Long-term ocean temperature trend and marine heatwaves

Marine heatwaves(MHWs)can cause irreversible damage to marine ecosystems and livelihoods.Appropriate MHW characterization remains difficult,because the choice of a sea surface temperature(SST)temporal baseline strongly influences MHW identification.Following a recent work suggesting that there should be a communicating baseline for long-term ocean temperature trends(LTT)and MHWs,we provided an effective and quantitative solution to calculate LTT and MHWs simultaneously by using the ensemble empirical mode decomposition(EEMD)method.The long-term nonlinear trend of SST obtained by EEMD shows superiority over the traditional linear trend in that the data extension does not alter prior results.The MHWs identified from the detrended SST data exhibited low sensitivity to the baseline choice,demonstrating the robustness of our method.We also derived the total heat exposure(THE)by combining LTT and MHWs.The THE was sensitive to the fixed-period baseline choice,with a response to increasing SST that depended on the onset time of a perpetual MHW state(identified MHW days equal to the year length).Subtropical areas,the Indian Ocean,and part of the Southern Ocean were most sensitive to the long-term global warming trend.

Effects of temperature and precipitation on drought trends in Xinjiang, China

The characteristics of drought in Xinjiang Uygur Autonomous Region(Xinjiang),China have changed due to changes in the spatiotemporal patterns of temperature and precipitation,however,the effects of temperature and precipitation—the two most important factors influencing drought—have not yet been thoroughly explored in this region.In this study,we first calculated the standard precipitation evapotranspiration index(SPEI)in Xinjiang from 1980 to 2020 based on the monthly precipitation and monthly average temperature.Then the spatiotemporal characteristics of temperature,precipitation,and drought in Xinjiang from 1980 to 2020 were analyzed using the Theil-Sen median trend analysis method and Mann-Kendall test.A series of SPEI-based scenario-setting experiments by combining the observed and detrended climatic factors were utilized to quantify the effects of individual climatic factor(i.e.,temperature and precipitation).The results revealed that both temperature and precipitation had experienced increasing trends at most meteorological stations in Xinjiang from 1980 to 2020,especially the spring temperature and winter precipitation.Due to the influence of temperature,trends of intensifying drought have been observed at spring,summer,autumn,and annual scales.In addition,the drought trends in southern Xinjiang were more notable than those in northern Xinjiang.From 1980 to 2020,temperature trends exacerbated drought trends,but precipitation trends alleviated drought trends in Xinjiang.Most meteorological stations in Xinjiang exhibited temperature-dominated drought trend except in winter;in winter,most stations exhibited precipitation-dominated wetting trend.The findings of this study highlight the importance of the impact of temperature on drought in Xinjiang and deepen the understanding of the factors influencing drought.

Spatial and Temporal Analysis of Maximum and Minimum Temperature Trends in Northern Sudan during (1990-2019)

The study addresses an urgent and globally significant issue of climate change by focusing on the detailed spatial and temporal analysis of temperature trends in Northern Sudan. It fills a critical research gap by providing localized data over a substantial period (1990-2019), which could help in understanding the nuanced impacts of climate change in Sahel regions like Northern Sudan. In addition, the comprehensive coverage of both spatial and temporal dimensions, supported by a substantial dataset from five meteorological stations, provides a thorough understanding of the subject area. The utilization of robust statistical methods (Mann-Kendall test and Sen’s slope analysis) for analyzing temperature trends adds scientific rigor and credibility to the findings. Our results reveal a consistently increasing trend in maximum temperatures across most stations, particularly during the hot season (AMJ). However, the wet season (JAS) shows high maximum temperatures but no significant trend. Moreover, significant increasing trends in minimum temperatures were observed in all stations except Abu Hamed, where the trend, although increasing, did not reach statistical significance during the hot and cold seasons, and the coldest temperatures were observed during the cold season. These findings underscore the complex temperature dynamics in Northern Sudan and highlight the need for continued monitoring and adaptive measures in response to ongoing climate changes in the region.

Analysis of Temperature Trends and Variations in the Arabian Peninsula’s Upper Atmosphere

In this study, the trends of upper-air temperatures are analysed by utilising radiosonde observations for the barometric levels at 700, 500, 300, 200, 150, 100 and 50 hPa from five meteorological stations within the Arabian Peninsula from January 1986 to August 2015. The mean monthly variations of the temperatures at these levels are characterised and established. The magnitudes of the annual trends of the mean temperatures for each site for the selected barometric levels are studied and statistically tested using Mann-Kendall rank statistics at different significance levels. The temperature trends at different pressure levels show that the upper troposphere and lower stratosphere are warming, while the middle troposphere is cooling which is consistent with the findings of other studies. The variations in upper air temperature observed in this study can be attributed to a range of factors, including increasing greenhouse gas concentrations, changes in atmospheric circulation patterns, variations in solar activity, aerosols and volcanic eruptions, and land use and land cover change.

