Spatiotemporal Changes in Temperature and Precipitation in West Africa. Part I: Analysis with the CMIP6 Historical Dataset

Climate variability and change constitute major challenges for Africa, especially West Africa (WA), where an important increase in extreme climate events has been noticed. Therefore, it appears essential to analyze characteristics and trends of some key climatological parameters. Thus, this study addressed spatiotemporal variabilities and trends in regard to temperature and precipitation extremes by using 21 models of the Coupled Model Intercomparison Project version 6 (CMIP6) and 24 extreme indices from the Expert Team on Climate Change Detection and Indices (ETCCDI). First, the CMIP6 variables were evaluated with observations (CHIRPS, CHIRTS, and CRU) of the period 1983–2014; then, the extreme indices from 1950 to 2014 were computed. The innovative trend analysis (ITA), Sen’s slope, and Mann–Kendall tests were utilized to track down trends in the computed extreme climate indices. Increasing trends were observed for the maxima of daily maximum temperature (TXX) and daily minimum temperature (TXN) as well as the maximum and minimum of the minimum temperature (TNX and TNN). This upward trend of daily maximum temperature (Tmax) and daily minimum temperature (Tmin) was enhanced with a significant increase in warm days/nights (TX90p/TN90p) and a significantly decreasing trend in cool days/nights (TX10p/TN10p). The precipitation was widely variable over WA, with more than 85% of the total annual water in the study domain collected during the monsoon period. An upward trend in consecutive dry days (CDD) and a downward trend in consecutive wet days (CWD) influenced the annual total precipitation on wet days (PRCPTOT). The results also depicted an upward trend in SDII and R30mm, which, additionally to the trends of CDD and CWD, could be responsible for localized flood-like situations along the coastal areas. The study identified the 1970s dryness as well as the slight recovery of the 1990s, which it indicated occurred in 1992 over West Africa.

Analysis of Temperature Extremes over India Using Sheffield & IMD Dataset

Temperature extremes significantly contribute to climate change; therefore, the analysis of temperature extremes is essential in detecting and attributing climate change. The present study aims to analyze the spatiotemporal variations in the temperature extremes over India, using 0.25° × 0.25° high-resolution Sheffield temperature gridded dataset for a period of 62 years (1951–2012). In addition, the spatial distribution, statistical relation and trend pattern of Sheffield’s temperature dataset is compared with 1°×1°, gridded temperature dataset of Indian Meteorological Department (IMD). The mean of temperature indices show nearly similar spatial distribution in both datasets; however trend pattern of extreme indices show significant differences over different homogeneous temperature regions of India. There is mostly disagreement between the two datasets, for trend patterns of extreme indices at different homogeneous regions, but few grids show reasonable agreement for similar trend pattern. Both datasets reported a significant decreasing trend in TX10p (amount of cool days) and TN10p (amount of cold nights) at maximum grids for the 1951–2012 period. In addition, a significant increasing trend in TX90p (amount of hot days) and WSDI (warm spell duration indicator) at maximum grids during post-1981 and 1951–2012 is observed in both datasets. A comprehensive insight into different characteristics (spatial distribution, statistical relation and trend patterns) of Sheffield’s temperature dataset will help in understanding the applicability of Sheffield temperature dataset for climate modeling and prediction studies over India.

Daily Climate Extremes of Temperature and Precipitation Over Quetta Valley, Pakistan During 1961-2019

Climate extremes are imperative to study the impacts of climate change that is significantly observed for the management of scarce water resources of the Quetta Valley. The daily data of temperature and precipitation are used to model the climate extreme indices for Quetta Meteorological Station from1961 to 2019. The statistical tests were performed by using Mann Kendal and Sen’s Slope method at the 95% confidence level. The overall change in minimum to maximum temperatures and precipitation-based climate extreme indices specify the frequencies of extreme events are increasing. That would cause heatwaves, gradual warming, steady dryness, and extreme precipitation events in the long term over the Quetta Valley. The minimum and maximum temperature-based indices inclusively indicate positive trends. That ultimately leads to a warming climate with a significant increase in summer as 5 days/decade, tropical nights as 5.3 days/decade, daily maximum as 0.28°C/decade, warm nights as 1.7 days/decade and warm days as 1.9 days/decade. For precipitation, all the indices show positive trends with a significant increase in consecutive wet days for 0.1 days/decade and an annual contribution of very wet days 0.8% per decade. The monthly increase in temperature and decrease in precipitation would increase the evaporative demands which may arise the water stress conditions over the valley and may put pressure over groundwater reservoirs.

