Changed Butwal: From a Remote Sensing perspective

 Butwal is one of the most rapidly growing city  of Nepal. Places in major city centres are overcrowded and bare land is hardly seen. It lies in the intersection of Siddhartha Highway and Mahendra Highway and is only 33km far from neighbouring Indian border.

For better education, health facilities and employment opportunities many  people from Palpa, Gulmi, Arghakhanchi and neighbouring districts have migrated to this city. Over  the period of time , increasing population  has shown adverse effects on its natural resources. In this article I will be showing you how the city has changed with time using remote sensing.

fig showing 3D view of Butwal, interactive 3D map can be viewed here

First let's understand what is remote sensing? It is the art or science of acquiring information about distant objects without being physically present. For example our eyes  through which we can see distant objects without being there. Similarly, there are satellites in space which are constantly observing the Earth and getting information about it called ‘space borne remote sensing’. The very advantage of space remote sensing is that they provide a synoptic view (birds eye view) with which we can see things to a  large extent. Among various satellites present in the space Landsat is one of the series of earth observing satellite missions jointly managed by NASA and U.S. Geological Survey. Data provided by Landsat is historic  and free of cost .  In this context, I will be using two satellite images from Landsat5 and Landsat8 of October 1988 and October 2021 and their respective false color composite to show the changes.

 False color composite  is an image with a band (range of wavelength in electromagnetic spectrum) combination of at least one non-visible(infrared) wavelength and other visible wavelengths. As compare to true color image false image increases interpretability of data and has greater information content. Using false color we can get insights about plant health as plants reflect more infrared wavelengths and absorb red and green wavelengths. Generally, in such an image vegetation is represented by red, water body with black or dark blue and urban with gray color. Here for false color composite,  bands 5, 4, 3 and bands 4, 3, 2 of Landsat8  and Landsat5 are used respectively.

For this analysis google earth engine(gee), a  planetary-scale platform for Earth science data & analysis is used. The best thing about gee is that with a little bit of coding you can get amazing results. Both images are of the same month and have cloud cover of 0%.  The interactive map with split layers of image 1988 and 2021 can be viewed here. Click and drag split layer from left to right to see changes. Code link here.

fig showing gif image of Butwal in 1988 and 2021; red color represents vegetation, gray urban and black water.

On comparing the two images massive changes in vegetation, river, urban area and forest can be observed. The Tinau river which flows through the heart of the city seems to be shrinking and is occupied by settlement. Clearance of forest around ‘Butwal Mandap’ area and new built up things can also be seen. Vegetations in Sukkhanagar, Deepnagar, Shivnagar and  Devinagar have decreased greatly. Likewise urban region in these area have increased. Water bodies like lakes  have increased especially in Semlar area. 

The city has gone through a lot of changes in these thirty  three years. It has developed in the  field of infrastructure and facilities but at the same time its beauty is being lost due to human activities. Recent landslides  are also evidence of it. So, where do you see Butwal in upcoming years?