Analysis Of Rainfall Patterns Research Articles

Spatial and temporal precipitation variability in the Okavango–Kwando–Zambezi catchment, southern Africa

In southern Africa, multi-decadal trends over the latter half of the 20th century indicate declining mean annual precipitation, increasing variability, and increased number of warm phase ENSO events. One suggestion for the change in precipitation pattern is a shift in the global coupled ocean–atmosphere system during the late 1970s. We investigate the variability in inter-annual regional precipitation dynamics pre/post the late 1970s climate shift within the Okavango–Kwando–Zambezi (OKZ) catchment in southern Africa through a descriptive spatio-temporal analysis of rainfall patterns from 1950 to 2005. Annual precipitation totals for each basin are calculated and numbers of wet (upper tercile) and dry (lower tercile) years in two periods (1950–75 and 1980–2005) are compared. Rainfall associated with, and frequency of, El Niño Southern Oscillation (ENSO) events are also investigated. Coincidences of extremes in local and regional rainfall are examined to determine how association in precipitation patterns may vary across the catchment. Results indicate decreasing precipitation and increased dry years with warm phases of ENSO across all three sub-catchments. This has important implications for the future Kavango–Zambezi Transboundary Conservation Area (KAZA), a region that provides a vital wildlife corridor through which local precipitation and exotic streamflow constitute important water sources in an otherwise water-limited ecosystem.

An analysis of rainfall patterns in Nigeria

The paper is designed to study the rainfall patterns and its implications in Nigeria. Rainfall data from 28 stations for the period of 1970 – 2002 were collected from the Nigeria Meteorological Station, Lagos. While the vegetation map of Nigeria between 1973 and 1995 forms the basis of biodiversity change analysis. The results among others show that rainfall decreases from 1350 mm (1941–1970) to 1276 mm (1970–2002). While there is a general decrease in rainfall in Nigeria, the coastal area is experiencing slight increase. Apart from the general southward shift in rainfall patterns, the duration has also reduced from 80-360 (1941-1970) to 40-280 (1970-2002) rainy days per year. This has created ecological destabilisation and altered the pattern of the vegetation belt especially in the northern fringes of the country. The rainfall pattern has also enhanced wind erosion/desertification, soil erosion and coastal flooding in the north, east and coastal areas of Nigeria respectively. With these impacts, the paper therefore recommends some adaptive and mitigation measures that could help to revert the current situation.Keywords: changing climate, vegetation belts, rainfall pattern and shiftGlobal Journal of Environmental Sciences Vol. 4(2) 2005: 139-145

Variabilités interannuelle et intra-saisonnière des pluies aux échelles hydrologiques. La mousson ouest-africaine en climat soudanien / Seasonal cycle and interannual variability of rainfall at hydrological scales. The West African monsoon in a Sudanese climate

West African rainfall is characterized by a strong variability, both at decadal and interannual scales. In order to quantify the hydrological impacts of such a variability, analysis of rainfall patterns at fine scales is highly essential. This diagnostic study aims to characterize the Sudanese rainfall regime at hydrological scales, using a raingauge data set collected on the upper Oueme River catchment (Benin) between 1950 and 2002. A long-term drought is observed during the 1970s and 1980s, as in the Sahel. However, the interannual variability remains significant in the Sudanese region. The study of the seasonal cycle, based on the distinction between the oceanic and continental monsoon regimes, shows that the majority of rainfall changes occur in the continental regime. On the one hand, the rainfall peak associated with this regime that has been observed for the last 50 years has occurred increasingly earlier in the season. On the other hand, the annual rainfall deficit is mainly linked to the decrease in the number of large events during the continental part of the season.

