Abdesselam Megnounif

In semiarid climates, precipitation is the most important hydrometeorological event, as it remains the main source of water. In the context of climate change, the analysis of its spatio-temporal trends provides useful information for effective planning and management of water resources. Daily rainfall data collected from 12 meteorological stations in the downstream Mekkera Basin, Northwest Algeria, between 1975 and 2011 were analyzed using the innovative polygon trend analysis method. The analysis focused on trends in average monthly rainfall, average number of rainy days, average daily intensity, maximum daily rainfall, and maximum number of dry days per month. The results reveal a contrasting trend in monthly precipitation averages between dry and wet season months. Precipitation drops by 55 times during the spring months, with a significant decrease in February and March. In winter, there was a less noticeable decrease, though the intensity of maximum daily events increased. August and September show a significant increase in maximum daily precipitation across all stations, consistent with the overall 52 detected cases of increasing rainfall in the dry season. In addition, 70% of time series show that an increase in rainy days led to a decrease in the maximum number of dry days, whereas 52% of time series with fewer rainy days experienced more dry days. These findings offer crucial insights that can assist water managers in developing adaptive strategies to tackle the changing precipitation patterns in the region.

This study aims to provide a brief overview of four regional climate model (RCM) estimations for (Daily, Monthly, Seasonal, and Annual) averaged precipitation over the Wadi Chemora Basin in northeastern Algeria for the historical period (1970–2005) and future forecasts (2006–2100). Data from seven ground stations were compared to data from four RCMs: RCA4 driven by ICHEC-EC-EARTH and NOAA-GFDL-GFDL-ESM2M from MENA-CORDEX domain with intermediate resolution (25 km, 0.22°) and ALADIN and RegCM4 from MED-CORDEX domain with high resolution (12 km, 0.11°). In most time steps (Annual, Seasonal, Monthly, and Daily), the raw RCMs overestimated precipitation, but their performance improved significantly after applying gamma quantile mapping (GQM) bias correction method. The bias-corrected projections indicate decreases of seasonal rainfall for the near future (2010–2039), mid-century (2040–2069), and end of century (2070–2100) periods. Overall decreases in all seasons lead to the projected decrease in annual rainfall of an average of 66% by the end of the 21st century.

A large variety of hysteresis shapes is observed in the suspended-sediment concentration-discharge relationship. The analysis of such forms encompasses two main axes; a qualitative classification and a quantitative description. In this study, a new automated procedure is presented to facilitate hysteresis loop analysis. The classification is based on a numerical transformation to distinguish the combination of the 3 behaviors exhibited by a hysteresis loop (Linear, Clockwise, Anticlockwise) whereby the hysteresis shape and class are identified. In accordance, the hysteresis loop is quantitatively described in a partial format using normalized and real scale metrics. As proof of concept, the method was tested on 314 suspended sediment-discharge events issued from 9 USGS stations from 4 different regions to ensure a wide variety of shapes. The automated classification identified 32 different shapes. Partial description was found to provide more insight into the different phases of sediment transport in combined shapes such as the figure of eight. Real scale quantification linked each hysteresis behavior to its natural impact. The approach was found to be highly compatible with a large variety of data types so that it can be generalized to other relationships found to produce hysteresis loops.

Over a long multi-year period, flood events can be classified according to their effectiveness in moving sediments. Efficiency depends both on the magnitude and frequency with which events occur. The effective (or dominant) discharge is the water discharge which corresponds to the maximum sediment supply. If its calculation is well documented in temperate or humid climates and large basins, it is much more difficult in small and semi-arid basins in which short floods with high sediment supplies occur. Using the example of 31 years of measurements in the Wadi Sebdou (north-west Algeria), this paper compares the two main statistical approaches to calculate the effective discharge (the empirical method based on histograms of sediment supply by discharge classes and an analytical calculation based on a hydrological probability distribution and on a sediment rating curve) to a very simple proxy: the half-load discharge, i.e. the flow rate corresponding to 50 % of the cumulative sediment yield. Three types of discharge subdivisions were tested. In the empirical approach, two subdivisions provided effective discharge close to the half-load discharge. Analytical solutions based on log-normal and log-Gumbel probability distributions were assessed but they highly underestimated the effective discharge, whatever the subdivision used to adjust the flow frequency distribution. Furthermore, annual series of maximum discharge and half-load discharge enabled the return period of hydrological years with discharge higher than the effective discharge (around 2 years) to be inferred and showed that more than half of the yearly sediment supply is carried by flows higher than the effective discharge only every 7 hydrological years. This study was the first to adapt the analytical approach in a semi-arid basin and to show the potentiality and limits of each method in a such climate.

The runoff coefficient (RC) is a parameter that is very often used in surface hydrology in order to characterize the drainage capacity of a watershed. The traditional estimate of this coefficient is often made from abacuses based on 2 or 3 parameters to the maximum. In this work, three numerical models are presented. Two models are based on experimental work. The first one is based on three criteria, namely the vegetation cover, the type of soil, and the slope. The second one considers the size of the watershed, the maximum daily rainfall and the type of soil. In practice, it is not easy to estimate the coefficient of runoff by simultaneously considering the influence of several criteria. In order to overcome this problem, a third model is developed and presented; it allows capitalizing the information from the first two models mentioned above. The objective of the present work is to be able to verify the comparability of these criteria and to assess the relative importance of each of them.

In this study, the spatial variation of daily and monthly concentration precipitation index and its aggressiveness were used in 23 rainfall stations in the extreme north-east of Algeria over the period 1970–2010. The trend was analysed by the Mann–Kendall (MK) test. The results show that daily precipitation concentration index (CI) values are noticeably higher in places where the amount of total precipitation is low, the results of MK test show that areas of high precipitation concentration tend to increase. The seasonality and aggressiveness of precipitation are high in the eastern and western parts of the study region (eastern and central coastal of Constantine catchments), whereas a moderately seasonal distribution with low aggressiveness is found in the middle of the study area (plains and central Seybouse catchment). As a result, the modified Fournier index (MFI) has a significant correlation with annual precipitation, whereas theCIand monthly precipitation concentration index (PCI) show an opposite correlation in relation to annual precipitation.