The Mann-Kendall test for trend has gained a lot of attention in a range of disciplines, especially in the environmental sciences. One of the drawbacks of the Mann-Kendall test when applied to real ...data is that no distinction can be made between meaningful and non-meaningful differences in subsequent observations. We introduce the concept of partial ties, which allows inferences while accounting for (non)meaningful difference. We introduce the modified statistic that accounts for such a concept and derive its variance estimator. We also present analytical results for the behaviour of the test in a class of contiguous alternatives. Simulation results which illustrate the added value of the test are presented. We apply our extended version of the test to some real data concerning blood donation in Europe.
•We examined annual precipitation and temperature trends in Qinghai, Northwest China.•We detected four major sub-regions of drought with different climatic variabilities.•Spatiotemporal ...characteristics of four different drought sub-regions were studied.•We investigated periodical features of drought in Qinghai.
It is vital to understand long-term drought variability and its causes for better water resource management in precipitation deficit regions. In order to assess the characteristics and potential risk of drought in Qinghai Province (as a typical arid and semi-arid area in China), the temporal trends of precipitation and temperature data (daily records from 1961 to 2006) of 44 stations across this province were firstly detected using the Mann–Kendall trend test. The self-calibrating Palmer drought severity index (PDSI), rotated empirical orthogonal function (REOF), and continuous wavelet transform (CWT) were used to further evaluate and investigate spatial patterns, temporal variations and periodicities of dryness/wetness conditions in Qinghai. The results show that: (1) A significant increasing trend in annual mean temperature can be detected in most parts of Qinghai over the last five decades, especially in Qaidam Basin. A non-significant downward trend in annual precipitation can be found in the eastern and southeastern regions of the province; (2) Four dominantly geographical sub-climate regions of dryness/wetness conditions were identified – the source region (Tuotuo River) of the Yangtze River, Qaidam Basin, the Qilian Mountains area, and the eastern agricultural area; (3) With respect to temporal variations of dryness/wetness conditions in each sub-region, only the source region (Tuotuo River) of the Yangtze River indicates a long-term wet tendency over the past 46 years; (4) A 3–5-year significant (at 95% confidence level) periodical oscillation can be detected in the PDSI series of the source region of the Yangtze River and 5–7-year and 8–10-year periods exist in Qaidam Basin. However, periodical features in the Qilian Mountains and eastern agricultural area are not statistically noticeable. The results of this study will be beneficial for water resource management, forecasting, and preparations for potential drought hazards in Qinghai Province and also be a valuable reference for other arid and semi-arid areas.
The present study performs the spatial and temporal trend analysis of the annual and 24‐hr maximum rainfall of a set of 145 precipitation gauging stations of Iran. The study shows that the annual ...rainfall is decreasing at 67% of the stations while the 24‐hr maximum rainfall is increasing at 50% of the stations. The negative trends of annual rainfall are mostly observed in northern and northwestern regions, whereas positive trends of 24‐hr maximum rainfall are mostly located in arid and semiarid regions of Iran. However, the Kolmogorov‐Smirnov test for Mann‐Kendall (MK) statistics show that the regional trend of annual rainfall is significant, but it is not significant for 24‐hr maximum rainfall. On the other hand, the sequential MK test reveals that the trends of annual rainfall and 24‐hr maximum rainfall began since 1970s for most of the stations. The negative trend of the rainfall for most of the country may show the initial stages of climate change in Iran, but further information and analysis is required for future studies.
Coal fires pose great threats to valuable energy resources, the ecological environment, and human safety. They are one of the most persistent fires on the Earth, which can burn for an extremely ...long-term period from decades to hundreds or even thousands of years. Remote sensing detection of coal fires is of significance for mitigating coal fire hazards. Nevertheless, short-term or temporal discrete land surface temperature (LST) data have limited capability in characterizing the persistent coal fire. This study proposed a methodology to monitor persistent coal fires using long-term Landsat thermal images and further to analyze spatiotemporal dynamics of coal fires. A total of 1118 high-quality Landsat images (each image containing <inline-formula> <tex-math notation="LaTeX">446\times446 </tex-math></inline-formula> pixels) spanning 35 years from 1986 to 2020 in the Wuda coalfield area (China) were processed to retrieve the LST. LST time series of each pixel was decomposed into the seasonal, trend, and remainder components. Coal fire areas were demarcated by using the range of the trend components. To trace the trend and change point of the LST time series, the Mann-Kendall test was applied to the trend components, and the Pettitt test was employed to the original time series vectors of those pixels located in the coal fire areas, respectively. The random sample consensus algorithm was utilized to identify the background temperature (inliers) and high temperature (outliers) and, thus, judge the coal fire burning period, and the symbolic aggregate approximation algorithm was used to evaluate the robustness of the judgment. The calibration was conducted according to the filed surveys, obtaining spatiotemporal 3-D coal fire dynamics. The proposed methodology was testified by comparisons with fieldwork and regional anomaly extractor algorithm, demonstrating good performance in comprehensive monitoring of persistent coal fires.