Climate Trends and Their Impact on Sorghum Production in Marigat, Baringo County: A Historical Analysis

Climate is subject to fluctuations in the majority of the world, mainly caused by rainfall as well as temperature variations. Climate fluctuations in Kenya have resulted in the spread of desert-like conditions in the ASALs region, such as Marigat in Baringo County. As a county, Baringo experiences great variations in climate annually, as well as uncertainty in expected rains, thereby negatively impacting the production of crops such as sorghum. This study applied the rainfall anomaly index (RAI), standardised precipitation evapotranspiration index (SPEI), standard precipitation index (SPI), and Mann-Kendall (MK) statistical test for trends on historical climatic data in analysing both temperature and precipitation data over the period 1990 to 2022 to determine their trend, patterns and how they affect the production of sorghum crops. The machine learning method (R studio) with inputs was used to calculate the SPI, SPEI, RAI and MK trend test. The rainfall varied from below average to above average during the study period with no clear pattern in the RAI, SPEI and SPI values. The years 2020 and 2000 stood out as they had higher and lower rainfall than usual, respectively. The Marigat area generally experienced more rainfall during the high/long rainfall season (AMJJ). The MK trend test on average monthly rainfall, SOND, AMJJ, and annual precipitation confirmed a positive trend in precipitation. However, the short rainy season (SOND) was found to be the most variable period for rainfall, and there was a slight increase in daily average temperatures during this season.

The Variation Trend of Temperature and Rainfall in Chengdu and Its Effect on Agriculture

By using the ground climate observation data of Chengdu from 1951 to 2009,the time variation sequence of mean temperature,total rainfall,seasonal mean temperature and precipitation were studied.The results showed that there was a trend of decreasing-increasing with the temperature and a trend of decreasing with the rainfall in Chengdu.The main temperature increasing occurred in spring and main rainfall decreasing occurred in summer.With the M-K method analysis,the spring temperature change time was in 1968,and the summer rainfall change time was in 1977 in Chengdu.With the temperature increasing in spring,the accumulated temperature would be higher,and it was beneficial to the agriculture.With the rainfall decreasing in summer,there was more summer drought.We needed to build more water facilities to protect agriculture production in Chengdu.

Characteristics and Trend Variation of Light,Temperature and Water Resources in Dongling District of Shenyang Province in Recent 49 Years

The meteorological data of light,temperature and water during 1961-2009 were selected to analyze the trend variation of climatic resources and provide the basis for developing and utilizing local climate resources.The results indicated that light resource presented the decreasing tendency in Dongling District,annual radiation reduced by 528 MJ/m2,and annual sunshine duration decreased by 333 h.The heat resource presented the increasing tendency,the average annual temperature increased by 1.04 ℃,and active accumulated temperature increased by 228 ℃.The general trend of annual precipitation declined slightly,precipitation resource during every age changed slightly and would tend to be stable.

Trends of Temperature Extremes in China and their Relationship with Global Temperature Anomalies

Changes of temperature extremes over China were evaluated using daily maximum and minimum temperature data from 591 stations for the period 1961-2002. A set of indices of warm extremes, cold extremes and daily temperature range （DTR） extremes was studied with a focus on trends. The results showed that the frequency of warm extremes （F WE） increased obviously in most parts of China, and the intensity of warm extremes （I WE） increased significantly in northern China. The opposite distribution was found in the frequency and intensity of cold extremes. The frequency of high DTR extremes was relatively uniform with that of intensity： an obvious increasing trend was located over western China and the east coast, while significant decreases occurred in central, southeastern and northeastern China; the opposite distribution was found for low DTR extreme days. Seasonal trends illustrated that both F WE and I WE showed signifi- cant increasing trends, especially over northeastern China and along the Yangtze Valley basin in spring and winter. A correlation technique was used to link extreme temperature anomalies over China with global temperature anomalies. Three key regions were identified, as follows： northeastern China and its coastal areas, the high-latitude regions above 40~0N, and southwestern China and the equatorial eastern Pacific.

