monthly precipitation trend decreases in December, January, February and March in all regions according to the linear regression analysis results. Annual precipitation decreased at five stations. In drought analysis by the SPI, in a short time period (such as 3 months) drought is more frequent but shorter, and as the period increases the duration of drought also increases but frequency decreases. Winter droughts are beginning to occur in the class of 'severe' in recent years. In this study carried out for different time periods according to SPI values in all stations, the highest ranges are in the normal and mild drought degrees. In addition, severe and extreme droughts are also seen intensely frequently. Trend analysis of precipitation and drought is compared. The trend analyses of precipitation are in parallel with the results of drought analyses. [ABSTRACT FROM AUTHOR]

Urban stormwater is a major cause of urban flooding and natural water pollution. It is therefore important to assess any hydrologic trends in urban catchments for stormwater management and planning. This study addresses urban hydrological trend analysis by examining trends in variables that characterize hydrological processes. The original and modified Mann-Kendall methods are applied to trend detection in two French catchments, that is, Chassieu and La Lechere, based on approximately 1 decade of data from local monitoring programs. In both catchments, no trend is found in the major hydrological process driver (i.e., rainfall variables), whereas increasing trends are detected in runoff flow rates. As a consequence, the runoff coefficients tend to increase during the study period, probably due to growing imperviousness with the local urbanization process. In addition, conceptual urban rainfall-runoff model parameters, which are identified via model calibration with an event based approach, are examined. Trend detection results indicate that there is no trend in the time of concentration in Chassieu, whereas a decreasing trend is present in La Lechere, which, however, needs to be validated with additional data. Sensitivity analysis indicates that the original Mann-Kendall method is not sensitive to a few noisy values in the data series. [ABSTRACT FROM AUTHOR]

Backflow, the temporary reversal of discharge at the outlet of a lake, is an important mechanism controlling flow and transport in many connected river-lake systems. This study used statistical methods to examine long-term variations and primary causal factors of backflow from the Yangtze River to a laterally connected, large floodplain lake (Poyang Lake, China). Additionally, the effects of backflow on the lake hydrology were explored using a physically based hydrodynamic model and a particle-tracking model. Although backflow into Poyang Lake occurs frequently, with an average of 16 backflow events per year, and varies greatly in magnitude between years, statistical analysis indicates that both the frequency and magnitude of backflow reduced significantly during 2001-2010 relative to the previous period of 1960-2000. The ratio of Poyang Lake catchment inflows to Yangtze River discharge can be used as an indication of the daily occurrence of backflow, which is most likely to occur during periods when this ratio is lower than 5%. Statistical analysis also indicates that the Yangtze River discharge is the main controlling factor of backflow during July to October, rather than catchment inflows to the lake. Hydrodynamic modelling reveals that, in general, backflow disturbs the normal northward water flow direction in Poyang Lake and transports mass ~20 km southward into the lake. The effects of backflow on flow direction, water velocities and water levels propagate to virtually its upstream extremity. The current study represents a first attempt to explore backflow and causal factors for a highly dynamic floodplain lake system. An improved understanding of Poyang Lake backflow is critical for guiding future strategies to manage the lake, its water quality and ecosystem value, given proposals to modify the lake-river connectivity. Copyright © 2016 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

ABSTRACT Evapotranspiration is a sensitive parameter for assessing climate change. It controls energy and mass exchange and is a descriptor of drought in arid- and semi-arid regions. Using the Mann- Kendall ( M-K) test, Sen's slope estimator, and the stepwise regression, temporal, and spatial variations in potential evapotranspiration ( ET0) and its dominant factors were analysed. The analysis was based on data from 173 meteorological stations in a desertification-prone region of China over the period from 1960 to 2013. The annual ET0 decreased prior to 1990s and increased thereafter. The majority of stations had a decreasing ET0 trend, especially in summer, in which the average slope of all stations was −2.43 mm decade−1. Analysis of determining factors showed that a decrease in wind speed was the primary factor associated with decreasing ET0. The trend magnitude of ET0 increased from −2.25 mm decade−1 to −7.43 mm decade−1 as wind speed increased, then decreased to −3.00 mm decade−1. Decreasing ET0 and increasing P in the western region led to decrease in the aridity index, suggesting a wetter climate and reduced desertification. Increasing aridity index in the eastern region reduced the vegetation cover and facilitated desertification processes, which might be a disadvantage for ecological reconstruction and desertification control. Better understanding of the response of ET0 to regional climate change may facilitate efficient use of limited water resources and establish management strategies that can combat desertification and maintain ecological security in a desertification-prone region. [ABSTRACT FROM AUTHOR]