Time-series of annual rainfall, number of rainy-days per year and monthly rainfall of 20 stations were analyzed to assess climate variability in arid and semi-arid regions of Iran. The results showed ...mixed trends of increasing and decreasing rainfall, which were statistically significant (
p<0.05 and
p<0.01) only for Sabzevar and Zahedan stations by the Mann–Kendall test. Also, with the exception of Kashan and Torbat stations there was no statistically significant trend in the mean number of rainy-days per year. Increasing and decreasing monthly rainfall trends were found over large continuous areas in the study region. These trends were statistically significant mostly during the winter and spring seasons, suggesting a seasonal movement of rainfall concentration. Results also showed that there is no significant climate variability in the arid and semi-arid environments of Iran.
ABSTRACT
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.
Locations of the selected 200 daily stations in NSW, Australia.
Studying weekend-weekday variation in ground-level ozone (O3) allows one to better understand O3 formation conditions, with a potential for developing effective strategies for O3 control. Reducing ...inappropriately the O3 precursors emissions can either produce no reduction or increase surface O3 concentrations. This paper analyzes the weekend-weekday differences of O3 at 300 rural and 808 urban background stations worldwide from 2005 to 2014, in order to investigate the O3 weekend effect over time and assess the effectiveness of the precursors emissions control policies for reducing O3 levels. Data were analyzed with the non-parametric Mann-Kendall test and Theil-Sen estimator. Rural sites typically did not experience a weekend-weekday effect. In all urban stations, the mean O3 concentration on the weekend was 12% higher than on weekdays. Between 2005 and 2014, the annual mean of daily O3 concentrations increased at 74% of urban sites worldwide (+ 0.41 ppb year−1) and decreased in the United Kingdom (- 0.18 ppb year−1). Over this time period, emissions of O3 precursors declined significantly. However, a greater decline in nitrogen oxides (NOx) emissions caused an increase in Volatile Organic Compounds (VOCs) to NOx ratios leading to O3 formation. In France, South Korea and the United Kingdom, most urban stations showed a significant upward trend (+ 1.15% per year) for O3 weekend effect. Conversely, in Canada, Germany, Japan, Italy and the United States, the O3 weekend effect showed a significant downward trend (- 0.26% per year). Further or inappropriate control of anthropogenic emissions in Canada, Southern Europe, Japan, South Korea and the United States might result in increased daily O3 levels in urban areas.
•Urban ozone levels generally showed increasing trends over time: + 0.35 ppb year−1.•Ozone pollution is becoming a major environmental concern in cities.•The ozone weekend effect increased in France, South Korea, and the United Kingdom: + 1.15% year−1.•It did not increase in Canada, Germany, Italy, Japan and the United States: - 0.26% year−1.•Ozone control in cities should be planned considering the ozone chemical regime.
