The Economics of Desertification, Land Degradation, and Drought

Drought
Drought episodes have been increasing over time in the drier areas of the world. Kemp (1994) stated that
drought is a rather imprecise term dealing with moisture deficiency in terms of its impact on human
activities. Drought describes a naturally occurring phenomenon in which precipitation is significantly
below normal recorded levels, which have been established through long-term observations. Droughts are
generally considered a temporary event (Kemp 1994). From an agricultural and economic viewpoint, a
drought is characterized as adversely affecting land resource production systems (Akhtar-Schuster, Bigas,
and Thomas 2010) by leading to reduced crop yields or even crop failure. In accordance with that
characterization, UNCCD defines drought as “the naturally occurring phenomenon that exists when
precipitation has been significantly below normal recorded levels, causing serious hydrological
imbalances that adversely affect land resource production systems” (UNCCD, 1996, Part1, Article 1c).
From a natural science point of view, drought is defined as a period of duration D (months) with a
soil moisture quantile value q(θ) less than an arbitrary threshold level q0(θ) that is preceded and followed
by a value above this level. The departure below this level at any particular time is the drought
magnitude: M = q0(θ) – q(θ). The mean magnitude over the drought duration is the intensity.
A recent study showed that there is increasing wetness globally but with contrasting regional
differences (Table 2.4). From 1950 to 2000, North America showed increased wetness, whereas Europe
and southern and southeastern Asia did not experience significant changes. On the other hand, drought
spatial extent has increased in the drier areas of western Africa. However, other studies have shown that
the regreening of the Sahelian region was due to the recovery from the great Sahelian droughts that
affected the region in the 1970s and 1980s (Herrmann, Anyamba, and Tucker 2005). The general
circulation models (GCMs) have generally predicted that wet areas and those in high latitudes will
experience wetter conditions, whereas drier areas will experience drier and more frequent droughts (Cline
2007; Christensen et al. 2007). The severity and frequency of droughts, heat waves, and floods in most
Sub-Saharan African countries are also expected to increase, resulting in significant impacts on natural
resources (Christensen et al. 2007).
The Hadley Center predicts an increase in the global area expected to experience severe drought
at any point in time from 10 percent of the world’s land surface in 2005 to 40 percent in the future, for a
given global warming of 3–4 degrees Celsius (Stern 2006). Frequencies of droughts are also expected to
increase.
Table 2.5 shows the change in four regions in which drought frequency is expected to increase in
the year 2030, with a 0.2 degree Celsius increase each decade from 2009 to 2030. Assuming low-,
medium-, and high-impact scenarios, Webster et al. (2008) predicted that drought frequency will increase
by 10 percent in southeastern and southern Asia and by 20 percent in East Africa and Central America
from their levels during the baseline period of 1992–2008. As noted earlier, drought will be more frequent
in drier areas.
Table 2.4—Trends in the spatial extent of drought for various baseline values
Location 10 20 30 40 50
World -0.021 - 0.032 - 0.035 - 0.027 - 0.021
Europe
Northern Europe - 0.102 - 0.143 - 0.139 - 0.139 -0.140
Mediterranean 0.014 0.022 0.022 0.026 0.022
Africa
West Africa 0.068 0.179 0.319 0.435 0.527
East Africa 0.029 0.064 0.088 0.117 0.154
Southern Africa 0.038 0.09 0.15 0.203 0.234
North Asia
Northern Asia 0.055 0.102 0.129 0.139 0.14
Central Asia -0.049 -0.098 - 0.151 - 0.176 - 0.203
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