Temperature and precipitation extremes under current, 1.5°C and 2.0°C global warming above pre-industrial levels over Botswana, and implications for climate change vulnerability

Climate extremes are widely projected to become more severe as the global climate continues to warm due to anthropogenic greenhouse gas emissions. These extremes often cause the most severe impacts on society. Therefore, the extent to which the extremes might change at regional level as the global climate warms from current levels to proposed policy targets of 1.5 and 2.0 °C above preindustrial levels need to be understood to allow for better preparedness and informed policy formulation. This paper analysed projected changes in temperature and precipitation extremes over Botswana at 1.0, 1.5 and 2.0 °C warming, a country highly vulnerable to the impacts of climate change. Projected changes in temperature extremes are significantly different from each other at the three levels of global warming. Specifically, at 2.0 °C global warming, relative to preindustrial, for the ensemble median: (a) country average Warm Spell Duration Index (WSDI) ensemble median increases ensemble range by 80, 65, 62 days per year across different climatic zones, approximately three times the change at 1.0 °C and twice the change at 1.5 °C; (b) cold night (TN10P) and cold day (TX10P) frequencies decrease by 12 and 9 days per year across all regions, respectively, while hot nights (TN90P) and hot days (TX90P) both increase by 8-9 days across all regions. Projected changes in drought related indices also distinct at different warming levels. Specifically: (a) projected mean annual precipitation decreases across the country by 5-12% at 2°C, 3-8% at 1.5 °C and 2-7% at 1.0 °C; (b) the dry spell length (ALTCDD) increases by 15-19 days across the three climatic zones at 2.0 °C, about three (two) times as much as the increase at 1.0 (1.5) °C. Ensemble mean projections are for increases in heavy rainfall indices, but not statistically significant. The implications of these changes for key socio-economic sectors are explored, and reveal progressively severe impacts, and consequent adaptation challenges for Botswana as the global climate warms from its present temperature of 1.0 °C above preindustrial levels to 1.5, and then 2.0 °C

A baseline appraisal of water-dependant ecosystem services, the roles they play within desakota livelihood systems and their potential sensitivity to climate change

This report forms part of a larger research programme on 'Reinterpreting the Urban-Rural Continuum', which conceptualises and investigates current knowledge and research gaps concerning 'the role that ecosystems services play in the livelihoods of the poor in regions undergoing rapid change'. The report aims to conduct a baseline appraisal of water-dependant ecosystem services, the roles they play within desakota livelihood systems and their potential sensitivity to climate change. The appraisal is conducted at three spatial scales: global, regional (four consortia areas), and meso scale (case studies within the four regions). At all three scales of analysis water resources form the interweaving theme because water provides a vital provisioning service for people, supports all other ecosystem processes and because water resources are forecast to be severely affected under climate change scenarios. This report, combined with an Endnote library of over 1100 scientific papers, provides an annotated bibliography of water-dependant ecosystem services, the roles they play within desakota livelihood systems and their potential sensitivity to climate change. After an introductory, section, Section 2 of the report defines water-related ecosystem services and how these are affected by human activities. Current knowledge and research gaps are then explored in relation to global scale climate and related hydrological changes (e.g. floods, droughts, flow regimes) (section 3). The report then discusses the impacts of climate changes on the ESPA regions, emphasising potential responses of biomes to the combined effects of climate change and human activities (particularly land use and management), and how these effects coupled with water store and flow regime manipulation by humans may affect the functioning of catchments and their ecosystem services (section 4). Finally, at the meso-scale, case studies are presented from within the ESPA regions to illustrate the close coupling of human activities and catchment performance in the context of environmental change (section 5). At the end of each section, research needs are identified and justified. These research needs are then amalgamated in section 6

Impact of Stratospheric Aerosol Geoengineering on Extreme Precipitation and Temperature indices in West Africa using GLENS simulations

