Abstract In this study, the weather conditions of the accident at Maroua-Salak airport on 02 August 2020 are analyzed. This C130 aircraft accident took place under bad weather conditions. This bad weather is diagnosed using the models as CFS, GFS and GEFS that reanalyze outputs of the results. At the end of this re-analysis, the result obtained shows that the event which took place at the Maroua-Salak airport was predictable. However, the analysis of these results has made it possible to present the rainfall cumul between 05 and 10 mm for this day. In addition, a comparative study of the rainfall cumul obtained by the CFS, GFS and GEFS models and that estimated by the satellites has been carried out. These models can significantly improve the prevention of such disasters in the region.

Abstract Climate change has led human beings to take an interest in the study of me teorological and climatic phenomena. In fact, the main impact of climate change on different sectors of society is caused by extreme events since the occurrence of extreme events leads to more impact related to change in mean climate. Unfortunately, the West African region is vulnerable to extreme rainfall impact because its economy is based on rain-fed agriculture. This study examined the seasonal variability of extreme rainfall in West Africa. Eight (8) climate indices were chosen from among the 27 defined by the Ex pert Team on Climate Change Detection and Indices (ETCCDI). The nonpa rametric Mann-Kendall test was used to assess the seasonal trends. The in dices of the same types (frequency or intensity) were compared to assess the intra-seasonal variation of extreme precipitation. The results indicate that, regardless of the season, the Gulf of Guinea receives more rainfall than the Sahel. This phenomenon is due to the fact that the coastal part of West Africa is under the influence of evaporation which is observed at the Atlantic Ocean and during the monsoon, while the other part is dominated by the desert. Mann-Kendall’s test revealed upward and downward trends during each sea son. The increase in extreme rainfall trends in the number of consecutive dry days suggests that droughts, due to global warming, could be observed and could have severe consequences in terms of water availability, energy supply, agricultural yields and ecosystems in West Africa. In addition, it can lead to the loss of biodiversity and health issues. It is therefore essential for policy makers or decisions makers to determine strategies and mitigation measures against climate change and its impacts on populations.

Abstract The relationship between some meteorological parameters and variation of total column ozone (TCO) concentration in Nigeria is studied from 1998-2012. The results using a descriptive analysis revealed a seasonal ozone variation having the same trend in all the stations during the period of study. High variability of TCO occurred between December and March coinciding with the period of dry season and low variability of TCO was observed in August coinciding with the period of rainy season. The observed trends in all the stations show that the TCO variation in Nigeria is mostly caused by natural occurrences. Calabar and Port Harcourt stations showed a high percent of TCO variability, while Kano and Maiduguri indicated a low percentage of TCO variability. Using Spearman correlation analysis, TCO concentration has a strong nega tive correlation with temperature in some stations with correlation coefficient (r) (−0.8392, −0.8531, −0.7832, −0.8881 and −0.7902) for Calabar, Port Har court, Makurdi, Lagos and Ilorin respectively. Kano and Maiduguri showed a weak positive correlation coefficient (r) 0.4965 and 0.3776 respectively. Posi tive correlation observed in Kano and Maiduguri could be as a result of high dehydration of water vapour in these stations due to seasonal harmattan and latitudinal effects. Probably, some of the substances that could deplete ozone such as HCl, aerosol are soluble in water thereby being washed off by rain during wet season leading to maximum TCO concentration during rainy sea son. Consequently, the observed phenomenon is through transportation of ozone content through the influence of Brewer-Dobson circulation. Again, during wet season, there is the mechanism of low pressure and lower tropopause height phenomenon, therefore, total ozone enhancement. Interestingly, ariation in TCO is part of symbolic tools for tropospheric meteorology alteration and this invariably leads to climate change.

Abstract This study examines the inter-annual variability of rainfall and Mean Sea Level Pressure (MSLP) over west Africa based on analysis of the Global PrecipitationClimatology Project (GPCP) and National Center for Environmental Predic tion/National Center for Atmospheric Research (NCEP/NCAR) Reanalysis respectively. An interconnection is found in this region, between Mean Sea Level Pressure (MSLP) anomaly (over Azores and St. Helena High) and monthly mean precipitation during summer (June to September: JAS). We also found that over northern Senegal (15˚N - 17˚N; 17˚W - 13˚W) the SLP to the north is strong; the wind converges at 200 hPa corresponding to the position of the African Easterly Jet (AEJ) the rotational wind 700 hPa (corre sponding to the position of the African Easterly Jet (AEJ) coming from the north-east is negative. In this region, the precipitation is related to the SLP to the north with the opposite sign. The Empirical Orthogonal Functions (EOF) of SLP is also presented, including the mean spectrum of precipitation and pressures to the north (15˚N - 40˚N and 50˚W - 25˚W) and south (40˚S -10˚S and 40˚W - 0˚E). The dominant EOF of Sea Level Pressures north and south of the Atlantic Ocean for GPCP represents about 62.2% and 69.4% of the variance, respectively. The second and third EOFs of the pressure to the north account for 24.0% and 6.5% respectively. The second and third EOFs of the pressure to the south represent 12.5% and 8.9% respectively. Wet years in the north of Senegal were associated with anomalous low-pressure areas over the north Atlantic Ocean as opposed to the dry years which exhibited an anomalous high-pressure area in the same region. On the other hand, over the South Atlantic, an opposition is noted. The wavelet analysis method is applied to the SLP showings to the north, south and precipitation in our study area. The indices prove to be very consistent, especially during intervals of high variance.

