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Spatial and Temporal Analysis of Rainfall and Temperature Extreme Indices in Tanzania  [PDF]
Ladislaus B. Chang’a, Agnes L. Kijazi, Philbert M. Luhunga, Hashim K. Ng’ongolo, Habiba I. Mtongor
Atmospheric and Climate Sciences (ACS) , 2017, DOI: 10.4236/acs.2017.74038
Abstract: Climate extreme indices in Tanzania for the period 1961-2015 are analyzed us-ing quality controlled daily rainfall, maximum and minimum temperatures data. RClimdex and National Climate Monitoring Products (NCMP) software developed by the commission for climatology of the World Meteorological Organization (WMO) were used for the computation of the indices at the respective stations at monthly and annual time scales. The trends of the extreme indices averaged over the country were computed and tested for statistical significance. Results showed a widespread statistical significant increase in temperature extremes consistent with global warming patterns. On average, the annual timescale indicate that mean temperature anomaly has increased by 0.69°C, mean percentage of warm days has increased by 9.37%, and mean percentage of warm nights has increased by 12.05%. Mean percentage of cold days and nights have decreased by 7.64% and 10.00% respectively. A non-statistical significance decreasing trends in rainfall is depicted in large parts of the country. Increasing trend in percentage of warm days and warm nights is mostly depicted over the eastern parts of the country including areas around Kilimanjaro, Dar-es-Salaam, Zanzibar, Mtwara, and Mbeya regions. Some parts of the Lake Victoria Basin are also characterized by increasing trend of warm days and warm nights. However, non-statistical significant decreasing trends in the percentage of warm days and warm nights are depicted in the western parts of the country including Tabora and Kigoma regions and western side of the lake Victoria. These results indicate a clear dipole pattern in temperature dynamics between the eastern side of the country mainly influenced by the Indian Ocean and the western side of the country largely influenced by the moist Congo air mass associated with westerly winds. The results also indicate that days and nights are both getting warmer, though, the warming trend is much faster in the minimum temperature than maximum temperature.
Trends of Extreme Temperature and Rainfall Indices for Arid and Semi-Arid Lands of South Eastern Kenya  [PDF]
Samwel N. Marigi, Andrew K. Njogu, William N. Githungo
Journal of Geoscience and Environment Protection (GEP) , 2016, DOI: 10.4236/gep.2016.412012
Abstract: Extreme climate events have profound impacts on economies and livelihoods of many regions of the world. In Kenya, the extreme climate events often have strong impacts on agriculture production systems in the Arid and Semi-Arid Lands (ASALs). A small change in the mean climate condition can cause large changes in these production systems. There is a paucity of information on trends in climate and climate extremes in the country. However, a joint World Meteorological Commission for Climatology/World Climate Research Programme (WCPRP) project on climate Variability and Predictability (WMO CCl/CLIVAR) Expert Team (ET) on Climate Change Detection, Monitoring and Indices has defined 27 core climate indices mainly focusing on extreme events which can be derived through the use of RClimDex Software. In this study, therefore, the RClimDex software has been used to derive climate extreme indices for five stations in the ASALs of South-Eastern Kenya based on climate data for the period 1961 to 2009. The objective was to examine trends in these extremes to aid agricultural planning and practice. These indices have shown decreasing trends in annual rainfall, rainfall intensity and consecutive wet days but increasing trends in consecutive dry days. Steady warming patterns were evident in both the maximum and minimum temperature indices. This paper concludes that indeed significant changes in climate extremes are apparent in the ASALs of the country and recommends a re-thinking of planning and practice of rain-fed agriculture in the ASALs of South-Eastern Kenya.
