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Fury of nature: evaluating the impact of hailstorm on vegetation using sentinel 2 data at Moran, India

Neog Rituraj

Acta Geophysica

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2023

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Vol. 71, no. 6

3025--3039

EN

The primary objective of the study is to analyze the impact assessment of hailstorms on vegetation in the Moran region of Assam. The experiments employed sentinel-2A data of December, 2022 and January, 2023 for the computation of the NDVI, GNDVI, and MSAVI indices and their temporal dynamics. Further, LandScan gridded (1 k × 1 km) population data of 2021 have been used to portray the population affected in the study area. The result evidenced a significant decline in the mean NDVI (Normalized Difference Vegetation Index), GNDVI (Green Normalized Difference Vegetation Index), and MSAVI (Modified Soil Adjusted Vegetation Index) from the pre-hailstorm to the post-hailstorm period. The above indices declined from 0.270, 0279 and 0.416 in pre-hailstorm (24 December, 2022) period to 0.257, 0.269 and 0.410 in post-hailstorm period (3 January, 2023). Similarly, the area under healthy vegetation decreased from 72.06 and 103.55 sq km in 2022 to 60.74 and 96.35 sq km in 2023, based on GNDVI and MSAVI, respectively. The hailstorm affected the majority of villages as well as the population lying to the east of the NH-37, i.e., the Charaideo district of Assam. The Villages such Bagtali Sonowal, Demorukinar Changmai, Hatkhola gaon and Mout gaon experienced maximum damage to vegetation. Overall, 125.355 and 132.07 sq km of area considering both assessments (MSAVI & GNDVI with population) with a total population of about 131,342 are severely affected by hailstorm phenomena.

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Thermal stress and urban heat island effect in Jorhat urban environment as a result of changing land use and land cover

Neog Rituraj, Hazarika Jiten

Acta Geophysica

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2022

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Vol. 70, no 6

2771--2783

EN

The objective of the study is to determine the impact of land use and land cover (LULC) change on land surface temperature (LST) and thermal stress at Jorhat from 2009 to 2021. The experiment used Landsat TM (Thematic Mapper) for 2009 and OLI (Operational Land Imager)/TIRS (Thermal Infrared Sensor) for 2021 from earth.explorer.usgs.gov. Landsat data were employed to calculate the LST and LULC changes. Utilizing UTFVI (urban thermal field variance index), thermal stress over the ground surface has been computed. Thermal discomfort is computed simultaneously using the relative strain index (RSI) and net effective temperature (NET) index. Jorhat evidenced significant rise in built-up land to 281.25 hectares with reduced vegetation cover of 480.96 hectares from 2009 to 2021. These modifications caused significant rises in LST of 4.28 °C, 2.33 °C and 3.01 °C in September, October and December from 2009 to 2021. According to UTFVI from 2009 to 2021, Jorhat experienced declining ecologically excellent area with a rising proportion of ecologically worse land. In September and October 2009, the Jorhat city had just 10 days of bioclimatic discomfort and 19 days of bioclimatic comfort, as opposed to 24 and 10 days in 2021, respectively. Similarly, NET estimated 21 very hot days in October 2021, as opposed to just 9 days in 2009. Compared to 2009, there are now 6 and 4 days in December 2021 that are classified as warm or slightly hot, respectively. This leads to the conclusion that Jorhat's thermal condition is significantly impacted by changes in land use and land cover.

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Analyzing dynamic behavior of land use and land surface temperature in the city of Imphal, India

Neog Rituraj

Acta Geophysica

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2021

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Vol. 69, no. 6

2275--2290

EN

The study has been conducted over the Imphal city using multi-temporal satellite imageries. The study investigated the pattern land surface temperature (LST) development over the hill city of Imphal and its relation to land use pattern and population density. The result revealed an ascending growth of LST as a consequence of population growth and rapid land use dynamics. The Imphal city exhibited a remarkable change in the land use structure, especially in the built-up land, vegetation and crop land. Addition of built-up land of 667.44 hectares in the city territory has consequently upsurged the mean LST of the city from 23.23 °C to 30.30 °C in summer and 14.74–18.10 °C in winter during the period of 26 years (1994–2020). Summer season witnessed a consistently increasing intensity of LST in the city whereas winter depicted a completely opposite scenario during 1994–2020. Among all the land use classes, built-up land expressed maximum LST dynamics in both seasons during the period 1994 to 2020. The high positive correlation coefficient between built-up land with LST and strong negative correlation between vegetation cover and LST paved the way for maximum LST development in the city province.