Mohamed A. M. Abd Elbasit

Spatiotemporal Changes of Rainfall Erosivity in Loess Plateau, China

The reason for the severity of soil erosion in Loess Plateau can be attributed to three nonanthropogenic factors: rainfall erosivity, slope gradient, and loess soil. The rainfall erosivity is controlled by the rainfall characteristics. Generally, rainfall characteristics change drastically in space and time. The rainfall erosivity has been investigated using the modified Fournier index (MFI), annual rainfall, and precipitation concentration index (PCI). The study showed a decrease in average MFI by 10%. However, the difference between the MFI in 1960s and 1990s was found to decrease in a large area in Loess Plateau, whereas there was an increase in MFI at the high latitude. The maximum decrease in the rainfall erosivity was higher in the southeast than that in the north and west. The was found to have a trend similar to the MFI, which further indicates that the MFI follows, to a high extent, the annual rainfall trend. The PCI was found to have trend opposite to MFI and . The PCI increased in the north and west and decreased toward the southeast. The average temporal difference in the PCI between the 1960s, and 1990s was two percent.

Application of piezoelectric transducers in simulated rainfall erosivity assessment

Abstract Rainfall simulators have often been used to mimic natural rainfall for studies of various land-surface and water interaction processes. The characteristics of the simulated rainfall are the main indicators used to judge the performance of the rainfall simulators. The aim of this study is to investigate the potential of piezoelectric transducers for measuring and evaluating a dripper-type simulated rainfall drop-size distribution (DSD) and kinetic energy (KE). The directly measured KE was significantly correlated with the estimated KE using the drop-size distribution and empirical rain drop fall velocity relationships. This result emphasizes the potential use of the piezoelectric sensor to directly measure and evaluate rainfall kinetic energy. Also, the relationship between rainfall intensity and KE showed good patterns of agreement between simulated rainfall and natural rainfall. Citation Abd Elbasit, M. A. M., Yasuda, H. & Salmi, A. (2011) Application of piezoelectric transducers in simulated rainfall erosivity assessment. Hydrol. Sci. J. 56(1), 187–194.

Diurnal fluctuation of groundwater levels caused by the invasive alien mesquite plant.

Invasive alien plants such as mesquite (Prosopis juliflora) alter patterns of groundwater uptake. We measured the groundwater level beneath a mesquite stand in an arid area in Sudan. The changes in groundwater level closely followed plant water uptake. The groundwater level started to decline a few hours before sunrise, recovered around noon, and then continued to decline until a few hours after sunset, before recovering again during the night. Thus, groundwater level showed two peaks: just before sunrise and around midday. The midday recovery was due to the depression of photosynthesis by heat and light.

Evaluation of the Effect of a Rain Pulse on the Initial Growth of Prosopis Seedlings

Prosopis juliflora is a useful “multi-purpose” tree, but it invades rapidly in arid and semi-arid environments, causing livelihood degradation of local communities. A rain pulse under drought conditions has been reported to be an important factor to promote plant invasion. The purpose of this research was to evaluate the effect of a rain pulse on the invading process of Prosopis juliflora and to propose a feasible plan to control the expansion of this species in Sudan. First, seed germination was examined under eight irrigation conditions, corresponding to 4–32 mm of rainfall. Most seeds imbibed in all the irrigation conditions, about half or more of the imbibed seeds germinated in 12 mm or more of irrigation. Twenty mm or more of irrigation induced seed emergence. Second, initial growth of germinated seeds was examined under ten irrigation conditions (1–32 mm rainfall) over 54 hours or 138 hours of cultivation. Radicle elongated most vigorously in 24 mm irrigation, and extended over 20 cm in length. Allocation to radicle was dominant, and its elongation was promoted in higher soil moisture condition. Based on these results, we propose that seedlings of P. juliflora should be eradicated within a few weeks after a single large rainfall, which might be convenient and effective to control additional expansion of this species in Sudan.

Impact of Rainfall Microstructure on Erosivity and Splash Soil Erosion Under Simulated Rainfall

Rainfall represents the major driver of soil detachment in erosion processes. The potential of rainfall to detach soil has been defined as rainfall erosivity. The relationship between rainfall intensity and rainfall drop size distribution (DSD) controls various rainfall characteristics including the rainfall erosivity (Abd Elbasit et al., 2010). The relationship between rainfall intensity and rainfall erosivity differs due to geographical location under natural rainfall (Hudson 1965; Wischmeier and Smith, 1978; Zanchi and Torri, 1980; Van Dijk et al., 2002) and due to type and configuration of rainfall simulators under simulated rainfall (Hall, 1970; Olayemi and Yadav, 1983; Auerswald et al., 1992; Salles and Poesen, 2000). The role of rainfall microstructure on the determination of rainfall erosivity has attracted several researchers in the past. However, our understanding on this subject is still limited due to the lack of equipments that are able to measure the rainfall drop parameters and ultimately the rainfall kinetic energy. Several indices have been suggested to quantify the rainfall erosivity (Abd Elbasit et al., 2010). Generally, the suitable erosivity index must include the drop mass and velocity as major variables for raindrop power determination. The erosivity index has been described by Epema and Riezebos, 1983 as follows:

Simulated rainfall erosivity: Measurement and evaluation using piezoelectric sensors

Rainfall simulators have been used intensively in order to mimic natural rainfall for various land-surface and water interaction processes. The characteristics of the simulated rainfall are the main indicators to judge the performance of the rainfall simulator. This study attempted to investigate the potential of piezoelectric transducers to measure and evaluate dripper-type simulated rainfall drop size distribution (DSD) and kinetic energy (KE). The directly measured KE was significantly correlated with the estimated KE using the drop size distribution and empirical rain drop fall velocity relationships. This result emphasizes the potential use of the piezoelectric sensor to directly measure and evaluate rainfall kinetic energy.