Exploring hydro meteorological drought patterns over the Greater Horn of Africa (1979 2014) using remote sensing and reanalysis products
Spatio temporal patterns of hydrological droughts over the Greater Horn of Africa (GHA) are explored based on total water storage (TWS) changes derived from time variable gravity field solutions of Gravity Recovery And Climate Experiment (GRACE, 2002 2014) together with those simulated by Modern Retrospective Analysis for Research Application (MERRA, 1980 2014) These hydrological extremes are then related to meteorological drought events estimated from observed monthly precipitation products of Global Precipitation Climatology Center (GPCC, 1979 2010) and Tropical Rainfall Measuring Mission (TRMM, 1998 2014) The major focus of this contribution lies on the application of spatial Independent Component Analysis (sICA) to extract distinguished regions with similar rainfall and TWS with similar overall trend and seasonality. Rainfall and TWS are used to estimate Standard Precipitation Indices (SPIs) and Total Storage Deficit Indices (TSDIs) respectively that are employed to characterize frequency and intensity of hydro meteorological droughts over GHA. Significant positive (negative) changes in monthly rainfall over Ethiopia (Sudan) between 2002 and 2010 leading to a significant increase in TWS over the central GHA region were noted in both MERRA and GRACE TWS (2002 2014) However, these trends were completely reversed in the long term (1980 2010) records of rainfall (GPCC) and TWS (MERRA) The four independent hydrological sub regions extracted based on the sICA (i.e. Lake Victoria Basin, Ethiopia Sudanese border, South Sudan, and Tanzania) indicated fairly distinct temporal patterns that matched reasonably well between precipitation and TWS changes. While meteorological droughts were found to be consistent with most previous studies in all sub regions, their impacts are clearly observed in the TWS changes resulting in multiple years of extreme hydrological droughts. Correlations between SPI and TSDI were found to be significant over Lake Victoria Basin, South Sudan, and Tanzania. The low correlations between SPI and TSDI over Ethiopia are likely related to inconsistency between TWS and precipitation signals. Further, we found that hydrological droughts in these regions were significantly associated with Indian Ocean Dipole (IOD) events while El Nino Southern Oscillation (ENSO) plays a secondary role.