Mann-Kendall Test Results Research Articles

Long-Term Land Use Land Cover Change in Urban Centers of Southwest Ethiopia From a Climate Change Perspective

Long-term urban land use land cover change (LULCC) dynamics and climate change trends in Southwest Ethiopia's four urban centers were examined for 60 years. Remote sensing, aerial photos, and Landsat, temperature, and rainfall data were analyzed from a climate change perspective over the Jimma, Bedelle, Bonga, and Sokorru urban centers of southwest Ethiopia from 1953 to 2018. Based on geospatial analysis and maximum likelihood supervised image classification techniques to classify LULCC categories, the Mann-Kendall test was applied to perform trend analyses on temperature and rainfall. The LULCC analysis revealed that built-up areas over the urban centers had shown an increasing trend, with the highest increment by 2,360 hectares over Jimma, while vegetation, wetland, and cropland declined due to conversion of plain lands to built-up areas and other similar zones. The pronounced decline of vegetation coverage was 1,427, 185,116, and 32 hectares in Jimma, Bedelle, Bonga, and Sokorru, respectively. Mann-Kendall test results showed a significant sign of intra-seasonal and inter-annual variability of rainfall while the summer and annual rainfall patterns remained less variable compared to other seasons. This study's findings revealed that when the mean between the two climatic normals of 1953–86 is compared with 1987–2018, the temperature has significantly increased in the latter three decades. The rapid expansion of built-up areas coupled with a sharp decline of green space or vegetation and agricultural/croplands could lead to gradual changes in LULCC classes, which have contributed to the changing of the local climate, especially the surface temperature and rainfall over the urban centers of southwest Ethiopia. Therefore, we recommend that the local urban administrations emphasize sustainable urban development by integrating urban planning policies with land use to protect the environment by adopting local municipal adaptation and national climate change strategies. Restoration of the local environment and creation of climate-smart cities could be critical to the resilience of urban dwellers and ecosystems to the changing climate by enhancing grass-root climate services. To that end, we recommend further advanced research to understand how urban LULC-related changes and other factors contribute to local and regional climates, as urban areas of Southwest Ethiopia are undergoing a rapid transformation of their rural surroundings.

Trends of Annual Whole-body Occupational Radiation Exposure for Industrial Practices in China (2009-2018).

The national status and dose trends on the occupational exposure to ionizing radiation in industrial practices for 2009-2018 in China are presented in terms of seven occupational categories. A total of 504,538 industrial radiation workers were monitored for the period 2009-2018, with a continuous increase in the number of workers from 23,789 in 2009 to 66,017 in 2018. The annual average effective doses were 0.399, 0.425, 0.392, 0.376, 0.346, 0.355, 0.312, 0.305, 0.270, and 0.230 mSv from 2009 to 2018, respectively, which were well lower than the recommended occupational dose limit of 20 mSv y-1 for radiation workers. The Mann-Kendall test result shows a statistically significant decreasing trend at a rate of 0.02 mSv y-1 in average annual effective doses (p<0.001). In addition, more than 95.4% of radiation workers in industrial practices received an average annual effective dose less than the public dose limit of 1 mSv. It was also found that the average annual effective doses in industrial radiography and well logging were significantly higher than those in five other categories (p<0.001). Based on these observations, it is still necessary to control and manage the workplace and radiation workers to control occupational exposure as low as reasonably achievable, especially for the workers engaged in these two activities.

Spatio-temporal analysis of dry and wet periods in Iran by using Global Precipitation Climatology Center-Drought Index (GPCC-DI)

In this study, the temporal and spatial characteristics of droughts in Iran, including severity, duration, frequency, and extent, were studied using the GPCC-DI, in a 68-year period from 1952 to 2019. To display and analyze these features, time trend components, intensity, duration, and area diagrams, Mann-Kendall non-parametric test and Kriging geostatistical method were used. The result of plotting intensity-duration-frequency maps shows an increasing trend in regional drought severity and spread. It was also found that the most severe droughts occurred in the 12- and 24-month periods from 2000 onward. Mann-Kendall test results also show that significant increases in droughts occurred in the central desert basins of Hamoon basin and south Baluchistan in the southeastern Iran. In addition, decrease in occurrences of dry and wet periods happened in the western, northwestern, and coastal regions of the Caspian Sea. The pattern of spatial variations of drought severity indicated two major drought foci in southeast and central Iran. The number of drought centers in Iran has also increased over time. The results of the analysis of the time trends of dry and wet periods point to the occurrence of continuous droughts in 12- and 24-month periods.

