Climate change has caused changes to environmental and socioeconomic system not just in India, but also in other parts of the world. Global warming as a result of climate change is the newest and most talked-about topic in today's globe, since it represents the most serious threat to life on the earth. Assam is the largest agrarian state among North-East India and climate variability has already been noticed in Assam, with irregular monsoons, frequent floods, drought-like conditions, and a hotter winter
Rainfall and temperature are the two most influential variables in climate and hydrology research, since they influence the environmental elements that affect agricultural output in a certain location
The primary objective of this study is to look at the trends of climatic variables in the Karimganj district of Assam.
Some recent research works have been reviewed which are very relevant to this study. A research work exposed that the Monthly rainfall for the months of July, October, and November in the Cherrapunji in Megalaya, India, has been increasing while monthly rainfall for the months of February to June, August, and September has been decreasing for the period 1872-2007. These results are statistically significant
Karimganj district is located between the longitudes of 92°15' and 92°35' east and the latitudes of 24°15' and 25°55' north. Bangladesh and Cachar district border the district on the north; Mizoram and Tripura states border it on the south; Bangladesh and Tripura border it on the west; and Hailakandi district borders it on the east. The map of the district is presented at below.
Data on monthly and annual maximum temperatures (°C), minimum temperatures (°C) total rainfall (mm) and relative humidity (%) for the period 1981-2020 have been collected from https://power.larc.nasa.gov/data-access-viewer/ which is free to access (Retrieved on 15th December 2021). District level datasets have been downloaded from the portal using latitudes and longitudes for Karimganj district. The Indian Meteorological Department (IMD classified four meteorological seasons over India which are: Winter Season: January-February, Pre-Monsoon Season: March-May, Monsoon or also called South West Monsoon Season: June- September and Post Monsoon Season: October -December
The Mann-Kendall (MK) approach
Where n is the time series length, x denotes the data point at times j and k (k>j), and equation denotes the sign function (2).
If n is less than 10, the value of [S] is directly compared to Mann Kendall's theoretical distribution of S. The statistic S is considered to be asymptotically normal for n=10 or greater, with a mean E(S)= 0 and variance as follows:
Where t is the size of a specific tie, and
Where Z (c) follows a normal distribution, positive Z (c) and negative Z (c) reflect an upward and downward trend throughout the time period, respectively. In a two-sided trend test, the null hypothesis Ho should be accepted if [Z]> Z (/2), at a level of significance. In this study, the null hypothesis is tested at a 95% confidence level. A simple non-parametric approach proposed by Sen was also used to assess the magnitude of a time series trend
where
The trends of seasonal and annual temperature maximum (Tmax), temperature minimum (Tmin), rainfall and relative humidity for the Karimganj district of Assam spanning the period 1981-2020 have been obtained by Mann Kendall (MK) test. In addition, Sen’s slope test has been used to detect the magnitudes. Our study is in line with other similar studies conducted in Northeast India as well as in different other parts of India
The annual trends of temperature maximum (Tmax), temperature minimum (Tmin), rainfall and relative humidity are presented in
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Tmax |
-230 |
-2.6681* |
0.0076 |
-0.05 |
Tmin |
131 |
1.5151 |
0.1297 |
0.02 |
Rainfall |
462 |
5.3711* |
<0.0001 |
43.48 |
Relative Humidity |
455 |
5.2906* |
<0.0001 |
0.32 |
*Indicates statistically significant at 5% level of significance
During winter season, temperature maximum (Tmax) is showing a significant negative trend whereas temperature minimum and relative humidity are showing significant positive trends (
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Tmax |
-253 |
-2.9363* |
0.0033 |
-0.04 |
Tmin |
159 |
1.841** |
0.0656 |
0.02 |
Rainfall |
69 |
0.7923 |
0.428 |
0.11 |
Relative Humidity |
392 |
4.5568* |
<0.0001 |
0.57 |
*Indicates statistically significant at 5% level of significance
The temperature maximum (Tmax) is showing a significant negative trend in pre-monsoon season also. Temperature minimum (Tmin), rainfall and relative humidity are showing statistically significant positive trends over the period (
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Tmax |
-263 |
-3.0528* |
0.0022 |
-0.06 |
Tmin |
253 |
2.9367* |
0.0033 |
0.03 |
Rainfall |
378 |
4.3924* |
<0.0001 |
4.29 |
Relative Humidity |
358 |
4.1594* |
<0.0001 |
0.42 |
*Indicates statistically significant at 5% level of significance
In case of monsoon season, again temperature maximum (Tmax) is showing a statistically significant negative trend whereas temperature min (Tmin), rainfall and relative humidity are showing significant positive trends (
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Tmax |
-245 |
-2.843* |
0.0044 |
-0.03 |
Tmin |
418 |
4.859* |
<0.0001 |
0.02 |
Rainfall |
472 |
5.4876* |
<0.0001 |
6.50 |
Relative Humidity |
384 |
4.4623* |
<0.0001 |
0.11 |
*Indicates statistically significant at 5% level of significance
During post Monsoon season, Temperature maximum (Tmax) is showing a negative trend but statistically insignificant. However, Temperature minimum (Tmin), rainfall and relative humidity are showing significant positive trends over the period (
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Tmax |
-56. |
-0.6408 |
0.5216 |
-0.01 |
Tmin |
360 |
4.1833* |
<0.0001 |
0.05 |
Rainfall |
244 |
2.8312* |
0.0046 |
1.39 |
Relative Humidity |
470 |
5.4643* |
<0.0001 |
0.22 |
*Indicates statistically significant at 5% level of significance
This piece of study is an attempt to establish the occurrence of climate change in the Karimganj district of Assam, India. In this study, the variability and long-term trends of seasonal and annual temperature maximum, temperature minimum, average rainfall and relative humidity for the Karimganj district of Assam are examined. The study is unique and innovative for Karimganj district of Assam to best of our knowledge. It has been observed that annual and seasonal temperature maximum (Tmax) are showing a statistically significant negative trend over the period 1981-2020 during all seasons except for post monsoon season. The magnitude of trend for annual Tmax is -0.05 as indicated by Sen’s slope. The annual temperature minimum (Tmin) series does not show any significant trends whereas seasonal mean temperature minimum is showing a positive trend at different levels of significance during all four seasons. Except winter season, annual rainfall series and all other seasonal average rainfall series are showing significant positive trends. The magnitude of annual rainfall trend is 43.48. The Annual and seasonal average relative humidity are showing statistically significant positive trends over the period. The magnitude of annual average relative humidity is 0.32. This study confirms that climate change is occurring in the Karimganj district of Assam. Suitable adaptation strategies and government’s policy intervention regarding mitigation are crucial to combat the present and future potential impacts of climate change.