Comparative analysis of indices of extreme rainfall events: Variations and trends from southern México
Atmósfera , 2009,
Abstract: studies from throughout much of the world have shown a general increase in extreme precipitation events over the past few decades, although most of these studies have focused on mid-to-high latitude land-based locations, particularly in the northern hemisphere. many tropical and subtropical areas have not been analyzed due in part to non-existent or non-continuous data required for assessments of longer-term trends in extreme events. however, in this investigation, we assembled daily precipitation records for 142 stations in southern méxico over the period 1960-2004 and calculated 23 different annual indicators of extreme precipitation events that have been widely used in the professional literature. ultimately using 44 of these stations with the most complete records, we used various univariate and multivariate statistical procedures to uncover the underlying significant upward trend in the occurrence of extreme events. furthermore, we found that the variations in extreme events were significantly related to el ni?o-southern oscillation (enso) and the pacific decadal oscillation (pdo), with extreme events tending to occur more frequently during la ni?a periods and during the positive phase of the pdo.
Recent Trends in Climate Extreme Indices over Sri Lanka  [PDF]
I. M. Shiromani Priyanthika Jayawardena, D. W. T. Thanuja Darshika, H. M. Roshan C. Herath
American Journal of Climate Change (AJCC) , 2018, DOI: 10.4236/ajcc.2018.74036
Abstract: Trends in 20 extreme indices of temperature and precipitation are examined for Sri Lanka using high-quality datasets for 19 meteorological stations, for a period between 1980 and 2015. It is evident that annually averaged mean minimum temperatures are increasing across most of Sri Lanka. The difference between maximum and minimum temperatures, diurnal temperature range is decreasing, indicating that the minimum temperature is increasing faster than the maximum temperature. Significant decrease in the annual occurrence of cold nights and increase in the annual occurrence of warm nights are also obvious. When compared with temperature changes, less spatially coherent pattern of change and a lower level of statistical significance were observed in precipitation indices. The annual total precipitation (PRCPTOT) has indicated a significant increasing over 1980-2015. More than 80% of stations showed an increasing trend in precipitation indices. The trends in extreme precipitation events such as maximum one-day precipitation, maximum five-day precipitation, and total precipitation on extreme rainfall days (R95p and R99p) are increasing at most locations, indicating that the intensity of the rainfall is increasing. Increase of precipitation extreme trends indicates that occurrence of extreme rainfall events notably influences total annual precipitation in Sri Lanka. Therefore, the observed increases in total rainfall observed in many locations may be due in part to an increase in of extreme rainfall events. Patterns of change in precipitation extremes are more heavily influencing the climate variability by aggravating the variability, significantly influencing climate sensitive sectors such as agriculture and water resource management.
Vulnerability assessment of Central-East Sardinia (Italy) to extreme rainfall events  [PDF]
A. Bodini,Q. A. Cossu
Natural Hazards and Earth System Sciences (NHESS) & Discussions (NHESSD) , 2010,
Abstract: In Sardinia (Italy), the highest frequency of extreme events is recorded in the Central-East area (3–4 events per year). The presence of high and steep mountains near the sea on the central and south-eastern coast, causes an East-West precipitation gradient in autumn especially, due to hot and moist currents coming from Africa. Soil structure and utilization make this area highly vulnerable to flash flooding and landslides. The specific purpose of this work is to provide a description of the heavy rainfall phenomenon on a statistical basis. The analysis mainly focuses on i) the existence of trends in heavy rainfall and ii) the characterization of the distribution of extreme events. First, to study possible trends in extreme events a few indices have been analyzed by the linear regression test. The analysis has been carried out at annual and seasonal scales. Then, extreme values analysis has been carried out by fitting a Generalized Pareto Distribution (GPD) to the data. As far as trends are concerned, different results are obtained at the two temporal scales: significant trends are obtained at the seasonal scale which are masked at the annual scale. By combining trend analysis and GPD analysis, the vulnerability of the study area to the occurrence of heavy rainfall has been characterized. Therefore, this work might support the improvement of land use planning and the application of suitable prevention systems. Future work will consider the extension of the analysis to all Sardinia and the application of statistical methods taking into account the spatial correlation of extreme events.
