Agricultural Drought Indices - US Department of Agriculture

adverse climatic impacts on agricultural production at the national level. The worst year for the
agrarian sector in this period was 1995, with a reduction of 10% in final production. The main
crops affected were irrigated herbaceous crops, mainly cereals. In the cereal-producing sector,
the 1995 yield experienced a decrease of 30%, compared to the average of the 1986-1991 period.
Perennial crops were less affected, but with the persistence of dry conditions, the vineyards,
olives, and citrus fruits were affected from 1994 on. In the 1994-95 season, olive oil production
was reduced by 20% from the average of the four previous seasons. The viticultural sector was
also affected, and average vine production decreased in 1994 and 1995 by 25% compared with
1993 and 40% compared with 1992. Cattle production was also affected by the decrease in the
capacity of pasture lands to sustain cattle.
This prolonged drought severely affected the forested areas in southern Spain, where it caused a
high mortality of Pinus pinaster and severe withering symptoms in oak groves, scrub, gall oaks,
stone pines (Pinus pinea), and cork oak. Forest fire risk conditions also increased. In the southern
half of Spain, the area affected by forest fires increased by 63% in 1991-95 in comparison with the
mean of the previous 10 years.
2004-2005 (Hydrological Year) Drought Episode
This drought episode had an extraordinary intensity at the time scale of one year. Figure 13 shows
SPI values for a one-year scale and all the main peninsular Spanish basins. As can be seen, all of
them are under -1, and under -2 in the case of the Atlantic basins. Peninsular Spain, taken as a
whole, was also under -2, making the 2004-2005 hydrological year the driest of the series.
Figure 13. The map shows SPI values on September 30, 2005, for a 12-month scale, in the main
Spanish basins.
SPI values for a 12-month scale reached a second minimum value on record in the series of Tajo
and Guadiana basins in September 2005. The SPI value for all of peninsular Spain (-2.2) was
near the absolute minimum value of the series (-2.5), reached in November 1981. The minimum of
2004-2005 was mainly due to a near-absolute absence of precipitation in the whole country in
November, usually one of the wetter months in extended zones of Spain. Unlike the drought
episodes of the 1990s, a striking aspect of the 2004-2005 drought episode was that it
simultaneously affected all regions. This caused the 12-month SPI for the entire country to reach
very low values when compared with those of the different basins.
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