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Manipulation of Normalized Difference Vegetation Index (NDVI) for Delineating Drought Vulnerable Areas



Uzma Rabab*
Visitng Faculty Member
NUST Institute of Geographical Information System (IGIS)
Postal Address: 112-A, Street # 37, F-10/1, Islamabad, Pakistan
Tayyab I. Shah & M. Iqbal Tabbsum, GIS/RS Experts
E-mail: uzma_rubab@yahoo.com, iqbaltabbsum@yahoo.com, tayyabishah@yahoo.com

*The work was originally carried out as partial fulfilment of the requirement of Degree of Masters in Environmental Sciences (2002), Fatima Jinnah Women University, The Mall, Rawalpindi, Pakistan

Abstract
Timely information about the onset of drought, extent, intensity, duration and impacts can limit drought-related losses of life, human suffering and decrease damage to economy and environment. The present research work has been carried out with the aim to integrate SRS and GIS for the identification of drought vulnerable areas in Sindh and major part of Balochistan. Arid and extremely arid conditions prevail in these areas and the amount of rainfall varies with time and space. This departure of rainfall results in the emergence of drought condition. The vegetation cover is directly linked with water availability and a decrease in vegetation cover can be alarming. . NOAA AVHRR derived NDVI can be used to obtain vegetation status on regular basis. Although spatial resolution of NOAA is coarse, yet, the onset of drought conditions for a large area in a given year can be predicted by comparative analysis of trend of derived NDVI of that year relative to the trend in a normal year. It is better to develop a multi date NDVI composite for the study area and consider it as a normal for comparison. Thus, for a developing country like Pakistan, regular monitoring of the vegetation status (application of NOAA derived NDVI data) along with the other layers including climate, soil type, hydrology and socioeconomic condition of people is needed to delineate the areas that are drought vulnerable. This multidisciplinary information can be effectively and accurately handled with GIS. Spatial analysis in GIS can lead to a decision support system for the concerned government departments, NGO’s and others to help drought vulnerable people and others living in potential drought areas.

1. Introduction
Drought is the single most important weather-related natural disaster. Its impacts on society result from the interplay between a natural event (less precipitation than expected resulting from natural climatic variability) and the demand people place on water supply. Recent droughts in both developing and developed countries and the resulting economic and environmental impacts and personal hardships have underscored the vulnerability of all societies to this "natural" hazard. A very key aspect to drought vulnerability is whether a population gets its water from a well or other reliable source, or if it relies on rainfall. Those that are using rain for the source of water are particularly vulnerable to food insecurity in times of drought, due to the lack of water for agriculture and domestic purposes. Drought has a differential impact by wealth status (i.e., access to labor, capital and improved input). In a study from Ethiopia, wealthier households achieved drought-year yields three times higher than poor households. The wealthier households did change their diet, but less than poor households changed their food intake (Webb, 1993).

Unlike earthquake, drought always has a slow onset, which is quite observable. It is not an event rather is a process, which can be understood and forecasted quite well before time (Bhatti, 2000). Many drought indices have been used over the globe to monitor and forecast drought. Drought indices assimilate thousands of bits of data on rainfall, snow pack, stream flow and other water supply indicators into a comprehensible big picture. For example, the Palmer Drought Severity Index has been widely used by the U.S. Department of Agriculture, but the Palmer is better when working with large areas of uniform topography. Western states, with mountainous terrain and the resulting complex regional microclimates, find it useful to supplement Palmer values with other indices such as the Surface Water Supply Index, which takes snow pack and other unique conditions into account. Australian Drought Authorities are using deciles (NDMC, 2000).

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