Chapter 3       Drought risks

Unlike the risks associated with tropical cyclones and floods, those associated with drought remain less well understood. Drought, therefore, is often a less visible risk. Losses and impacts are not systematically captured, global standards for measuring drought hazard are only slowly being introduced, and there are difficulties regarding data collection. As a result, comprehensive assessments of drought risks are only just beginning and, as yet, there is no credible global drought risk model. Case studies indicate that the impacts of drought can only be partly attributed to deficient or erratic rainfall, as drought risk appears to be constructed over time by a range of drivers. These include: poverty and rural vulnerability; increasing water demand due to urbanization, industrialization and the growth of agribusiness; poor soil and water management; weak or ineffective governance; and climate variability and change. Such drivers are increasing vulnerability and exposure, and translate drought hazard into risk. Impacts and drivers may be strongly interrelated but, as many relate to poor, rural households, there is currently little political or economic incentive to address the risk. Yet, strengthening drought risk management, as an integral part of risk governance, will be fundamental to sustaining the quality of life in many countries during the coming decades. This chapter is only a first step in presenting the complexities of global drought risk. Understanding and revealing the full spectrum is a challenge that must be addressed in the years to come.

3.1 Drought risk in the Navajo Nation

Between 1999 and 2009, the Navajo Nation experienced a drought of historic proportions. Many springs sampled for a 1999 water-quality study had run dry by 2002 and have remained dry ever since. Wells and aquifers became so saline that they could no longer be used for drinking, by humans or livestock. More than 30,000 cattle perished between 2001 and 2002 alone, and entire communities ran out of water (Redsteer et al., 2010). Though the drought officially began in 1999, data suggest that it may have begun in 1996 or even 1994; the uncertainty due to large portions of the reservation being poorly monitored.



Some of the causes of this disaster were not directly due to decreasing rainfall during the drought period. Annual snowfall has been decreasing during the past 80 years (Figure 3.2), and by the 1960s more than 30 major rivers and bodies of water upon which the Navajo relied for livestock and agricultural production had dried up (Figure 3.1) (Redsteer et al., 2010). Since then, the soil has become drier due to higher temperatures during the warmest months, further increasing water stress (Weiss et al., 2009).


However, it was factors like political marginalization and rural poverty that translated meteorological drought into a disaster for the Navajo people. The Navajo reservation was established in 1868 in a vast and remote region spanning four states (Arizona, Colorado, New Mexico and Utah). The majority of the reservation occupies the driest third of the Navajo’s traditional homeland, because ranchers had claimed the best rangelands for themselves (Redsteer et al., 2010). During the 1930s, the government began requiring permits to raise livestock, limiting the numbers each family could own, and demanding that they had to remain within one of 20 newly demarcated grazing districts (Young, 1961; White, 1983; Kelley and Whiteley, 1989). This final restriction interrupted a traditional Navajo drought impact management practice of moving livestock across district boundaries to less drought affected areas (White, 1983; Kelley and Whiteley, 1989; Iverson, 2002). Some Navajo traditions and practices also increased drought risk, such as their continued preference of cattle over other species, added to by US Government and Navajo Nation policies that require families to have livestock in order to validate traditional land use rights, even if they have lived on the same land for generations (Redsteer et al., 2010). Even with grazing restrictions, herds have exceeded the carrying capacity of the land since the 1960s (Young, 1961; Redsteer et al., 2010).

Such policies in a context of decreasing water availability led to endemic poverty even before the last drought began. In 1997, average annual per capita income was less than US$6,000, and 60 percent of the Navajo lived in poverty, in houses without water and electricity. Savings mitigate drought impacts, but because the Navajo often invest their savings in livestock, this safety net is in itself vulnerable to drought (Redsteer et al., 2010). Risk drivers, such as inappropriate development, badly managed water resources, weak local governance and inequality, all played their part in translating the most recent meteorological drought into a further series of cascading losses and impacts.

3.2 Drought hazard

Unlike the risks associated with tropical cyclones and earthquakes, drought risk remains poorly understood. Although meteorological drought is increasingly well characterized, the measurement of agricultural and hydrological drought remains a challenge (see Box 3.1 for definitions). Far less attention has been given to identifying, let alone addressing, the underlying risk drivers. Attempts to build credible global drought risk models have proved elusive, and drought losses and impacts are not systematically recorded. Despite increasing evidence of the magnitude of drought impacts, few countries have developed drought risk management policies or frameworks, and the political and economic imperative to invest in reducing drought risk remains weakly articulated.

Meteorological droughts are usually defined as deficiencies in rainfall, from periods ranging from a few months to several years or even decades. Long droughts often change in intensity over time and may affect different areas. For example, the 1991–1995 meteorological drought in Spain migrated from west to east and then south (Figure 3.3).


Until the recent adoption of the Standard Precipitation Index (SPI) (see Box 3.2), there was no agreed global standard to identify and measure meteorological drought. National weather services used different criteria, making it difficult to establish exactly when and where droughts occur.


The application of the SPI could strengthen the capacity of countries to monitor and assess meteorological drought. Despite its simplicity, many countries have difficulty using it due to an insufficient number of rainfall stations in some areas, due to the low priority awarded to hazard monitoring in government budgets. The number of rainfall stations maintained by Spain’s national meteorological agency, AEMET, for example, has declined to almost half of the peak of the mid-1970s (Figure 3.5) (Mestre, 2010).

In Central America, more weather stations are located nearer to the Pacific coast (Figure 3.6), presenting an obstacle to making accurate SPI calculations on the Caribbean side required for regional drought monitoring and planning (Brenes Torres, 2010). Remote sensing can partly fill this gap, but SPI models still need to be calibrated using physical rainfall data (Dai, 2010). Because meteorological drought is a climatic phenomenon, rather than a hazard per se, additional data is required to identify and measure drought hazard.

Experts have now reached a consensus that agricultural drought should be measured using composite indices that consider rainfall, soil moisture, temperature, soil and crop type, streamflow, groundwater, snow pack, etc., as well as historical records of drought impacts (WMO, 2010).¹  However, such indices require data that is available only in a handful of countries at present, mostly in North America and parts of Africa. Work is also ongoing to identify indicators of hydrological drought, but this is also challenged by data constraints and modelling complexities.² 









Notes