Visual and statistical inference of hourly and sub-hourly extreme rainfall trends Central Anatolia, Turkey case

The analysis of long-term rainfall data in a changing climate is important because it has many sectoral applications such as agriculture, infrastructure, and water resources management. Statistical analyses of the annual maximum rainfall data were performed using the Mann–Kendall (MK) trend test to evaluate the annual maximum trend characteristics of the rainfall time series, the innovative trend analysis (ITA) method to detect categorial trends, and the ITA indicator to digitize the ITA results. Storm durations of 5, 10, 15, 30 min and 1, 3, 6, 24 h annual maximum rainfall series at 13 central stations in Central Anatolia, Turkey were used. According to the MK test results, there were no significant upward or downward monotonic trend at four stations, whereas the remaining nine stations showed a significant upward or downward monotonic trend. Significant negative and positive trends were identified for the sub-hourly and hourly rainfall, whereas significant positive trends were detected for hourly storm durations. Significant trend results were mostly consistent with the general ITA results. The sub-hourly storm duration data were more consistent in terms of significant trends. Conversely, when evaluated according to low, medium, and high data values in the rainfall series (categories), the high data values showed different trends. Although no trend was detected with the MK test, the ITA results showed an upward or downward trend for 25 rainfall series. 29 of 30 significant MK test results were consistent with the ITA indicator results, compared with 24 of 30 results of the visually inspected ITA results.

Temporal variability and trend analysis of temperature and rainfall in the Northern highlands of Ethiopia

ABSTRACT This study investigates the temporal variability and trend of temperature and rainfall in Gelana sub-watershed, northern highlands of Ethiopia. The study employed a mixed methods approach, but overwhelmingly relied on gridded monthly rainfall and maximum and minimum temperature data at a resolution of 10 × 10 km. The quantitative data were analyzed using standardized rainfall anomaly, precipitation concentration index, coefficient of variation and Mann-Kendall (MK) trend analysis. The results indicated that rainfall over “Kiremit” and “Belg” seasons is found highly variable in the study area. The annual total rainfall has shown an increasing trend of 0.05 mm per year. The MK test results showed that “Kiremit” rainfall has a positive increasing trend, while Belg rainfall showed a statistically significant decreasing trend. A warming trend of annual maximum and minimum temperature has been observed over the study area. The study suggests strategies to enhance the adaptive capacity of agricultural systems and to reduce the likelihood of production risks.

Long-term changes in climatic variables over the Bharathapuzha river basin, Kerala, India

The current study analyzes the changes in the climate pattern of Bharathapuzha river basin in Kerala, India, which experiences a significant imbalance in water availability since 1990. The analysis of the climatic variables shows that there are three climatic zones existing in the basin. The trend in the historic climatic variables is estimated using the non-parametric Mann-Kendall test and the Sen slope analysis. A discrete wavelet analysis is also performed to separate only the long period component of the signal, and its trend is also studied. A significant decreasing trend is observed in the rainfall. However, a monotonous long-term increasing trend is detected for monthly average temperatures and monthly minimum temperatures. The sequential Mann-Kendall test result shows a significant change in the climatic pattern after 1980. The rainfall effectiveness of the basin is analyzed using indices. A drought analysis is also conducted using Standardized Precipitation Index (SPI) in different time scales since climatic zones 2 and 3 in the catchment are drought-prone areas in recent years. A detailed analysis on the existence of climate change in this region is conducted for the first time. These results can be further used for planning and development of climate change adaptation policies for the basin.

Changes in reference evapotranspiration and its driving factors in peninsular Malaysia

