•The increments in future PET showed a strong spatial variability.•PET will increase by 12.7%–23.9% at the end of this century.•Future PET trend was detected by Mann–Kendall and Sen’s slope estimator ...tests.•Magnitude of the future PET trend showed a very strong spatial variability.•Magnitude of the PET trend ranged from 10.4mm/10yr to 29.7mm/10yr in 2011–2100.
The spatiotemporal change and trend of annual potential evapotranspiration (PET) over the Loess Plateau of China from 2011 to 2100 are assessed in this work. PET is calculated using the Hargreaves model with monthly mean, maximum, and minimum temperatures and a 1km spatial resolution, which are generated using the Delta downscaling method and general circulation models (GCMs) with four representative concentration pathway (RCP) scenarios. The PET trend is detected via Mann–Kendall and Sen’s slope estimator tests. The following results are drawn: (1) the Delta downscaling method shows a favorable performance in detecting GCM monthly temperatures based on the mean absolute error and regression analysis between downscaled data and independent surface observations. Among the 28 GCMs, the NorESM1-M and GISS-E2-R models show the best performance in reproducing the monthly mean/maximum and minimum temperatures over the Loess Plateau, respectively; (2) the average annual PET over this region will increase by 12.7%–23.9% from 1961 to 1990 to the end of this century (2071–2100). However, these increments show strong spatial variations; (3) the annual PET during the 2011–2100 period at each grid of the region demonstrates a significantly increasing trend under each RCP scenario, while RCP2.6, RCP4.5, RCP6.0, and RCP8.5 have average magnitudes of trend of 10.4mm/10yr, 17.7mm/10yr, 21mm/10yr, and 29.7mm/10yr, respectively; (4) the annual PET with significant trends during the other three periods (2011–2040, 2041–2070, and 2071–2100) present various spatial distributions in their magnitudes of trend under the aforementioned RCP scenarios. RCP2.6 showed a significant decrease during 2041–2070 and 2071–2100, although such trends are only observed at 0.3% and 1.2% of the Loess Plateau, respectively; and (5) the spatial results provide some information, such as locations and area ratios, which are valuable in assessing future PET changes and trends. These spatiotemporal results represent the PET changes and trends in detail and provide insights for developing flexible adaptation and mitigation strategies to combat the effects of global warming in this region.
The polycyclic aromatic hydrocarbon (PAH) family is of environmental concern due to its toxicity, prompting the need of monitoring their long-term trends. Three monitoring programs in Hong Kong ...report concentrations of ambient PAHs, namely (1) respirable suspending particle (RSP) speciation program that monitored benzoapyrene (BaP) (1997 to March 2000), (2) total suspended particle speciation program that monitored BaP (1997–1999), and (3) toxic air pollutant monitoring program that monitors BaP and 16 other PAHs in the combined gas and particulate phases at two general urban stations once or twice a month since January 1998. In this work, we review all the available PAH measurements in Hong Kong during 1997–2016, with emphasis on the temporal trends of BaP and the other 16 PAHs. PAHs of 5–6 rings exhibit an ambiguous decline trend since 1998, with a negative Sen’s slope that is statistically significant. Specifically, BaP was reduced by 78% from 1998 to 2016, with a Sen’s slope of −0.013 ng m-3 year−1. Correlations of BaP with RSP major species of high source specificity and PAH diagnostic ratios are employed to explore the source origins of PAHs. Our analysis reveals that PAHs mainly come from a combination of vehicular emissions and biomass/coal combustion. The decline trend of PAHs is further found in consistence with the declined particulate matter emissions from vehicular exhaust and biomass/coal combustion. This study fills the data vacancy in the long-term trends of ambient PAHs for the Pearl River Delta region, one of the economically more advanced regions in China.
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•Benzoapyrene decreased at the rate of 0.013 ng/m3/year during 1998–2016.•Other 5–6 ring PAHs show similar declining trends.•Major sources of PAHs are biomass burning, coal combustion and vehicular exhaust.•Reductions in emission amounts of these sources have led to the declines in PAH levels.
