Improving early warning of droughts near onset and middle of a growing season

Early warning of drought is crucial for mitigation of the most adverse impacts of water and food insecurity to lives and livelihoods. Recent advances in routine production (i.e., weekly) and open access to NMME SubX—subseasonal climate forecasts—provide an unprecedented opportunity to improve drought early warning near the onset and middle of the crop-growing season. Near the onset of a season, subseasonal precipitation forecasts have the potential to provide early indication of delay in rain onset, which, as shown in a recent study (Shukla et al., 2021, PLOS ONE), can be a reliable indicator of agricultural drought development. This is particularly relevant for some of the most food-insecure regions in East Africa. Additionally, subseasonal forecasts have the potential to improve drought forecasting during the middle of the season—several months before the harvests—when they are used in combination with to-date observations. Integration of near-real-time observations with subseasonal climate forecasts can enhance drought detection capabilities by leveraging the skill that is derived from initial conditions (as of middle of the season) and complementing it with the skill of subseasonal climate forecasts. Here, we first describe how onset of the rainy season is a reliable indicator of agricultural droughts. The results indicate that in the administrative units in sub-Saharan Africa, which  have the highest risk of acute food insecurity, a delay of about 20 days in the rainy season onset can double the probability of agricultural droughts. We then describe the results of an analysis examining the performance of subseasonal climate forecasts in identifying the timing of the onset of the rainy season in those administrative units. Next, we describe a SERVIR-AST-supported project, which uses subseasonal climate forecasts to develop a West Africa-focused water-deficit forecasting system in collaboration with AGRHYMET, primarily  for agropastoral usage. Here, we make  use of a widely used crop water balance model, the Water Requirement Satisfaction Index (WRSI), to generate improved forecasts of crop water stress, and hence, crop production outcomes, during the middle of the rainy season in West Africa (June through September). We compare the performance of these forecasts with the forecasts generated using climatology only. Finally, we briefly describe how these subseasonal climate forecasting products are being disseminated, communicated, and used in the focus regions.