Trends in reference evapotranspiration (ETo) have been found highly diverse in different regions of the globe due to the contradictory changes in the meteorological variables that define ETo. Despite a significant impact of ETo in water resources and ecology, knowledge on the changes and the cause of the changes in ETo is very limited in tropical regions. The trends in ETo, the factors influencing the changes in ETo and the change point (year) that made the trend significant were evaluated in this study for tropical peninsular Malaysia. The modified version of Mann-Kendall (MK) test was used for the assessment of unidirectional changes in ETo and the driving meteorological variables. The innovative trend analysis (ITA) was conducted to understand the variations in change with time. Sobol's method was used to measure the sensitivity of ETo to different meteorological factors and the Sequential MK test was employed to identify the change point. The study revealed an increase in annual (0.009–0.026 mm/year) and seasonal (0.014–0.027 mm/year during southwest monsoon and 0.015–0.074 during northeast monsoon) ETo in peninsular Malaysia which contradicts to evapotranspiration paradox found in many regions. The minimum temperature (31.5–48.2%) was found as the most influencing factor followed by wind speed (15.1–32.8%.) in defining ETo in peninsular Malaysia. Analysis of ITA and sequential MK test results revealed that the rise in minimum temperature is the major cause of the increase in ETo in peninsular Malaysia. A faster rise in minimum temperature after 1981–1985 caused an increase in ETo after 1993–1996 in most of the locations. The minimum temperature in the region was noticed to rise much faster compared to the global average which indicates a large and continuous increase in ETo due to global warming and thus, reduction in atmospheric water balance in peninsular Malaysia.

Trend Analyses of Meteorological Variables and Lake Levels for Two Shallow Lakes in Central Turkey

Trend analyses of meteorological variables play an important role in assessing the long-term changes in water levels for sustainable management of shallow lakes that are extremely vulnerable to climatic variations. Lake Mogan and Lake Eymir are shallow lakes offering aesthetic, recreational, and ecological resources. Trend analyses of monthly water levels and meteorological variables affecting lake levels were done by the Mann-Kendall (MK), Modified Mann-Kendall (MMK), Sen Trend (ST), and Linear trend (LT) methods. Trend analyses of monthly lake levels for both lakes revealed an increasing trend with the Mann-Kendall, Linear, and Sen Trend tests. The Modified Mann-Kendall test results were statistically significant with an increasing trend for Eymir lake levels, but they were insignificant for Mogan lake due to the presence of autocorrelation. While trend analyses of meteorological variables by Sen Test were significant at all tested variables and confidence levels, Mann-Kendall, Modified Mann-Kendall, and Linear trend provided significant trends for only humidity and wind speed. The trend analyses of Sen Test gave increasing trends for temperature, wind speed, cloud cover, and precipitation; and decreasing trends for humidity, sunshine duration, and pan evaporation. These results show that increasing precipitation and decreasing pan evaporation resulted in increasing lake levels. The results further demonstrated an inverse relationship between the trends of air temperature and pan evaporation, pointing to an apparent “Evaporation Paradox”, also observed in other locations. However, the increased cloud cover happens to offset the effects of increased temperature and decreased humidity on pan evaporation. Thus, all relevant factors affecting pan evaporation should be considered to explain seemingly paradoxical observations.

Analysis and prediction of vegetation dynamics under the background of climate change in Xinjiang, China.

BackgroundVegetation dynamics is defined as a significant indictor in regulating terrestrial carbon balance and climate change, and this issue is important for the evaluation of climate change. Though much work has been done concerning the correlations among vegetation dynamics, precipitation and temperature, the related questions about relationships between vegetation dynamics and other climatic factors (e.g., specific humidity, net radiation, soil moisture) have not been thoroughly considered. Understanding these questions is of primary importance in developing policies to address climate change.MethodsIn this study, the least squares regression analysis method was used to simulate the trend of vegetation dynamics based on the normalized difference vegetation index (NDVI) from 1981 to 2018. A partial correlation analysis method was used to explore the relationship between vegetation dynamics and climate change; and further,the revised greyscale model was applied to predict the future growth trend of natural vegetation.ResultsThe Mann-Kendall test results showed that th e air temperature rose sharply in 1997 and had been in a state of high fluctuations since then. Strong changes in hydrothermal conditions had major impact on vegetation dynamics in the area. Specifically, the NDVI value of natural vegetation showed an increasing trend from 1981 to 2018, and the same changes occurred in the precipitation. From 1981 to 1997, the values of natural vegetation increased at a rate of 0.0016 per year. From 1999 to 2009, the NDVI value decreased by an average rate of 0.0025 per year. From 2010 to 2018, the values began an increasing trend and reached a peak in 2017, with an average annual rate of 0.0033. The high vegetation dynamics areas were mainly concentrated in the north and south slopes of the Tianshan Mountains, the Ili River Valley and the Altay area. The greyscale prediction results showed that the annual average NDVI values of natural vegetation may present a fluctuating increasing trend. The NDVI value in 2030 is 0.0196 higher than that in 2018, with an increase of 6.18%.ConclusionsOur results indicate that: (i) the variations of climatic factors have caused a huge change in the hydrothermal conditions in Xinjiang; (ii) the vegetation dynamics in Xinjiang showed obvious volatility, and then in the end stage of the study were higher than the initial stage the vegetation dynamics in Xinjiang showed a staged increasing trend; (iii) the vegetation dynamics were affected by many factors,of which precipitation was the main reason; (iv) in the next decade, the vegetation dynamics in Xinjiang will show an increasing trend.