The aim of the present study was to investigate 50 years (1964–2013) of seasonal and annual rainfall trends and their fluctuation over time in northern Bangladesh. After testing the autocorrelation, ...non-parametric Mann–Kendall test along with Sen Slope estimator was used to examine rainfall trends and their magnitudes. The sequential Mann–Kendall test was used to identify any fluctuations in the trends over time and to detect the possible points of change in the rainfall series. We found that pre-monsoon and post-monsoon rainfall is increasing in most of the rainfall stations. The only decrement in pre-monsoon rainfall was found for Ishurdi (1.28mm/year). However, the sequential Mann–Kendall test detected decreasing pre-monsoon rainfall trend after early the 1990s. Monsoon rainfall showed a decreasing trend in the majority of the area studied. The maximum decrement in monsoon rainfall was found for Sylhet station (8.10mm/year) and minimum in Mymensingh (1.53mm/year). An upward monsoon rainfall trend was found for Rangpur (2.02mm/year). Annual rainfall followed the monsoon rainfall trend. However, all of the positive and negative trends were found statistically non-significant at 95% confidence limit with the only exception for monsoon and annual rainfall at Rajshahi station. Rajshahi station was the only region where the monsoon and annual rainfall has a significant negative trend at 95% confidence limit. The sequential Mann–Kendall test detected several non-significant points of change for seasonal and annual rainfall at most of the stations. Periodic fluctuations were also detected. We observed that there were decreasing seasonal rainfall trend after early the 1990s for the majority of the stations.
•We studied the seasonal and annual rainfall trend, their fluctuations, and possible change point for northern Bangladesh.•Monsoon rainfall is decreasing non-significantly in most of the northern Bangladesh.•Pre-monsoon and post-monsoon rainfall shows a non-significant (at 95% confidence limit) increasing trend in most of the study area.•The sequential Mann–Kendall test reveals periodic fluctuations for seasonal rainfall at majority of the stations.•Decreasing seasonal rainfall trend were found after the early 1990s in most of the stations
In the last few decades, climate changes have become the most important topic in the field of climatology. Reference evapotranspiration (ET0) is often used to identify regions prone to drought or ...aridity. In this paper, we used monthly data recorded in 57 weather stations in Romania over the period 1961–2007. The FAO Penman–Monteith method, based on air temperature, sunshine duration, relative humidity and wind speed, was employed in order to calculate ET0. Seasonal, annual, winter wheat and maize growing seasons data sets of ET0 were generated. The trends were detected using the Mann–Kendall test and Sen's slope, while an ArcGIS software was employed for mapping the results. The main findings of the study are: positive slopes were found in 71% of the data series considered and almost 30% of the total number of series were found significant at α=0.05; the highest frequency of the increasing trends as well as their absolute maximum magnitude were detected during summer and maize growing season; in winter, significant increasing changes are specific mainly to the extra-Carpathians regions; in autumn decreasing ET0 is specific to more than 80% of the locations, but the significant decrease characterizes mainly the southern half of the country; during the growing seasons of maize and winter wheat, the increase of the ET0 is dominant for the entire country. The relative change decreases with the increase of the length of the period considered: the most intense changes were detected for climatic seasons, followed by crop growing seasons and annual values. Among the climatic seasons, the highest relative increase is specific to winter followed by summer, spring and autumn, while for the crop growing seasons the values detected are similar.
•Annual ET0 is higher than precipitation, mainly in the extra-Carpathian regions.•The annual ET0 is increasing in Romania in more than 70% of the locations.•ET0 increases during summer in 91% of the 57 weather stations considered.•In autumn, ET0 is decreasing in 84% of the locations.•Relative change of ET0 is more intense in winter than in summer.
•California has shown a wide range of ombroxeric levels (OXI).•Upper strong dry level was found in the north of the State.•Lower weak arid level was found in both the Sonora and Mojave ...deserts.•Annual trend results have shown an increase in bioclimatic drought throughout California.•June, July and August are the months that show the highest levels of bioclimatic drought.