This study assesses changes in extremes precipitation and temperature in West Africa under a high greenhouse gas scenario, i.e. a representative concentration pathway 8.5 (RCP8.5), and under a scenario of stratospheric aerosol geoengineering (SAG) deployment using the NCAR Community Earth System Model version 1 (CESM1-WACCM). We use results from the Geoengineering Large Ensemble (GLENS) simulations, where SAG is deployed to keep global surface temperatures at present day values. This impact study evaluates changes in some of the extreme climate indices recommended by the Expert Team Monitoring on Climate Change Detection and Indices (ETCCDI). The results indicate that SAG would effectively keep surface temperatures at present day-conditions across a range of indices compared to the control period, including Cold days, Cold nights and Cold Spell Duration Indicator which show no significant increase compared to the control period. Regarding the extremes precipitation, GLENS shows mostly a statistically significant increase in annual precipitation and statistically significant decrease in the number of heavy and very heavy precipitation events relative to the control period in some regions of Gulf of Guinea. In the Sahel, we notice a mix of statistically significant increase and decrease in Max 1-day and Max 5-days precipitation amount relative to the control period at the end of the 21st century when large amounts of SAG has been applied. The changes in extreme precipitation indices are linked to changes in Atlantic Multidecadal Oscillation (AMO), NINO3.4 and Indian Ocean Dipole (IOD) and these changes in extreme precipitation are driven by change in near surface specific humidty and atmospheric circulation

PROJECTED EXTREME RAINFALL INDICES IN GUINEA AND SUDANO-SAHELIAN ECOLOGICAL ZONES, NIGERIA

Drought and Flood episodes are twin issues that are consequences of extreme rainfall events. The negative impact of extreme rainfall events makes understanding their behaviour under the future climate change necessary for regional planning. Hence, the objective of the study is to project extreme rainfall indices in Guinea and Sudano-Sahelian ecological zones, Nigeria. A set of four extreme rainfall indices namely: maximum 5-day rainfall (Rx5day), heavy rainfall days (R10mm), consecutive wet days (CWD) and consecutive dry days (CDD) were adopted. The data and computation were done using KNMI Climate Explorer. Projections were produced for the near-term 2019-2048, mid-term 2049-2078 and long-term 2079-2100 periods with reference to the 1959-1988 and 1989-2018 baselines. The multi-model ensemble mean of couple model intercomparison project 5 (CMIP5) under representative concentration pathways (RCPs) 2.6, 4.5, and 8.5 were used. Mann-Kendal statistical test was adopted to analyze the trends in extreme rainfall indices at the 0.05 significance level. Based on the results, it can be deduced that there is a significant positive trend in the whole Guinea and Sudano-Sahelian ecological zone as a region for maximum 5-day rainfall with respect to all the three RCPs. As for heavy rainfall, itreveals that there is no significant positive trend for RCP2.6 with respect to the three projected periods under consideration but significant positive trends with respect to 2049-2078 for RCP4.5 as well as RCP8.5 with respect to 2049-2078 and 2079-2100 periods. Increase in CDD, as well as a decrease in CWD, were both not significant at the 0.05 confidence level. Therefore, it is expected that this study will aid guidance to the understanding of the ongoing changes as well as possible changes in rainfall and rainfall-related extremes. It is also important for future planning of water resources management and agriculture in Guinea and Sudano-Sahelian ecological zones of Nigeria. KEYWORDS: Extreme rainfall indices, Guinea, Sudano-Sahelian, Ecological zones, Nigeri

