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Non-climatic reasons, such as station replacement and changing the measurement device and calculation method, may make climate data unrepresentative of the actual variation of the regional climate. Data quality control and homogenization tests for climate data are critical. Thus, this study aims to evaluate the quality and homogeneity level of precipitation time series in arid and semi-arid climatic zones and specify the breakpoint in the datasets. The proposed methodology has been used to conduct arid and semi-arid representative case studies comprising 40 annual precipitation series for Iraq between 1979 and 2014. A Box-Cox transformation has been used to adjust the non-normally distributed datasets. Outliers have been censored by truncating extreme values. The results of the outliers indicate that they may be caused more by climate variability than by human-induced reasons. Homogeneity adjustments have been developed by applying these four homogeneity tests: Pettitt's test, the Standard Normal Homogeneity method, Buishand's test, and von Neumann's check. Approximately 40% of the series (i.e., 16 stations out of 40) were homogeneous. Each homogeneity test was evaluated separately, and non-homogeneous stations were identified. Then, the series was classified into three groups that were assigned the labels "useful", "doubtful", and "suspect". The results indicated that twenty-one stations were associated with the class 'suspect', three of the stations belonged to the class 'doubtful', and sixteen locations were within the class 'useful'. Furthermore, the data analysis indicated no influence of the outliers on the results of the homogeneity tests. Accordingly, the study recommends further research on homogeneity tests that can be applied without considering outlier tests for similar case studies. [ABSTRACT FROM AUTHOR]

Since 1968 when the Kainji dam was built on the R. Niger in Nigeria, many other large dams, and more than 10 formal, large‐scale irrigation schemes have been constructed in the R. Niger drainage basin. By the early 1990s, a perception had developed in the Niger Delta, the floodplain and tidal region comprising the terminal distributaries of the R. Niger, that the operations of these dams and upstream land use have caused a marked reduction in river discharges in the Delta. Concurrently with the dam construction era (1964–1995), there was a 30‐year (1968–1998) drought particularly in the Sudan‐Sahel Zone of West Africa, a significant section of the R. Niger drainage basin. This negatively impacted the flow regime in the Delta. The long‐term low flow regime appears to have influenced the direction of settlement growth in the region. Rainfall started reverting to pre‐drought levels circa 1995, promoting spate flows on the R. Niger, its tributaries and the Delta. The consequence has been debilitating quasi‐annual flooding also perceived in the Niger Delta as another result of dam operations. This study attempts to elucidate the cause of flooding in the Niger Delta, and particularly the roles of dam operations, local rainfall, and direction of settlement growth on the flooding phenomena. Flooding and flood impact mitigating solutions are proffered. [ABSTRACT FROM AUTHOR]

Non-climatic reasons, such as station replacement and changing the measurement device and calculation method, may make climate data unrepresentative of the actual variation of the regional climate. Data quality control and homogenization tests for climate data are critical. Thus, this study aims to evaluate the quality and homogeneity level of precipitation time series in arid and semi-arid climatic zones and specify the breakpoint in the datasets. The proposed methodology has been used to conduct arid and semi-arid representative case studies comprising 40 annual precipitation series for Iraq between 1979 and 2014. A Box-Cox transformation has been used to adjust the non-normally distributed datasets. Outliers have been censored by truncating extreme values. The results of the outliers indicate that they may be caused more by climate variability than by human-induced reasons. Homogeneity adjustments have been developed by applying these four homogeneity tests: Pettitt’s test, the Standard Normal Homogeneity method, Buishand’s test, and von Neumann’s check. Approximately 40% of the series (i.e., 16 stations out of 40) were homogeneous. Each homogeneity test was evaluated separately, and non-homogeneous stations were identified. Then, the series was classified into three groups that were assigned the labels “useful”, “doubtful”, and “suspect”. The results indicated that twenty-one stations were associated with the class ‘suspect’, three of the stations belonged to the class ‘doubtful’, and sixteen locations were within the class ‘useful’. Furthermore, the data analysis indicated no influence of the outliers on the results of the homogeneity tests. Accordingly, the study recommends further research on homogeneity tests that can be applied without considering outlier tests for similar case studies.