Long-Term Variation of the Wave Power Density in the South China Sea Over the Past 28 Years

Based on 28 years of hindcast data, this paper describes in detail the long-term variation trend of wave power density in the South China Sea. WAVEWATCH-III (WW3), the third generation wave computing model, which plays an important role in wave prediction. WW3 was used for inverse calculation of wave parameters, with spatial resolution of $0.25^{\circ }\times 0.25^{\circ }$ and time resolution of 6h. The validity of the data was verified by three typhoon processes and the significant wave height data of the satellite altimeter in 2010. According to 28-year(1990–2017) hindcast data set, the author respectively mapped the South China Sea mean monthly, seasonal, annual wave power density (WPD) and the change trend diagram, including the long-term trend of WPD Mann-Kendall (MK) test, come the following conclusions: (1) Influencing the area WPD change trend of the dominant increasing season is winter (DJF), in which season average growth of WPD is about 1kW/m, and the largest waters is closed to 3kW/m. (2)The dominant growing month for WPD is in December, by compared with the before and next month in the largest growing sea area, it shows an increase and decrease trend of 10kW/m and 20kW/m respectively. (3)MK test results indicate that the long-term change of WPD keep on an increasing trend, but it is not significant, among which WPD had an increased mutation in 2000. (4)The dominant sea area is around Luzon Strait-Taiwan Strait- D.S Islands (116°E, 21°N). The average growth of WPD among these area in 28 years are about 0.15–0.25(kW/m)/yr.

Hydrological drought assessment of the Tisza river

Drought is a natural phenomenon that occurs when the availability of water is significantly below the normal levels during a shorter or longer period of time and cannot meet the necessary demand. This study focused on hydrological drought assessment of the Tisza River on four gauging stations: Vasarosnameny, Szolnok, Szeged, and Senta for the period 1964–2018. An effective Streamflow Drought Index (SDI) has been recently proposed and widely used for determining hydrological droughts. Both long- and short-term droughts have very severe impacts on the investigated locations. Two drought periods can be singled out: the first period was from 1983 to 1993, with the exceptions in 1985 and 1987. This period is characterized by higher absolute SDI values on Vasarosnameny (–0.84) and Szolnok (–0.87) than on Szeged (–0.29) and Senta (–0.40) stations. The second period was more severe and lasted from 2011 to 2015, with an average SDI value of –1.32 on Vasarosnameny, –1.08 on Szolnok, –0.53 on Szeged, and –0.57 on Senta station. The Mann-Kendall test results indicate that there is no trend indicating transition from humid towards more arid condition over the investigated period.

The Watershed Structures in Controlling Runoff - Case Study of Sardasht Basin in IRAN

In order to investigate the performance of constructed structures in Sardasht watershed, Soil and Water Assessment Tools model for simulation of runoff and sediment during the studied period of 1996-2012 was carried out for two cases of existence and absence of flood control structures. From 2007 onwards by performing watershed operations in these sub-basins, the average runoff rate decreased about 250 l/s for sub-basin 1 and 150 l/s for sub-basin 3. This indicates the flood was controlled in these basins. On average, the runoff volume has decreased by 0.25 and 0.15 m3 in the sub-basins 1 and 3 respectively in the presence of the structure compared to the absence of structures. A daily, Monthly simulation time stage and a continuous-time step restrict the usage of the SWAT pattern for comprehensive, occurrence-based flood simulation. The occurrence of acridities and unexpected projections in numerous sectors of IRAN, also the density on basic conveniences precious by mass growth, has owing to a broader difference in deliberation to the problematic of water straight in the alliance. Calibrating a hydrologic model of Sardasht Basin. Using SWAT. Subjective Workload Assessment Technique (SWAT) is a multidimensional scaling method designed to assess time load, mental effort load and stress load. According to the results of Mann-Kendall Test, Watershed management in the Sardasht basin for flood control and runoff can be considered acceptable. Before the watershed operation, the occurrence of runoff with the probability of 80% was zero, which after the operation, the probability of occurrence was reduced by 60%, indicating a positive effect construction of flood and sediment control structures in the Sardasht basin. The results of the hydrological regime curve show that the changes in the monthly runoff ratio to the average monthly runoff before the watershed operations had been more. Due to the limitations, current Soil and Water Assessment Tools simulations in tropical and subtropical regions face a series of problems related to relative humidity, water balance and sediment. Soil and Water Assessment Tools model is also used to estimate the maximum daily flow rate.

