Annual Fluctuations In Rainfall Research Articles

Annual reproductive cycle of males of the great fruit-eating bat, Artibeus lituratus: Testicular variations, abiotic regulation and sperm analysis

Artibeus lituratus is one of the most well-known bat species in the Neotropics, probably due to its high abundance and the ability to inhabit urban areas. It plays an important ecological role in the ecosystem due to its ability to disperse seeds, which contributes to the regeneration of degraded areas. Actually, the species has been used as an important experimental model for ecotoxicological studies of the impact of pesticides on male reproduction. Despite that, the reproductive pattern of A. lituratus is still controversial due to inconsistent descriptions of the reproductive cycle. Thus, the aim of the present work was to evaluate the annual variations of the testicular parameters and sperm quality of A. lituratus and analyze their responses to annual variations in abiotic factors in the Cerrado area in Brazil. Testes of five specimens were collected each month for one year (12 sample groups) and submitted to histological, morphometric, and immunohistochemical analyses. Analyses of the sperm quality were also performed. Results demonstrate that A. lituratus presents a continuously active process of spermatogenesis throughout the year, with two significant peaks in spermatogenic production (September-October and March), which indicates a bimodal polyestric pattern of reproduction. These reproductive peaks seem to be related to an increase in proliferation and, consequently, in the number of spermatogonia. Conversely, seasonal variations in testicular parameters are correlated with annual fluctuations in rainfall and photoperiod but not with temperature. In general, the species presents smaller spermatogenic indexes with a similar sperm quantity and quality to other bat species.

Climate Elasticity of Annual Runoff: Observation in Fifteen Forested Catchments on a Latitudinal Gradient in East Asia

In order to overview the impact of climate change on runoff from forested catchments over Asian countries, we collected water balance data from fifteen long-term catchment monitoring stations (total monitoring period 1975–2018, not continuous), spanning from Sabah, Malaysia (our southernmost site), to Hokkaido, Japan (our northernmost site). We then employed an elasticity analysis to the dataset to examine how the annual runoff from each catchment responded to inter-annual fluctuations in annual rainfall and annual mean air temperature. As a result, we found that (1) the annual runoff was sensitive to annual rainfall for all the catchments examined. In addition, (2) the annual runoff from seven of the fifteen catchments was sensitive to inter-annual changes in the mean air temperature, which was likely due to changes in forest evapotranspiration. Three catchments, however, exhibited an increased runoff in a hot year. Finally, (3) the annual rainfall from the previous year (carry-over soil moisture) was important in explaining the variation in annual runoff in two tropical montane forest catchments. This study may serve as one of the pilot studies toward a comprehensive understanding of the climate elasticity of runoff in countries over Asia, because the examined catchments are unevenly and sparsely distributed over the area.

Hydroclimatic variability and riparian wetland restoration control the hydrology and nutrient fluxes in a lowland agricultural catchment

Climate change and riparian management are major drivers of hydrological change, with important implications for nutrient fluxes in lowland streams. However, the coupling of hydrological and nutrient dynamics is complex due to time-variant flow paths, interacting biogeochemical processes and variation in land use, fertilization levels and management measures. Here, we assessed the long-term (30 year) changes in climate, discharge, groundwater levels and stream water quality in a mixed land use catchment (Demnitzer Mill Creek catchment, DMC) in northern Germany. The catchment was subject to wetland restoration and subsequent beaver (Castor fiber) recolonization over the last 15 years. Climatic variability is the primary driver of the hydrological regime, with discharge and groundwater variations closely coupled to increases in annual air temperature and fluctuations of annual rainfall. Over the past 8 years, stream flows have been greatly reduced during a prolonged drought period. Meanwhile, beaver dams have also moderated flow regimes and facilitated groundwater recharge. In terms of water quality regimes, the concentration-discharge (C-Q) relationship for nitrate (NO3-N) and soluble reactive phosphate (SRP) showed positive and negative chemodynamic behavior respectively, whilst dissolved organic carbon (DOC) exhibited chemostatic behavior. These differences were dictated by the intrinsic properties of each solute in terms of contrasting catchment storage and immobilization processes. Moreover, the changing hydrological conditions regulated such patterns and strengthened the C-Q relationships for nutrients during the drought. As an integrated result of drought and wetland restoration, nutrient concentrations and fluxes in stream water have been reduced in recent years. Headwater catchments like DMC, where much of the hydrochemical signature of larger, downstream river networks are generated, are critical observatories for integrating understanding of the linkages between water quality and land management in an era of climate change.

