Revealing changes in the boundary layer height in different land use classes the Case study of Lorestan province

ABSTRACT
The height of the boundary layer is one of the most important determining factors, the extent of mixing of pollutants and suspended particles and the quality of air near the surface of the earth. The main goal of this research is to reveal the relationship between land cover changes and boundary layer height changes during the last 3 decades in Lorestan province. In this regard, two sets of data were used, which include the land cover classes of the MODIS sensor and the height of the boundary layer of the ECMWF climate database version ERA5. These data were selected on a monthly scale (January) to check the cold period and (July) to check the warm period and were checked in 7 time periods with 5-year steps during the statistical period of 1990-2020. In this research, the cross-matrix analysis technique was used in the ARC-GIS environment and the average height of the boundary layer on each land use was extracted and compared in 7 time steps of 5 years, separately from the cold and warm periods of the year. The results showed that firstly, the height of the boundary layer during the warm period is significantly higher than the cold period of the year, and secondly, the minimum and maximum spatial pattern of the boundary layer height in the cold and warm periods of the year is different in the province. In the cold period, the maximum height of the boundary layer is in the western parts. and southwest (low-altitude lands with forest cover), while in the warm period of the year, the maximum boundary layer is concentrated in the barren and mountainous lands of the east of the province. In addition, it was observed that in the hot period of the year, agricultural lands with a boundary layer height of 1263 and pasture lands with a boundary layer height of 1243 have the highest boundary layer height among the investigated use classes, while in the cold period of the year, urban and residential lands with a height of 192 meters, It has the highest boundary layer height and the spatial average of the boundary layer height of the province has had an increasing trend
Extended Abstract
Introduction
The height of the boundary layer is one of the most important determining factors, the extent of mixing of pollutants and suspended particles and the quality of air near the surface of the earth. The main goal of this research is to reveal the relationship between land cover changes and boundary layer height changes during the last 3 decades in Lorestan province. In this regard, two sets of data were used, which include the land cover classes of the MODIS sensor and the height of the boundary layer of the ECMWF climate database version ERA5. These data were selected on a monthly scale (January) to examine the cold period and (July) to examine the warm period and were examined in the form of 7 time periods of 5 years during the statistical period of 1990-2020. In this research, the cross-matrix analysis technique was used in ARC-GIS environment, and the average height of the boundary layer on each land use was extracted and compared in 7 time steps of 5 years, separately from the cold and hot periods of the year. The results showed that, firstly, the height of the boundary layer in the warm period of the year is significantly higher than in the cold period of the year, and secondly, the minimum and maximum spatial pattern of the height of the boundary layer in the cold and warm period of the year is different in the province, in the cold period of the year, the maximum height The boundary layer is in the parts of the west and southwest parts (low-altitude lands with forest cover), while in the warm period of the year, the maximum boundary layer is concentrated in the barren and mountainous lands of the east of the province. In addition, it was observed that in the hot period of the year, agricultural lands with a boundary layer height of 1263 and pasture lands with a boundary layer height of 1243 had the highest boundary layer height among the studied land use classes, while in the cold period of the year, urban and residential lands with a height of 192 meters , has had the highest boundary layer height and the spatial average of the boundary layer height of the province has had an increasing trend.
Methodology
In this research, two types of data were used. The first set of data was related to the land cover classes of the composite product of the MODIS sensor with a spatial resolution of 1 km and hierarchical data format (MCD12Q2 product) which was obtained from the database of this sensor. In order to complete the coverage of the province, two video blocks H21V05 and H22V05 were used. Land cover data were selected from the classification of the International Geosphere Program, Biosphere, which generally has 17 land cover classes. Of these classes, 11 classes are related to natural vegetation, 3 classes are related to non-vegetable land covers, and 3 classes are related to composite covers. The overall accuracy index of this product is 73.6%. The second set of data was downloaded from the ECMWF climate database version ERA5. These data were selected on a monthly scale (January) to check the cold period and (July) to check the warm period and were checked in the form of 7 periods of 5 years (1990, 1995, 2000, 2005, 2010, 2015, 2020).
 