Impact of climate change on the rainfall pattern of Klip River catchment in Ladysmith, KwaZulu Natal, South Africa

Rainfall trend analysis has been of major focus in the past century because of the attention given to climate change by the science and engineering community. According to some latest studies, rainfall is one of the main parameters in any catchment which plays a significant role in flood frequency, flood control as well as water resources planning and management. Ladysmith town in South Africa is flooded almost every year resulting in loss of lives as well as properties and businesses. Thus, this study aimed at determining the monthly and annual rainfall pattern in relation to climate change. The monthly, seasonal and annual rainfall trends for the period 1985 – 2018 were analyzed using Mann-Kendall test and Sen’s slope estimation. Results of this study indicated a variability in seasonal rainfall, with a rainfall increase during December and January of summer months whose Mann-Kendall test results were 1.88 and 0.73, and a major decrease showed in autumn months (March, April, and May) with Mann-Kendall test values of -2.76, -3.53 and -4.09. Thus, the overall results suggest a minor significant change for both Ladysmith and upstream of the Klip river catchment. Based on the analysis, it can be concluded that climate change has an impact on the rainfall spatial pattern of the study area. This correlates well with similar analysis carried out in other areas around the world.

Evaluation of long-term water quality management policy effect using nonparametric statistical methods

Long term water quality change was analyzed to evaluate the effect of the Total Maximum Daily Load (TMDL) policy. A trend analysis was performed for biochemical oxygen demand (BOD) and total phosphorus (TP) concentrations data monitored at the outlets of the total 41 TMDL unit watersheds of the Nakdong River in the Republic of Korea. Because water quality data do not usually follow a normal distribution, a nonparametric statistical trend analysis method was used. The monthly mean values of BOD and TP for the period between 2004 and 2015 were analyzed by the seasonal Mann-Kendall test and the locally weighted scatterplot smoother (LOWESS). The TMDL policy effect on the water quality change of each unit watershed was analyzed together with the results of the trend analysis. From the seasonal Mann-Kendall test results, it was found that for BOD, 7.8 % of the 41 points showed downward trends, 26.8 % and the rest 65.9% showed upward and no trends. For TP, 51.2% showed no trends and the rest 48.8% showed downward trends. From the LOWESS analysis results, TP began to decrease in most of the unit watersheds from mid-2010s when intensive chemical treatment processes were introduced to existing wastewater treatment plants. Overall, for BOD, relatively more points were improved in the main stream compared to the points of the tributaries although overall trends were mostly no trend or upward. For TP, about half of the points were improved and the rest showed no trends.

Reconstruction of sunspot activity, cold and warm events, and drought and flood events in the central plain of China during the northern Song Dynasty using historical documents