Solar Powered Smart Irrigation System with GSM for Agriculture

Most of the Indian people are dependent on agriculture and for this reason our country’s economy is mainly dependent on agriculture, so efficient agriculture requires proper irrigation and can improve our country’s economy accordingly. We can achieve this with the help of various electronic devices and through its use we can get proper irrigation in this field in an automated manner. Project Irrigation and Water Level Control using AT89S52 designed to address agricultural sector issues related to irrigation and water monitoring systems with available water resources. Prolonged periods of dry weather conditions due to fluctuations in annual rainfall can significantly reduce agricultural yields. Profiteering companies need an efficient irrigation system as their intolerance to the cost and drought of establishing these crops. On this project we're the usage of AT89s52 (8051 microcontroller), humidity sensor, dc water pump, relay driving force, level sensor, gsm modem, sun panel, battery etc. A sprinkler turns on / off depending on soil moisture condition and condition. The motor can be displayed in text messages via the GSM model on a 16X2 LCD. Also, the water level can be monitored by level sensors. It helps to know the availability of water at the input source

Recent CO2 rise has modified the sensitivity of tropical tree growth to rainfall and temperature.

Atmospheric CO2 (c a) rise changes the physiology and possibly growth of tropical trees, but these effects are likely modified by climate. Such c a × climate interactions importantly drive CO2 fertilization effects of tropical forests predicted by global vegetation models, but have not been tested empirically. Here we use tree‐ring analyses to quantify how c a rise has shifted the sensitivity of tree stem growth to annual fluctuations in rainfall and temperature. We hypothesized that c a rise reduces drought sensitivity and increases temperature sensitivity of growth, by reducing transpiration and increasing leaf temperature. These responses were expected for cooler sites. At warmer sites, c a rise may cause leaf temperatures to frequently exceed the optimum for photosynthesis, and thus induce increased drought sensitivity and stronger negative effects of temperature. We tested these hypotheses using measurements of 5,318 annual rings from 129 trees of the widely distributed (sub‐)tropical tree species, Toona ciliata. We studied growth responses during 1950–2014, a period during which c a rose by 28%. Tree‐ring data were obtained from two cooler (mean annual temperature: 20.5–20.7°C) and two warmer (23.5–24.8°C) sites. We tested c a × climate interactions, using mixed‐effect models of ring‐width measurements. Our statistical models revealed several significant and robust c a × climate interactions. At cooler sites (and seasons), c a × climate interactions showed good agreement with hypothesized growth responses of reduced drought sensitivity and increased temperature sensitivity. At warmer sites, drought sensitivity increased with increasing c a, as predicted, and hot years caused stronger growth reduction at high c a. Overall, c a rise has significantly modified sensitivity of Toona stem growth to climatic variation, but these changes depended on mean climate. Our study suggests that effects of c a rise on tropical tree growth may be more complex and less stimulatory than commonly assumed and require a better representation in global vegetation models.

Inter-Decadal Nature of Rainfall Character Over Sudano-Sahel, North-West Nigeria

The study investigated the spatial pattern of decadal variations in annual rainfall amounts in the Sokoto-Rima River Basin, Northwestern Nigeria. Rainfall dataset which is available on high-resolution (0.5 x 0.5 degree) grids resolution from the Climatic Research Unit CRU TS 3.21 of the University of East Anglia, Norwich, United Kingdom was used for the period 1943-2012 for Bunza, Dakindari southwest of the study area, Gulma, Augi, northwest of the Sokoto-Rima basin, Goronyo, Galadi, northeast Maje and Dan-Dume stations southeast of the basin. Correlation of CRU TS dataset was performed with measured rainfall data (Yelwa climatic station) from Nigerian Meteorological Agency, using the Pearson Product Moment Correlation statistic at 0.05 significant levels. In general, the study found that periods of downward fluctuations in annual rainfall below mean values corresponded with period of rise in global temperature occasioned by anthropogenic greenhouse gases emission. The study revealed a significant decrease in the annual rainfall from late 1980 onwards.Key Word: Rainfall, decadal departure, River Basin, Rainfall variation. Climate Research Unit