Dry soils can intensify mesoscale convective systems

Soil moisture can feed back on rainfall through the impact of surface fluxes on the environment in which convection develops. The vast majority of previous research has focused on the initiation of convection, but in many regions of the world, the majority of rain comes from remotely triggered mesoscale convective systems (MCSs). Here we conduct a systematic observational analysis of soil moisture feedbacks on propagating MCSs anywhere in the world and show a strong positive impact of drier soils on convection within mature MCSs. From thousands of storms captured in satellite imagery over the Sahel, we find that convective cores within MCSs are favored on the downstream side of dry patches ≥200 km across. The effect is particularly strong during the afternoon–evening transition when convection reaches its diurnal peak in intensity and frequency, with dry soils accounting for an additional one in five convective cores. Dry soil patterns intensify MCSs through a combination of convergence, increased instability, and wind shear, all factors that strengthen organized convection. These favorable conditions tend to occur in the vicinity of a surface-induced anomalous displacement of the Sahelian dry line/intertropical discontinuity, suggesting a strong link between dry line dynamics and soil moisture state. Our results have important implications for nowcasting of severe weather in the Sahel and potentially in other MCS hotspot regions of the world

Benefits of simulating precipitation characteristics over Africa with a regionally-coupled atmosphere–ocean model

High-quality climate information at appropriate spatial and temporal resolution is essential to develop and provide tailored climate services for Africa. A common method to produce regional climate change data is to dynamically downscale global climate projections by means of regional climate models (RCMs). Deficiencies in the representation of the sea surface temperatures (SSTs) in earth system models (ESMs) and missing atmosphere–ocean interactions in RCMs contribute to the precipitation bias. This study analyzes the influence of the regional atmosphere–ocean coupling on simulated precipitation and its characteristics over Africa, and identifies those regions providing an added value using the regionally coupled atmosphere–ocean model ROM. For the analysis, the MPI-ESM-LR historical simulation and emission scenario RCP8.5 were dynamically downscaled with ROM at a spatial resolution of 0.22° × 0.22° for the whole African continent, including the tropical Atlantic and the Southwest Indian Ocean. The results show that reduced SST warm biases in both oceans lead to more realistic simulated precipitation over most coastal regions of Sub-Saharan Africa and over southern Africa to varying degrees depending on the season. In particular, the annual precipitation cycles over the coastal regions of the Atlantic Ocean are closer to observations. Moreover, total precipitation and extreme precipitation indices in the coupled historical simulation are significantly lower and more realistic compared to observations over the majority of the analyzed sub-regions. Finally, atmosphere–ocean coupling can amplify or attenuate climate change signals from precipitation indices or even change their sign in a regional climate projection

Extreme Rainfall Indices in Southern Levant and Related Large-Scale Atmospheric Circulation Patterns: A Spatial and Temporal Analysis

This study aims to provide a comprehensive spatio-temporal analysis of the annual and seasonal extreme rainfall indices over the southern Levant from 1970 to 2020. For this, temporal and spatial trends of 15 climate extreme indices based on daily precipitation at 66 stations distributed across Israel and Palestine territories were annually and seasonally analyzed through the nonparametric Mann–Kendall test and the Sen’s slope estimator. The annual averages for frequency-based extreme indices exhibited decreasing trends, significantly for the Consecutive Dry Days. In contrast, the percentiles- and intensity-based extreme indices showed increasing trends, significant for extremely wet days, Max 1- and 3-day precipitation amount indices. The study area had expanding periods of extreme dry spells for spring and correspondingly shortening extreme wet spells for spring, winter and the combined winter–spring. Moreover, most of spring indices showed negative trends. Conversely, most winter indices displayed positive trends. Regarding the influence of large-scale circulation patterns, the North Sea Caspian pattern, the Western Mediterranean Oscillation, and ENSO were the primary regulators of the winter, spring, and autumn extreme indices, respectively. These findings contribute to a better understanding of extreme rainfall variability in the Levant region and could be utilized in the management of water resources, drought monitoring, and flood control.FEDER/Junta de Andalucia-Consejeria de Transformacion Economica, Industria, Conocimiento y Universidades P20_00035Ministry of Science and Innovation through the FEDER funds from the Spanish Pluriregional Operational Program 2014-2020 (POPE), LifeWatch-ERIC action line LifeWatch-2019-10-UGR-0