Abstract The present work is a comparative study between the foF2 variabilities for two equatorial regions (Ouagadougou: lat. 12˚21'N; long. 1˚30'E, dip. 1.43˚ in Africa and Huancayo: Lat. 12˚S; Long. 75˚12'W in America) during solar cycles 20 and 21 minima and maxima phases under geomagnetic extreme conditions (quiet and disturb). Profiles from these two stations are very simi lar for all the seasons over the solar cycles. However, measured data from Huancayo station are higher than those from Ouagadougou station during winter with a reverse phenomenon for summer. The investigations suggest that the gap between foF2 values and the reverse phenomenon observed for the two stations may be explained by their hemispheric location (Huancayo in south hemisphere and Ouagadougou in North one). Longitudinal irregu larities in ionosphere may also contribute to that little difference observed during the time interval of our investigation.

Abstract "Two simulations of five years (2003-2007) were conducted with the Regional Climate models RegCM4, one coupled with Land surface models BATS and the other with CLM4.5 over West Africa, where simulated air temperature and precipitation were analyzed. The purpose of this study is to assess the performance of RegCM4 coupled with the new CLM4.5 Land surface scheme and the standard one named BATS in order to find the best configuration of RegCM4 over West African. This study could improve our understanding of the sensitivity of land surface model in West Africa climate simulation, and provide relevant information to RegCM4 users. The results show fairly realis tic restitution of West Africa’s climatology and indicate correlations of 0.60 to 0.82 between the simulated fields (BATS and CLM4.5) for precipitation. The substitution of BATS surface scheme by CLM4.5 in the model configuration, leads mainly to an improvement of precipitation over the Atlantic Ocean, however, the impact is not sufficiently noticeable over the continent. hile the CLM4.5 experiment restores the seasonal cycles and spatial distribution, the biases increase for precipitation and temperature. Positive biases already existing with BATS are amplified over some sub-regions. This study concludes that temporal localization (seasonal effect), spatial distribution (grid points) and magnitude of precipitation and temperature (bias) are not simultaneously improved by CLM4.5. The introduction of the new land surface scheme CLM4.5, therefore, leads to a performance of the same order as that of BATS, albeit with a more detailed formulation."

Abstract The need to investigate diurnal weather cycles in West Africa originates from the fact that complex interactions often result between mesoscale and synoptic weather processes. This study investigates diurnal cycles of rainfall and convective properties using six (6) hour interval data from the ERA-Interim and de rived products from the Tropical Rainfall Measurement Mission (TRMM). Results showed that the land-ocean warming contrast is more strongly sensitive to the seasonal cycle, being very weak during March-May (MAM) but clearly spelled out during June-September (JJAS). Dipoles of wind convergence/divergence and wet/dry precipitation, between CASS and Nigeria Savannah zones, were identified in the morning and evening hours of MAM, whereas distinct night and day anomalies, same location in CASS, were found to be consistent during the JJAS season. The locations of flash count and system sizes agree with the climatology of convective properties, that morning and day-time hours are dominated by stratiform precipitation and small system sizes. Most results clearly showed that the eastern locations of Sudano and Sahel are consistently dry because rainfall and precipitation features are predominantly few. Very unique results about the dipole of wind and precipitation between two zones and the unusual dry zones of Sudan and Sahel have been found. Results presented had shown the importance of diurnal variation in understanding precipitation, flash count, system sizes patterns at diurnal scales, and understanding land-ocean contrast, recipitation and wind field anomaly at diurnal scales.