<strong>A study of stonefly taxa (Insecta: Plecoptera) inhabiting a saline stream (Arroyo Salado) in southern Spain</strong>

Few studies of the ecology of Mediterranean saline streams exist. The strong selective pressure exerted by salinity greatly limits the presence of many taxa, Plecoptera (stoneflies) among them. However, a few species of stoneflies have been reported inhabiting saline streams, particularly components of the thermophilous biocoenosis seemed to have adapted to salinity pulses caused by fluctuations in annual rainfall. For two years, three sites within a saline stream, Arroyo Salado in southern Iberian Peninsula, were sampled to determine the stonefly species composition. Conductivity at the three sites ranged from 2290 to 87792, 2550 to 90824, and 206 to 2818 μS/cm, respectively. A total of seven different stonefly taxa were identified at the three sites: Brachyptera auberti Consiglio, Nemoura lacustris Pictet, Capnioneura libera (Navás), Tyrrhenoleuctra sp., Hemimelaena flaviventris (Pictet), Protonemura alcazaba Aubert, and Perla marginata (Panzer), the latter two only at the site where the stream flowed continuously and conductivity was lower. The possible strategies enabling these stonefly species to surviving in Arroyo Salado are discussed.

Influence of stochastic processes and catastrophic events on the reproductive dynamics of the endangered Maroon‐fronted Parrot Rhynchopsitta terrisi

Stochastic and catastrophic events may strongly impact the dynamics of wild populations. Annual fluctuations in rainfall may affect parrot populations, but few studies address the impact of other stochastic or catastrophic events on their population dynamics. The Maroon‐fronted Parrot Rhynchopsitta terrisi is an endangered species that nests colonially in cavities and crevices in limestone cliffs. From 1995 to 2010, we quantified Parrot attendance at nesting colonies throughout its breeding range, and reproductive output of nesting Parrots from 1997 to 2010 at the two most important nesting colonies. There was significant variation among colonies in the number of cavities occupied by Parrots each year. Rainfall significantly influenced both the number of occupied cavities and productivity, which declined after very dry years. Natural unpredictable events such as hurricanes did not modify the nesting activity of Maroon‐fronted Parrots at breeding colonies. However, wildfires increased in dry years, negatively affecting attendance at breeding colonies. The Maroon‐fronted Parrot may overcome the impacts of climatic variability, natural stochastic processes, and human‐induced catastrophic events by using nesting colonies as a network of resources throughout the breeding range. Given the current trends in climate change, it is likely the species may suffer stronger and more frequent unpredictable catastrophic events, potentially putting at risk its survival in the long term.

Rainfall stochasticity controls the distribution of invasive crayfish and its impact on amphibian guilds in Mediterranean temporary waters

Invasive crayfish have severely impacted invaded aquatic ecosystems worldwide. We studied temporal and spatial variation in the range expansion of the red swamp crayfish at one of the first European localities to which it was introduced: Donana National Park (SW Spain). In contrast to the rapid range expansion witnessed in other areas, this invasive crayfish has not spread across the entire park. Instead, its distribution has expanded during wet periods, but contracted during drought periods. The red swamp crayfish has caused steep amphibian declines in other invaded areas. However, after approximately 35 years of crayfish presence in Donana National Park, we have yet to detect a reduction in the number or occurrence of amphibian species. Amphibians may thus be protected by the large abundance of temporary ponds in the area, which provides them with an effective refuge network. We show that natural fluctuations in annual rainfall and in the number of ponds filled can temporarily eliminate invasive crayfish from particular areas. This fact should be taken into account when attempting to reduce the impact of crayfish on aquatic communities, intensifying crayfish removal during particularly dry years, when it is most effective.

