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.
Streamflow trends in Indiana are evaluated for 31 USGS gauging stations that have 50
years or more continuous unregulated streamflow records. Trends are computed for selected streamflow statistics to ...include annual and seasonal low, medium, and high flow conditions by using four variations of the Mann–Kendall test. These variations include: (i) Mann–Kendall without autocorrelation, (ii) Mann–Kendall with lag-1 autocorrelation and trend-free pre-whitening, (iii) Mann–Kendall with complete autocorrelation structure, and (iv) Mann–Kendall with long term persistence. Mann–Kendall test is also applied to the precipitation data using the above four approaches to explore the relationship between precipitation and stream flow trends. Overall, there is an increasing trend in low and medium flow conditions across Indiana. However, these trend results are affected by the selection of flow statistic, annual/seasonal statistics, data length and consideration of autocorrelation structure. Specifically, the number of stations that show trends in low and medium flow statistics decreases significantly (up to 70%) when autocorrelation structure is considered in the analysis. The precipitation trends, however, are not affected by the autocorrelation structure, suggesting that factors other than precipitation trends are related to streamflow trends in Indiana. In addition, high flows are found to be less correlated to precipitation compared to low flows in heavily drained northern Indiana. This suggests that the subsurface drainage is playing a role in the observed streamflow trends in Indiana, but this issue needs further investigation. Overall, this study provides an elaborate view of past streamflow trends in Indiana which should be useful for further research including understanding the impact of future biofuel activities on Indiana hydrology and climate.
The Loess Plateau is the most severe soil and water loss area in the world. The changing trends of annual mean temperature and annual precipitation over the last 50years in the Loess Plateau Region ...(LPR) are investigated using observed time series from all available stations. The trends are assessed for both the entire LPR and its five integrated management divisions using the gridded data. It is shown that the region-averaged annual mean temperature has significantly increased over the last 50years (1.91°C/50yr), whereas the region-averaged annual precipitation shows a non-significant negative trend (−29.11mm/50yr). Spatially, there is an enhanced warming gradient but an obvious drying to weak wetting gradient from the southeast to the northwest across the region. On divisional scales, a significant warming trend is detected for all the divisions. A significant drying trend and a nearly significant drying trend are found for the first and second divisions, respectively, and a non-significant positive trend for other divisions. Therefore the region can be divided into the southeast warming and drying sub-region (SESR) and the northwest warming and weak wetting sub-region (NWSR). Further analysis shows that the SESR has a significant warming trend (1.71°C/50yr) and a significant drying trend (−47.62mm/50yr), and the NWSR has a significant warming trend (2.25°C/50yr) but a non-significant wetting trend (15.20mm/50yr). These results may have important implication in addressing the challenge of climate change in terms of the integrated management of the LPR.
► The changing trends are tested with the gridded data based on all 214 station series. ► The tests are conducted for the five management divisions of the region as well. ► The warming rate is over two times larger than the Northern Hemisphere average. ► The region-averaged annual precipitation shows a non-significant negative trend. ► The Loess Plateau Region can be divided into two sub-regions in terms of climate change.
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.
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. 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.
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.
Diagnosing the evolution trends of vegetation and its drivers is necessary for ecological conservation and restoration. However, it remains unclear what the underlying distribution pattern of these ...trends and its correlation with some drivers at large spatial-temporal scales. Here we use the normalized difference vegetation index (NDVI) to quantify the activity of vegetation by Theil–Sen median trend analysis and the Mann–Kendall test, Pearson correlation analysis and Boosted regression trees (BRT) model. Results show that about 34% of the global continent area has experienced greening in the grid annual NDVI from 1982 to 2015. The major greening areas were observed in the Sahel, European, India and south China. Only 10% of the global continent land areas were browning, and these were observed in Canada, South America, central Africa and Central Asia. BRT model shows that rainfall is the most important factor affecting vegetation evolution (63.1%), followed by temperature (15%), land cover change (8.6%), population (6.5%), elevation (6.4%) and nightlight (0.4%). It’s about 21% of the world’s continent were affected by rainfall, mainly in arid regions such as central Asia and Australia. The main temperature-affected areas accounted for 36%, located near the equator or in high latitudes.
