Droughts are increasing in frequency and intensity in many African countries. Their occurrences severely affect agricultural production and thus potentially contribute to human displacement. Yet, the way in which droughts influence patterns of human settlements remain poorly understood. Here we show that drought occurrences across Africa are often associated with (other things being equal) human displacements towards rivers and cities. Our results show that 73-81% of African countries exhibit larger human mobility towards water bodies and urban areas during drought conditions, as compared to non-drought periods. This may result into increasing floodplain population, and thus into potentially larger flood losses, or overcrowding urban areas. As such, our results shed light on the interplay between hydrologic extremes and society, bolstering the analysis on the spatiotemporal dynamics of drought risks in a warming world.

How to cite: Ceola, S., Mård, J., and Di Baldassarre, G.: Droughts influence patterns of human settlements in Africa, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-11856, https://doi.org/10.5194/egusphere-egu23-11856, 2023.

Semiarid regions shaped as a mosaic of savanna-type rangelands, croplands, and other uses such as livelihoods, or natural reserves, cover large areas in Southern Africa. They constitute an essential example of multiple uses of natural resources, combining a high environmental value with great importance in the rural economy and development. These systems are water-limited and highly sensitive to changes in climate, environmental conditions, and land management practices. Although the vegetation of these areas is adapted to variable climatic conditions and dry periods, the increase in drought intensity, duration, and frequency precipitate their degradation. 

In Southern Africa, recurrent droughts have strained rainfed agriculture and pasture production, decimating livestock and wildlife. During 2015 and 2016, South African savannas were subjected to a severe drought associated with a strong El Niño event. Open-source satellite time series provide vital information to assess water availability and long-term drought, to help design early warning and conservation strategies. 

In this work, we applied the TSEB (Two Source Energy Balance) model integrating MODIS-derived products (1 km) from 2000 to 2021 over the Kruger National Park (KNP) in South Africa. The model was previously validated over the Skukuza experimental site with good agreement. ET followed precipitation rates, although some years with low precipitation maintained average ET values. This may be caused by the ability of the trees to reach groundwater (deep fractured aquifers and alluvial aquifers can be found in the KNP). During some years (e.g., 2004, 2009), annual total ET was much higher than mean annual values. This may be caused by an extreme annual evaporative atmospheric demand and relatively high precipitation. The anomalies of the ratio of ET to reference ET were used as an indicator of agricultural drought on annual scales, and 2002/2003, 2007/2008 and 2015/2016 years stood out for their negative values. The approach helped to model drought over Kruger Park in the long term, providing an insight into the characteristics of the events.

Acknowledgment: This work has been carried out through the project "DroughT impACt on the vegeTation of South African semIarid mosaiC landscapes: Implications on grass-crop-lands primary production" funded by the European Space Agency in the framework of the "EO AFRICA R&D Facility".

How to cite: Dube, T., Ramoelo, A., Shoko, C., Dominic, M., Gonzalez-Dugo, M. P., Nieto, H., and Andreu, A.: Drought monitoring over the Kruger National Park (2000-2020) integrating remote sensing data., EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6608, https://doi.org/10.5194/egusphere-egu23-6608, 2023.

Data-sparse hydroclimates across the globe are often the most vulnerable to climate shocks and their populations to food insecurity. Drought monitoring and famine early warning in these regions have for too long relied on poor parameterizations of atmospheric evaporative demand (E₀)—no less than the demand side of drought and of consumptive use by agriculture—either relying on physically poor process representations of E₀ or on climatological mean estimates. However, by exploiting the advent of long-term, spatially distributed, and accurate reanalyses of the land-atmosphere system and its drivers we can put new data to use to save livelihoods and lives by improving drought monitoring, famine early warning, and multi-scale agricultural risk assessment.

Here we describe one such effort—to create a daily, long-term, accurate, global operational dataset of E₀. Funded by the Famine Early Warning Systems Network (FEWS NET) and its partners, we have developed a nearly 42-year long, daily, 0.125-degree, global dataset of Penman-Monteith reference evapotranspiration as a fully physical metric of E₀. This new E₀ dataset is driven by the Modern-Era Retrospective analysis for Research and Applications, Version 2 (MERRA-2)—an accurate, fine-resolution land-surface/atmosphere reanalysis. We verified the accuracy of the dataset against (i) point-estimates of E₀ derived by Southern African Science Service Centre for Climate Change and Adaptive Land Management (SASSCAL) initiative in Southern Africa, a region with sparse ground-truth data and significant humanitarian need, and (ii) on a spatially distributed basis against E₀ derived from other reanalyses (Global Data Assimilation System and Princeton Global Forcing) that, although global, are otherwise unsuitable for operational food-security decision-making.

We summarize the various uses to which the new E₀ dataset is already being put in support of food-security monitoring and decision-making in food-insecure countries within the FEWS NET framework: to provide input data for a global implementation of the Evaporative Demand Drought Index (EDDI), which examines anomalies in E₀ to permit early warning and ongoing monitoring of agricultural flash drought and hydrologic drought, both crucial drivers of food insecurity; and to diagnose the anomalies in E₀ that lead to or signal drought into the relative contributions from its drivers, examining canonical droughts across Africa (e.g., the 2015 drought in Malawi, and the 2016 Horn of Africa drought, and the current multi-year East African drought). We also present use-cases that verify the operational applicability of the new E₀ dataset in long-established drought, famine, crop- and pastoral-stress metrics, and in predictability assessments of drought forecasts. Driven by this new dataset, these analyses should significantly contribute to a more holistic understanding of drought and food-security across the African continent and the rest of the world.

