THE DETECTION OF CLIMATE ABRUPT CHANGE WITH MANN-KENDALL RANK STATISTICS

The characteristics of Mann-Kendall Rank Statistics and its applications in detecting abrupt change of climate have been described.At the same time,a new method is put forward to detect the abrupt change in variance.

On Performance Characteristics of a Nonparametric Subset Selection Procedure with a Small Randomized Block Experimental Design

This article addresses the issue of computing the constant required to implement a specific nonparametric subset selection procedure based on ranks of data arising in a statistical randomized block experimental design. A model of three populations and two blocks is used to compute the probability distribution of the relevant statistic, the maximum of the population rank sums minus the rank sum of the “best” population. Calculations are done for populations following a normal distribution, and for populations following a bi-uniform distribution. The least favorable configuration in these cases is shown to arise when all three populations follow identical distributions. The bi-uniform distribution leads to an asymptotic counterexample to the conjecture that the least favorable configuration, i.e., that configuration minimizing the probability of a correct selection, occurs when all populations are identically distributed. These results are consistent with other large-scale simulation studies. All relevant computational R-codes are provided in appendices.

Analysis of Concentration Levels of Atmospheric Pollutants in Warri, Nigeria

A critical environmental problem facing the Niger Delta region is Air Pollution. This study therefore analyses concentration levels of atmospheric pollutants in the region. Statistical analysis of CH4 and O3 concentrations for the period of 2003 to 2012 and NO2 and CO2 concentrations for the period of 2011 to 2014 were carried out. The results showed that concentration levels of the pollutants were lower during the rainy season than during the dry year time. This is due to higher occurrences of atmospheric instability during the rainy season. On the other hand, ozone (O3) concentration reached its peak value during the peak period of the rainy season unlike the other pollutants. In all likelihood, some of the ozone-depleting substances such as aerosols and atmospheric hydrogen chloride become soluble in water and are being washed off by precipitation during rainy season, thereby leading to increased tropospheric ozone concentration during the rainy season. The study also revealed a steady increase in the concentration of CO2 within the period of investigation. This steady increase in CO2 can be traced to the alarming increase in anthropogenic activities which appreciably increases the amount of CO2 in the atmosphere. Methane (CH4) had higher standard deviation values than carbon dioxide (CO2), meaning that on a per molecule basis, a proportional rise in CH4 is much more effective as a greenhouse gas than a similar increase in CO2. However, CO2 has a greater effect than CH4 on climate change owing to its higher atmospheric concentration. The Mann-Kendall rank statistics of the atmospheric pollutants revealed that the standardization variables U(ti) and U'(ti) have a sequential fluctuating behavior around a zero level.

Edgeworth Expansion of Densities of Order Statistics with Fixed Rank

We give an Edgeworth expansion for densities of order statistics with fixed rank k. The Edgeworth expansion for densities of extreme values is then obtained as a special case k = 1.

Changes in hourly precipitation may explain the sharp reduction of discharge in the middle reach of the Yellow River after 2000

The Hekou-Longmen reach, together with local floods, is the main source area for coarse sedimenta- tions into the Yellow River. When total rainfall slightly increased in the area, discharge dramatically decreased by 40%-70% after the year of 2000, and attracting extensive attention in the context of global climate change. High temporal resolution precipitation （timescales between 1 and 4 h） data from the June to September period from 270 rain gauges over the past three decades was mined in order to help explain the phenomenon. Each rainfall event was classified as light/moderate rain, large rain, heavy rain or rainstorm by the event＇s rainfall amount, and further classified as low intensity rain, medium intensity rain and high intensity rain by the event＇s rainfall intensity. The Mann-Kendall trend test was applied to detect the presence and significance of monotonic trends, and to find the change points in the mean and variance of the precipitation characteristics series, including the amount, intensity, frequency and duration of each rainfall category. Results show that although the total amount of precipitation has slightly increased, the average rainfall intensity has significantly decreased. The larger change happened in light/moderate rain events and low/medium intensity rain events, and the intensity changes have a great extent occurred around the threshold of Non-Runoff Rainfall regime, which was proposed for the approximate calcula- tion of initial losses. Changes in rainfall distribution between different classes of the Runoff Rainfall regime in the 2000s could lead to 0.9 mm less runoffdepth （17.3% of the total reduction） than the 1980-1999 period. The study indicates that changes in hourly precipitation may be responsible for the sharp reduction of discharge.