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In regions characterized by a high concentration of small reservoirs, there is often public debate about the effectiveness of these structures in locally adapting to and mitigating drought impacts, bearing in mind their potential to modify or induce drought events in downstream areas. In this study, we investigated the influence of a Dense Network of Small Reservoirs (DNR) on the emergence and intensification of drought impacts at catchment scale, as well as their local social benefits. This analysis was based on the Socio-Hydrological-Agricultural-Reservoir (SHARE) model, specially developed for this purpose, with a medium-sized catchment in the semi-arid region of Brazil as a case study. We identified that, while a DNR can prolong the effects of a hydrological drought on storage in a large strategic reservoir at the catchment outlet by obstructing surface-runoff connectivity, it plays a crucial role in mitigating drought impacts at a local level. Specifically, the presence of small reservoirs has the potential to boost local agricultural production by up to 5 times compared to scenarios without these structures. In addition, our simulation results suggest there is a notable reduction in the need for emergency water distribution by water trucks in the presence of a DNR. This study highlights the need for a balanced approach to implementing public policies, weighing the local benefits of small reservoirs against the possible downstream impacts on large reservoirs.

Drought management is currently informed by a variety of approaches, mostly responding to drought crisis when it happens. Toward more effective and integrated drought management, we introduce a conceptual drought diagnosis framework inspired by diagnostic concepts from the field of medicine. This framework comprises five steps: 1. Initial diagnostic assessment; 2. Diagnostic testing; 3. Consultation; 4. Communication of the diagnosis; and 5. Treatment and prognosis. To illustrate the need for the proposed approach, four case studies of recently drought-affected regions were selected: the city of Cape Town, the state of California, the Northeast region of Brazil, and the Horn of Africa. Contrasting elements for these cases include the geographic extent and political boundaries, climate, socio-economics, and the relevance of different water resources (e.g., rainfall, reservoirs, and aquifers). For each case, we identified documented practices and policies and reflected on them in terms of drought misdiagnosis or incomplete diagnosis that have aggravated socio-economic and environmental drought impacts. A common example is the preference for technical solutions (e.g., installing infrastructure to augment water supply), rather than measures that reduce vulnerability. Analysis of these four drought case studies confirmed the anticipated need for a comprehensive approach to drought diagnosis for more successful treatment and prevention of drought. Using an analogy with medical science can be helpful toward comprehensively diagnosing droughts for a variety of contexts and assessing the effectiveness of proposed interventions. This framework can help drought managers to be more proactive in enabling drought-affected regions to become more drought resilient in the future.

Building reservoirs is a response to cope with drought in drylands. However, this human modification to the landscape may trigger both positive and negative effects. Here, we investigate how a network of reservoirs influences the propagation of meteorological drought (MD) into hydrological drought (HD) in a large semi-arid catchment in Brazil. We applied 12-month standardized indices to classify droughts. Then, the drought series were compared to each other. The downstreamness concept was used to describe the spatial water distribution. The onset of reservoir drought (RD) was much later than MD, but the delay between MD and RD peaks was even longer. Streamflow drought started with a small delay after MD, but it transformed into a similar RD. RD was initially more severe downstream. When the drought severity was at its highest, upstream and downstream RD equalized. The perceptual model of drought propagation may help in developing reservoir management systems in drylands.