scholarly journals The Greening and Wetting of the Sahel Have Leveled off since about 1999 in Relation to SST

2020 ◽  
Vol 12 (17) ◽  
pp. 2723
Author(s):  
Tiexi Chen ◽  
Shengjie Zhou ◽  
Chuanzhuang Liang ◽  
Daniel Fiifi Tawia Hagan ◽  
Ning Zeng ◽  
...  
Keyword(s):  
Piecewise Linear ◽  
Vegetation Indices ◽  
Positive Trend ◽  
Causality Analysis ◽  
Area Index ◽  
Piecewise Linear Regression ◽  
Significant Positive Trend ◽  
Tropical Oceans ◽  
Regression Approach

The Sahel, a semi-arid climatic zone with highly seasonal and erratic rainfall, experienced severe droughts in the 1970s and 1980s. Based on remote sensing vegetation indices since early 1980, a clear greening trend is found, which can be attributed to the recovery of contemporaneous precipitation. Here, we present an analysis using long-term leaf area index (LAI), precipitation, and sea surface temperature (SST) records to investigate their trends and relationships. LAI and precipitation show a significant positive trend between 1982 and 2016, at 1.72 × 10 −3 yr −1 (p < 0.01) and 4.63 mm yr−1 (p < 0.01), respectively. However, a piecewise linear regression approach indicates that the trends in both LAI and precipitation are not continuous throughout the 35 year period. In fact, both the greening and wetting of the Sahel have been leveled off (pause of rapid growth) since about 1999. The trends of LAI and precipitation between 1982 and 1999 and 1999–2016 are 4.25 × 10 − 3 yr −1 to − 0.27 × 10 −3 yr −1, and 9.72 mm yr −1 to 2.17 mm yr −1, respectively. These declines in trends are further investigated using an SST index, which is composed of the SSTs of the Mediterranean Sea, the subtropical North Atlantic, and the global tropical oceans. Causality analysis based on information flow theory affirms this precipitation stabilization between 2003 and 2014. Our results highlight that both the greening and the wetting of the Sahel have been leveled off, a feature that was previously hidden in the apparent long-lasting greening and wetting records since the extreme low values in the 1980s.

scholarly journals The Ongoing Greening in Southwest China despite Severe Droughts and Drying Trends

2021 ◽  
Vol 13 (17) ◽  
pp. 3374
Author(s):  
Xin Chen ◽  
Tiexi Chen ◽  
Qingyun Yan ◽  
Jiangtao Cai ◽  
Renjie Guo ◽  
...  
Keyword(s):  
Vegetation Change ◽  
Vegetation Index ◽  
Southwest China ◽  
Vegetation Indices ◽  
Climate Extremes ◽  
Global Scale ◽  
Area Index ◽  
Huge Impact ◽  
Increasing Trends

Vegetation greening, which refers to the interannual increasing trends of vegetation greenness, has been widely found on the regional to global scale. Meanwhile, climate extremes, especially several drought, significantly damage vegetation. The Southwest China (SWC) region experienced massive drought from 2009 to 2012, which severely damaged vegetation and had a huge impact on agricultural systems and life. However, whether these extremes have significantly influenced long-term (multiple decades) vegetation change is unclear. Using the latest remote sensing-based records, including leaf area index (LAI) and gross primary productivity (GPP) for 1982–2016 and enhanced vegetation index (EVI) for 2001–2019, drought events of 2009–2012 only leveled off the greening (increasing in vegetation indices and GPP) temporally and long-term greening was maintained. Meanwhile, drying trends were found to unexpectedly coexist with greening.

Long-term outcomes of laparoscopic cholecystectomy: a prospective piecewise linear regression analysis

2010 ◽  
Vol 25 (7) ◽  
pp. 2132-2140 ◽  
Author(s):  
Hon-Yi Shi ◽  
Hao-Hsien Lee ◽  
Meng-Han Tsai ◽  
Chong-Chi Chiu ◽  
Yih-Huei Uen ◽  
...  
Keyword(s):  
Regression Analysis ◽  
Laparoscopic Cholecystectomy ◽  
Linear Regression ◽  
Piecewise Linear ◽  
Linear Regression Analysis ◽  
Long Term Outcomes ◽  
Piecewise Linear Regression

