Despite the availability of studies on the frequency density of landslide areas in mountainous regions, frequency-area distributions of historical landslide inventories in populated hilly regions are absent. This study revealed that the frequency-area distribution derived from a detailed landslide inventory of the Flemish Ardennes (Belgium) is significantly different from distributions usually obtained in mountainous areas where landslides are triggered by large-scale natural causal factors such as rainfall, earthquakes or rapid snowmelt. Instead, the landslide inventory consists of the superposition of two populations, i.e. (i) small (b 1-2 · 10 − 2 km 2 ), shallow complex earth slides that are at most 30 yr old, and (ii) large (N 1-2 · 10 − 2 km 2 ), deep-seated landslides that are older than 100 yr. Both subpopulations are best represented by a negative power-law relation with exponents of −0.58 and −2.31 respectively. This study focused on the negative power-law relation obtained for recent, small landslides, and contributes to the understanding of frequency distributions of landslide areas by presenting a conceptual model explaining this negative power-law relation for small landslides in populated hilly regions. According to the model hilly regions can be relatively stable under the present-day environmental conditions, and landslides are mainly triggered by human activities that have only a local impact on slope stability. Therefore, landslides caused by anthropogenic triggers are limited in size, and the number of landslides decreases with landslide area.The frequency density of landslide areas for old landslides is similar to those obtained for historical inventories compiled in mountainous areas, as apart from the negative power-law relation with exponent −2.31 for large landslides, a positive power-law relation followed by a rollover is observed for smaller landslides. However, when analysing the old landslides together with the more recent ones, the present-day higher temporal frequency of small landslides compared to large landslides, obscures the positive power-law relation and rollover.

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Landslide hazard remains poorly characterized on regional and global scales. In the tropics in particular, the lack of knowledge on landslide hazard is in sharp contrast with the high landslide susceptibility of the region. Moreover, landslide hazard in the tropics is expected to increase in the future in response to growing demographic pressure and climate and land use changes. With precipitation as the primary trigger for landslides in the tropics, there is a need for an accurate determination of rainfall thresholds for landslide triggering based on regional rainfall information as well as reliable data on landslide occurrences. Here, we present the landslide inventory for the central section of the western branch of the East African Rift (LIWEAR). Specific attention is given to the spatial and temporal accuracy, reliability, and geomorphological meaning of the data. The LIWEAR comprises 143 landslide events with known location and date over a span of 48 years from 1968 to 2016. Reported landslides are found to be dominantly related to the annual precipitation patterns and increasing demographic pressure. Field observations in combination with local collaborations revealed substantial biases in the LIWEAR related to landslide processes, landslide impact, and the remote context of the study area. In order to optimize data collection and minimize biases and uncertainties, we propose a threephase, Search-Store-Validate, workflow as a framework for data collection in a data-poor context. The validated results indicate that the proposed methodology can lead to a reliable landslide inventory in a data-poor context, valuable for regional landslide hazard assessment at the considered temporal and spatial resolutions.

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23Geomorphometry may be a powerful tool to describe the characteristics of the landscape's response to 24 tectonic signals, but the meaning of morphometric indices is often obscured by the interplay between the 25 many variables controlling the geomorphological evolution. Moreover, although the so-called hypsometric 26 integral refers to the basin scale, most indices are generally derived from the river long profiles and thus focus 27 mainly on the short-term response of a drainage network to base level change, providing limited information 28 in regions of older and/or moderate uplift. Here, using the Rhenish shield (western Europe), an area of 29 moderate Quaternary uplift, as a test case, I attempt to build an index yielding a comprehensive view of the 30 stage attained by the landscape's response and, indirectly, an evaluation of the timing of the triggering base 31 level change. This index, called R 1 , is a ratio of differences between the three integrals linked respectively to 32 the classical basin's hypsometric curve, to the main river's long profile, and at the intermediate level, to a 33 'drainage network's hypsometric curve'. While its ratio form minimizes the lithological effect on R 1 , this index 34 is strongly correlated with basin size (regional correlation coefficients are in the range 0.88-0.93), reflecting 35 the way an erosion wave propagates from the outlet of a basin toward its headwaters. Therefore, it is not 36 directly usable as a proxy for relative uplift age. However, one can show that the relation between R 1 and basin 37 size is theoretically expected to change with time. Following uplift, the slope S r of the linear relation R 1 = f 38 (lnA) first increases rapidly but briefly, then it gradually diminishes over several million years. This is fully 39 confirmed by the analysis of R 1 and S r in the study area. Once its initial increase is completed (assumedly in a 40 few ten thousand years), S r appears to be a reliable indicator of relative uplift (or any other cause of base level 41 lowering) age.42