Evapotranspiration is an important component of the hydrological cycle, which integrates atmospheric demands and surface conditions. Research on spatial and temporal variations of reference evapotranspiration (ETo) enables understanding of climate change and its effects on hydrological processes and water resources. In this study, ETo was estimated by the FAO-56 Penman-Monteith method in the Jing River Basin in China, based on daily data from 37 meteorological stations from 1960 to 2005. ETo trends were detected by the Mann-Kendall test in annual, seasonal, and monthly timescales. Sensitivity coefficients were used to examine the contribution of important meteorological variables to ETo. The influence of agricultural activities, especially irrigation on ETo was also analyzed. We found that ETo showed a decreasing trend in most of the basin in all seasons, except for autumn, which showed an increasing trend. Mean maximum temperature was generally the most sensitive parameter for ETo, followed by relative humidity, solar radiation, mean minimum temperature, and wind speed. Wind speed was the most dominant factor for the declining trend in ETo. The more significant decrease in ETo for agricultural and irrigation stations was mainly because of the more significant decrease in wind speed and sunshine hours, a mitigation in climate warming, and more significant increase in relative humidity compared with natural stations and non-irrigation stations. Changes in ETo and the sensitivity coefficient of meteorological variables in relation to ETo were also affected by topography. Better understanding of ETo response to climate change will enable efficient use of agricultural production and water resources, which could improve the ecological environment in Jing River Basin. Copyright © 2015 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

The Changwu tableland is located in the semi-humid to semi-arid transition area of the Loess Plateau, China. In the present study, the daily potential evapotranspiration (ET0) of the Changwu tableland was calculated using the FAO Penman-Monteith (FPM) equation for the years 1957-2012, and the temporal variation and frequency distribution characteristics were analysed. The results indicate that the annual average ET0 of the Changwu tableland was 949.3 mm, varying from 789.2 to 1093.3 mm; a slight downward trend with a rate of -0.48mm year-1 was found. An abrupt increase occurred in 1994. The ET0 values that correspond to frequencies of 5, 10, 25, 50, 75, 90 and 95% were 1076.8, 1047.6, 999.7, 947.8, 897.3, 853.0 and 827.0 mm, respectively. The recurrence intervals of maximum and minimum ET0 were both more than 50 years. The contributions of Tmax, Tmin, vapour pressure, wind speed and sunshine hours to changes in ET0 were 0.74, 0.07, -0.51, -0.57 and -0.23, respectively. The change in ET0 and the meteorological factors in the Changwu tableland are worthy of attention; measures to reduce the negative impacts of climate change are necessary. [ABSTRACT FROM AUTHOR]

ABSTRACT Snowfall in mountainous areas provides indispensable water sources for arid and semi-arid watersheds. Changes in snowfall and snowmelt regimes have significantly impacted the water resources' variations and management. This study addresses the ratio of snowfall to precipitation (S/P) in the Tian Shan Mountains, China. It aims to examine changes in S/P ratio and its synchronization with climate change. The results show that the average S/P ratio experienced a downward trend under the precipitation and snowfall increases as well as temperature increases during the cold seasons in 1961-2010. Spatially, the S/P ratios show an increasing trend in the Boertala Valley and the southern slope of the middle Tian Shan Mountains, but a decreasing trend in Yili Valley, and the western and the northern slope of the middle Tian Shan Mountains. The S/P ratios decreased significantly in middle altitudes with elevation ranging from 1500 to 2500 m, but either decreased or increased at elevations below 1500 m due to a temperature inversion in the elevation belt. In high altitudes with elevation over 3500 m, the magnitudes of the decreased S/P ratios were small because the temperature was always below freezing. The decreases in S/P ratio was mainly attributed to the relative changes in snowfall (dS/S) being less than that in precipitation (dP/P), whereas the increases in S/P ratio resulted from the relative changes in snowfall (dS/S) being more than that in precipitation (dP/P). Temperature increases have also lead to the decreases in S/P ratios to some extent. [ABSTRACT FROM AUTHOR]