Assessment of Annual, Monthly, and Seasonal Trends in the Long Term Rainfall of the Garhwal Himalayas

2016 ◽  
pp. 222-241
Author(s):  
Seema Rani
Keyword(s):  
Climate Change ◽  
Monthly Rainfall ◽  
The Other ◽  
Seasonal Rainfall ◽  
Positive Trend ◽  
Significant Positive Trend ◽  
Garhwal Himalayas ◽  
Slope Estimator

Climate change is one of the very significant apprehension argued in the recent two decades. Its influence on rainfall has brought in considerable attention worldwide. Hence, this chapter focuses on assessing the trends in the rainfall during 1901-2012 in the Dehradun, Haridwar, Uttarkashi, Tehri-Garhwal, Pauri-Garhwal, Rudraprayag and Chamoli districts of the Garhwal Himalayas by applying non-parametric Mann-Kendall and the Theil-Sen's Slope Estimator tests for the determination of trend and its magnitude. The findings revealed a statistically significant positive trend in annual and monthly rainfall (May and July) of Dehradun district. Rainfall shows a statistically significant positive trend in May (Haridwar and Tehri Garhwal) and a significant negative trend in January (Uttarkashi and Chamoli). On the other hand, Pauri Garhwal and Rudraprayag indicates no significant trend in monthly rainfall. An insignificant trend has also been observed in seasonal rainfall of most of the districts. Annual, monthly and seasonal rainfall shown no particular pattern in the region.

scholarly journals Mean age of stratospheric air derived from AirCore observations

2017 ◽  
Vol 17 (11) ◽  
pp. 6825-6838 ◽  
Author(s):  
Andreas Engel ◽  
Harald Bönisch ◽  
Markus Ullrich ◽  
Robert Sitals ◽  
Olivier Membrive ◽  
...  
Keyword(s):  
Low Cost ◽  
Positive Trend ◽  
Data Set ◽  
Model Calculations ◽  
Significant Positive Trend ◽  
Stratospheric Balloon ◽  
Term Data ◽  
Better Than ◽  
Good Agreement

Abstract. Mean age of stratospheric air can be derived from observations of sufficiently long-lived trace gases with approximately linear trends in the troposphere. Mean age can serve as a tracer to investigate stratospheric transport and long-term changes in the strength of the overturning Brewer–Dobson circulation of the stratosphere. For this purpose, a low-cost method is required in order to allow for regular observations up to altitudes of about 30 km. Despite the desired low costs, high precision and accuracy are required in order to determine mean age. We present balloon-borne AirCore observations from two midlatitude sites: Timmins in Ontario/Canada and Lindenberg in Germany. During the Timmins campaign, five AirCores sampled air in parallel with a large stratospheric balloon and were analysed for CO2, CH4 and partly CO. We show that there is good agreement between the different AirCores (better than 0.1 %), especially when vertical gradients are small. The measurements from Lindenberg were performed using small low-cost balloons and yielded very comparable results. We have used the observations to extend our long-term data set of mean age observations at Northern Hemisphere midlatitudes. The time series now covers more than 40 years and shows a small, statistically non-significant positive trend of 0.15 ± 0.18 years decade−1. This trend is slightly smaller than the previous estimate of 0.24 ± 0.22 years decade−1 which was based on observations up to the year 2006. These observations are still in contrast to strong negative trends of mean age as derived from some model calculations.

scholarly journals Mean age of stratospheric air derived from AirCore observations

2017 ◽  
Author(s):  
Andreas Engel ◽  
Harald Bönisch ◽  
Markus Ullrich ◽  
Robert Sitals ◽  
Olivier Membrive ◽  
...  
Keyword(s):  
Low Cost ◽  
Positive Trend ◽  
Data Set ◽  
Model Calculations ◽  
Significant Positive Trend ◽  
Stratospheric Balloon ◽  
Term Data ◽  
Better Than