The Northern Song Dynasty was an important and prosperous dynasty in the history of China, and it existed during a period of climate abnormality. Climate change research for the Northern Song Dynasty era has significance for understanding the interaction between agricultural civilizations in the central plains and nomadic populations in northern China, transfer of the economic and cultural centers of China, and the vicissitudes of the Northern Song Dynasty. There is currently considerable disagreement regarding climate change in the Central Plain during the Northern Song Dynasty era. Many precious and valuable historical documents and records about the Northern Song Dynasty have been collected, and abundant records of sunspot activity, cold and warm weather, drought and flood events have been compiled. Using the Mann-Kendall test, wavelet analysis, R/S analysis, and frequency analysis etc. mathematical statistics methods, sunspot activity, cold and warm events, and drought and flood events were quantitatively reconstructed. There are 15 sunspot maximum years and 16 sunspot minimum years, the cycle length of sunspot activity is 8–14 years, and the average cycle length is 11 years. Hot years account for 11.3% of the total years; warm years account for 12.7%; cold years account for 20.7%; and freezing cold years account for 3.3%. Mann-Kendall test results show that cold and warm variations are natural fluctuations, and there is no indication of abrupt climate change during the Northern Song Dynasty. Morlet wavelet analysis indicates that there are weak high-frequency oscillations and short oscillation periods with three years before 1052 AD, and there are oscillation periods of six years and clear alternations between warmth and cold during 1060-1120 AD. R/S analysis indicates that the Hurst index (H) of cold and warm index series is 0.6155, and the fractal dimension (D) is 1.3845. Since 0.5 < H < 1 and 1 < D < 1.5, fractal structures are evident in the time series of cold and warm indexes, past increments are positively correlated with future increments, and the average cycle length in the time series for cold and warm indexes is 6 years. Temperatures first decreased rapidly followed by a slow increase with long-term fluctuations, and the mean temperature during the Northern Song Dynasty era is 0.4 °C higher than that in the period 1880–1979 AD. Severe drought, moderate drought, moderate flood, severe flood and normal years account for 15.3%, 25.3%, 11.3%, 6.7%, 41.4% of all years, respectively. Frequency analysis indicates that cooling, warming, drought and flood events show a close relationship to sunspot activity.

A Scenario-Based Approach for Assessing the Hydrological Impacts of Land Use and Climate Change in the Marboreh Watershed, Iran

In separate analyses of the impacts of land use change and climate change, a scenario-based approach using remote sensing and hydro-climatological data was developed to assess changes in hydrological indices. The data comprised three Landsat TM images (1988, 1998, 2008) and meteorological and hydrological data (1983–2012) for the Aligudarz and Doroud stations in the Marboreh watershed, Iran. The QUAC module and supervised classification maximum likelihood (ML) algorithm in ENVI 5.1 were used for remote sensing, the SWAT model for hydrological modelling and the Mann-Kendall and t test methods for statistical analysis. To create scenarios, the study period was divided into three decades (1983–1992, 1993–2002, 2003–2012) with clearly different land use/land cover (LULC). After hydrological modelling, 10 hydrological indices related to high and low flow indices (HDI and LDI) were analysed for seven scenarios developed by combining pre-defined climate periods and LULC maps. The major changes in land use were degradation of natural rangeland (− 18.49%) and increasing raid-fed farm area (+ 16.70%) and residential area (+ 0.80%). The Mann-Kendall test results showed a statistically significant (p < 0.05) decreasing trend in rainfall and flow during 1983–2012. In the scenarios evaluated, hydrological index trends were more sensitive to climate change than to LULC changes in the study area. Low flow indices were more affected than high flow indices in both land use and climate change scenarios. The results show little impact of land use change and indicate that climate change is the main driver of hydrological variations in the catchment. This is useful information in outlining future strategies for sustainable water resources management and policy decision-making in the Marboreh watershed.

Evidence of climate variability from rainfall and temperature fluctuations in semi-arid region of the tropics

The pattern of rainfall and temperature behaviour in the Hadejia River Basin (HRB) has been assessed. The behaviour of rainfall and temperature have been used as proxies in detecting the presence of climate variability. Historical rainfall and temperature monthly data spanning thirty-six years (1980–2015) obtained from the Nigerian Meteorological Agency (NIMET) was used in this study. ANOVA and Mann-Kendall trend test was used for the data analysis. The ANOVA results showed significant variation in rainfall, maximum and minimum temperature between the stations. The Mann-Kendall trend test result shows an increasing trend in both rainfall and temperature in annual statistics, though statistically insignificant. However, the monthly trends result showed mixed results of both significant and insignificant as well as increasing and decreasing trends. The mean, standard deviation and the coefficient of variation were spatially interpolated using inverse distance weightage technique for easy comprehension. Even though the annual increasing trends result was statistically insignificant except for two out of the ten stations, it is still crucial for planning water-related activities and programs considering the sensitivity and fragility of the region to minor climatic variations.

