Intraseason and seasonal drought trends in Ethiopia were studied using a suite of drought indicators—standardized precipitation index (SPI), standardized precipitation evapotranspiration index (SPEI), Palmer drought severity index (PDSI) and Z-index for Meher (long-rainy), Bega (dry), and Belg (short-rainy) seasons—to identify drought-causing mechanisms. Trend analysis indicated shifts in late-season Meher precipitation into Bega in the southwest and southcentral portions of Ethiopia. Droughts during Bega (October–January) are largely temperature controlled. Short-term temperature-controlled hydrologic processes exacerbate rainfall deficits during Belg (February–May) and highlight the importance of temperature- and hydrology-induced soil dryness on production of short-season crops such as tef. Droughts during Meher (June–September) are largely driven by precipitation declines arising from the narrowing of the intertropical convergence zone (ITCZ). Increased dryness during Meher has severe consequences on the production of corn and sorghum. PDSI is an aggressive indicator of seasonal droughts suggesting the low natural resilience to combat the effects of slow-acting, moisture-depleting hydrologic processes. The lack of irrigation systems in the nation limits the ability to combat droughts and improve agricultural resilience. There is an urgent need to monitor soil moisture (a key agro-hydrologic variable) to better quantify the impacts of meteorological droughts on agricultural systems in Ethiopia.

Brazilian Cerrado biome is the largest and richest tropical savanna in the world. In order to understand the effects of climate changes on the hydrology of the Cerrado basins, this paper investigates the hydrological impacts of climate change throughout the 21st century under different emissions scenarios on the streamflow and on the droughts in the Sono, Manuel Alves da Natividade and Palma basins, located in the Brazilian Cerrado. For this purpose, the SWAT hydrological model driven by the downscaling of the HadGEM2‐ES and MIROC5 global climate models associated with RCP4.5 and RCP8.5 scenarios were used in three time slices (2011–2040, 2041–2070 and 2071–2099). The Standardized Precipitation Index (SPI) and the Standardized Streamflow Index (SSFI) were used to characterize droughts. In general, the results showed that the duration, intensity and frequency of the meteorological and hydrological droughts are expected to increase during the future periods. However, the hydrological droughts are projected to be larger than the meteorological droughts. Reductions in the streamflow are indicated in all future time slices and under both RCPs, especially, during dry periods, which may cause negative impacts in the ecological functions of the Cerrado biome, risk for reduction of the recharge of aquifers and risk for the electric energy production in northern Brazil.

Extraction of dense, nonaqueous-phase liquid (DNAPL) contaminants trapped in groundwater aquifers is a major problem in environmental remediation because existing field techniques, such as pump and treat, have limited effectiveness. We present new laboratory experimental evidence that low-frequency (100 Hz or less) stress waves could increase the mobility and transport of DNAPL by an order of magnitude or more during pump and treat. This unproven technology could decrease the time and cost of groundwater remediation efforts and reduce the final amount of contaminant trapped in an aquifer. A sand core was confined in a specialized flow apparatus and contaminated with a small amount of trichloroethylene (TCE). Steady-state water flow was then initiated through the core, and effluent TCE concentrations were measured using gas chromatography (GC). At various stages of water flow, axial stress cycling at 25–100 Hz was applied by mechanical coupling of a magnetostrictive actuator to the sand core's outlet face. During most of the stimulated runs pure-phase TCE droplets were produced in the effluent and the effective TCE concentration increased by as much as a factor of 20. Numerous flow runs were performed to investigate the effects of stimulation frequency, amplitude, and duration, as well as water flow rate and background effluent TCE concentration. Calibrated accelerometer and pore pressure measurements allowed determination of the stimulation threshold parameters required to achieve enhanced TCE production. The physical mechanisms responsible for the observed phenomenon are not fully understood. Further research is required before this promising new technology can be applied reliably to contaminated groundwater aquifers.