Temporal and spatial variations of stable oxygen (18O) and hydrogen (2H) isotope measurements in precipitation act as important proxies for changing hydro-meteorological and regional and global climate patterns. Temporal trends in time series of the stable isotope composition in precipitation were rarely observed, and they are poorly understood. These might be a result of a lack of proper trend detection tools and effort for exploring trend processes. Here, we investigate temporal trends of δ18O in precipitation at 17 observation stations in Germany between 1978 and 2009. We test if significant trends in the isotope time series from different models can be observed. Mann-Kendall trend tests are applied on the isotope series, using general multiplicative seasonal autoregressive integrate moving average (ARIMA) models, which account for first and higher order serial correlations. Effects of temperature, precipitation, and geographic parameters on isotope trends are also investigated in the proposed models. To benchmark our proposed approach, the ARIMA results are compared with a trend-free pre-whitening procedure, the state of the art method for removing the first order autocorrelation in environmental trend studies. Moreover, we further explore whether higher order serial correlations in isotope series affects our trend results. Overall, three out of the 17 stations show significant changes when higher order autocorrelation are adjusted, and four show a significant trend when temperature and precipitation effects are considered. The significant trends in the isotope time series generally occur only at low elevation stations. Higher order autoregressive processes are shown to be important in the isotope time series analysis. Results suggest that the widely used trend analysis with only the first order autocorrelation adjustment may not adequately take account of the high order autocorrelated processes in the stable isotope series. The investigated time series analysis method including higher autocorrelation and external climate variable adjustments is shown to be a better alternative. Copyright © 2014 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

ABSTRACT In this study, a comprehensive analysis of long-term trends of the Koshava wind during the period between 1949 and 2010 is carried out. Koshava is a strong wind that blows from southeast quadrant over Serbia, Bulgaria and Romania. The Siberian high and West-Mediterranean cyclones, together with the orography of the eastern Balkan, are the main drivers of the Koshava wind. The trend analyses are performed on wind data sets from five synoptic weather stations, all situated in the region where the Koshava wind is fully developed. Koshava wind speeds are divided into two categories: (1) all wind speeds and (2) wind speeds above 5 ms−1. Two homogeneity tests are used to inspect the quality of wind speed and wind direction time series. The Mann-Kendall test and Sen's slope estimator are used to analyze trends of the Koshava wind speeds and the annual number of days with the Koshava wind. Statistically significant negative trends of the Koshava wind speeds and wind activity are observed at all five weather stations and are more pronounced for wind speeds above 5 ms−1. The negative trends of the Koshava wind are mostly related to the changes in the synoptic circulation, temperature and weakening of the Siberian high and West-Mediterranean cyclones. It is shown that the observed decline of the Koshava wind has a significant impact on reducing the wind energy potential in the region. [ABSTRACT FROM AUTHOR]

Spatial and temporal variations of reference evapotranspiration (ET0) are useful for regional agricultural and water resources management as well as required in most distributed hydrological modelling. In the current study, the Penman-Monteith estimated ET0 in the arid land of Northwestern China has been explicitly explored using the Mann-Kendall test. Most stations in the study region exhibited significant decreasing trend of ET0 ( P < 0.05) with only few occasions showing significant increasing trend ( P < 0.05), despite the increase of temperature in the entire region. Analysis results revealed that the overall decreasing wind speed contributed most to the decreasing trend of ET0, whereas the contributions of relative humidity and sunshine duration were limited. Temperature played the second important role on determining ET0 trend, but its effect was opposite to that of wind speed and was largely offset by the decreasing wind speed. Furthermore, sensitivity analysis suggested the impact of temperature to ET0 was much larger than formerly reported if its effect on saturated vapour deficit was taken into account. The results obtained in the current study will help for better understanding of the effects of climate changes to water resource management in the arid land of northwest China. Copyright © 2013 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

A comprehensive dataset of daily rainfall covering the period from 1972 to 2002 was used to compute the climatology and trend of occurrence and intensity of heavy, weak and normal events of rainfall on Northeast Brazil (NEB). For selection of rainfall events, we used the technique of quantiles and the trend was identified using the nonparametric Mann-Kendall test. The heavy events are modulated by La Niña and El Niño occurrences and in general they presented negative trend concerning to number of episodes and positive trend to daily rainfall. [ABSTRACT FROM AUTHOR]