Francesco D' Asaro,Giovanni Grillone
Journal of Agricultural Engineering , 2008, DOI: 10.4081/jae.2008.1.11
Abstract: The study regarded the regional frequency analysis of extreme rainfall in Sicily, using rainfall annual maximum series of duration 1, 3, 6, 12 and 24 hours in 235 sites, stationed in all Sicily and for the period 1928-1998. The applied regional models, after the appropriate verifications, were: the TCEV hierarchical model (Rossi et al.), the model based on the use of the linear moments LM (Hosking et al.) and the MGs parametric model (Maione et al.). For ungaged sites, as in a flood index approach, the index value of each model was evaluated through maps derived from spatial interpolation. The three models regional estimations were compared with the at-site estimation, computed by GEV and Gumbel distribution, for the stations with record length n≥45 and return period T =200 years. The comparison was carried out taking into consideration, for the regional models, the index value estimation in the two following cases: Case 1: Index value estimated by historical series; Case 2: Index value estimated by interpolated maps. The results indicate that, in Case 1, the MGs regional model performs better than the other two regional models for each duration t but, in Case 2, the performance of MGs model is weakly better than the other regional models studied only for t=1÷12 hours. Furthermore, we observe the same behavior of TCEV and GEV-LM models, also detected by Brath in center-northern Italy [4].
Mapping an index of extreme rainfall across the UK  [PDF]
D. S Faulkner,C. Prudhomme
Hydrology and Earth System Sciences (HESS) & Discussions (HESSD) , 1998,
Abstract: Distance from the sea, proximity of mountains, continentality and elevation are all useful covariates to assist the mapping of extreme rainfalls. Regression models linking these and other variables calculated from a digital terrain model have been built for estimating the median annual maximum rainfall, RMED. This statistic, for rainfall durations between 1 hour and 8 days, is the index variable in the rainfall frequency analysis for the new UK Flood Estimation Handbook. The interpolation of RMED between raingauge sites is most challenging in mountainous regions, which combine the greatest variation in rainfall with the sparsest network of gauges. Sophisticated variables have been developed to account for the influence of topography on extreme rainfall, the geographical orientation of the variables reflecting the prevailing direction of rain-bearing weather systems. The different processes of short and long-duration extreme rainfall are accounted for by separate regression models. The technique of georegression combines estimates from regression models with a map of correction factors interpolated between raingauge locations using the geostatistical method of kriging, to produce final maps of RMED across the UK.
Investigating possible changes of extreme annual rainfall in Zimbabwe
D. Mazvimavi
Hydrology and Earth System Sciences Discussions , 2008,
Abstract: There is increasing concern about the perceived decline in rainfall which is sometimes attributed to global warming. Some studies have concluded that average rainfall in Zimbabwe has declined by 10% or 100 mm/yr during the last 100 yrs. This paper investigates the validity of the assumption that rainfall is declining in Zimbabwe. Time series of annual rainfall, and total rainfall for a) the early party of the rainy season, October-November-December (OND), and b) the mid to end of the rainy season, January-February-March (JFM) are analysed for the presence of trends using the Mann-Kendall test, and changes in extreme rainfall using quantile regression analysis. The analysis has been done for 40 rainfall stations with records starting during the 1892–1940 period and ending in 2000, and representative of the major rainfall regions. The Mann-Kendal test did not identify a significant trend at all the 40 stations, and therefore there is no proof that the average rainfall at each of these stations has changed. Quantile regression analysis revealed a decline in annual rainfall less than the tenth percentile at only one station, and increasing rainfall for rainfall greater than the ninetieth percentile at another station. All the other stations revealed no changes over time in both the extreme low and high rainfall at the annual interval. Therefore, there is no evidence that the frequency and severity of droughts has changed during the 1892 to 2000 period. The general perception about declining rainfall is likely shaped by a comparison of the recent drought years (1980's–1990's) to recent wet periods (1970's). There have however been periods with similar dry years beyond the recallable memory, e.g. 1926–1936, 1940's. Crop failures and livestock losses attributed to declining rainfall are most likely due to poor agricultural practices such as production of crops in unsuitable climatic regions, degradation of rangelands partly due to increasing livestock populations. Rainfall in Zimbabwe has high inter-annual variability, and currently any change due to global warming is not yet statistically detectable. The annual renewal rate of water resources from rainfall has therefore not changed, and an adaptive water resources management approach is called to overcome problems arising from increasing water demand, and variability of available water resources.