Abstract. Mean age of stratospheric air can be derived from observations of sufficiently long lived trace gases with approximately linear trends in the troposphere. Mean age can serve as a tracer to investigate stratospheric transport and long term changes in the strength of the overturning Brewer-Dobson circulation of the stratosphere. For this purpose, a low-cost method is required in order to allow for regular observations up to altitudes of about 30 km. Despite the desired low costs, high precision and accuracy are required in order to allow determination of mean age. We present balloon borne AirCore observations from two mid latitude sites: Timmins in Ontario/Canada and Lindenberg in Germany. During the Timmins campaign five AirCores sampled air in parallel from a large stratospheric balloon and were analysed for CO2, CH4 and partly CO. We show that there is good agreement between the different AirCores (better than 0.1 %) especially when vertical gradients are small. The measurements from Lindenberg were performed using small low-cost balloons and yielded very comparable results. We have used the observations to extend our long term data set of mean age observations at Northern Hemi-sphere mid latitudes. The time series now covers more than 40 years and shows a small, statis-tically not significant positive trend of 0.15 ± 0.18 years/decade. This trend is slightly smaller than the previous estimate of 0.24 ± 0.22 years/decade which was based on observations up to the year 2006. These observations are still in contrast to strong negative trends of mean age as derived from some model calculations.

scholarly journals THE ESTIMATE OF THE SPATIAL-TEMPORAL FEATURES OF VEGETATION COVER OF KAZAKHSTAN BASED ON TIME SERIES SATELLITE INDECES IN 2000-2015

2016 ◽  
Vol XLI-B8 ◽  
pp. 1067-1071
Author(s):  
I. Vitkovskaya ◽  
M. Batyrbayeva ◽  
L. Spivak
Keyword(s):  
Time Series ◽  
Vegetation Index ◽  
Vegetation Indices ◽  
Weather Conditions ◽  
Condition Index ◽  
Negative Trend ◽  
Positive Trend ◽  
High Productivity ◽  
Temporal Features

The article presents the evaluation of spatial-temporal characteristics of Kazakhstan arid and semi-arid areas' vegetation on the basis of time series of differential and integral vegetation indices. It is observed the negative trend of integral indices for the period of 2000-2015. This fact characterizes the increase of stress influence of weather conditions on vegetation in Kazakhstan territory during last decade. Simultaneously there is a positive trend of areas of zones with low values of IVCI index. Zoning of the territory of Kazakhstan was carried out according to the long-term values of the normalized integral vegetation index, which is characteristic of the accumulated amount of green season biomass. Negative trend is marked for areas of high productivity zones, long-term changes in the areas of low productivity zones have tend to increase. However long-term values of the area of the middle zone are insignificantly changed. Location boundaries of this zone in the latitudinal direction connects with a weather conditions of the year: all wet years, the average area is located between 46&deg;- 49&deg;N, and the all dry years - between 47&deg;30'- 54&deg;N. The map of frequency of droughts was formed by low values of the integral vegetation condition index which calculated from satellite data.

scholarly journals A bio-physicochemical perspective of the Bay of Bengal

2020 ◽  
Vol 100 (4) ◽  
pp. 517-528
Author(s):  
Subrata Sarker ◽  
Essowè Panassa ◽  
M. Shahadat Hossain ◽  
Sayedur Rahman Chowdhury ◽  
Atul Kumar Yadav ◽  
...  
Keyword(s):  
Primary Productivity ◽  
Bay Of Bengal ◽  
World Ocean ◽  
Vertical Gradient ◽  
Spatial And Temporal Variability ◽  
Positive Trend ◽  
Significant Positive Trend ◽  
Open Sea ◽  
Strong Gradient

AbstractKnowledge of bio-physicochemical variables is essential to better understand the functioning of tropical marine ecosystems, which are rich in biodiversity and provide nutrition and livelihoods to billions of people in the developing countries. This study analysed the spatial and temporal variability of phytoplankton and zooplankton with chlorophyll, primary productivity, temperature, salinity, oxygen and nutrients in the Bay of Bengal (BoB), collecting data from the World Ocean, and COPEPOD and Aqua MODIS records. The results indicated a strong gradient in bio-physicochemical conditions of the BoB, from the coast to the open sea. Specifically, the spatial variability in chlorophyll was negatively correlated (R2 = 0.59) with temperature and zooplankton, while a positive correlation (R2 = 0.70) was noted between chlorophyll and silicate, nitrate, phosphate, dissolved oxygen and salinity. All the variables exhibited a strong vertical gradient at depths up to 500 m. Temperature, nutrients, zooplankton and to a lesser extent salinity and rainfall had an influence on the annual abundance of phytoplankton. Over the long term, a significant positive trend in temperature and a significant negative trend in primary productivity were observed in the BoB. The findings of this study will be useful to draw insights on the state of fisheries habitats and the overall environmental conditions of the BoB in response to future climate changes.