Regional climate model: investigating the impacts of climate change on water availability in Nigeria.

Nigeria and the rest of African nations, despite the fact that they produce less than 4% of global greenhouse gas emissions, are considered the world’s most vulnerable regions with regard to the effects of climate change due to the fragility of their economies. However, it is still very difficult to assess the extent of such changes and the specific environmental impacts particularly on water supply and management over most Africa nations due to poor technological development and inadequate research work on this topical subject. In this paper, the third version of the ICTP regional climate model (RegCM3) and the observed surface data were used to investigate the evidence of climate change over Nigeria in the past years (1958 to 2007) with a view to determining the impacts of climate change on the water supply and management - one of the key areas where the climate change impact is adjudged most. The results of the study showed that in the recent past, the region had been witnessing higher temperatures, increased fluctuations in annual rainfall and increase in the salinity of soils and large areas of surface and underground water due to the increasing aridity of the climate; inadequate water supply and control installations as well as intensified marine pollution which are inimical to the health of the millions of Nigerians particularly along the coast of the Atlantic ocean. Key words: Climate change, impact, rainfall, temperature, water resources.

Temporal and spatial variability of breeding in Australian birds and the potential implications of climate change

Climate change has profound implications for biodiversity worldwide. To understand its effects on Australia's avifauna, we need to evaluate the effects of annual climatic variability and geographical climate gradients. Here, we use national datasets to examine variation in breeding of 16 species of common and widespread Australian landbirds, in relation to four variables: altitude, latitude, year and the Southern Oscillation Index. Analysis of <30 years of nesting records confirmed that breeding was generally later in colder altitudes and latitudes (geographic variation), but was not consistently related to year or the Southern Oscillation Index (temporal variation). However, power to detect expected temporal effects was low. The timing ofbreeding became significantly earlier with year only in south-eastern Australia. In contrast, an index of breeding activity (the proportion of atlas records for a species for which breeding was reported) increased with increasing winter values of the Southern Oscillation Index (generally wetter conditions) for all 16 species across Australia. This suggests that annual fluctuations in rainfall can have dramatic and immediate effects on breeding, even for largely sedentary, seasonally breeding species. If, as expected, climate change creates drier conditions over much of Australia, we predict a marked negative effect on bird breeding.

Response of native ungulates to drought in semi‐arid Kenyan rangeland

AbstractThe distribution and abundance of native ungulates were measured on commercially managed, semi‐arid rangeland in central Kenya over a 3‐year period that encompassed severe drought and above‐average rainfall. Native ungulate biomass density averaged 5282 kg km−2 over the study and was dominated by elephant (Loxodonta africana), impala (Aepyceros melampus) and dik‐dik (Madoqua kirkii). Biomass density of domestic cattle (Bos taurus) averaged 2280 kg km−2 during the study. Responses of native ungulates to severe drought were variable. Impala densities were similar to or greater than densities for similar habitat in protected areas, and varied from 12 to 16 km−2 during and following the drought to 24–29 km−2 following above‐average rainfall. Dik‐dik densities were also greater than densities reported for protected areas and were surprisingly stable throughout the study despite the wide annual fluctuations in rainfall. Elephant migrated out of the region during drought but were present at high densities (2.9–5.2 km−2) during wet seasons, consistent with telemetry studies emphasizing the importance of Acacia bushland habitat on commercial rangelands for the migratory portion of the Laikipia–Samburu elephant population. Results show that substantial densities of native browsing and mixed‐feeding ungulates can occur on rangeland managed for commercial beef production and suggest that the capacity for ungulates to move over large spatial scales (&gt;100 km2) and to shift distributions in response to locally variable thunderstorms may be important for sustaining these populations.