Drought occurs naturally all over the world. Global warming has led an increase in the areas affected by this phenomenon. The study of drought involves the analysis of indicators and indices used to assess changes in the hydrological cycle of a region. A large number of indices developed for drought monitoring are based on meteorological and hydrological variables. This research has applied the Ombroxeric Index for the first time in California. It is based on the concept of ombroxericity: a condition of the territory characterised from an ombrothermic point of view, which can develop in relatively humid areas/zones, depending on the time scale of the study (i.e. monthly, seasonal or annual basis). Temperatures and precipitation from 180 meteorological stations have been considered for a period of observation from 1980 to 2016. In order to know the evolution of this index, a modified trend analysis based on the Mann-Kendall test and a modified Sen slope analysis were used. Empirical Bayesian Kriging was applied as an interpolation technique. Results are presented in both surface and contour maps. California showed a wide range of ombroxeric levels that went from upper strong dry in northern zones, to lower weak arid. Trend results showed an increase in bioclimatic drought throughout the whole State. In addition, summer showed the highest levels on the Ombroxeric Index. An increase in drought trends was observed at the seasonal level, being more pronounced in summer and spring. In both cases are increases in the central (+5 and +3.6 units year−1 respectively) and the southern (+4 and +4.5 units year−1 respectively) areas of the State. Increasing frequency and severity of droughts could have implications for the management of water resources and the survival of Californian vegetation types, such as conifers.
Assessing the long-term precipitation changes is of utmost importance for understanding the impact of climate change. This study investigated the variability of extreme precipitation events over ...Pakistan on the basis of daily precipitation data from 51 weather stations from 1980-2016. The non-parametric Mann–Kendall, Sen’s slope estimator, least squares method, and two-tailed simple t-test methods were used to assess the trend in eight precipitation extreme indices. These indices were wet days (R1 ≥1 mm), heavy precipitation days (R10 ≥ 10 mm), very heavy precipitation days (R20 ≥ 20 mm), severe precipitation (R50 ≥ 50 mm), very wet days (R95p) defining daily precipitation ≥ 95 percentile, extremely wet days (R99p) defining daily precipitation ≥ 99 percentile, annual total precipitation in wet days (PRCPTOT), and mean precipitation amount on wet days as simple daily intensity index (SDII). The study is unique in terms of using high stations’ density, extended temporal coverage, advanced statistical techniques, and additional extreme indices. Furthermore, this study is the first of its kind to detect abrupt changes in the temporal trend of precipitation extremes over Pakistan. The results showed that the spatial distribution of trends in different precipitation extreme indices over the study region increased as a whole; however, the monsoon and westerlies humid regions experienced a decreasing trend of extreme precipitation indices during the study period. The results of the sequential Mann–Kendall (SqMK) test showed that all precipitation extremes exhibited abrupt dynamic changes in temporal trend during the study period; however, the most frequent mutation points with increasing tendency were observed during 2011 and onward. The results further illustrated that the linear trend of all extreme indices showed an increasing tendency from 1980- 2016. Similarly, for elevation, most of the precipitation extremes showed an inverse relationship, suggesting a decrease of precipitation along the latitudinal extent of the country. The spatiotemporal variations in precipitation extremes give a possible indication of the ongoing phenomena of climate change and variability that modified the precipitation regime of Pakistan. On the basis of the current findings, the study recommends that future studies focus on underlying physical and natural drivers of precipitation variability over the study region.
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.
A widespread dimming with a magnitude of about −4.3 and −1.7% per decade was observed under all‐ and clear‐sky conditions in Iran since the 2000s. This decrease in the amount of all‐sky global solar ...radiation was overall in agreement with the trends observed in cloud cover (CC) and seems to have occurred as a combined effect of aerosols and CC increase over Iran.
ABSTRACT
This study investigates the spatio‐temporal variations of global solar radiation and its relationships with cloud cover (CC) during 1998–2015 in Iran, where no previous information about the variations of solar radiation based on direct measurements exists. The variations in the mentioned variables were detected using a modified Mann–Kendall trend test and the magnitudes of trends were estimated by using the Theil–Sen's slope estimator method. A widespread dimming with a magnitude of about −4.3 and −1.7% per decade is found under all‐ and clear‐sky conditions in Iran since the 2000s (median over nine observation sites). A significant increase in CC was observed at most of the stations studied, at 20.0% per decade (median over nine sites). The decrease in the amount of all‐sky global solar radiation seems to have occurred as a combined effect of aerosol and CC increase over Iran. However, in the south of Iran and at the station Tehran dimming appears to be mostly due to an increase in the amount of aerosol loadings.
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