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

There have been numerous drought propagation studies in data-rich countries, but not much has been done for data-poor regions (e.g.,such as the Horn of Africa ([HOA)]). In tThis study, we characteriszes meteorological, soil moisture, and hydrological droughts and the propagation from one to the other for 318 catchments in the HOA to improve the understanding of the spatial variability of the the drought hazard. We calculate the StandardizedStandardised 10 Precipitation Index ([SPI)], StandardizedStandardised Soil Moisture Index ([SSMI)], and StandardizedStandardised Streamflow Index ([SSI)]. AdditionallyIn addition, we use the variable threshold method to calculate the drought duration of drought below a predefined percentile threshold for precipitation, soil moisture, and discharge. The relationship between meteorological and soil moisture is investigated by finding the SPI accumulation period that has the highest correlation between SPI and SSMI and the relationship between meteorological and hydrological drought 15 is analysed by the SPI accumulation period that has the highest correlation between SPI and SSI time series. Additionally, we calculated these relationships with the ratio between the threshold-based meteorological drought duration and soil moisture drought duration, and the relation between threshold-based meteorological drought duration and streamflow drought durationThe relationship between meteorological, soil moisture, and hydrological drought is examined by finding the SPI accumulation period that shows the highest correlation between SPI and vs SSMI, and 20 SPI and vs SSI timeseries. A, and , by calculating the ratio between the threshold-based precipitation drought duration and vs soil moisture drought duration, respectively meteorological drought duration vs streamflow drought duration is calculated. Finally, we investigate the influence of climate and catchment characteristics on these propagation metrics. The Rresults indicate show that (1) the propagation from SPI to SSMI and the mean drought duration ratio of meteorological precipitation to soil moisture ([P/SM) ] mean duration ratio are mainly influenced by soil properties 25 and vegetation, with the short accumulation periods (1-to 4 months) of SPI found in catchments with croplandarable land, high mean annual precipitation, and low sand and silt content, while longer accumulations (5 to -7 months) are found in catchments with low upstream mean annual precipitationmean annual upstream precipitation, and shrub vegetationation; (2) the propagation from SPI to SSI and precipitation to streamflow duration ratio are highly influenced by the climate and catchment control, i.e., geology, elevation and land cover, with the short accumulation 30 times in catchments with high annual precipitation, volcanic permeable geology, and cropland, and the longer accumulations in catchments with low annual precipitation, sedimentary rocks and shrubland; and (3) the influence of upstream mean annual precipitationmean annual upstream precipitation is more important for the propagation from SPI to SSI than from SPI to SSMI. Additionally, precipitation accumulation periods of approximately 1 to -4 months in wet western areas of HOA, and of approximately 5 to -7 months in the more dryland regions are found. This can