Abundance and diversity of small-bird assemblages in the Monte desert, Argentina

Assemblages of small bird species (<90 g body mass) from the Monte desert in Argentina were studied to analyze spatial and temporal variation in abundance and species richness. Mean species richness was higher during breeding season than in non-breeding season. The same pattern was observed in aerial insectivores, while granivores and substrate insectivores did not differ between breeding and non-breeding seasons. Overall bird abundance was similar across seasons. Species richness was positively correlated with bird abundance and negatively correlated with dominance; bird abundance and dominance were not correlated. These patterns could be explained by distinct responses of functional groups of birds; dominant species were granivores in the non-breeding season and aerial insectivores during the breeding season, and bird abundance in functional groups changed according to food supply. Most species are residents or regular migrants, while there are few nomadic and transient species. Predictable annual fluctuations in rainfall and resource availability should favor a migratory strategy more than nomadic movements. Similarly, breeding is strongly seasonal and most species start breeding when the first summer rains have generally not yet fallen. Finally, concordances in assemblage structure at local and regional scale suggest that similar mechanisms are acting on the local bird assemblages across the Monte.

Population limitation in migrants

Unlike resident bird species, the population sizes of migratory species can be influenced by conditions in more than one part of the world. Changes in the numbers of migrant birds, either long‐term or year‐to‐year, may be caused by changes in conditions in the breeding or wintering areas or both. The strongest driver of numerical change is provided in whichever area the per capita effects of adverse factors on survival or fecundity are greatest. Examples are given of some species whose numbers have changed in association with conditions in breeding areas, and of others whose numbers have changed in association with conditions in wintering areas. In a few such species, the effects of potential limiting factors have been confirmed locally by experiment. In theory, population sizes might also be limited by severe competition at restricted stopover sites, where bird densities are often high and food supplies heavily depleted, but (with one striking exception) the evidence is as yet no more than suggestive. In some species, habitats occupied in wintering and migration areas, and their associated food supplies, can influence the body condition, migration dates and subsequent breeding success of migrants. Body reserves accumulated in spring by large waterfowl serve for migration and for subsequent breeding, and females with the largest reserves are most likely to produce young. Hence, the conditions experienced by individuals in winter in one region can affect their subsequent breeding success in another region. Such effects are apparent at the level of the individual and at the level of the population. Similarly, the numbers of young produced in one region could, through density‐dependent processes, affect subsequent overall mortality in another region. Events in breeding, migration and wintering areas are thus interlinked in their effects on bird numbers. Although in the last 30–40 years the numbers of some tropical wintering birds have declined in western Europe and others in eastern North America, the causes seem to differ. In Europe, declines have mainly involved species that winter in the arid savannas of tropical Africa, which have suffered from the effects of drought and increasing desertification. In several species, annual fluctuations in numbers and adult survival rates were correlated with annual fluctuations in rainfall, and by implication in winter food supplies. In North America, by contrast, numerical declines have affected many species that breed and winter in forest, especially those eastern species favouring the forest interior. Declines have been attributed ultimately to human‐induced changes in the breeding range, particularly forest fragmentation, which have led to increases in the densities of nest predators and parasitic cowbirds. These in turn are thought to have caused declines in the breeding success of some neotropical migrants, which is now too low to offset the usual adult mortality, but as yet convincing evidence is available for only a minority of species. The breeding rates and population changes of some migratory species have been influenced by natural changes in the availability of defoliating caterpillars. In other species, tropical deforestation is likely to have played the major role in population decline, and if recent rates of tropical deforestation continue, it is likely to affect an increasing range of migratory species in the future. Not all such species are likely to be affected adversely by deforestation, however, and some may benefit from the resulting habitat changes.

HYDROLOGICALLY DRIVEN HIERARCHICAL COMPETITION–COLONIZATION MODELS: THE IMPACT OF INTERANNUAL CLIMATE FLUCTUATIONS

A hierarchical competition–colonization model extensively used in ecological dynamics is driven by the stress conditions resulting from the annual fluctuations in rainfall in water-limited ecosystems. The results show that ecosystem composition is very sensitive to the inclusion of realistic amounts of interannual rainfall variability. The evolutionary dynamics of competing trees and grasses exhibit scale-invariance characteristics (i.e., a power law spectra) for the temporal changes in the relative density of the species. This temporal scaling results from the internal dynamics of the competition–colonization process, which is driven by Markovian annual rainfall amounts. The model was also implemented to approximately describe the conditions of two ecosystems characterized by grass–tree competition, one near La Copita, Texas, and one in Nylsvley, South Africa. Long-term simulations run for many different characteristics of the annual rainfall amounts show that the diversity of dynamic states in the tertiary grass/tree/bare soil system (i.e., its information entropy) is at a maximum near historically observed rainfall characteristics. This suggests that, under commonly observed interannual rainfall fluctuations, water-controlled ecosystems tend to self-organize in a manner that maximizes the richness of relative species abundances. Corresponding Editor: W. K. Lauenroth.

