Exploring the link between drought indices and socio-economic impacts in East Africa

In recent years, East Africa (EA) has been affected by numerous drought events. To better understand the drought hazard and its implications, it is important to analyze the propagation of dry conditions through the hydrological system and identify at what point it leads to negative impacts on society. This way, we define drought events as dry conditions during which actual impacts are felt by communities (i.e. ‘impactful droughts’) rather than using a predefined relative threshold. This study explores the link between standardized and threshold-based drought indices and drought impacts in EA. Drought propagation from meteorological to soil moisture to hydrological drought to finally socio-economic impacts has been investigated in the data-rich regions around the world (i.e. Europe). However, not much has been done in data-poor regions (i.e. Africa), with very different climatic and socio-economic characteristics.

We identify meaningful indicators for region- and sector-specific impact occurrences, focusing on three impact types: crop yield and livestock losses, changes in pasture represented by Normalized Drought Vegetative Index (NDVI), and people affected. In this study, we link these impact types to various drought hazard indices calculated from time series of precipitation, evaporation, soil moisture and discharge for every administrative unit in Kenya, Ethiopia and Somalia. The standardized indices are used with varying accumulation periods (1,3,6,12,24,48 months) to find the best predictors. We use independent but complementary machine learning techniques (correlation, logistic regression and random forest modelling) to identify which indices link best to which drought impacts.

Using the variable threshold based analysis to analyse drought propagation in Isiolo county in Kenya, we find an increase in frequency and duration of hydrological droughts. This has been confirmed in other studies. The correlations and relationships between crop yield anomalies and indices are different in each of the administrative units. The findings in this research will lead to a greater understanding of the effects of drought hazards to communities, and contribute to improved drought monitoring and forecasting. This research can also form the basis for follow up work to explore the effects of adaptation options (i.e. irrigation) on drought hazard and impacts in East Africa.