What we write: Rhoda Odongo

Posted on by afvanloon

Propagation from meteorological to hydrological drought in the Horn of Africa using both standardized and threshold-based indices

Rhoda A. Odongo, Hans De Moel & Anne Van Loon

Drought is a pressing concern, particularly in data-poor regions like the Horn of Africa (HOA). We recently published a study on the propagation of the drought signal from meteorological drought to hydrological drought in the Horn of Africa using standardized and threshold-based indices.

We delve into the intricate relationships between meteorological, soil moisture, and hydrological droughts across 318 catchments in the HOA. By characterizing these drought types and analysing their propagation, this study sheds light on the spatial variability of drought hazard in the region. We employed a multi-faceted approach to unravel the drought dynamics by utilizing well-established indices like the Standardized Precipitation Index (SPI), Standardized Soil Moisture Index (SSMI), and Standardized Streamflow Index (SSI) to quantify meteorological, soil moisture, and hydrological droughts, respectively. Additionally, we implemented the variable threshold method to gauge the duration of drought periods below specific percentile threshold (70th percentile) for precipitation, soil moisture, and streamflow.

We calculated the ratio between the duration of precipitation drought and soil moisture drought (P/SM) and streamflow drought (P/Q) to indicate propagation from meteorological to soil moisture and meteorological to discharge drought respectively. These ratios represent the speed with which precipitation deficits affect soil moisture availability and eventually discharge deficits. We also tested the influence of possible governing factors of climate and catchment characteristics on propagation.

The findings unveil crucial insights into the relationship between various drought types and how these is influenced by climate and catchment characteristics. It sheds light on the complex interplay between climate, geography and land characteristics.

  1. Meteorological and Soil Moisture Drought Propagation:
    • Short SPI accumulation periods (1 to 4 months) correlate with arable land, high annual precipitation, and low sand/silt content in catchments.
    • Longer SPI accumulation periods (5 to 7 months) are linked to regions characterized by low annual upstream precipitation and shrub vegetation.
  2. Meteorological and Hydrological Drought Propagation:
    • Short SPI accumulation times coincide with high annual precipitation, permeable volcanic geology, and cropland.
    • Longer SPI accumulation times are observed in catchments with low annual precipitation, sedimentary rocks, and shrubland.
  3. Regional Insights:
    • Precipitation accumulation periods of 1 to 4 months are significant in the wetter western areas of the HOA.
    • Accumulation periods of 5 to 7 months hold importance in the more arid regions.

In conclusion, this study offers valuable insights into the propagation of drought through the hydrological cycle in the HOA. By identifying correlations between drought types and diverse environmental factors, the research underscores the intricate relationships that govern drought hazard distribution. This knowledge is crucial for devising effective forecasting and management strategies tailored to specific regions within the HOA. In a region where drought poses significant challenges, understanding the underlying dynamics is a vital step towards building resilience and ensuring sustainable water resource management.

Paper reference:

Odongo, R. A., De Moel, H., and Van Loon, A. F. (2023) Propagation from meteorological to hydrological drought in the Horn of Africa using both standardized and threshold-based indices, Nat. Hazards Earth Syst. Sci., 23, 2365–2386. https://doi.org/10.5194/nhess-23-2365-2023