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DROUGHT MONITORING IN SPAIN USING NOAA-AVHRR MULTITEMPORAL IMAGES 
F. González Alonso!, A. Calle?, J.L. Casanova?, J.M. Cuevas!, A. Vázquez! 
(? Instituto Nacional de Investigación y Tecnología Agraria y Alimentaria, INIA. Ministry of Agriculture. Spain. 
Crta de la Corufía. Km 7. 28040 Madrid. Spain 
Tel: 34-91-3476828 ; Fax: 34-91-3572293 
e-mail: alonso@inia.es 
O Remote Sensing Laboratory, LATUV. University of Valladolid. Spain. 
Laboratorio de Teledetección (LATUV) ; Departamento de Física Aplicada 
Prado de la Magdalena s/n. 4707 1-Valladolid. Spain 
Tel: 34-983-423130 ; Fax: 34-983-423130 
e-mail : abel@rigel.fal.cie.uva.es 
KEY WORDS: Drought monitoring, NOAA-AVHRR images. 
ABSTRACT: 
Spain is a country which is particularly affected by the phenomenon of drought given that over half the years 
between 1880 and 1990 were dry or very dry. 
In the current decade of the 90s, the period from 1992-1995 was also dry and the year 1995 was especially 
dramatic as more than 12 million people were affected by water restrictions. 
The identification of areas affected by drought using the information supplied by the AVHRR sensor of the 
NOAA satellite appears to be fairly viable and may be of great use in the monitoring of this type of this type of 
phenomenon. 
1. INTRODUCTION 
Definitions of drought may vary greatly and in a 
general manner it may be considered that drought exists 
when there is a serious decrease in rainfall which leads to 
a significant reduction in plant growth and development, 
both crops or natural vegetation. 
Spain is a country which is particularly affected 
by drought as over 50% of the years between 1880 and 
1990 were very dry. 
During the 1980s, seven years were classified as 
dry or very dry and in the 1990s five years have 
warranted the same classification. 
1994-1995 was the worse period since the 
beginning of the decade as it was dry over the whole of 
Spain except in isolated areas of Galicia, the Basque 
Country and Catalonia and it was very dry in the south. 
In 1995, after four years of drought the situation 
in Andalusia became critical and extreme as 40% of the 
population suffered drinking water restrictions. In July 
the number of people affected had reached 12 million. 
Water reserves in January 1995 in the 
autonomous community” of Andalusia were 9% of their 
capacity and in the province of Cadiz were only 4%. 
According to agricultural organisations, during 
the period 1992-1995 financial losses caused by drought 
in the agricultural sector were over one and a half billion 
pesetas (around 10 000 million US dollars) and in 1995 
alone were over half a billion. 
Various authors have tested the use of vegetation 
indices derived from NOAA-AVHRR images in the 
identification and monitoring of areas affected by drought 
ata regional scale with fairly satisfactory results (Tucker 
and Choudhury, 1987; Gutman, 1990; Teng, 1990; Liu 
and Massambani, 1994). 
The aim of this work is the development of a 
methodology which permits the identification and 
monitoring of areas affected by drought in Spain using 
vegetation indices (NDVI) from NOAA-AVHRR images 
in an operational form in such a way that this information 
may be useful for management in decision making on 
agricultural and environmental policy. 
2. METHODOLOGY 
Since 1993 HRPT format NOAA-AVHRR 
images have been received at The University of 
Valladolid Remote Sensing Laboratory. 
Intemational Archives of Photogrammetry and Remote Sensing. Vol. XXXII, Part 7, Budapest, 1998 709