Evaluation of satellite-based rainfall products for hydrological modelling in Morocco

ABSTRACT

Several satellite-based precipitation estimates are becoming available at a global scale, providing new possibilities for water resources modelling, particularly in data-sparse regions and developing countries. This work provides a first validation of five different satellite-based precipitation products (TRMM-3B42 v6 and v7, RFE 2.0, PERSIANN-CDR, CMORPH1.0 version 0.x) in the 1785 km² Makhazine catchment (Morocco). Precipitation products are first compared against ground observations. Ten raingauges and four different interpolation methods (inverse distance, nearest neighbour, ordinary kriging and residual kriging with altitude) were used to compute a set of interpolated precipitation reference fields. Second, a parsimonious conceptual hydrological model is considered, with a simulation approach based on the random generation of model parameters drawn from existing parameter set libraries, to compare the different precipitation inputs. The results indicate that (1) all four interpolation methods, except the nearest neighbour approach, give similar and valid precipitation estimates at the catchment scale; (2) among the different satellite-based precipitation estimates verified, the TRMM-3B42 v7 product is the closest to observed precipitation, and (3) despite poor performance at the daily time step when used in the hydrological model, TRMM-3B42 v7 estimates are found adequate to reproduce monthly dynamics of discharge in the catchment. The results provide valuable perspectives for water resources modelling of data-scarce catchments with satellite-based rainfall data in this region.

Editor M.C. Acreman; Associate editor N. Verhoest     

Comparison of two snowmelt modelling approaches in the Dudh Koshi basin (eastern Himalayas,Nepal)

Abstract

The glaciers in the Nepalese Himalayas are retreating due to rising temperatures. Lack of data and information on Nepal’s cryosphere has impeded scientific studies and field investigations in the Nepalese Himalayas. Therefore, IRD France and Ev-K2 CNR Italy have conducted the PAPRIKA (CryosPheric responses to Anthropogenic PRessures in the HIndu Kush-Himalaya regions: impacts on water resources and society adaptation in Nepal) project in Nepal with the financial support of the French and Italian scientific agencies. This project aims to address the current and future evolution of the cryosphere in response to overall environmental changes in South Asia, and its consequences for water resources in Nepal. Thus, two hydrological models, the GR4J lumped precipitation–runoff model and the snowmelt runoff model (SRM), were used in the Dudh Koshi basin. The GR4J model has been successfully applied in different parts of Europe. To obtain better results in such a harsh and rugged topography, modifications needed to be made, particularly in the snow module. The runoff pattern is analysed herein both for past years and, in a sensitivity analysis, for possible future climatic conditions (i.e. precipitation and temperature) using the SRM and GR4J modelling approaches. The results reveal a significant contribution of snow- and glacier-melt to runoff, and the SRM model shows better performance in Nepalese catchments than the GR4J model.

Editor D. Koutsoyiannis; Associate editor D. Gerten     

Internal waves near the turning point

Abstract

A uniformly valid solution of internal wave equations is presented, using Langer's method, for an arbitrary density profile. The dispersion relation and mean square values of the velocity components are obtained. Particular emphasis is placed on the turning point problem and on estimating the errors involved in the approximations in a recent paper by Garrett and Munk (1972). Expressions are given for various spectral ratios of interest.     

A hierarchical generalized linear model with variable selection: studying the response of a representative fish assemblage for large European rivers in a multi-pressure context

Global change calls for an understanding of how temperature and flow regimes influence aquatic ecosystems. Fish assemblages are a major component of river ecosystems and are thought to exhibit more integrative informative responses than single species to environmental variations, whether rare and sudden or gradual and continuous. The use of long-term datasets is thus of primary importance, allied to statistical modeling. For each of three previously identified species clusters, we performed Bayesian variable selection and inference within a hierarchical log Poisson Generalized Linear Model using a spike and slab normal prior to pinpoint which subset of environmental variables is of importance for each fish assemblage. Fish counts from electrofishing experiments are known to provide overdispersed data and, not surprisingly, the contribution of recorded environmental effects is found to be weak compared with those of other intra-assemblage sources of variation. The posterior distribution of the regression parameters is in coherence with what was expected from biological knowledge of the three species clusters. In particular, thermophilic species tend to benefit from warmer waters, whereas the recruitment of cold water species decreases due to global warming effects. Our study provides an example of the advantages of hierarchical modeling for quantifying interspecies ecological effects and selecting common environmental variables of importance.     

Chemical and K–Ar systematics of a mylonitic mica after natural and experimental interactions with varied fluids

Flow-through and batch-leaching experiments combining mineralogical, chemical and K–Ar isotopic analyses of mica separates from a mylonitic sample of the Tyndrum faulting system in Scotland (U.K.) were conducted to evaluate and simulate the natural interaction with H₂SO₄-loaded river water at pHs of 3–4. The flow-through experiments with H₂SO₄-loaded and pure deionized water completed by a batch-leaching experiment with 1 M HCl at room temperature had varied effects on soluble mineral phases, such as Fe-sulfates and Ca/Mg-carbonates, that were present in the varied mica size fractions, but none caused the mineralogical and K–Ar characteristics of the mica to differ from separates of the natural environment.Despite the limited number of K–Ar ages, size fractionation of the mylonitic mica identified two generations of mica with different REE patterns. The coarser (2–8 μm) fraction yielded a high La/Yb ratio of 4.3 and crystallized at 359 ± 6 Ma at a temperature of 250–300 °C, probably during a major tectonic-thermal activity. The smaller (< 0.5 μm) fraction yielded a La/Yb ratio of 2.1, a younger K–Ar age at 315 ± 5 Ma and a lower crystallization temperature of about 200 °C.     

The palaeomagnetism and magnetic fabric of sediments from Peak Cavern, Derbyshire

Summary. This paper describes the magnetic remanence and susceptibility anisotropy of 42 samples of laminated clay from Peak Cavern. The sediments are shown to have acquired a stable remanent magnetization due to the depositional alignment of magnetite grains. The magnetic fabric data confirm the existence of alteration within a reddened surface layer. A record of geomagnetic secular variation in the underlying clay is compared to a dated lake sediment magnetostratigraphy to suggest that deposition occurred around 7000 yr bp . A method for estimating water current directions based on the remanence and magnetic fabric data is critically assessed before deducing the sense of palaeoflow in the cave.