The local hydrological, agricultural and economic activities heavily depend on micro-level rainfall. Therefore, this study examines trends and variability of rainfall in Uttarakhand state of western Himalaya, India. The season and station-wise results of this study differ from India level results. The annual rainfall declined in high altitudes. Similarly, the monsoon rains declined in high altitudes and increased in low altitudes, whereas winter rainfall show mixed trends. The variability of monsoon rainfall was lowest for all stations and seasons, while the winters show low variability. Inter-seasonal variability is recorded highest in plains and lowest in high altitudes. [ABSTRACT FROM AUTHOR]

ABSTRACT The daily snow cover data from Interactive Multisensor Snow and Ice Mapping System ( IMS) by National Oceanic and Atmospheric Administration's National Environmental Satellite Data and Information Service ( NOAA/ NESDIS) covering the 2004-2012 time period is used in this study. In the first part of the study, daily IMS product is validated over Turkey using daily ground truth snow depth measurements from 219 climatological and synoptic sites. The categorical statistics of probability of detection ( POD) and false alarm rates ( FAR) are provided both for whole Turkey and with respect to geographical sub-regions. The overall POD and FAR amounts for Turkey are obtained as 73.55 and 25.11%, respectively. The performed analysis indicates an increase in IMS accuracies as the snowpack depth at the stations increase. In the second part of the study, the nonparametric Mann-Kendall test is performed to analyse the snow cover trend over Turkey with respect to sub-regions considering the whole year and each season separately. A negative trend in snow-covered area percentage is obtained for Turkey at the significance level of α = 0.05. From the seasonal perspective for Turkey, negative trend for spring and summer seasons, positive trend for autumn season and combination of negative and no trend for winter season are obtained at the same significance level. Almost the same results are valid for the sub-regions with some local and seasonal variations. [ABSTRACT FROM AUTHOR]

ABSTRACT There is little dispute that global surface air temperature has increased and the anthropogenic-induced global warming is likely to play an important role in the management of water resources of a river basin. Therefore, this study was undertaken for Godavari River basin, a large southern peninsular river basin in India. After removing the effect of significant lag-1 serial correlation by pre-whitening procedure, the Mann-Kendall ( MK) test was employed to investigate trends in maximum temperature ( Tmax), minimum temperature ( Tmin) and mean temperature ( Tmean) at 35 stations in the basin. At seasonal (monthly) time scales, a majority of the stations exhibited no trends in Tmean, Tmax and Tmin in any of the four seasons (12 months) with the exception of post-monsoon (December) for Tmax and monsoon (July and September) for Tmin. About 60% (45%) of the stations exhibited increasing trends in Tmax ( Tmin) in different durations: the month of December and post-monsoon season (the months of July and September and monsoon season) indicating the presence of an element of seasonal cycle in temperature over the Godavari basin. Results of tests of spatial and temporal homogeneity of trends by the Van Belle and Hughes method showed that trends in temperature over the Godavari basin were not homogeneous for different months or at different stations. In spite of the warmer climate in the basin, the evaporation (Epan) has been found to decrease significantly over the Godavari basin. Strong decreases in wind speed and increases in relative humidity may have actually caused the Epan decreases over the southern peninsular region of India. [ABSTRACT FROM AUTHOR]

ABSTRACT Variability and trends in daily and monthly near-surface temperatures in Uganda, collected over the period 1960-2008 (49 years), are analysed. For this purpose, daily observational maximum and minimum temperature records from eight selected stations in Uganda were acquired from the Uganda Meteorological Department ( UMD). Data collected by the UMD are quality controlled through a rigorous process before being archived. The data received were tested for homogeneity, gaps were filled and correlation analyses were used for validation of area average series. Statistical techniques (e.g. Mann-Kendall and Linear Regression) were employed to analyse temperature variability and to obtain temperature trends. Findings indicate that intra-annual temperature shows reduced variability over recent decades, but which is not statistically significant. Results also demonstrated that maximum temperatures are more variable compared to minimum temperatures in Uganda. An increasing trend in hot days, hot nights, warm nights and warm spells were also detected. At seven of the stations, annual temperature range and diurnal temperature range trends were found to be negative. The finding that intra-annual and intra-monthly variance is declining suggests that fewer anomalously extreme temperature episodes occur. The gap between maximum and minimum extremes is reducing, which supports the observation that minimum temperatures are on the increase. [ABSTRACT FROM AUTHOR]