Inter-reanalysis differences of the temperature trends in the MERRA-2.0 and ERA-Interim: comparison of the middle and lower atmosphere

Studying the long-term temperature variations and trends helps to understand the role of human activities in climate change. We present the temperature trends (calculated by the linear regression method) in the Northern hemisphere in all seasons for the period of 1980–2016 for the ERA-Interim and MERRA-2.0 reanalyses. The temperature trends are analyzed for the six standard post-processed pressure levels (850, 500, and 250 hPa for the troposphere and 70, 10, and 2 hPa for the stratosphere). In addition, we calculate the non-parametric Mann-Kendall test to detect the statistically significant temperature trends in different pressure levels and seasons. It is found that both reanalyses have a negative temperature trend (cooling) in the stratosphere, and the magnitude of the cooling rates increases with increasing height. While the largest cooling trend (by considering all pressure levels and seasons) occurs in the autumn for the MERRA-2.0 (− 0.167 K/year), the largest cooling trend is in winter for the ERA-Interim (− 0.118 K/year). Furthermore, the results of the MANN-Kendall test reveal considerable differences in terms of statistically significant temperature changes between two reanalyses at 10 hPa where the cooling trends are statistically significant at 99% level in all seasons in MERRA-2.0 reanalysis while the temperature changes are only significant at 99% level in autumn in ERA-Interim. In general, the magnitude of the cooling trends in the middle and upper stratosphere is higher for the MERRA-2.0 than ERA-Interim. Positive temperature trends (warming) are found for the bulk of troposphere, though the magnitude of the temperature changes over the study period is higher in the lower troposphere (at 850 hPa at 99% confidence level) for both reanalyses. The largest warming rates are found during autumn season where the magnitude of the temperature changes are + 0.031 (K/year) and + 0.033 (K/year) for the MERRA-2.0 and ERA-Interim, respectively. Our results suggest a high level of uncertainty in the temperature trends in the middle and upper stratosphere and a reasonable agreement between ERA-Interim and MERRA-2.0 warming trend in the troposphere. We also briefly discuss the role of different sources of uncertainty of the temperature trends in the middle and upper stratosphere.

Assessing the Spatio-temporal Variability of Meteorological Drought in Jordan

In the last decade, severe drought impacts have been witnessed in Jordan and there is an immense need to develop drought management strategy and policy framework to tackle this problem. This study aimed to investigate the spatio-temporal variability of precipitation based on long-term data using Standardized Precipitation Index (SPI) to assess the trend and intensity of drought in Jordan. In this context, the data of 29 meteorological stations of the last 37 years have been obtained from Jordan Meteorological Department. SPI-3, SPI-6 and SPI-12 have been calculated to assess short- and long-term drought events, and Mann–Kendall and linear regression tests were applied to detect the drought trend in the study region. Drought of varying duration and intensity was detected at each time scale (3-, 6-, and 12-month SPI) as well as at each meteorological station. The SPI results show that Jordan faces an increasing frequency of drought with a probability of occurrence once in every 2 or 3 years. On contrary to this, long-term drought occurs in whole country once in every 15–20 years which have more than 2-year consecutive duration. The Mann–Kendall test result shows significant temporal decrease in the amount of precipitation at all meteorological stations except Madaba. The results of linear regression test indicate significant increase in magnitude of drought with the rate 0.02/annum with a significance of 0.0001 using SPI values. This study concluded that there is an increasing drought trend and the situation will become more severe in future as the amount of rainfall is decreasing gradually in Jordan.

Spatio-temporal analysis of the climate impact on rice yield in north-west India

The effects of climate, fertilizers and irrigation on rice yield and spatial variations of growing season climatic variability were analyzed in the three regions (North-west, Central and South-west) of Indian Punjab from 1974 to 2013. There was a linear increase in rice yield in Punjab (30 kg ha−1 year−1 in north-east, 29 kg ha−1 year−1 in central and 34 kg ha−1 year−1 in south-west region) over 40 years. The results of Mann-Kendall test and Sen’s slope estimator showed an increase in minimum temperature (0.03 °C year−1 in North-east Punjab and, 0.04 °C year−1 each in Central and South-west Punjab) but no significant trend in maximum temperature and rainfall during the rice growing season (June–September). Among different climatic and technological variables, 49% of the variance in rice yield was explained by minimum temperature. Irrigation explained 33% of the remaining 51% variance in rice yield. The larger effect of climatic variables than fertilizer and irrigation suggest that adoption of climate smart and water conservation technologies are required to reduce rice yield variability in the future and improving food security. Spatial variations in yield, rainfall and temperature across Punjab were substantial and these have important consequences for food security by indicating the need for region-specific technologies.