Almost every accessible piece of land today is being utilized for some or the other purpose directly affecting human needs. Not only is the land being used intensively, but is also evolving and changing with time. What was agricultural land 10 years ago, is most likely to be urban land today. What was forest land is probably a plantation right now. The rapid and intensive changes in land use and land cover (LULC) has created the need to quantify these changes in numbers and maps, so that we can understand and leverage this information to the best use possible.
Land use and land cover: The distinction
Land use and land cover are often interchangeably used, but mean different things. Land use, is activity that is being practiced on a piece of land. This is a very human-centric term. Land cover, on the other hand, is the type of cover over land surface. It doesn’t matter if the land is being used by humans or not; the land is as it is and is covered by a particular type of resource/material. Changes in LULC do not always have to be driven by humans; the land can also undergo changes through the forces of nature.
LULC change detection
The process of land use and land cover change (LULC) is very complex and takes different forms, with differences in magnitude and rate. Entire bureaus are created in world governments, purely focused on mapping and studying these changes. LULC change detection studies are usually not conducted alone; it is generally connected to a larger problem. For example, for my Master’s thesis, I am assessing the impact of LULC change on the groundwater recharge potential. Other fields where LULC change detection is required are in sustainable management programs, natural resources census and mapping, social studies, ecological studies, detecting the growth and direction of urban sprawls, etc.
The detection of such changes give planners and policy makers answers to some important questions:
- What type of land is more severely under threat?
- Where do forests need protection?
- Which direction is an urban centre growing, and is that posing any dangers to the natural environment?
- How is the changing land use affecting the atmosphere and nearby water resources?
- Where do we have the best opportunity to exploit land as a natural resource?
- How is land use changes affecting natural ecosystems?
LULC change detection using remote sensing and GIS
In the last few decades, the methods used to study LULC has undergone a huge transformation. Early LULC studies were notoriously painstaking; it involved the use of ground surveying, GPS markers, tabulating the surveys extensively, statistical records for each type of land use in each area and finally validating these results. By the time a study was completed, it would most probably be redundant because in that period of 2-3 years, the land use would have already changed. The results of such studies were usually used as a historical reference and only for major policy decisions.
Thus, the need for updated and current land use change detection came up. The U.S. Geological Survey (USGS) began such studies with the use of aerial photography, the predecessor of satellite imaging. They prepared LULC maps from photographs between 1970-80 at an impressive 1:250,000 scale.
With the advent of satellite imaging and GIS applications, LULC studies have been far more detailed, current and reliable. Remote Sensing and GIS allows us to study and manipulate geographic information for large areas easily and effectively. The process also takes up very little time as compared to manual studies.
For example, The National Land Cover Database (NLC) of South Africa was derived from a 1:250,000 scale georectified, single data LANDSAT Thematic Mapper (TM) satellite imagery of 1994-95. In India, the first major effort to map the LULC of the country came under LULC 2005- ISRO Geoshpere-Biosphere Program LULC Dynamics Project. It mapped the entire country at a 1:250,000 scale using multi-temporal AWiFS datasets. The primary aim of this project was to understand the changes in sowing area of agricultural crops in different seasons.
Most LULC studies make the use of images from Landsat (TM), Cartosat, LISS series and other satellites. Landsat 8 and ETM+ images can be procured for free from USGS Earth Explorer’s website.
LULC is an important part of landscape studies and sustainable management studies. Land use planning is now an important aspect of government policies. In India, the National Bureau of Soil Survey and Land Use Planning takes care of all such requirements.
Why is this such an important and growing area of science? Well, land itself is a natural resource. And a scarce one at that. We need to effectively manage what little usable land we have left to ensure that humans continue to develop and support the growing populations of the species. Too much land has already been lost to land degradation, and more land is being lost to processes like erosion and desertification. Land mismanagement, through deforestation and overgrazing, have also resulted in huge losses.
This is a resource we cannot afford to take lightly.
- Paudel, B., Yi-li Zhang, Shi-cheng Li, Lin-shan Lui, Xue Wu, and Narendra Raj Khanal. 2016. “Review of studies on Land Use and Land Cover change in Nepal.” Journal of Mountain Science 13 (4): 643-660.
- NRSA. 2006. “National Land Use and Land Cover Mapping using multi-temporal AWiFS Data.” Natural Resources Census. Hyderabad, India.