Abstract
Drought is a temporal decrease in water availability and occurs in all climatic regions. Droughts propagate through the hydrological cycle, e.g., meteorological drought propagates to groundwater recharge drought. This research investigated drought propagation in the hydrological cycle in a semiarid context. Meteorological drought severity was determined using a standardized precipitation index (SPI). A variable threshold method and standardized groundwater index (SGI) was implemented to investigate groundwater recharge drought. Comparing meteorological drought (SPI) and groundwater drought (SGI) helps to assess drought propagation in the hydrological cycle. For drought analysis, time-series of rainfall and groundwater recharge needs to be available with high spatial and temporal resolution. Therefore, for this study, daily rainfall measurements were collected from 11 meteorological stations, and water balance modeling was used to estimate temporally and spatially distributed groundwater recharge. This research was carried out in the Bilate River catchment in the Rift Valley basin of Ethiopia. Results show that meteorological droughts were observed before every groundwater recharge drought and they propagate to groundwater recharge drought. Furthermore, analysis of the drought propagation indicates that not all meteorological droughts are propagated. The analysis also shows that a combination of mild to severe meteorological droughts can propagate to groundwater recharge and result in a major groundwater-recharge drought event.
Highlights
Droughts are regional, and regional climatic parameters govern their occurrence
The study about temporal and spatial meteorological drought characterization in Ethiopia by Bisrat and Berhanu (2019) indicated that water scarcity occurred in the hydrological year of 2001–2002 and 2008–2009 because of meteorological drought
The result of this study confirmed that more frequent meteorological droughts happened in these hydrological years
Summary
Regional climatic parameters govern their occurrence. Semiarid environments regularly experience low water availability since the mean annual potential evapotranspiration is 2–5 times the mean annual precipitation (Pandey and Ramasastri 2002; Ponce et al 2000; Schwabe et al 2013a; Stahl and Hisdal 2004; WMO 1975). In Ethiopia, meteorological drought, agricultural drought, and food security have been studied; the impact of drought on groundwater resources, i.e., groundwater drought, has not received much attention. Regardless of its surface-water and groundwater resource potential, Ethiopia has been facing drought at an increasing frequency throughout the past decades (Edossa et al 2010; Zewdie 1994). The drought frequency used to be once in 5 years in Ethiopia based on the recent records (Edossa et al 2010). All these studies are based on meteorological, surface water, or agricultural data; the country needs to investigate its potential for groundwater resources due to its reliability, in periods of drought
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