Change of extreme rainfall indexes at Ebro River Basin  [PDF]
J. L. Valencia,A. M. Tarquis,A. Saá-Requejo,J. M. Gascó
Natural Hazards and Earth System Sciences (NHESS) & Discussions (NHESSD) , 2012, DOI: 10.5194/nhess-12-2127-2012
Abstract: Extreme rainfall events are a serious concern for regional hydrology and agriculture in the Ebro River Basin. Repeated anomalous rainfall in recent decades has had a devastating impact on this region, both socially and economically. Some studies developed in Italy and USA have shown that there is a change in seasonal patterns and an increasing frequency of extreme rainfall events, whereas other studies have pointed out that no global behaviour could be observed in monthly trends due to high climatic variability. The aim of this work is to test which of these scenarios is the case for the Ebro River Basin. For this purpose, 14 meteorological stations were selected based on the length of the rainfall series and the climatic classification to obtain a representative untreated dataset from the river basin. Daily rainfall series from 1957 to 2002 were obtained from each meteorological station. First, classical climatic indexes were analysed with an autoregressive test to study possible trends in rainfall. The results can be explained following the evolution of the NAO and WeMO indexes, which indicate that the initial period should be subdivided in two periods (1957–1979 and 1980–2002) to assume stationarity and to analyse the rainfall distribution functions. The general results obtained in this study for both sub-periods, through the generalised Pareto distribution (GPD) parameters and the maximum expected return values, do not support the results previously obtained by other authors that affirm a positive trend in extreme rainfall indexes and point to a slight reduction indicated by others. Three extreme precipitation indexes show negative statistical significant trends. GPD-scale parameters decrease except for only one rain gauge, although this decrease is only statistically significant for two rain gauges. Another two locations show statistical significance decreased for maximum expected return values.
On the representation of regional characteristics by hydrographic measurements at central stations in four deep basins of the Baltic Sea  [PDF]
J. H. Reissmann
Ocean Science (OS) & Discussions (OSD) , 2006,
Abstract: In this work the eddy resolving data sets of salinity, temperature, and oxygen content aquired in the framework of the German-Russian project MESODYN (MESOscale DYNamics) in the Arkona Basin, the Bornholm Basin, the Stolpe Furrow, and the Eastern Gotland Basin during summer and winter stratification situations are utilized to examine to which extent the observations at the central monitoring stations within these basins are representative for the spatial mean state of the corresponding region with respect to comparative monitoring purposes of the whole Baltic Sea. The investigation covers profiles of salinity, potential temperature, oxygen content, potential density, and squared buoyancy or Brunt-V is l frequency. Moreover, some parameters of the halocline, namely its depth, thickness, and upper and lower boundaries, and the first baroclinic Rossby radii are subject to the investigation. The profiles match best for the squared buoyancy or Brunt-V is l frequency. The profiles of salinity match best in the Eastern Gotland Basin and worst in the Arkona Basin both for summer and winter stratification situations. The overall agreement for the halocline parameters is good. The baroclinic Rossby radii match their spatial mean values well, if the depth range considered for their calculation is restricted to the mean depth in each region at the bottom side. In doing so they also match the spatial mean values of the first baroclinic Rossby radii calculated considering the whole depth range at each station. Overall, the regional characteristics of the investigated quantities and parameters are represented well by the hydrographic measurements at the central stations in the four regions in spite of some significant differences between the spatial mean states and the observations at the central stations. In particular, the observations at the central stations seem to be usefull for comparisons between these regions. However, the observed differences may affect regional investigations covering just a single region.
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