Trends of sea surface temperature and sea surface temperature fronts in the South China Sea during 2003–2017

The trends of the sea surface temperature(SST) and SST fronts in the South China Sea(SCS) are analyzed during2003–2017 using high-resolution satellite data. The linear trend of the basin averaged SST is 0.31°C per decade,with the strongest warming identified in southeastern Vietnam. Although the rate of warming is comparable in summer and winter for the entire basin, the corresponding spatial patterns of the linear trend are substantially different between them. The SST trend to the west of the Luzon Strait is characterized by rapid warming in summer, exceeding approximately 0.6°C per decade, but the trend is insignificant in winter. The strongest warming trend occurs in the southeast of Vietnam in winter, with much less pronounced warming in summer. A positive trend of SST fronts is identified for the coast of China and is associated with increasing wind stress. The increasing trend of SST fronts is also found in the east of Vietnam. Large-scale circulation, such as El Ni?o, can influence the trends of the SST and SST fronts. A significant correlation is found between the SST anomaly and Ni?o3.4 index, and the ENSO signal leads by eight months. The basin averaged SST linear trends increase after the El Ni?o event(2009–2010), which is, at least, due to the rapid warming rate causing by the enhanced northeasterly wind. Peaks of positive anomalous SST and negatively anomalous SST fronts are found to co-occur with the strong El Ni?o events.

A shift in the upper-ocean temperature trends in the South China Sea since the late 1990s

In this paper, the interdecadal variability of upper-ocean temperature in the South China Sea（SCS） is investigated based on several objectively analyzed data sets and two reanalysis data sets. The trends of the SCS sea surface temperature（SST） have changed from warming to cooling since the late 1990 s. A heat budget analysis suggests that the warming of the surface mixed layer during 1984-1999 is primarily attributed to the horizontal heat advection and the decrease of upward long wave radiation, with the net surface heat flux playing a damping role due to the increase of upward latent and sensible heat fluxes. On the other hand, the cooling of the surface mixed layer during 2000-2009 is broadly controlled by net surface heat flux, with the radiation flux playing the dominant role. A possible mechanism is explored that the variation of a sea level pressure（SLP） over the North Pacific Ocean may change the prevailing winds over the SCS, which contributes to the change of the SST in the SCS through the horizontal heat advection and heat fluxes.

Trends in Temperature and Precipitation Extremes over Circum-Bohai-Sea Region,China

Trends in temperature and precipitation extremes from 1961 to 2008 have been investigated over Circum-Bohai-Sea region, China using daily temperature and precipitation data of 63 meteorological stations. The re- suits show that at most stations, there is a significant increase in the annual frequency of warm days and warm nights, as well as a significant decrease in the annual frequency of cold days, cold nights, frost days, and annual diurnal tem- perature range （DTR）. Their regional averaged changes are 2.06 d/1 0yr, 3.95 d/10yr, -1.88 d/10yr, -4.27 d/10yr, -4.21 d/10yr and -0.20℃/10yr, respectively. Seasonal changes display similar patterns to the annual results, but there is a large seasonal difference. A significant warming trend is detected at both annual and seasonal scales, which is more contributed by changes of indices defined by daily minimum temperature than those defined by daily maximum tem- perature. For precipitation indices, the regional annual extreme precipitation displays a weak decrease in terms of magnitude and frequency, i.e. extreme precipitation days （RD95p）, intensity （RINTEN）, proportion （RPROP） and maximum consecutive wet days （CWD）, but a slight increase in the maximum consecutive dry days （CDD）, which are consistent with changes of annual total precipitation （PRCPTOT）. Seasonally, PRCPTOT and RD95p both exhibit an increase in spring and a decrease in other seasons with the largest decrease in summer, but generally not significant. In summary, this study shows a pronounced warming tendency at the less rainy period over Circum-Bohai-Sea region, which may affect regional economic development and ecological protection to some extent.

Long-Term Trends in Extreme Temperatures in Hong Kong and Southern China

The observed long-term trends in extreme temperatures in Hong Kong were studied based on the meteorological data recorded at the Hong Kong Observatory Headquarters from 1885-2008. Results show that, over the past 124 years, the extreme daily minimum and maximum temperatures, as well as the length of the warm spell in Hong Kong, exhibit statistically significant long-term rising trends, while the length of the cold spell shows a statistically significant decreasing trend. The time-dependent return period analysis also indicated that the return period for daily minimum temperature at 4°C or lower lengthened considerably from 6 years in 1900 to over 150 years in 2000, while the return periods for daily maximum temperature reaching 35°C or above shortened drastically from 32 years in 1900 to 4.5 years in 2000. Past trends in extreme temperatures from selected weather stations in southern China from 1951-2004 were also assessed. Over 70% of the stations studied yielded a statistically significant rising trend in extreme daily minimum temperature, while the trend for extreme maximum temperatures was found to vary, with no significant trend established for the majority of stations.