Accurate precipitation data are fundamental for understanding and mitigating the disastrous effects of many natural hazards in mountainous areas. Floods and landslides, in particular, are potentially deadly events that can be mitigated with advanced warning, but accurate forecasts require timely estimation of precipitation, which is problematic in regions such as tropical Africa with limited gauge measurements. Satellite rainfall estimates (SREs) are of great value in such areas, but rigorous validation is required to identify the uncertainties linked to SREs for hazard applications. This paper presents results of an unprecedented record of gauge data in the western branch of the East African Rift, with temporal resolutions ranging from 30 min to 24 h and records from 1998 to 2018. These data were used to validate the Tropical Rainfall Measuring Mission (TRMM) Multisatellite Precipitation Analysis (TMPA) research version and near-real-time products for 3-hourly, daily, and monthly rainfall accumulations, over multiple spatial scales. Results indicate that there are at least two factors that led to the underestimation of TMPA at the regional level: complex topography and high rainfall intensities. The TMPA near-real-time product shows overall stronger rainfall underestimations but lower absolute errors and a better performance at higher rainfall intensities compared to the research version. We found area-averaged TMPA rainfall estimates relatively more suitable in order to move toward regional hazard assessment, compared to data from scarcely distributed gauges with limited representativeness in the context of high rainfall variability.

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The recent observation by Schally & co-authors (1971) that the release of both LH and FSH is dependent upon the one`r eleasing' hormone (LH-RH) has made the study of the hypothalamus\p=m-\pituitary\p=m-\testis axis much more complex. Furthermore, the normal maintenance of both spermatogenesis and testosterone secretion depends upon LH and FSH acting synergistically. It may, therefore, be surmised that there is no absolute specificity of gonadal steroids or other substances in the regulation of secretion of gonadotrophins.Nevertheless, FSH and LH secretion appear to be dissociated in certain pathological conditions. When the Leydig cells are normal but the germinal epithelium has been damaged or destroyed, as after irradiation, certain viral infections, the administration of anti-fertility agents or in idiopathic infertility, the LH levels stay within the normal range whilst those for FSH are elevated (Franchimont, 1966(Franchimont, , 1971(Franchimont, , 1972Paulsen et al., 1968;Rosen & Weintraub, 1971;de Kretser et al., 1972;Leonard et al., 1972; van Thiel et al., 1972).It is intended in this paper to examine the basal secretion of the gonado¬ trophins (mainly LH and to a lesser extent FSH) and the response in males to administration of steroids and LH-RH, and also the relationship between spermatogenesis and gonadotrophins. EFFECT OF ANDROGENS ON GONADOTROPHINSIt is well accepted that the administration of testosterone to males is followed by a decrease in plasma LH levels. The effects on FSH, however, are controversial ( Table 1). The reasons for the conflicting results obtained using virtually the same amounts of testosterone propionate (TP) are obscure. They may reflect the differences in the number of subjects studied, the route of administration, the action of sex hormone-binding protein and/or the particular radioimmuno¬ assay used for FSH determination.In general, TP administered in small doses preferentially suppresses serum LH as compared to serum FSH (Dufy-Barbe & Franchimont, 1972;Swerdloff et al., 1972;Demoulin et al., 1973;Stewart-Bentley et al., 1974). For example, when five normal men were treated intramuscularly with 50 mg TP daily for 5 days, plasma LH levels were lowered but FSH was not affected. The release of FSH and LH is unaffected by the administration of TP if 25 µg LH-RH are given intravenously before treatment (see Text- fig. 1). These results are in agreement with those of von zur Mühlen & Kobberling (1973) who have shown that four intramuscular injections of 100 mg TP for 1 week significantly decreas-335