Karnataka state has the second highest rainfed agricultural land in India, where agricultural output relies heavily on rainfall. The Shimsha basin, a sub-basin of Cauvery in the state, comes under a ...semi-arid region and predominantly consists of rainfed agricultural land. Rainfall patterns have changed dramatically with time resulting in frequent floods and droughts. Understanding the spatiotemporal distribution of rainfall and its change patterns in the area would benefit sustainable agriculture planning and water resources management practices. The current study aims to determine the variability and trend in rainfall. The daily rainfall data of the Shimsha basin from 1989 to 2018 is collected, and the annual, seasonal, and monthly rainfall totals and the number of rainy days are derived. All the time series are subjected to statistical methods to examine rainfall variability and trend. The mean, standard deviation, coefficient of variation (CV), and Standardized Anomaly Index are used for the preliminary and variability analysis, while the coefficient of skewness and kurtosis are used to understand the rainfall distribution characteristics. The homogenous and serially independent series are identified by homogeneity and serial correlation tests. The trend in the homogenous and serially independent series is identified by Mann–Kendall and Spearman’s rank correlation tests, while the magnitude of the trend is quantified using the Sen’s slope technique, and the trend change point is evaluated using the sequential Mann–Kendall test. Based on the study, the average rainfall in the study area is 801.86 mm, with CV ranging from 43.3 to 22.27%. The southwest monsoon (SWM) season brings the greatest rain to the basin, followed by the post-monsoon (PM), summer, and winter seasons. In the annual time frame, except one station, all other stations have shown significant or insignificant increasing trends. The seasonal rainfall has shown insignificant rising trends during the summer and winter seasons while insignificant increasing and decreasing trends during the PM season. The SWM season has indicated significant increasing trends, insignificant increasing and decreasing trends. Overall, the study area has noticed an increased annual and seasonal rainfall except for the post-monsoon season, during which the rainfall showed a considerable decline. The findings of the study are helpful in water resource management, agricultural planning, and socioeconomic development in the study area.
In this paper, the Mann–Kendall test and F-test were combined to analyze the annual and seasonal streamflow variations and aberrance points for the twin rivers from 1963 to 2011. The Tennant method ...was subsequently used to evaluate the ecological flow assurance and deficit. Finally, the Double Mass Curve method was applied to identifying the human activities affecting the streamflow variations. The results were as follows: (1) Three similar stages of the streamflow variations were found for the twin rivers: fluctuations before 1980, the tiny downward trends from the 1980s to the 1990s, and the notably downward trends in the 2000s. (2) The seasonal streamflow also decreased continuously and dramatically, especially in summer, by 80.9% for the Chaohe River and 86.0% for the Baihe River. (3) During the spawning season, 83.3% and 73.1% of streamflow was not at the appropriate level for the Chaohe and Baihe Rivers, respectively, which indicated that the ecological environment was not optimal for the reproduction and breeding of aquatic organisms. While in other periods, the ecological flow assurance was better than that in spawning seasons for the Chaohe and Baihe Rivers, respectively. This indicated that the streamflow regimes of the twin rivers were not always optimal and conducive to the development of the aquatic ecosystem. (4) The streamflow variations of the twin rivers were influenced by increasingly intensive human activities such as changes of land use and land cover, and excessive exploitation and utilization of water resources. These influences were cumulative and showed a gradually increasing tendency. This research is helpful for understanding the streamflow regime and for forecasting of the regional extreme climate, such as drought and floods, and can provide a basis for decision making and formulating adaptive ecological security countermeasures in response to climate changes and human activities.
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•Streamflow variations of the twin rivers were compared at a basin scale.•The MK test and F-test were combined to evaluate streamflow variations and aberrance.•Ecological flow assurance and deficit were considered for river ecosystem protection.•Impacts of human activities on streamflow variations were detected for twin rivers.
Climate change affects many meteorological parameters that could result in spatiotemporal variations of the hydrological cycle. These variations can affect local rainfall intensities or design ...storms; therefore, it is necessary to assess the local effects of climate change in different areas. Therefore, the current research aims at evaluating the accuracy of the precipitation data of the most recent Coupled Model Intercomparison Project phases 5 and 6 (CanESM2 from CMIP5 and CanESM5 from CMIP6 models), over a historical period from 1953 to 2010, as well as the predicted data for the future between 2010 and 2050 for the Quebec City rain gauge Station (Jean Lesage Intl). In this regard, precipitation data were analyzed using a statistical index to find the most accurate model for the study area. The results of this evaluation showed that CanESM5 is more accurate than CanESM2 for most of the evaluation indices. However, both of these models did not perform well since the precipitation prediction for CanESM5 (as the accurate model) R index was 0.48 for the monthly and was 0.75 in the seasonal scale. In addition, the Bias index revealed that both models underestimated rainfall prediction with negative index values for both scales and models. The trend of future precipitation under socio–economic scenarios (4.5 (pessimistic) and 8.5 (optimistic)) shows that the changes in future precipitation are not significant. In addition, for scenario 4.5, the trend of precipitation decreases for almost half of the year, while for scenario 8.5, the magnitude of the decrease and the number of months with a decreasing trend of precipitation are significantly reduced when compared to scenario 4.5.
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