The Regions with the Most Significant Temperature Trends During the Last Century

Having analyzed a global grid temperature anomaly data set and some sea level pressure data during the last century, we found the following facts. Firstly, the annual temperature change with a warming trend of about 0.6°C/ 100 years in the tropical area over Indian to the western Pacific Oceans was most closely correlated to the global mean change. Therefore, the temperature change in this area might serve as an indi-cator of global mean change at annual and longer time scales. Secondly, a cooling of about -0.3°C/ 100 years occurred over the northern Atlantic. Thirdly, a two-wave pattern of temperature change, warming over northern Asia and northwestern America and cooling over the northern Atlantic and the northern Pa-cific, occurred during the last half century linked to strengthening westerlies over the northern Atlantic and the weakening Siberian High. Fourthly, a remarkable seasonal difference occurred over the Eurasian con-tinent, with cooling (warming) in winter (summer) during 1896–1945, and warming (cooling) in winter (summer) during 1946-1995. The corresponding variations of the North Atlantic Oscillation and the South-ern Oscillation were also discussed. Key words Temperature trend - Mann-Kendall’s Test - Significance - Regional difference - Correlation coefficient This study was supported by the Ministry of Science and Technology Projects G1999043400 and Na-tional Key Project- “Studies on Short-Term Climate Prediction System in China” under Grant No.96-908-01-04.

Analysis of Sampling Error Uncertainties and Trends in Maximum and Minimum Temperatures in China

In this paper we report an analysis of sampling error uncertainties in mean maximum and minimum temperatures （Tmax and Tmin） carried out on monthly,seasonal and annual scales,including an examination of homogenized and original data collected at 731 meteorological stations across China for the period 1951-2004.Uncertainties of the gridded data and national average,linear trends and their uncertainties,as well as the homogenization effect on uncertainties are assessed.It is shown that the sampling error variances of homogenized Tmax and Tmin,which are larger in winter than in summer,have a marked northwest-southeast gradient distribution,while the sampling error variances of the original data are found to be larger and irregular.Tmax and Tmin increase in all months of the year in the study period 1951-2004,with the largest warming and uncertainties being 0.400℃ （10 yr）-1 ＋ 0.269℃ （10 yr）-1 and 0.578℃ （10 yr）-1 ＋ 0.211℃ （10 yr）-1 in February,and the least being 0.022℃ （10 yr）-1 ＋ 0.085℃ （10 yr）-1 and 0.104℃ （10 yr）-1 ＋0.070℃ （10 yr）-1 in August.Homogenization can remove large uncertainties in the original records resulting from various non-natural changes in China.

The changing process and trend of ground temperature around tower foundations of Qinghai-Tibet Power Transmission line

After the construction of Qinghai-Tibet Highway and Railway, the Qinghai-Tibet Power Transmission(QTPT) line is another major permafrost engineering project with new types of engineering structures. The changing process and trend of ground temperature around tower foundations are crucial for the stability of QTPT. We analyzed the change characteristics and tendencies of the ground temperature based on field monitoring data from 2010 to 2014. The results reveal that soil around the tower foundations froze and connected with the artificial permafrost induced during the construction of footings after the first freezing period, and the soil below the original permafrost table kept freezing in subsequent thawing periods. The ground temperature lowered to that of natural fields, fast or slowly for tower foundations with thermosyphons,while for tower foundations without thermosyphons, the increase in ground temperature resulted in higher temperature than that of natural fields. Also, the permafrost temperature and ice content are significant factors that influence the ground temperature around tower foundations. Specifically, the ground temperature around tower foundations in warm and ice-rich permafrost regions decreased slowly, while that in cold and ice poor permafrost regions cooled faster. Moreover, foundations types impacted the ground temperature, which consisted of different technical processes during construction and variant of tower footing structures. The revealed changing process and trend of the ground temperature is beneficial for evaluating the thermal regime evolution around tower foundations in the context of climate change.

Historical Trends in Surface Air Temperature Estimated by Ensemble Empirical Mode Decomposition and Least Squares Linear Fitting

Ensemble empirical mode decomposition(EEMD) and least squares linear fitting(LSLF) are applied to estimate the historical trends of surface air temperature(SAT) from observations and Coupled Model Intercomparison Project Phase 5(CMIP5) simulations during the period 1901–2005. The magnitudes of trends estimated by the two approaches are comparable. The trend calculated by the EEMD approach is larger than that by the LSLF approach in most(23/27) of the models during 1901–2005. During the slow warming period, the EEMD trend is smaller than the LSLF trend. The rootmean-square errors(RMSEs) between the raw and reconstructed times series by the LSLF approach are larger than those by the EEMD trend component and multi-decadal variability components during 1901–2005 in most of the models and observations. During 1901–70(or 1971–2005), the RMSEs between the raw and reconstructed times series by LSLF are larger than those by the EEMD trend component. In this sense, the EEMD trend is a better choice to obtain the climate trends in observations and CMIP5 models, especially for short time periods. This is because the trend estimated by LSLF cannot capture the internal variability and the cooling in some years. The estimated global warming rates(trend) are consistently larger(smaller) than those from observations in 11 of 27 CMIP5 models during 1901–2005 in the slow and rapid warming periods. This implies these 11 models have consistent responses to greenhouse gases for any period.