Potential Implications of Future Climate Change And Extremes On Health, Agriculture, Water, And Cryosphere Sectors In The Kabul River Basin

Increasing temperature and variability in precipitation are affecting different sectors in the Himalayan region. This study aims to quantify the future scenario and related extreme indices in the Kabul River Basin of the western Himalaya using high-resolution climate data sets. We selected the representative global climate model simulations for RCP4.5 and 8.5, based on their abilities to represent the historical climate cycle. By using a three-step methodology, we selected four models for RCP4.5 and four for RCP8.5. The analysis shows that, overall, precipitation will increase by 4 and 12 per cent for RCP4.5 and 8.5 respectively by the end of the 21st century, and the seasonal analysis shows decreasing pattern during the winter and pre-monsoon seasons. However, temperatures will increase consistently by 3OC to 5OC in RCP4.5 and 8.5 scenarios. The extreme indices were calculated based on the selected models. The extremes, like consecutive summer days, warm days, and heatwave will increase, whereas the frost days, cold nights, and cold waves will decrease towards the end of this century. Notably, more warm days and heatwaves than the baseline period are projected in future scenarios. Besides, the extremes are not homogenous in time and space. We also discussed the potential implications of these climatic extremes as related to human health, agricultural productivity, water availability, and the cryosphere. We strongly urge prompt climate actions in order to increase the adaptive capacity against these extreme changes and to build a resilient livelihood in the Kabul River Basin.

Projected Changes in Extreme Temperature and Precipitation Indices Over CORDEX-MENA Domain

In this study, projected changes in climate extreme indices defined by the Expert Team on Climate Change Detection and Indices were investigated over Middle East and North Africa. Changes in the daily maximum and minimum temperature- and precipitation- based extreme indices were analyzed for the end of the 21st century compared to the reference period 1971–2000 using regional climate model simulations. Regional climate model, RegCM4.4 was used to downscale two different global climate model outputs to 50 km resolution under RCP4.5 and RCP8.5 scenarios. Results generally indicate an intensification of temperature- and precipitation- based extreme indices with increasing radiative forcing. In particular, an increase in annual minimum of daily minimum temperatures is more pronounced over the northern part of Mediterranean Basin and tropics. High increase in warm nights and warm spell duration all over the region with a pronounced increase in tropics are projected for the period of 2071–2100 together with decrease or no change in cold extremes. According to the results, a decrease in total wet-day precipitation and increase in dry spells are expected for the end of the century.

Twentieth Century Precipitation Trends in the Upper Mzingwane Sub-catchment of the Northern Limpopo Basin, Zimbabwe

This study evaluates precipitation trends in the upper Mzingwane sub-catchment (UMS) of Zimbabwe for the variables of annual precipitation, extremely wet days, consecutive wet days and consecutive dry days. The UMS is of strategic socio-economic significance in terms of its provision of water security and sustenance to livelihoods. The analysis is undertaken at four stations: Bulawayo Goetz, Filabusi, Mbalabala and Matopos National Park, and for the period 1921–2000. In general trends were found not to have local statistical significance, with the exception of the Matopos station (in the westernmost extent of UMS) which records significant increasing (declining) trends for most dryness (wetness) extreme indices. A general north to south-western declining precipitation gradient during the past ~ 69 years over the UMS was also found. The findings provide a baseline for future extended historical and future precipitation trend studies, and are important in the context of the socio-economic impacts of extreme events in this region.