Spatial organization in Europe of decadal and interdecadal fluctuations in annual rainfall

AbstractThe spatial patterns of decadal and bidecadal fluctuations in annual rainfall in Europe are identified. Filtering of time series of the anomaly in annual rainfall is carried out using the Morlet wavelet technique. Reconstruction is achieved by summing the contributions from bands of wavelet time scales; the decadal band and the bidecadal band are composed of contributions from the bands of the (10 to 17 year) and (17 to 27 year) time scales respectively. Results indicate that (1) the spatial organization of the decadal and bidecadal components of annual rainfall are standing‐wave‐like organized patterns. Three standing decadal fluctuations zonally aligned formed the spatial pattern from 1900 until 1931; thereafter the pattern changed into a NW–SE orientation. The decadal band shows an average 12 year period. (2) The spatial organization of the bidecadal component was composed of three standing fluctuations from 1903 to 1986. After 1987, two standing bidecadal fluctuations were located over Europe. The orientation of the bidecadal fluctuations changed during the period under study. Until 1913 the spatial pattern of the bidecadal component was zonally aligned. Since 1913 and until 1986 the three bidecadal fluctuations composing the spatial pattern were aligned SW–NE; starting in 1987, the spatial pattern is composed of two standing fluctuations zonally aligned. The bidecadal spatial pattern shows an average period of 20 to 22 years in length. (3) At the decadal and bidecadal time scales, the first principal component of the spatial field of anomaly in annual rainfall and the North Atlantic oscillation (NAO) index are connected. The upper positive third (lower negative third) of values of the first principal component are indicative of an extensive area with positive (negative) anomalies in annual rainfall. (4) At the decadal time scale the relative phase between the first principal component and the NAO index changes through the period under study; these changes define three regimes. (i) During the regime covering the period 1900 (start of period under study) to about 1945, at the time of peak values in decadal NAO index there takes place a transition between extremes (a neutral state) of the decadal rainfall spatial pattern (first principal component takes small absolute values). In addition, for a positive (negative) peak value of NAO index the spatial pattern of annual rainfall evolves toward an area of predominantly positive (negative) anomalies. (ii) The second regime starts about 1946 and continues to the early 1980s. At the time of the negative (positive) peak in decadal NAO there is a prevailing spatial pattern of positive (negative) anomalies of decadal rainfall. (iii) The third regime starts around the late 1970s and continues to the end of the period under study (in 1996). There is a change of relative phase within this period in the late 1980s. In this regime a spatial pattern of prevailing positive or negative anomaly of decadal rainfall takes place during values of decadal NAO close to zero. (5) At the bidecadal time scale the relative phase between the first principal component and the NAO index remains almost constant through the period under study. The first principal component of the transformed bidecadal component of annual rainfall anomalies attains its positive (negative) peak about 3 years before the bidecadal component of NAO reaches its negative (positive) peak. Copyright © 2002 Royal Meteorological Society.

Water, nutrients and slope position in on-farm pearl millet cultivation in the Sahel