Rainwater harvesting could increase the resilience of ecosystems on the Loess Plateau and thus ensure the sustainability of livelihoods that depend on them. As such, it is a key component of strategies for adapting to global climate change. In this study, we used a new method to quantify the rainwater harvesting potential (RWHP) across the whole Loess Plateau and to characterize its spatial and temporal variation over the last four decades on the basis of the variable infiltration capacity model. It was found that that the mean RWHP of the study region was 731.10 × 108 m3, and the average water layer thickness was 114.34 mm. There is considerable scope for rainwater harvesting across the Loess Plateau as a whole, to the extent that it could potentially provide enough water to implement the 'Grain for Green' Project. The annual average RWHP decreased slightly from 1971 to 2010, and Hurst exponent analysis indicated that this trend will exhibit long-term persistence. The annual RWHP was highest in the southeast of the Loess Plateau and lowest in the northwest. Areas with high RWHP values tended to be clustered around the middle reach of the Yellow River. For most areas, there was no significant change between 1971 and 2010. Those areas for which there was a significant decrease in RWHP were primarily located around the upper-middle reaches of the Weihe River, the upper reach of Jinghe River, the eastern Guanzhong Plain, the Qinhe River watershed and the area around Dongsheng. Quantitative assessments of RWHP are likely to be useful for guiding the development and use of innovative rainwater harvesting technologies around the world and could help to relieve the problems caused by water shortages on the Loess Plateau while simultaneously eliminate the major cause of soil erosion. Copyright © 2012 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Hydrological processes change from the impacts of climate variability and human activities. Runoff in the upper reaches of the Hun-Taizi River basin, which is mainly covered by forests in northeast China, decreased from 1960 to 2006. The data used in this study were based on runoff records from six hydrological stations in the upper reaches of the Hun-Taizi River basin. Nonparametric Mann-Kendall statistic was used to identify change trends and abrupt change points and consequently analyze the change characteristics in hydrological processes. The abrupt change in the annual runoff in most subcatchments appeared after 1975. Finally, the effects of climate change and land cover change on water resources were identified using regression analysis and a hydrology model. Results of the regression analysis suggest that the correlation coefficients between precipitation and runoff prior to the abrupt change were higher compared with those after the abrupt change. Moreover, using hydrology model analysis, the water yield was found to increase because of the decrease in forest land. Copyright © 2012 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

The Mann-Kendall (MK) test is a popular test for monotonic trend when the observations are independent, but its null distribution properties under independence do not apply to the situation where the observations are dependent. We provide block and sieve bootstrap methods for approximating the null distribution of MK in such a situation. In the case of the block bootstrap, when the observations follow a weakly dependent β mixing process, such an approximation is based on the determination that MK and its block bootstrap counterpart are asymptotically normal. In addition, we note that sieve methods are applicable to a statistic that is asymptotically equivalent to MK. Simulations are conducted to compare the significance levels achieved by both block and sieve bootstrap methods for various models. An effective procedure is proposed for testing for trend when the form of the underlying process is unknown. Copyright © 2013 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

ABSTRACT We examined trends in minimum and maximum temperatures in the Oahu during the period of past 39 (1969-2007) and 25 (1983-2007) years. We found a strong spatial and temporal variability in the temperature trends on Oahu. During the past 39 years, island-wide minimum temperature has increased by 0.17 °C/decade and shows a considerable variability in trends at individual location. There was no detectable trend found in maximum temperature over the same time period. The year 1983 was identified as the change point in the island-wide minimum temperature. During the recent 25 years annual and summer maximum temperature showed a decline while minimum temperature continued to increase. Trend in diurnal temperature range ( DTR) shows a decline during the past 39 years with a stronger decreasing trend during the recent 25 years. The trend in DTR for Oahu is much higher compared to the global DTR trend indicating a rapid warming in minimum temperature. Extreme temperature indices show a general warming during the past 39 years. There has been significant increase in tropical and warm nights at the two urban stations. Maximum temperature generally followed the Pacific Decadal Oscillation ( PDO) except the period when there is an increase in Hawaii Rainfall Index ( HRI). In contrast, minimum temperature showed better agreement with HRI compared to the PDO, at least up until 1999 after which it showed an increase. Despite the relative cooling in PDO during the recent decade an increase in minimum temperature can be attributed to a decline in HRI. [ABSTRACT FROM AUTHOR]