Means and Extremes: Evaluation of a CMIP6 Multi-Model Ensemble in Reproducing Historical Climate Characteristics across Alberta, Canada

This study evaluates General Circulation Models (GCMs) participating in the Coupled Model Intercomparison Project Phase 6 (CMIP6) for their ability in simulating historical means and extremes of daily precipitation (P), and daily maximum (Tmax), and minimum temperature (Tmin). Models are evaluated against hybrid observations at 2255 sub-basins across Alberta, Canada using established statistical metrics for the 1983–2014 period. Three extreme indices including consecutive wet days (CWD), summer days (SD), and warm nights (WN) are defined based on the peak over the threshold approach and characterized by duration and frequency. The tail behaviour of extremes is evaluated using the Generalized Pareto Distribution. Regional evaluations are also conducted for four climate sub-regions across the study area. For both mean annual precipitation and mean annual daily temperature, most GCMs more accurately reproduce the observations in northern Alberta and follow a gradient toward the south having the poorest representation in the western mountainous area. Model simulations show statistically better performance in reproducing mean annual daily Tmax than Tmin, and in reproducing annual mean duration compared to the frequency of extreme indices across the province. The Kernel density curves of duration and frequency as simulated by GCMs show closer agreement to that of observations in the case of CWD. However, it is slightly (completely) overestimated (underestimated) by GCMs for warm nights (summer days). The tail behaviour of extremes indicates that GCMs may not incorporate some local processes such as the convective parameterization scheme in the simulation of daily precipitation. Model performances in each of the four sub-regions are quite similar to their performances at the provincial scale. Bias-corrected and downscaled GCM simulations using a hybrid approach show that the downscaled GCM simulations better represent the means and extremes of P characteristics compared to Tmax and Tmin. There is no clear indication of an improved tail behaviour of GPD based on downscaled simulations.

Spatio-temporal variations of climate variables and extreme indices over Iran during 1986-2015

<p>In order to better understand how climate changes have taken place in Iran, we carried out a comprehensive analysis of the spatio-temporal trends of various climate variables and extreme indices during 1986 to 2015 at the county-level across the country. Additionally, the interannual oscillation of the temperature and precipitation and their related extreme indices were examined throughout the research. In this study, ERA5-Land and AgrERA5 datasets with hourly, daily, and monthly temporal resolutions were aggregated to the county-level to calculate climate extreme indices. Subsequently, different approaches such as the original Mann-Kendall (MK) trend test, MK with block bootstrap modification, MK with variance correction modification, correlated seasonal MK (partial MK), original and seasonal Sen's Slope were implemented to detect the magnitude and the statistical significance of climatic trends for each county. Finally, the continuous wavelet transform was employed for whole country averages to investigate fluctuations and dominant periods of the variables and indices. The reanalysis model datasets offered us two advantages; firstly, it facilitates obtaining data in some regions with sparse weather stations and secondly, it allows us to inquire about some climate variables that were less studied in the literature, for instance, the wind speed, the surface air pressure, the solar radiation, the surface albedo, the runoff, the evaporation, and the skin reservoir content. The results showed a significant increasing trend in the temperature over all counties and a nonsignificant drying trend in the precipitation for almost the whole country. Other climate variables demonstrated more mixed spatio-temporal trends; however, generally, the wind speed and the solar radiation had an upward trend, the runoff, the skin reservoir content, and the surface albedo showed a downward trend, while the surface air pressure and the evaporation trends exhibited a great deal of variety. Furthermore, the hot climate extremes were increased throughout the country whereas the cold extremes and the extreme precipitations were quite in the opposite direction. It is noteworthy that the Continental and the Warm-Temperate climates were more vulnerable compare to the Arid and Semi-Arid Climates. At last, the wavelet power spectrum maps indicated the consistency between the temperature and precipitation and their related extremes and also showed a reduction in the fluctuation of the precipitation and a constant oscillation for temperature over the study period.</p>