Abstract The COVID-19 pandemic has created worldwide devastation in every sphere of human life. It has led to the economy slowing down and has aggravated life, health, and livelihood vulnerabilities. It spreads across the globe, pene trating indiscriminately through the cities of global north and south and has a greater urban orientation. The physical, social, economic and environmental circumstances determine the susceptibility of an individual, a community or the system to the impact of this pandemic. The degree of vulnerability of any community strongly influences management decisions. The concept of socie tal vulnerability to hazards involves demographic and socio-economic factors that reflect community resilience. This study employed secondary data drawn from different sources, to understand the vulnerability of Aligarh city (India) in the COVID-19 period, the study produced a comprehensive dataset about na tural vulnerability, built-up vulnerability, social vulnerability and economic vulnerability. This study focuses to present a comparative analysis of ward-wise vulnerability in Aligarh city for the COVID-19 pandemic. The study designed proxy variables to measure and compare different levels of vulnerabilities in Aligarh city. The study presented to provide a tool for ward-wise planning and response to the COVID-19 pandemic in Aligarh city. The present study indi cates that the vulnerability index is the outcome of the interaction between phy sical, built-up, social, and economic environment. These environmental con ditions are nterrelated and have some bearing on each other also.

Abstract New pattern urbanization, which is explored and developed in China for improving urban resilience and reducing urban vulnerability. Urban resilience is a comprehensive ability of a city for dealing with the uncertainty risk disasters through a combination of urban economy, urban engineering, urban society and urban ecology. When the city system and its subsystems have certain resilience in development, it will promote sustainable development. How to assess urban resilience? What is the spatial-temporal law on the development of urban resilience? These answers have an important practical signi ficance for promoting the construction of the modern urbanization and sus tainable development of cities and regions. Based on the above, this study constructed the measurement system on urban resilience, chose 21 cities of Sichuan province in China as a case, and analyzed the spatial-temporal law on the development of urban resilience empirically. The conclusions are as follows: The level of urban resilience was on the rise, and the characteristics of spatial heterogeneity on urban resilience were presented, and the spatial agglomeration degree increased gradually. The resilience of urban economic system, urban engineering system, and urban ecological system revealed a cluster characteristic in Sichuan province, but urban social system was not obvious.

Abstract The COVID-19 pandemic has created worldwide devastation in every sphere of human life. It has led to the economy slowing down and has aggravated life, health, and livelihood vulnerabilities. It spreads across the globe, pene trating indiscriminately through the cities of global north and south and has a greater urban orientation. The physical, social, economic and environmental circumstances determine the susceptibility of an individual, a community or the system to the impact of this pandemic. The degree of vulnerability of any community strongly influences management decisions. The concept of societal vulnerability to hazards involves demographic and socio-economic factors that reflect community resilience. This study employed secondary data drawn from different sources, to understand the vulnerability of Aligarh city (India) in the COVID-19 period, the study produced a comprehensive dataset about natural vulnerability, built-up vulnerability, social vulnerability and economic vulnerability. This study focuses to present a comparative analysis of ward-wise vulnerability in Aligarh city for the COVID-19 pandemic. The study designed proxy variables to measure and compare different levels of vulnerabilities in Aligarh city. The study presented to provide a tool for ward-wise planning and response to the COVID-19 pandemic in Aligarh city. The present study indicates that the vulnerability index is the outcome of the interaction between physical, built-up, social, and economic environment. These environmental conditions are interrelated and have some bearing on each other also.

Abstract The COVID-19 pandemic has created worldwide devastation in every sphere of human life. It has led to the economy slowing down and has aggravated life, health, and livelihood vulnerabilities. It spreads across the globe, pene trating indiscriminately through the cities of global north and south and has a greater urban orientation. The physical, social, economic and environmental circumstances determine the susceptibility of an individual, a community or the system to the impact of this pandemic. The degree of

Abstract The COVID-19 pandemic has created worldwide devastation in every sphere of human life. It has led to the economy slowing down and has aggravated life, health, and livelihood vulnerabilities. It spreads across the globe, penetrating indiscriminately through the cities of global north and south and has a greater urban orientation. The physical, social, economic and environmental circumstances determine the susceptibility of an individual, a community or the system to the impact of this pandemic. The degree of vulnerability of any community strongly influences management decisions. The concept of socie tal vulnerability to hazards involves demographic and socio-economic factors that reflect community resilience. This study employed secondary data drawn from different sources, to understand the vulnerability of Aligarh city (India) in the COVID-19 period, the study produced a comprehensive dataset about na tural vulnerability, built-up vulnerability, social vulnerability and economic vulnerability. This study focuses to present a comparative analysis of ward-wise vulnerability in Aligarh city for the COVID-19 pandemic. The study designed proxy variables to measure and compare different levels of vulnerabilities in Aligarh city. The study presented to provide a tool for ward-wise planning and response to the COVID-19 pandemic in Aligarh city. The present study indicates that the vulnerability index is the outcome of the interaction between physical, built-up, social, and economic environment. These environmental conditions are interrelated and have some bearing on each other also.