Influences of hydrological and hydrogeological conditions on debris flows in peri-vesuvian hillslopes

Abstract. The paper illustrates some results of research carried out to assess factors triggering debris flows which involve the pyroclastic overburdens covering carbonate mountains around Vesuvius. The aims of the research were to reconstruct a relationship between rainfall and debris flow occurrence and to highlight empirical hydrological thresholds through rainfall pattern analysis. The research was also aimed at investigating hydrogeological features of a pyroclastic cover-carbonate bedrock system to analyse factors inducing temporary hydraulic flow, critical for pyroclastic soil stability. The results of research are the following: i) rainfall pattern highlights empirical hydrological thresholds that differentiate the Lattari and Salerno Mountains from the Sarno Mountains; ii) in some sample areas of the Sarno Mountains close to the trigger zones of the landslides of May 1998 strong variation in hydraulic conductivity has been found in the first few meters below the surface; iii) these permeability variations would seem to justify temporary perched water tables that might affect the stability of the pyroclastic mantle.

Dynamic cropping strategies for risk management in dry-land farming systems

Low rainfall and soils with low water holding capacity are major features of the Mallee region of south-eastern Australia. To reduce risk related to likely water deficits, many growers adopt a conservative cropping strategy based on low-input cereal crops. This approach has, however, a substantial opportunity cost by missing the potential profit from more intense cereal cropping and high yielding oilseed crops in more favourable seasons. We tested the hypothesis that whole-farm profitability could be enhanced by the adoption of a dynamic cropping strategy shifting from a cereal-only, conservative strategy in dry years, to a more risky strategy involving both cereals and canola in wet years. To test this hypothesis, we used 40-years rainfall series to (1) investigate rainfall features in 11 locations in the Mallee, (2) test the skill of simple rules to predict seasonal rainfall, as developed by local farmers, and (3) calculate whole-farm profit for conservative, risky and dynamic cropping strategies. Rainfall and profit were linked with a whole-farm model that estimates crop yield as a function of seasonal rainfall (i.e. rainfall from April to October) and water-use efficiency. Among locations, annual rainfall ranged from 259 to 358 mm. For each location, two types of seasons were defined: likely wet, when April rain was above the median, and likely dry otherwise. The strength of the association between April and seasonal rain varied widely among sites; it was stronger in locations with more marked rainfall seasonality. Contrasting whole-farm profit responses to cropping strategies were found in locations with annual rainfall below or above a threshold around 300 mm. For wetter locations (annual rain above the threshold), the more risky cropping strategy including canola was generally more profitable than the more conservative strategy. For farms in drier areas, the cereal-based conservative strategy outperformed the more risky strategy in seasons predicted to be dry, but was less profitable in wet seasons. The dynamic cropping strategy had a substantial effect on extreme years, alleviating economic losses associated with the risky strategy in dry seasons, while being able to capture the benefits of more favourable seasons. Analysis of rainfall patterns, development of a rainfall forecasting procedure, and quantification of whole-farm profit in response to cropping strategies, all highlighted the need for decision support tools that account for small-scale variation in rainfall characteristics.

Modal morphing on meteorological radar data for rainfall pattern analysis

The authors present the application of a modal morphing technique to meteorological data obtained from radars. The procedure, based on the recently introduced modal matching method for shape analysis and description, allows efficient exploitation of the information about detected rainfall patterns and their evolution. After some considerations about the use of the modal matching method for meteorological data handling, the authors offer a simple method for the analysis of rainfall movements in a case study of a hurricane which occurred in Florida.

Eastern Equine Encephalitis (EEE): A Description of the 1989 Outbreak, Recent Epidemiologic Trends, and the Association of Rainfall with EEE Occurrence

An Eastern equine encephalitis (EEE) outbreak in 1989 led to nine human and 196 equine cases, chiefly in coastal Atlantic and Gulf Coast counties. In the past two decades, EEE age-specific incidence and mortality rates have declined compared with earlier years. Analysis of rainfall patterns in areas where human EEE cases occurred between 1983 and 1989 revealed an association between occurrence of human cases and excess rainfall. The association was stronger with data from local weather stations than from statewide rainfall averages and the predictive models were best when applied to northern states. The sensitivity and specificity of these measures varied, depending on the model used, but the positive predictive value was no better than 50%, regardless of the rainfall model applied.