Non-parametric methods including Mann-Kendall (M-K) test, continuous wavelet transform (CWT) and discrete wavelet transform analysis are applied in this paper to detect the trend and periodic trait of precipitation data series in Beijing area where the data set spans nearly 300 years from 1724 to 2009. First, the trend of precipitation variables is elaborated by the M-K test (Sequential M-K test). The results show that there is an increasing trend (the value of this trend is 1.98) at the 5%-significance level and there are not turning points in the whole data series. Then, CWT and wavelet variance are used to check for significant periodic characteristics of data series. In the plots of wavelet transform coefficients and figure of wavelet variance, some periodic events affect the trend of the annual total precipitation series in Beijing area. 85-year, 35-year and 21-year periodic events are found to be the main periodic series of long-term precipitation data, and they are all statistically significant. Moreover, the results of non-parametric M-K test are exhibited on seven different combinations of discrete wavelet components. D5 (32-year periodicity) periodic component is the effective and significant component on data. It is coincident with the result (35-year periodic event as one part of main periodicity) by using CWT analysis. Moreover, approximation mode shows potential trend of the whole data set because it is the residuals as all periodicities are removed from data series. Thus, the mode A + D5 is responsible for producing a real basic structure of the trend founded on the data. Copyright © 2012 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Trend identification is a substantial issue in hydrologic series analysis, but it is also a difficult task in practice due to the confusing concept of trend and disadvantages of methods. In this article, an improved definition of trend was given as follows: 'a trend is the deterministic component in the analysed data and corresponds to the biggest temporal scale on the condition of giving the concerned temporal scale'. It emphasizes the intrinsic and deterministic properties of trend, can clearly distinguish trend from periodicities and points out the prerequisite of the concerned temporal scale only by giving which the trend has its specific meaning. Correspondingly, the discrete wavelet-based method for trend identification was improved. Differing from those methods used presently, the improved method is to identify trend by comparing the energy difference between hydrologic data and noise, and it can simultaneously separate periodicities and noise. Furthermore, the improved method can quantitatively estimate the statistical significance of the identified trend by using proper confidence interval. Analyses of both synthetic and observed series indicated the identical power of the improved method as the Mann-Kendall test in assessing the statistical significance of the trend in hydrologic data, and by using the former, the identified trend can adaptively reflect the nonlinear and nonstationary variability of hydrologic data. Besides, the results also showed the influences of three key factors (wavelet choice, decomposition level choice and noise content) on discrete wavelet-based trend identification; hence, they should be carefully considered in practice. Copyright © 2012 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Rainfall is the key climatic variable that governs the regional hydrologic cycle and availability of water resources. Recent studies have analysed the changes in rainfall patterns at global as well as regional scales in Australia. Recent studies have also suggested that any analysis of hydroclimatic variables should be performed at the local scale rather than at a large or global scale because the trends and their effects may be different from one location to the other. Because no studies were found specific to the Yarra River catchment, which is an important catchment in Victoria, Australia, this study performs a spatiotemporal trend analysis on long-term rainfall records at 15 measuring stations within the catchment. The Mann-Kendall test was used to detect trends, and Sen's slope estimator was used to calculate the slopes in both monthly and annual rainfall. Moreover, a cumulative summation technique was used to identify the trend beginning year, and prewhitening criteria were tested to check for autocorrelation in the data. The results showed that the monthly rainfall has generally decreasing trends except in January and June. Significant decreasing rainfall trends were observed in May (among the autumn months of March, April and May) at most stations and also in some other months at several stations. A decreasing trend was also observed in the annual rainfall at all stations. This study indicates that there has been a consistent reduction in rainfall over the catchment, both spatially and temporally over the past 50 years, which will have important implications for the future management of water resources. Copyright © 2012 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Annual maximum rainfall data from 51 stations in Canada were analyzed for trends and changes by using the Mann-Kendall trend test and a bootstrap resampling approach, respectively. Rainfall data were analyzed for nine durations ranging from 5 min to 24 h. The data analyzed are typically used in the development of intensity-duration-frequency (IDF) curves, which are used for estimating design rainfall values that form an input for the design of critical water infrastructure. The results reveal more increasing than decreasing trends and changes in the data with more increasing changes and larger changes, noted for the longer rainfall durations. The results also indicate that a traditional trend test may not be sufficient when the interest is in identifying changes in design rainfall quantiles. Copyright © 2012 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Seasonal changes of extreme daily temperature indices (frequency of frost days, tropical nights, and 'summer' days) of 25 stations in the Iberian Peninsula (IP) from 1929 to 2005 are investigated. Cluster analysis is used to identify homogeneous groups of stations with similar thermal regimes. The Mann-Kendall test is applied to look for statistically significant trends. The results show a significant decreasing trend (−0.6 days/decade), especially from 1965 onwards, in the frequency of frost days for coastal stations, and significant increasing trends, from 1980 onwards, especially important to the southeast of the IP (+3.8 days/decade) for summer tropical nights, and in the southern stations (+2.3 days/decade) for summer days. The behaviour of the winter frost days index is related to the evolution of winter NAO and EA patterns (with increasing trends in the last decades of the 20th century). Although multiple regression models establish a relationship between summer indices and the SCAN pattern, the behaviour of residuals indicates that summer indices must be explained by other causal mechanisms. Copyright © 2011 Royal Meteorological Society [ABSTRACT FROM AUTHOR]