ABSTRACT: An analytical study was conducted to assess the long‐term influence, role, and impacts of El Niño‐Southern Oscillation (ENSO) on Puerto Rico's precipitation patterns and significant moisture deficits (droughts). Detection and attribution was addressed by evaluating local rainfall measures and ENSO‐related data to (1) detect ENSO signals and patterns, (2) quantify the magnitude of any impacts, and (3) determine if ENSO may be an important factor for local prediction of future droughts. Data were evaluated at different time periods and two spatial scales (island‐wide and internal climate regions of Puerto Rico). Although a signal was detected, it was weak, in both directions, varied regionally, and has inconsequential impacts. No evidence was found for a major control by ENSO over local monthly, seasonal, and yearly rainfall for any climate regions on the island. These results indicate that ENSO is not a main factor causing droughts in Puerto Rico for the study period and thus should not be a factor in predicting the potential for local dry periods or large precipitation deficits in the future. Any presumed teleconnections between Puerto Rico's dry periods and ENSO are not based on current climatological evidence. Thus, local drought prediction efforts should be focused on finding major causes of local rainfall variation other than ENSO. [ABSTRACT FROM AUTHOR]

This paper is the first of a two-part study that investigates summer convective afternoon rainfall (CAR) activity over the East Asian continent through simulation and projection. We focus on the CAR activity over Taiwan in Part I. In Part II, the changes in CAR activity over South China and Luzon are examined. Using the WRF (Weather Research and Forecasting) model driven by two super-high resolution global climate models: HiRAM (High Resolution Atmospheric Model) and MRI (Meteorological Research Institute Atmospheric General Circulation Model), this study evaluates the performance of models (HiRAM, MRI, and WRF) used to simulate the summer CAR activity over Taiwan. The evaluations focus on the spatialtemporal variations in CAR activity during two time periods: the present-day (1979 - 2003, historical run) and the future (2075 - 2099, RCP8.5 scenario). For the present-day simulations, analyses indicate that both HiRAM and MRI cannot accurately simulate the temporal evolution of diurnal rainfall. This timing shift problem can be fixed after dynamical downscaling using WRF. The WRF dynamical downscaling approach also helps generate a more realistic CAR amount simulation over western Taiwan, where most residents live. In future projections all models predict that a significant decrease in CAR amount will occur over southwest Taiwan. This decrease in CAR amount is suggested due to the decrease in CAR frequency, not a change in the CAR rate. All models suggest that the cause of decrease in CAR frequency over southwest Taiwan is weaker local afternoon surface wind convergence and thermal instability to suppress CAR genesis. [ABSTRACT FROM AUTHOR]

This study is the second of a two-part investigation into summer convective afternoon rainfall (CAR) simulation and projection over the East Asian continents. In Part I, we examined the CAR activity over Taiwan. In this study we focus on CAR activity over South China and Luzon using the WRF (Weather Research and Forecasting Model) driven by HiRAM (High Resolution Atmospheric Model) (i.e., WRF-HiRAM). These examinations focus on two time-sliced simulations assuming the climate conditions at present (1979 - 2003, historical run) and at the end of the 21st century (2075 - 2099, RCP 8.5 scenario). The results show that WRF-HiRAM is capable of simulating the spatial-temporal variation in CAR activity over South China and Luzon close to the recorded observations. In the future projections, WRF-HiRAM predicts that CAR events over most of South China and eastern Luzon will become fewer but stronger. Conversely, CAR events over western Luzon will become more frequent and stronger. Analyses also indicate that the projected change in CAR amount over most of South China (except for the coastal regions) and Luzon will be dominated by the change in CAR rate, not the change in CAR frequency. As for the cause of change in CAR rate, WRF-HiRAM projects that atmospheric humidity over South China and Luzon will increase significantly in the future. This will lead to an increase in local CAR rate. In contrast, the projected change in CAR frequency over South China and Luzon is suggested to be greatly modulated by the change in daytime surface wind convergence and thermal instability. Examinations were also performed to document the characteristics and causes of the projected change in CAR activity extracted from HiRAM. [ABSTRACT FROM AUTHOR]