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Handbook of Drought Indicators and Indices'


Why is it important to monitor droughts? Droughts are a normal part of the climate, and they can occur in any climate regime around the world, even deserts and rainforests. Droughts are one of the more costly natural hazards on a year-to-year basis; their impacts are significant and widespread, affecting many economic sectors and people at any one time. The hazard footprints of (areas affected by) droughts are typically larger than those for other hazards, which are usually constrained to floodplains, coastal regions, storm tracks, [1]

or fault zones. Perhaps no other hazard lends itself quite so well to monitoring, because the slow onset of droughts allows time to observe changes in precipitation, temperature, and the overall status of surface water and groundwater supplies in a region. Drought indicators, or indices, are often used to help track droughts and these tools can vary depending on the region and the season.

Like other hazards, droughts can be characterized in terms of their severity, location, duration, and timing. Droughts can arise from a range of hydrometeorological processes that suppress precipitation and/or limit surface water or groundwater availability, creating conditions that are significantly drier than normal or otherwise limiting moisture availability to a potentially damaging extent. The indicators and indices discussed in this Handbook of Drought Indicators and Indices provide options for identifying the severity, location, duration onset, and cessation of such conditions. It is important to note that the impacts of droughts can be as varied as the causes of droughts. Droughts can adversely affect agriculture and food security, hydropower generation and industry, human and animal health, livelihood security, personal security (e.g., women walking long distances to fetch water) and access to education (e.g., girls not attending school because of increased time spent on fetching water). Such impacts depend on the socioeconomic contexts in which droughts occur in terms of who, or what, are exposed to the droughts and the specific vulnerabilities of the exposed entities. Therefore, the type of impacts relevant in a particular drought monitoring and early warning context is often a crucial consideration in determining the selection of drought indicators.

A drought impact is an observable loss or change at a specific time because of drought. Drought risk management involves hazards, exposure, vulnerability and impact assessment, a drought early warning system (DEWS) (monitoring and forecasting, see Box 8.1), and preparedness and mitigation (WMO et al. 2013). It is important that drought indicators or indices accurately reflect and represent the impacts being experienced during droughts. As droughts evolve, the impacts can vary by region and by season.


Drought early warning systems typically aim to track, assess, and deliver relevant information concerning climatic, hydrologic, and water supply conditions and trends. Ideally, they have both a monitoring (including impacts) component and a forecasting component. The objective is to provide timely information in advance of, or during, the early onset of drought to prompt action (via threshold triggers) within a drought risk management plan as a means of reducing potential impacts. A diligent, integrated approach is vital for monitoring such a slow-onset hazard.

Monitoring different aspects of the hydrologic cycle may require a variety of indicators and indices. It is desirable to align these and their depiction with the impacts of emerging conditions on the ground and management decisions being taken by different individuals, groups, and organizations. Although a DEWS is ultimately concerned with impacts, drought impact assessment is a large gap in many DEWSs used around the globe at this time. Assessment of impacts is complicated, as socioeconomic factors other than the physical nature of droughts influence the levels and types of impacts related to drought exposure and vulnerability.

Understanding how droughts affect people, communities, businesses, or economic sectors is key to taking steps toward mitigating the impacts of future droughts.

Following publication of the Intergovernmental Panel on Climate Change report on extreme events (IPCC 2012), the issue of quantifying loss and damage from extreme climate events such as droughts has become important for policy implementation, especially with regard to the United Nations Framework Convention on Climate Change agenda. In addition, due to the magnitude of associated disaster losses, improved drought monitoring and management will be fundamental to implementing the Sendai Framework for Disaster Risk Reduction 2015-2030 and the sustainable development goals. Effective and accurate monitoring of hydrometeorological indicators is a key input to risk identification, to DEWSs, and for managing sector impacts. In light of this, the 17th World Meteorological Congress, held in June 2015, adopted Resolution 9: Identifiers for Cataloguing Extreme Weather, Water and Climate Events. This initiated a process of standardizing weather, water, climate, space weather and other related environmental hazards and risk information, and prioritized the development of identifiers for cataloging extreme weather, water, and climate events. This handbook will make an important contribution to these efforts.

The purpose of this handbook is to cover some of the most commonly used drought indicators/indices that are being applied across drought- prone regions, with the goal of advancing monitoring, early warning, and information delivery systems in support of risk-based drought management policies and preparedness plans. These concepts and indicators/indices are outlined in what is considered to be a living document that will evolve and integrate new indicators and indices as they become known and are applied in the future. The handbook is aimed at those who want to generate indicators and indices themselves, as well as for those who simply want to obtain and use products that are generated elsewhere. It is intended for use by general drought practitioners (e.g., meteorological/hydrological services and ministries, resource managers, and other decision makers at various levels) and aims to serve as a starting point, showing which indicators/indices are available and being put into practice around the world. In addition, the handbook has been designed with drought risk management processes in mind. However, this publication does not aim to recommend a "best" set of indicators and indices. The choice of indicators/indices is based on the specific characteristics of droughts most closely associated with the impacts of concern to the stakeholders.

This handbook does not attempt to address the full complexities of impacts and the entire range of socioeconomic drought indicators and indices. The indicators and indices included describe the hydrometeorological characteristics of droughts and do not cover socioeconomic and environmental factors such as those that may be needed to assess and anticipate drought-related impacts and outcomes. The handbook is intended as a reference, providing an overview and guide to other sources of information. The Integrated Drought Management Programme (IDMP) is establishing a complementary help desk on integrated drought management.

  • [1] Published with permission from the World Meteorological Organization (WMO) and GlobalWater Partnership (GWP). M. Svoboda and B.A. Fuchs. (2016). Handbook of Drought Indicators andIndices. Integrated Drought Management Programme (IDMP), Integrated Drought ManagementTools and Guidelines Series 2. WMO: Geneva, Switzerland; GWP: Stockholm, Sweden.
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