Investigation of Wind Chills changes in Zarrineh plain during the last three decades using Man-Kendall method

Extended abstract

Introduction

The effect of wind cooling in combination with temperature, which is expressed as a special feeling, is called Wind Chill, and the Wind Chill index is used to show the effects of cold. Wind Chills Apart from their beneficial effects on agriculture, they, as one of the natural disasters of atmospheric damage, sometimes cause a lot of financial and even human losses. Since temperature, precipitation and wind are the main elements of climate formation in any region, changes in their behavior can change the climate structure of any region. Therefore, the study of the past trends and behaviors of these climatic elements in the form of various indicators and scales of time and space, is very important and has been a large part of climate research. Researchers' past research shows that temperatures and changes are noticeable in many parts of the world. A review of these valuable sources shows that, so far, many efforts have been made with different approaches and perspectives on the quantitative and qualitative status of temperature and wind speed and related indicators. But what is certain is that no scientific and comprehensive study has been done in Kurdistan province regarding Wind Chills in Zarrineh Obato high plain. Therefore, conducting this study is a special necessity and can be a small step and a starting point to study and explain the specific environmental phenomena of this geographical area in the cold period of the year. One of the questions that arises is whether the behavior of Wind Chills in the Zarrineh Obato Plain has changed over the last three decades.



Research objectives

The main purpose of this study is to study climatic elements and changes in atmospheric phenomena, especially wind chills indexing and their classification in order to study and model the past behavior of Wind Chills during the last three decades using Mann-Kendall graphical statistical method and polynomial regression. To help decision-makers manage and reduce the effects of wind chills.



Research Methods

In order to investigate the past behavior of Wind Chills in Zarrineh Obato plain, after collecting and summarizing daily data on temperature and wind speed of stations around the plain during the statistical period of 32 years (1989-2020), the status of data in terms of quantity and quality control The normality and homogeneity of the data were assessed using the Run Test. Then, according to the latest model of the Canadian Meteorological Organization, the Wind Chill index was defined by establishing temperature conditions of at least 2 degrees Celsius and wind speeds above 4.8 meters per second on a five-point Likert scale. After that, the frequency and intensity of wind chills were calculated and used as the basis for descriptive statistics analysis in SPSS and Excel software. Then, to identify the linear and nonlinear behavior and fit the trend line and calculate its slope, polynomial nonlinear polynomial regression was used based on the least squares size method. In addition, Man-Kendall test and T statistic of Man-Kendall were used to investigate the possible deviation and to determine the type and time of change in the time series of mean temperature, wind speed and wind chill index for the station closest to Zarrineh plain.



Results

The results showed that in February, Wind Chills first (zero to -9 C˚) and second (-10 to -27 C˚) had the highest frequency of occurrence, and although based on the fit of the linear regression equation, The frequency of Wind Chills has been increasing overall, but unlike the second floor Wind Chills, this upward trend has been more related to the frequency of first floor Wind Chills and the significant increase in their number. The frequency of days with Wind Chill on the first floor was about 64% of the total Wind Chills and the frequency of Wind Chills on the second floor was about 36%. In the middle of the study period, there was a clear discrepancy and inconsistency between the frequencies of Wind Chills of the mentioned classes. This means that, in the years when the incidence of Wind Chills increased, the frequency of Wind Chills decreased relatively severely, both in number and severity. Although due to the mountainous nature of Kurdistan region and statistical limitations and lack of automated meteorological stations in the region, it is not easy and reliable to talk about climate and its changes, but the results of Mann-Kendall model analysis on the frequency of wind chills and The average annual temperature intensity of Wind Chills in the plain showed that, so far, there have been several jumps and the beginning of sudden changes in the frequency of Wind Chills during the 1990's. However, since the intersections of the two components U and U' related to the Man-Kendall statistical-graphic diagram within each other within the critical ±1.96 range intersected, so no significant jump was proven, but there are clear signs and signs of a decreasing trend. Wind chills are common in the time series, especially in the two decades of 2010-2020. The changes of the mentioned components for the annual average temperature of Wind Chills of different classes with the frequency of their occurrence have been completely different and vice versa. Thus, although the average temperature of Wind Chills has decreased in the two decades of 2000-2010, but as can be seen from the U' component diagram, the increasing annual average temperature of Wind Chills for the first and second temperature classes and the average temperature of total Wind Chills during the 2010's Shows an upward trend. This means that the average temperature of Wind Chills in the Zarrineh Obatovo Plain has increased significantly since the early 2020's. This issue was also emphasized by the field study and the statements of the villagers in the study area. The result of this research, with a slight difference in the study area, is consistent with the valuable work of many researchers on the beginning of the increasing trend of temperature in different regions of Iran during the last two decades.

In general, the winter temperature in the region has increased, and as a result, both the coldness of Wind Chills and the frequency of their occurrence have changed. Thus, the cooling temperature of Wind Chills has been decreasing and in 1990 it has experienced a significant jump. Since the mid-1990's, the annual frequency of the first floor of Wind Chills has been declining, showing several significant jumps, and has lost its long-term normal state.