scholarly journals Inter-annual and seasonal patterns of precipitable water vapour over Malaysia from 1990–2019 based on MERRA-2 reanalysis

2021 ◽  
Vol 30 (1) ◽  
pp. 208-218
Author(s):  
Ezekiel Makama ◽  
Hwee Lim
Keyword(s):  
Water Vapour ◽  
Precipitable Water ◽  
Regression Method ◽  
Least Square ◽  
Seasonal Patterns ◽  
Positive Trend ◽  
Precipitable Water Vapour ◽  
Significant Positive Trend ◽  
East Malaysia

In this study seasonal and inter-annual patterns as well as trend in the total precipitable water vapour (TPW) over Malaysia, based on a 30-year data from MERRA-2, have been evaluated using least square regression method. Indicator TPW revealed a pair of minima in February/August and maxima in May/November with highest and lowest long-term means found in East Malaysia. Long-term seasonal variability of TPW exhibited latitudinal dependency in both the NEM and SWM seasons. Indicator TPW showed respective southeast-northwest and southwest-northeast spatial distribution in West and East Malaysia, with the highest statistically significant positive trend found in the former.

scholarly journals THE ESTIMATE OF THE SPATIAL-TEMPORAL FEATURES OF VEGETATION COVER OF KAZAKHSTAN BASED ON TIME SERIES SATELLITE INDECES IN 2000-2015

2016 ◽  
Vol XLI-B8 ◽  
pp. 1067-1071
Author(s):  
I. Vitkovskaya ◽  
M. Batyrbayeva ◽  
L. Spivak
Keyword(s):  
Time Series ◽  
Vegetation Index ◽  
Vegetation Indices ◽  
Weather Conditions ◽  
Condition Index ◽  
Negative Trend ◽  
Positive Trend ◽  
High Productivity ◽  
Temporal Features

The article presents the evaluation of spatial-temporal characteristics of Kazakhstan arid and semi-arid areas' vegetation on the basis of time series of differential and integral vegetation indices. It is observed the negative trend of integral indices for the period of 2000-2015. This fact characterizes the increase of stress influence of weather conditions on vegetation in Kazakhstan territory during last decade. Simultaneously there is a positive trend of areas of zones with low values of IVCI index. Zoning of the territory of Kazakhstan was carried out according to the long-term values of the normalized integral vegetation index, which is characteristic of the accumulated amount of green season biomass. Negative trend is marked for areas of high productivity zones, long-term changes in the areas of low productivity zones have tend to increase. However long-term values of the area of the middle zone are insignificantly changed. Location boundaries of this zone in the latitudinal direction connects with a weather conditions of the year: all wet years, the average area is located between 46&deg;- 49&deg;N, and the all dry years - between 47&deg;30'- 54&deg;N. The map of frequency of droughts was formed by low values of the integral vegetation condition index which calculated from satellite data.

Identifying changes in trends in the age standardized incidence of melanoma in Australia

2019 ◽  
Vol 3 (4) ◽  
pp. 250-252 ◽  
Author(s):  
David M Hille
Keyword(s):  
Public Health ◽  
Linear Regression ◽  
Iterative Process ◽  
Linear Trend ◽  
Piecewise Linear ◽  
Health Issue ◽  
Public Health Issue ◽  
Piecewise Linear Regression ◽  
Significant Public Health ◽  
Males And Females

ObjectiveTo identify changes in the linear trend of the age-standardized incidence of melanoma in Australia for all persons, males, and females. MethodsA two-piece piecewise linear regression was fitted to the data. The piecewise breakpoint varied through an iterative process to determine the model that best fits the data.ResultsStatistically significant changes in the trendof the age-standardized incidence of melanoma in Australia were found for all persons, males, and females. The optimal breakpoint for all persons and males was at 1998. For females, the optimal breakpoint was at 2005. The trend after these breakpoints was flatter than prior to the breakpoints, but still positive.ConclusionMelanoma is a significant public health issue in Australia. Overall incidence continues to increase. However, the rate at which the incidence is increasing appears to be decreasing.

Sign in / Sign up

Export Citation Format

Share Document