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.
Extreme climate is one of the important variables which determine the capability of tropical peatland to act as either carbon sink and/or carbon source. The purpose of this study is to reveal the ...spatio-temporal trend in the long-term time series of extreme rainfall and temperature in Sarawak peatland cause by climate change. Gridded-based Princeton datasets were used for trend analysis spanning 68-year (1948–2016) based on Modified Mann-Kendall (m-MK) test which has the capability of distinguishing unidirectional trend with multi-scale variability. The m-MK test was also used to confirm the increasing or decreasing trend produce by Mann-Kendall (MK), and to discriminate the exaggeration in trend caused by serial auto-correlation due to the high effect of large scale climate events regulating the climate in the region. By using R-based program, RClimDex for extreme climate indices output, extreme climate under Northeast (NE) and Southwest (SW) monsoon showed lower grid point with significant changes under m-MK test compared to MK test at 95% significance level. Here, the exaggeration of trend by MK test has been reduced by using m-MK test which can accommodate the scaling effect in the time series due to inherent natural climate variability. Diurnal temperature range (DTR) was expected to decrease for both monsoons in the central-coastal region as minimum temperature (TN) increased more than maximum temperature (TX). Significant increase in extreme rainfall (R10, R20, Rnn) was spatially observed more during SW monsoon compared to NE monsoon, although with high spatial variability. Significant increase of TN indices of TNn and TN90p might cause increased rainfall intensity in the south and central-coastal region, while high TX indices of TXn might cause increased rainfall intensity in the north. Due to the imminent threat of climate change, this study gives scientists an essential view on the behavior of different extreme climate variables and its potential impact on the peatland area which is susceptible to flood and risk of fire during the NE and SW monsoon, respectively.
Trend analysis of climatic variables has received a great deal of attention from researchers recently. The main aim of this study was to investigate trends in maximum (T
max) and minimum (T
min) air ...temperatures in the annual, seasonal and monthly time-scales for 19 synoptic stations in the arid and semi-arid regions of Iran during 1966–2005. From the results it is clear that the majority of the trends in the annual, seasonal and monthly T
max and T
min time series showed increasing tendency during the last decades, while the increasing trends in the T
min series were stronger than those in the T
max series. The trend in annual T
max and T
min averaged over all 19 stations was 0.090 and 0.444
°C per decade, respectively. The T
max and T
min warming trends were more obvious in summer and winter than in autumn and spring. On the monthly basis, the highest T
max and T
min increases of 0.827 and 1.585
°C per decade were found at the stations located in the northeastern corner of the region in January and September, respectively.
► The T
max and T
min series significantly increased in the majority of the stations. ► The trend rates of T
min have been generally stronger than those in the T
max series. ► The winter and summer T
max and T
min series showed the strongest warming trends.
In this study, seasonal trends as well as dominant and significant periods of variability of drought variables were analyzed for 30 rainfall subdivisions in India over 141years (1871–2012). ...Standardized precipitation index (SPI) was used as a meteorological drought indicator, and various drought variables (monsoon SPI, non-monsoon SPI, yearly SPI, annual drought duration, annual drought severity and annual drought peak) were analyzed. Discrete wavelet transform was used in conjunction with the Mann-Kendall test to analyze trends and dominant periodicities associated with the drought variables. Furthermore, continuous wavelet transform (CWT) based global wavelet spectrum was used to analyze significant periods of variability associated with the drought variables. From the trend analysis, we observed that over the second half of the 20th century, drought occurrences increased significantly in subdivisions of Northeast and Central India. In both short-term (2–8years) and decadal (16–32years) periodicities, the drought variables were found to influence the trend. However, CWT analysis indicated that the dominant periodic components were not significant for most of the geographical subdivisions. Although inter-annual and inter-decadal periodic components play an important role, they may not completely explain the variability associated with the drought variables across the country.
•Trend and periodicity in monsoon, non monsoon and yearly SPI, drought severity, duration and peak over India is studied.•During the second half of 20th century, drought occurrences have increased over Northeast and Central India.•Inter-annual and inter-decadal periodic components play an important role in the observed trends in drought variables.•Inter-annual and inter-decadal periodic components may not completely explain the drought variability across the country.
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