Remote Sensing and Drought Monitoring

One of the natural calamities that affects us is lack of normal rainfall and consequent drought conditions which in turn affect agricultural productivity. Drought conditions can be monitored using data obtained from satellite. This system provides efficient and timely monitoring capability by integrating the timeliness and objectivity of space observations with details of ground perceptions.

During drought, physiognomic changes of vegetation may become apparent. Satellite sensors are capable of discerning many such changes through spectral radiance measures and manipulation of such measures into vegetation indices, which are sensitive to the rate of plant growth as well as to the amount of growth. Such indices are also sensitive to the changes in vegetation affected by moisture stress. The visible and near infrared bands on the satellite multi-spectral sensors allow monitoring of the greenness of vegetation. This property is used in the case of monitoring drought, as the stressed vegetation and other bare ground, water, etc. reflect differently. Besides, moisture stress in vegetation, resulting from prolonged rainfall deficiency, is reflected by lowering of vegetation index values. Such decrease could also be caused by other stresses such as pest/disease attack, nutrient deficiency or soil geo-chemical effects. But this does not show up well in coarse resolution data which covers very large areas at a time.

Reliable drought interpretation requires a Geographical Information System (GIS) based approach, since the topography, soil type, spatial rainfall variability, crop type and variety, irrigation support and management practices are all relevant parameters.

In recent years, many investigations have demonstrated the capability of satellite-borne sensors to provide information on various drought indicators, which helps to monitor drought more effectively. The following paragraphs discuss remote sensing of rainfall, soil moisture, and vegetation/crop conditions, which are helpful in delineating agricultural drought.

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