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The National Drought Mitigation Center and World Bank recently passed their decade-long anniversary of working together on new drought tools that can help countries increase their resilience to drought.

A composite drought indicator is a monitoring tool that combines several different elements of the climate and hydrological cycle into one objective measure of drought conditions. The NDMC and World Bank have worked together to develop CDIs—and facilitate country-level processes to increase in-house capacity—in several regions including Brazil. Most recently, the team wrapped up work creating the foundation for a region-wide composite drought indicator for southern Africa.

“Right now, there are so many things going on in each of these countries. They’re using different tools and different ways of defining drought, even within the same government,” said Nathan Engle, a climate change specialist at the World Bank. The CDI, he explains, “gives them an initial entry point into operationalizing, in a more objective and consistent way, what drought means.”

The Composite Drought Indicator

The CDI has several advantages as a drought monitoring tool, especially in areas where weather stations are few and far between or hard to access. The use of remotely sensed data, for example, makes it possible to track conditions consistently across an entire data-scarce region. Meanwhile, new machine learning techniques can help automate the process, making it possible to keep it going on a regular basis even in places with less technical capacity or resources.

“It’s a very flexible system,” said Mark Svoboda, director of the NDMC. “We can integrate national and subnational data at the local level, all the way up to these global datasets. It’s about using whatever resources and data a country has access to that they trust.”

The backbone of the process, Svoboda explained, is the convergence-of-evidence approach pioneered by the U.S. Drought Monitor. As with the USDM, developing a composite drought indicator involves pulling together and weighing various sources of data, from physical indicators of the hydrological and climate system to expert knowledge and local reports of conditions, into one standardized measure of drought. But, unlike the USDM, once the weights of the CDI inputs are established and validated for a country or region, the process is entirely computational, with no human interpretation involved.

“Every piece of information is important, but no one piece is 100% of the answer,” he explained. The opportunity to validate the model with on-the-ground observations is particularly important. “You need to get local folks to ground truth it, to give it a sanity check to ensure that the models you’re producing match what’s actually happening on the ground in terms of impacts,” said Svoboda.

Engle agrees that the real-time validation of conditions compared to the model’s output is essential for helping countries select the specific data—and the relative weights of different indicators—that best reflect their particular geography and climatology.

Right now, for example, the southern Africa CDI relies on four remotely sensed region-wide data sources: the Standardized Precipitation Index (a measure of rainfall), the Normalized Difference Vegetation Index (a measure of an area’s greenness and plant density), soil moisture and land surface temperature. In the future, though, Engle hopes that individual countries will develop the capacity to refine the product for their needs.

“The basic set of drought variables and indicators tend to work pretty well in this region,” he said, “but nothing is going to be perfect, so it has to be adapted to each particular country.”

Local Leadership

That kind of country-level refinement is already underway in southern Africa where three countries have really taken the lead on the region-wide effort.

In Eswatini, the lead agency is the National Disaster Management Agency. They produce regular bulletins for agricultural producers in the Lubombo region, which include the monthly CDI maps. They’re also working on creating a website where they’ll publish the maps each month as representatives in the country have taken ownership for carrying the project forward.

Meanwhile, in Botswana, the lead agency is the Department of Water Affairs. Unsurprisingly, they’re particularly interested in taking the CDI to the next level so it can reflect hydrological conditions in the drought-prone country.

In neighboring Zimbabwe, the Department of Civil Protection, in partnership with Bindura University of Science Education, has also made significant progress in refining the CDI and putting it into place as a drought policy tool.

“From all the natural hazards affecting Zimbabwe in recent decades, drought has come to be a leading cause of community livelihood losses,” said Emmanuel Mavhura, a lecturer at Bindura University who is helping lead efforts to develop the CDI. But, he adds, weather stations across the country aren’t evenly distributed and don’t have the kind of consistent records to make a multi-decade analysis possible. So, a CDI using remotely sensed data is essential for the country’s drought planning efforts.

“The CDI simplifies the complexity arising from objectively quantifying the characteristics of a drought,” he said. “It enables monitoring drought as it develops.” That kind of early warning system, Mavhura says, is essential for helping officials take proactive measures to manage and respond to drought.

The team leaders in Zimbabwe are in process of devising strategies to share the CDI with the public and incorporate it into decision making. Mahuvra says the government has identified specific agencies to lead each step in the process—from producing the CDI to sharing it with the public—and has held several training sessions already.

These three countries, Engle explained, have been leading the charge in the region. But, the ultimate hope is to create a region-wide process that can be owned by a regional entity like the Southern African Development Community. Then the SADC could, in Engle’s words, “stitch” the efforts of different countries together, lead capacity-building efforts at the country level and manage a region-wide CDI.

Once it’s regionally operational, with the SADC secretariat at the helm, the CDI will provide a standardized tool for transboundary drought monitoring and early warning across borders and river basins, potentially serving as the basis for a regional drought protocol. The ultimate goal, though, isn’t just to create a set of standardized maps of drought conditions, but also to inform policy and decision making. The hope of the NDMC, World Bank and on-the-ground partners is that individual countries develop the capacity to take over, and refine, their CDIs and then use the data as an objective trigger for potential drought management actions. It’s not just about analyzing data but about turning it into something useful and actionable.

Check out a factsheet with more information about the CDI process and progress to date in southern Africa.

-- Leah Campbell, NDMC Communications