On the total freshwater storage deficit of Ethiopia

As it receives one of the highest rainfall amount in the continent and the region,  Ethiopia is the water tower for the greater horn of Africa and the Nile. Because of its small-holder and traditional based  agrarian economy, but recurrent drought is the main development challenge. In the last decades, hydrologists developed  many drought indexes based on various hydrological and meteorological components like rainfall, evapotranspiration, and runoff to provide indexes for decision making. some of these are: Drought Severity Index (PDSI) (Palmer, 1965), Crop Moisture Index (CMI) (Palmer, 1968), Standardized Precipitation Index (SPI) (McKee et al., 1993), and Surface Water Supply Index (SWSI) (Shafer and Dezman, 1982). There are already  some efforts  to  understand the pattern of rainfall in the region,  mainly from the long term climate change perspective, and the findings are mixed.

The total available freshwater is the residual of all the hydrological fluxes. Hence, it is the integrated indicator of the water budget system of a basin.  On the contrary,  it  is the most difficult component to measure, if obtained with huge efforts, it is very specific and point information. NASA’s Gravity Recovery and Climate Experiment (GRACE) mission (Tapley et al., 2004) provides an independent satellite observation of change of the total water storage. Recently this data has been used to estimate the total water deficit of large basin, and it is evaluated positively. Here, I analyzed GRACE data to understand the total water storage of the Ethiopia. The objectives are:1. to estimate the long term water storage mean at monthly time steps; 2. to estimate the total water deficit of each months ("drought event" if longer than the months ); 3. to calculate the total water status according to the GRACE observation for the last one decade.Here are some results, and hoping to detail the methodology and extend the results in the near future. 

Fig 1: The long term mean monthly total water storage distribution of Ethiopia according to GRACE observation.

Fig 2: the long term monthly mean storage deficit maps of Ethiopia as observed from GRACE

Fig: Time series storage deficit (below zero ) at national level . At national scale, the water storage over the long term trend is more or less at constant level

 Fig 4: the time series storage deficit at four location in the country 

To be continued…..

References 

Palmer, W.C. Meteorological Drought; U.S. Department of Commerce, Weather Bureau: Washington, DC, USA, 1965. 

Shafer, B.A.; Dezman, L. Development of a Surface Water Supply Index (SWSI) to assess the severity of drought conditions in snowpack runoff Areas. In Proceedings of the Western Snow Conference, Reno, NV, USA, 19–23 April 1982. 

McKee, T.B., Doesken, N.J., Kleist, J., 1993. The relationship of drought frequency and duration to time scales. In: Proceedings of the 8th Conference on Applied Climatology, American Meteorological Society, Anaheim, CA, Boston, MA, 17–22 January, pp. 179–184.

Tapley, B. D., S. Bettadpur, J. C. Ries, P. F. Thompson, and M. M. Watkins (2004), GRACE measurements of mass variability in the Earth system, Science, 305(5683), 503–505, doi:10.1126/science.1099192.