ABSTRACT The interactions between precipitation, streamflow and groundwater are very complex. In cold temperate regions characterized by harsh winters, winter streamflow is mainly derived from aquifers that are recharged in the spring, during snowmelt, and in the fall, when evapotranspiration is subdued. Despite this complexity, the modes and trends in the interannual variability of spring (April, May, June and July) streamflow and fall (August, September, October and November) precipitation and streamflow were compared to the modes and trends in the interannual variability of winter (December, January, February and March) streamflow in southern Quebec from 1950 to 2000. Results indicate that the variability modes are identical for all four of these hydro-climatic variables: two modes (south-east and east modes) on the south shore of the St. Lawrence River on either side of the 47°N and a single mode (south-west mode) on the north shore. As for the trend, a significant increase in winter streamflow was observed on the north shore. This increase is comparable to that observed in spring streamflow, which suggests that winter streamflow on the north shore is mainly derived from groundwater recharge during the spring. Moreover, both spring and winter streamflows are positively correlated to the North Atlantic Oscillation climate index. On the south shore, south of the 47°N, a significant decrease was observed in the trend of the interannual variability of winter streamflow, this in spite of a significant increase in fall precipitation and streamflow. An increase in evaporation (decreased infiltration) due to a shift from forest cover to agricultural land cover in this region could account for this. However, fall precipitation and streamflow and winter streamflow are significantly correlated to the Atlantic Multidecadal Oscillation winter index. This correlation is negative with the first two variables but positive with the third. This study suggests that, in southern Quebec, the interannual variability of winter streamflow is mainly affected by spring recharge in non-agricultural catchments (east and south-west modes) and by farming in agricultural catchments (south-east mode). Copyright © 2011 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Mann-Kendall (MK) test for trend detection must be modified when the data are serially correlated, to prevent the detection of false trends. Various approaches are developed for this purpose, such as prewhitening, trend-free prewhitening, variance correction and block bootstrap. Each method has its own Type I and Type II errors. In this study, the errors of block bootstrapping MK test are estimated by a simulation study and compared with other methods. Optimal block length that minimizes the Type I error is determined as function of sample size and autocorrelation coefficient. It is shown that the power of block bootstrapping MK test is comparable with those of other modified MK tests. These tests are applied to some annual streamflow series with trend recorded in Turkish rivers, and their powers are compared. A modified form of the trend-free prewhitening procedure is proposed that has a smaller Type I error. Copyright © 2011 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Changing trends of peak flood and flood duration in the Wujiang River Basin are detected with the help of the Mann-Kendall test and the Pettitt analysis during the past 50 years. Results indicate that the peak flood and the flood duration at Lishi Station have different changing features. The peak flood showed only marginally increasing trend, whereas the flood duration exhibited decreasing trend at the significance level of 90%. The result shows a weak positive correlation between the peak flood and the flood duration. The changes of flood duration are influenced by the total rainfall duration, which is in downward trend at significance level 90%. In addition, the changing trends of peak flood are similar to the total rainfall amount. In the change-point analysis, it was found that the change points for the peak flood and flood duration series were in the years 1993 and 1966, respectively. Human activities such as the construction of reservoirs were the main driving forces causing the change of flood duration. The periodicity of the peak flood during the period 1955-2007 at Lishi Station is detected by using the wavelet analysis. The result indicates that the peak flood at Lishi Station displayed alternation between big floods and small floods on the 25- to 26-year period. At the same timescale, the peak flood of Wujiang River showed an evidence of change between big floods and small floods. It was essential to be prepared and aware of the consequences of climate changes and human influences affecting the water resources in the Wujiang River Basin. This result is expected to draw more attention from the local governments in its decision making and water resource management. Copyright © 2012 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]