Results and discussion
Five land cover classes in Lorestan province, including forest land, pasture land, agricultural land, built-up land, and barren land have been recognized as the main and major land covers of Lorestan province. The distribution of land cover classes in the province showed that the A large area of the center, north and east of Lorestan province has pasture cover (IGBP classification code 10, product MCD11Q2)). With an area of 16,300 square kilometers, this land use has the largest area in the province. Pasture cover in the eastern and northern parts (average annual rainfall of more than 350 mm) is considered as the dominant cover in this region of the province (Figure 2). Forest lands also cover a large part of the central, southern and western areas of Lorestan province, the largest area of these lands was equal to 8765 square kilometers. Agricultural lands (both irrigated, rainfed and horticulture) can be seen in the northern, central and western parts of the province. The spatial distribution of boundary layer height (BLH) in Lorestan province has been investigated using the networked data of ERA5 database. In Figures 3 and 4, the spatial distribution of the height of the boundary layer in Lorestan province during the cold and warm periods of the year is presented in 5-year time steps of the 7-year period from 1990 to 2020.
 
 
Conclusion
The results of the time-spatial analysis of the state of the boundary layer height index in the province showed that in the cold period of the year, the height of the boundary layer in the province reached 40 meters in the minimum state and 385 meters in the maximum state, while in the warm period of the year, the boundary layer height reached the minimum state. At the level of the province, it is about 700 meters and in the maximum state it has reached more than 1400 meters. The spatial distribution pattern of the boundary layer height in the province during the cold period is such that in the western parts of the province, the boundary layer height is the maximum and reaches more than 250 meters, while in the eastern parts of the province, the boundary layer height has reached less than 80 meters. The spatial distribution pattern of the boundary layer height in the warm period of the year is different from the cold period of the year in such a way that the northern and eastern parts of the province had the maximum boundary layer height that varied between 1400 and 1600 meters, while in the western and southern parts of the province the boundary layer height was 700 to It has reached 1000 meters. The results of the 30-year trend of the boundary layer height showed that in the hot and cold periods of the year, the boundary layer height of the 5 land covers of the province had an increasing trend with different acceleration. In general, the spatial average of the boundary layer height of the province also showed an increasing trend. In 1990, the average spatial height of the boundary layer during the warm period of the year in the province was equal to 870 meters, while with an increasing trend combined with periodic fluctuation, in 2020, the average boundary layer height of the province has reached 1300 meters. In the cold period of the year, a continuous increase along with fluctuations in the 30-year trend of the boundary layer height of the province has been seen. So that in 1990, during the cold period of the year, the average boundary layer height of the province was equal to 154 meters, while in 2020, the boundary layer height has reached more than 190 meters. In the cold period of the year, the forest lands in the south and southwest of the province had the highest boundary layer height, which was 227 meters on average, while the spatial average height of the boundary layer in the warm period of the year on the same land cover was at a minimum (compared to other land cover classes). and it was equal to 1059 meters. In the hot period of the year, agricultural lands with a boundary layer height of 1263 and pasture lands with a boundary layer height of 1243 have the highest boundary layer height among the investigated use classes, while in the cold period of the year, urban and residential lands with a height of 192 meters have the highest boundary layer height. had. In the cold period of the year, urban and residential land use had the highest boundary layer height, on the other hand, the periodical change trend of the boundary layer height on this land use was a continuous increase in the warm season and a mild increase along with fluctuations in the cold season. . On the other hand, the agricultural lands of the province have the highest height of the boundary layer during the warm period of the year. The trend of changes in the height of the boundary layer during the 30-year statistical period of 1990-2020 has been increasing on this land use both in the cold period and in the warm period.
 
Funding
There is no funding support.
 
Authors’ Contribution
All of the authors approved thecontent of the manuscript and agreed on all aspects of the work.
 
Conflict of Interest
Authors declared no conflict of interest.
 
Acknowledgments
We are grateful to all the scientific consultants of this paper.