Climatology and Trends of High Temperature Extremes across China in Summer

Based on the daily maximum air temperature data from 300 stations in China from 1958 to 2008, the climatological distribution of the number of days with high temperature extremes （HTEs, maximum temperatures higher than 35℃） are studied with a focus on the long-term trends. Although the number of HTE days display well-defined sandwich spatial structures with significant decreasing trends in central China and increasing trends in northern China and southern China, the authors show that the decrease of HTE days in central China occurs mainly in the early period before the 1980s, and a significant increase of HTE days dominates most of the stations after the 1980s. The authors also reveal that there is a jump-like acceleration in the number of HTE days at most stations across China since the mid 1990s, especially in South China, East China, North China, and northwest China.

Trends in extreme high temperature at different altitudes of Southwest China during 1961–2014

This study analyzed the trends in extreme high temperature in Southwest China based on the observed daily maximum temperature and average temperature data from 410 Chinese stations recently released by the China Meteorological Administration.The authors found that the trends in extreme high temperature at different altitudes of Southwest China exhibit staged variations during a recent 50-year period(1961–2014).The trends in mean temperature and maximum temperature also exhibit phase variation.All temperature-related variables increase gently during the period 1975–94,whereas they increase dramatically during the recent period of 1995–2014,with a rate that is approximately two to ten times more than that during 1975–94.In addition,the trends in mean temperature,maximum temperature,and the frequency of extreme high temperature in the low altitudes transit from negative to positive in the two periods,while they increase dramatically in the mid-and high-altitude areas during 1995–2014,the well-known global warming hiatus period.In particular,the maximum temperature increases much faster than that of average temperature.This result implies that the regional temperature trend could be apparently different from the global mean temperature change.

Analysis of Monthly, Seasonal and Annual Air Temperature Variability and Trends in Taiz City - Republic of Yemen

Climate change is one of the most important issues of today’s World. Climate scientists have concluded that the earth’s surface air temperature warmed by 0.6 ± 0.2℃ during the 20th century, accompanied by changes in the hydrologic cycle. Of all the climate elements, temperature plays a major role in detecting climate change brought about by urbanization and industrialization. This study focuses on the variability and trends of the mean annual, seasonal and monthly surface air temperature in Taiz city, Republic of Yemen, during the period 1979-2006. The results of the analysis of the whole period reveal a statistically significant increasing trend in practically all the months and seasons. A tendency has also been observed towards warmer years, with significantly warmer summer and spring periods and slightly warmer autumn and winter, an increase of 1.79℃ and 1.18℃ has been observed in the mean summer and mean winter temperature, respectively. Positive trends of about 1.5℃ in the annual mean temperature were found for the whole period. The air temperature time series are analyzed, so that the variability and trends can be described.

Urban Heat Island Effect over National Capital Region of India: A Study using the Temperature Trends

The local temperature is one of the major climatic elements to record the changes in the atmospheric environment brought about by industrialization, increasing population and massive urbanization. The present study deals with the annual and seasonal temperature trends and anomalies for maximum, minimum and mean temperatures of the four meteorological stations of the National Capital Region (NCR) of India namely Safdarjung, Palam, Gurgaon and Rohtak for the past few decades and their association with the development through urbanization processes. The annual mean maximum temperature did not show any specific trend;however a consistent increasing trend was seen in the annual mean minimum temperatures indicating an overall warming trend over the NCR especially after 1990. This warming trend is contrary to the cooling trend observed by earlier studies till 1980’s in various other cities of India including Delhi. However, the temperature trends in annual mean minimum temperatures reported in various countries (USA, Turkey, Italy, etc.) across the world showed warming trends to be associated to the urbanization process of the cities also. The current warming trends in temperature in the NCR Delhi based on the annual mean minimum temperatures have thus been supported by the trends in other parts of the world and could be utilized to infer the development process in this region. The urbanization pattern within Delhi is reflected by the trends of differences in annual mean minimum temperature of the two stations within the city namely Safdarjung and Palam. The significance of the warming trends of the annual minimum temperature for the urban heat island effect is also discussed.