Harouna Karambiri

IAHS decade on predictions in ungauged basins (PUB), 2003-2012: Shaping an exciting future for the hydrological sciences

Abstract Drainage basins in many parts of the world are ungauged or poorly gauged, and in some cases existing measurement networks are declining. The problem is compounded by the impacts of human-induced changes to the land surface and climate, occurring at the local, regional and global scales. Predictions of ungauged or poorly gauged basins under these conditions are highly uncertain. The IAHS Decade on Predictions in Ungauged Basins, or PUB, is a new initiative launched by the International Association of Hydrological Sciences (IAHS), aimed at formulating and implementing appropriate science programmes to engage and energize the scientific community, in a coordinated manner, towards achieving major advances in the capacity to make predictions in ungauged basins. The PUB scientific programme focuses on the estimation of predictive uncertainty, and its subsequent reduction, as its central theme. A general hydrological prediction system contains three components: (a) a model that describes the key processes of interest, (b) a set of parameters that represent those landscape properties that govern critical processes, and (c) appropriate meteorological inputs (where needed) that drive the basin response. Each of these three components of the prediction system, is either not known at all, or at best known imperfectly, due to the inherent multi-scale space—time heterogeneity of the hydrological system, especially in ungauged basins. PUB will therefore include a set of targeted scientific programmes that attempt to make inferences about climatic inputs, parameters and model structures from available but inadequate data and process knowledge, at the basin of interest and/or from other similar basins, with robust measures of the uncertainties involved, and their impacts on predictive uncertainty. Through generation of improved understanding, and methods for the efficient quantification of the underlying multi-scale heterogeneity of the basin and its response, PUB will inexorably lead to new, innovative methods for hydrological predictions in ungauged basins in different parts of the world, combined with significant reductions of predictive uncertainty. In this way, PUB will demonstrate the value of data, as well as provide the information needed to make predictions in ungauged basins, and assist in capacity building in the use of new technologies. This paper presents a summary of the science and implementation plan of PUB, with a call to the hydrological community to participate actively in the realization of these goals.

Using land cover changes and demographic data to improve hydrological modeling in the Sahel

At the beginning of the drought in the Sahel in the 1970s and 1980s, rainfall decreased markedly, but runoff coefficients and in some cases absolute runoff increased. This situation was due to the conversion of the land cover from natural vegetation with a low annual runoff coefficient, to cropland and bare soils, whose runoff coefficients are higher. Unless they are adapted, hydrological conceptual models such as GR2M, are unable to reproduce this increase in runoff. Despite the varying environmental and climatic conditions of the West African Sahel, we show that it is possible to increase the performance of the GR2M model simulations by elaborating a time-varying soil water holding capacity (WHC), and to incorporate this value in the annual maximum amount of water to be stored in reservoir A of the model. We looked for interactions between climate, rural society and the environment. These interactions drive land-cover changes in the Sahel, which in turn drive the distribution of rainfall between infiltration, evaporation and runoff, and hence the water resources, which are vital in this region. We elaborated several time series of key indicators linked to these interactions. We then integrated these changes in the runoff conditions of the GR2M model through the maximum value of the reservoir capacity. We calculated annual values of WHC using the annual values of four classes of land cover, natural vegetation, cultivated area, bare soil and surface water. We then used the hydrological model with and without this time-varying soil value of A, and compared the performances of the model under the two scenarios. Whatever the calibration period used, the Nash-Sutcliffe index was always greater in the case of the time-varying A time series. This article is protected by copyright. All rights reserved.

Analysis of the Performance of Base Flow Separation Methods Using Chemistry and Statistics in Sudano-Sahelian Watershed, Burkina Faso

This research aims to determine appropriate methods for base flow separation under Sudano-Sahelian climate in West Africa. Four Recursive Digital Filtering (RDF) methods and the Conductivity Mass Balance (CMB) method were used. Daily streamflow of the Mouhoun River (formerly Black Volta River) at Samendeni gauge station has been separated into base flow and runoff. The RDF methods are easy to use but cannot take into account the actual hydrological processes within the watershed, while CMB method does it well. But, given that regular discharge measurement is rarely coupled with Electrical Conductivity measurements, it is therefore not possible to apply CMB method over time at each outlet. The CMB method is frequently used on a short time as a reference to assess the performance or to calibrate RDF methods. In the present study, CMB method was used for the year 2017, especially during the rainy season (from July to October) to produce more realistic base flow values. Statistical analysis was used to compare RDF and CMB methods. It was found that all the four RDF methods used are significantly different from the CMB method in the study area. Among the RDF methods, the Eckhardt method which is two parameters filtering method was successfully calibrated using CMB method Base Flow Index (BFI) as constraint. With the calibration process, the parameter BFImax of the Eckhardt method was adjusted to 0.32 in the study area context. The achievements of this study can have several implications such as adequate base flow estimation over time at Samendeni gauge station and at other similar gauges of the Mouhoun watershed which will be particularly beneficial to the critical issue of assessment of climate change impact on base flow in the study area.

Relationship between soil water content and crop yield under sahelian climate conditions: case study of Tougou experimental site in Burkina Faso

This study aims at assessing the relationship between soil water stock and the yield of agricultural practices in Tougou catchment located in northern Burkina Faso. It is a region that has experienced a significant and continuous degradation of its natural resources, especially soils, due to the climate variability and the rapid increase of the population. Areas allocated to subsistence agriculture are increasing at the expense of pastoral land. This degradation causes a change in processes and mechanisms that control ecological systems. In order to provide solutions to this issue, some agricultural practices have been implemented to improve crop yield. This is particularly the case of traditional techniques:“zai”, “stony line” and “half-moon”, which can significantly improve the soil infiltration capacity and yield. Daily monitoring of soil moisture and pressure in experimental plots based on these agricultural practices show that half-moon and Zai provided good yield with 2180kg / ha and 1070 kg / ha respectively compared to that of the control plot with about 480 kg/ha. These important yields are due in large part to the improvement of the retention capacity of these soils, thus giving to crops the necessary water need for their development even in drought periods