Monitoring Major Droughts

United States

The United States is the world largest producer and leading exporter of agricultural products, including grains. Drought occurs almost every year somewhere in the nation, affecting agriculture (see chapter 9). Severe droughts occurred in the United States in 1988, 1989, 1996, and 2000. The 1988 drought cost around $40 billion in damages to the U.S. economy in human health, environment, and wildlife. Grain production fell below domestic consumption probably for the first time in the second half of last century (Reibsame et al., 1990; Kogan, 1995). AVHRR-based estimates show that by the end of June 1988, vegetation experienced stress in the most productive areas of the Great Plains, the U.S. grain basket (figure 6.1). Total world grain production in 1988 dropped by 3% (FAO, 2000).

Drought in 1989 and 1996 began early and by the end of April affected the primary winter wheat areas. Compared to earlier droughts, the 1988 vegetation stress (black color in figure 6.1) was not seen so early. By July the 1988 drought turned into a national disaster, affecting vegetation during the most critical mid-season period. The crop yield anomalies during the years of major droughts are well related to vegetation health indices (Kogan, 1995, 1997, 2000).

Former Soviet Union

If the United States is the largest seller of grains, the former Soviet Union (FSU) has been and will likely be the largest U.S. grain buyer. Since the breakup of the USSR in 1991, stagnation in technology-related grain growth in combination with frequent droughts led to serious grain shortages. Therefore, monitoring of the FSU grain production is very important for U.S. grain growers and traders.

Since 1991, FSU experienced droughts during different years, as identified by the AVHRR-based indices (figure 6.1, right panel) and affected 100-150 million acres of crops and rangeland, reducing the total FSU grain production by 10-15% (20-30 million metric tons). Independent countries incurred up to 30% of grain losses. The worse economic problems occurred when major drought affected both winter (mostly Ukraine and southern Russia) and spring grain crops (eastern regions in 1991, 1996, and 1998). These droughts were confirmed by climatological observations. In these cases, crop yield anomalies showed strong correlation with vegetation health indices (Kogan, 1997, 2001).

Argentina

Argentina is the second largest exporter (next to the United States) of corn and coarse grains, and the third largest exporter of wheat (FAO, 2000). Droughts and dry spells are frequent and devastating in this country. Since 1985, Argentina experienced two major and several minor droughts. By all standards, the most damaging droughts occurred during 1988-89 and 1989-90 crop seasons (figure 6.2), when the country lost between 15 and 20% of the total grain production. The minor droughts were less intensive and affected smaller areas, causing 5-10% reduction in crop yields. These results were validated by the ground measurements of wheat yield in Cordoba province (Seiler et al., 2000).

China

China produces grains and cotton, mostly for domestic consumption. From time to time, China also imports small amounts of agricultural commodities. However, in 1994, China unexpectedly imported a huge volume of cotton, exceeding by almost twofold the largest purchases since 1981. These imports were preceded by a cotton yield reduction three years in a row: 22% in 1992-93, 11% in 1993-94, and 7% in 1994-95. Our investigation indicated that this reduction can be attributed to unfavorable growing conditions (vegetation stress) across the main cotton-growing areas (figure 6.3).

Of all three years, the most severe vegetation stress (both moisture and thermal) occurred in 1992, which also showed the largest yield reduction. Some deterioration of vegetation conditions was also observed in 1994, but the drought-related stress was partially offset by a almost normal summer rainfall. Unlike the other two drought years, the 1993 drought was due to excessive moisture as revealed by the AVHRR-derived data.

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