In the Sahel, short periods of intra-seasonal drought, caused by unfavourable rainfall distribution, often have stronger effect on crop growth than fluctuations in annual rainfall. The interactive effects of nutrient deficiency and water shortage (during panicle initiation, flowering and grain filling) on yield and yield components of pearl millet (Pennisetum glaucum (L.) R. Br.), were studied on-farm along a cultivated slope, during three years with close to average annual rainfall. Grain yield was correlated to plant nutrient availability but not to annual rainfall, which was explained by the capacity of the crop to compensate for damage caused by water shortage during early growth phases. The performance of each yield component was positively correlated to cumulative rainfall during the growth phase when it was formed. Leaf area index (LAI) was very low, and leaf development followed rainfall distribution. Water and nutrients interacted during each growth phase for all fertility levels. Fertilised millet suffered less during water shortage at panicle initiation and at grain filling compared to non-fertilised millet. However, compared to favourable soil water conditions yield components were systematically lower for all treatments, indicating the synergistic effect of water and nutrients. The results suggest that water availability plays an exclusive role during flowering. Grain number dropped significantly due to water shortage and was similar for all treatments. Despite extremely high spatial variability in yields (varying with a factor 46 within the field), a significant slope effect was observed, of progressively increasing yields when moving downslope. Spatial redistribution of surface runoff resulting in higher soil water availability on lower slope positions, contributed to the yield gradient, which was reinforced for fertilised millet. For each drought period, yield components suffered systematically more upslope than downslope. This slope effect was smoothed out for manured millet, which indicates that manure increased soil infiltrability on crusted zones upslope. The slope interaction observed here – indicating that downslope (i) the risk for crop failure during droughts is lower and (ii) the response to fertilisers is greater – suggests that farmers can benefit relatively more from fertilisers applied in lower parts of the watershed. Taking advantage of spatial soil and water variability is an interesting system of low technology precision farming, which combined with water harvesting systems to master droughts, can constitute options for increased crop yields in the Sahel.

Le Sahel oublié

This work analyzes the problems of the Sahel by means of a description of certain systems of agriculture and livestock production. By the time the Sahel region came to the world's attention in the drought of the 1970s, it was a region undergoing perhaps irreversible change. The ecological and climatic zone of the Sahel is difficult to define precisely. There are Sahelian enclaves in the Sahara to the north and differing opinions as to the southern limits, with proposed boundaries extending well to the south of Bamako and Ouagadougou in some cases. A definition of an autonomous Sahel ecological zone has cited the seasonal concentrations and limited volume of rain delivered in a series of downpours, wide annual fluctuations in rainfall, and important role of annual grasses. The political Sahel is equally debatable, consisting of the 9 countries that formed the Intergovernmental Committee to Combat the Drought in the Sahel (CILSS) in 1971. 2 of the 9 countries, Gambia and Guinea-Bissau, are not truly Sahelian but joined the CILSS because their governments decided to after several years of agricultural deficits. Oral traditions compiled by anthropologists and research by geomorphologists, hydrologists, botanists, and others suggests that irregular rainfall has always been a feature of Sahel life. The history of each Sahelian region shows alternation of good harvests, difficult shortages, and subsistence crises that neither the colonial administrations nor the current governments have been able to control. If the effects of the most recent droughts prove to be more enduring, the cause probably will be found in the weight of increased human activity on the fragile ecosystem. The population of the Sahel has more than doubled in the past 50 years, herds have multiplied, and lands under cultivation have been extended at the expense of pasture. The capacity of farmers and herders to adapt to climatic risks has been reduced because of the weakening of family solidarity networks. The movement to extensive agriculture has been observed everywhere. All studies conclude that all types of vegetation have been degraded, that agriculture has been extended to marginal soils, and that the soils and grazing lands are saturated. Overgrazing, cutting of trees, and denuding of soils have led to "desertification". Droughts have aggravated the degradation already underway. It is not known to what extent the environmental deterioration is due to uncontrollable climatic factors and to what extent it is the result of human activity. More detailed descriptions of the changing systems of exploitation of 4 different groups in different Sahel countries illustrate the discussion.

Observations on the relation between rainfall and the inshore fishery along the Orissa coast

The relationship between rainfall and a coastal fishery has been studied for the first time in Indian waters. There was a significant correlation between the fluctuations in annual rainfall and the landings from a drift-gillnet fishery. The correlations between total rainfall and total catch rate and total rainfall and catch rate of plankton feeders were high (r = 0·847 and r = 0·790 respectively, d.f. = 8, P > 0·01). A significant correlation was only found for the rains associated with the southwest monsoon. It appears that the popular belief among fishermen in the northwestern part of the Bay of Bengal that “more rain brings more fish” has some foundation.

ブラジル北東部における年雨量の変動

ブラジル北東部における年雨量の変動