How to cite: Hobbins, M., Boiko, O., Dewes, C., Hoell, A., Husak, G., Jayanthi, H., Magadzire, T., McNally, A., Sarmiento, D., Senay, G., and Turner, W.: A new global reference evapotranspiration reanalysis: global opportunities in operational drought monitoring and famine early warning, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-16989, https://doi.org/10.5194/egusphere-egu23-16989, 2023.

Water accounting frameworks assess water availability and consumption of various users and are key tools to inform decision and policy making for integrated water resources management. This study presents a modelling framework that integrates a spatially explicit hydrological model and climate change scenarios with the Water Accounting Plus (WA+) tool to anticipate future water resource challenges and provide mitigation measures. The fully distributed mesoscale Hydrologic Model (mHM), spatially calibrated with multiple satellite remote sensing products, is used to predict water fluxes, stocks and flows in the transboundary Volta River basin (VRB) in West Africa. The mHM model is forced with a large ensemble of climate change projection data from eleven general circulation models (GCMs) downscaled by four regional climate models (RCMs) under the representative concentration pathway RCP8.5, obtained from CORDEX-Africa. Outputs from mHM are used as inputs to the WA+ framework to report on the state and trends of water resources over the historical baseline period 1991-2020 and the near-term future 2021-2050. The basin-scale WA+ reporting is reinforced with a multi-scale summary of water accounts across spatial domains including four climatic zones, four sub-basins and the six riparian countries.

The long-term multi-model ensemble mean of the net inflow to the basin is found to be 419 km³/year with an inter-annual variability of 11%, and is projected to slightly increase in the near-term future (2021-2050), due to the increase in rainfall, thereby highlighting the need for adaptation strategies to optimize the water-energy-food-ecosystem nexus in the VRB.

How to cite: Dembélé, M., Salvadore, E., Zwart, S., Ceperley, N., Mariéthoz, G., and Schaefli, B.: Multiscale water accounting under climate change in a transboundary West African basin, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-8955, https://doi.org/10.5194/egusphere-egu23-8955, 2023.

Rangeland water is critical to food security early warning systems in Africa.  Rangelands feed more than half of Africa’s livestock, providing a source of income to 268 million pastoralists and agropastoralists. Rangeland ponds are a vital source of water for pastoral livestock, directly contributing to household food security and health.  However, rangeland areas of the Sahel and East Africa are water-limited, drought prone, and very food insecure.  In December 2022, the United States Agency for International Development’s (USAID) Famine Early Warning Systems Network (FEWS NET) identified >35 million extremely food insecure people in the countries located in the Sahel and East Africa. 

The NASA-funded “Earth Observation-Based Monitoring and Forecasting of Rangeland Water Resources” (Rangelands Monitoring and Forecasting System) project partners with FEWS NET to develop new capabilities for monitoring and forecasting water availability in African rangeland ponds.  FEWS NET partner, the U.S. Geological Survey, maintains the Water Point Viewer (https://earlywarning.usgs.gov/fews/software-tools/25), an interactive map that monitors the relative depth and area of 338 water points across arid and semi-arid regions of the Sahel and East Africa, from Senegal to Somalia.  The Rangelands Monitoring and Forecasting System project aims to significantly expand and improve the existing FEWS NET Water Point Viewer by increasing the locations monitored, developing new time series of water point surface area using high-resolution satellite data, improving overall model physics, and developing new forecasting capabilities.  These advanced data streams aim to improve pastoral resilience to climate shocks by increasing the capacity of stakeholders to plan for and respond to drought emergencies.

In this presentation, we introduce the Rangelands Monitoring and Forecasting System project and present first results from the 2022 field season.  During the 2022 West African rainy season, Action Contre la Faim collected water level observations from staff gauges installed in twelve ephemeral ponds located along transhumance corridors in Senegal.  Over the same period, the surface water extent of each pond was estimated using Sentinel 1 synthetic aperture radar, Sentinel 2 multispectral data, and Landsat multispectral data.  Additionally, the FEWS NET Water Point Viewer simulated water levels in nearby ponds.  The observed water levels were compared to the modeled surface water levels and the satellite data-based surface water extents to understand how well the FEWS NET Water Point Viewer and remotely sensed data streams capture the seasonal variation of water availability in the ponds.

This presentation: 1) presents the comparison results and discusses the accuracy of the model- and satellite-based estimates of water availability; 2) discusses the limitations of using remotely sensed estimates of water availability in the West Africa Sahelian region; and 3) presents lessons learned from conducting a field campaign in rural areas of West Africa.  The results from the first year of the project will inform the development of the next generation of the FEWS NET Water Point Viewer and new satellite-based remote sensing data streams for monitoring water availability in pastoral regions.

How to cite: Slinski, K., Senay, G., Rowland, J., Budde, M., Shukla, S., McNally, A., Adoum, A., Fillol, E., Ndiaye, B., and Assane Diallo, C.: In Situ and Earth Observation-Based Monitoring of Water Availability in Rangeland Areas of the Sahel and East Africa, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-17140, https://doi.org/10.5194/egusphere-egu23-17140, 2023.

The African Flood and Drought Monitor (AFDM) is a satellite-model based system for monitoring and forecasting flood and drought conditions for the African continent. It has been running operationally since 2008 in various forms, providing useful information on flood and drought risks to a variety of end-users, as well as information for a wide range of water-related applications, including food and energy security, health risks, and migration. This paper provides an overview of the latest version of the system, which incorporates updated versions of hydrological models and meteorological data at high resolution, as well as the state-of-the-art short-term and seasonal forecast models. We also describe the tailoring of the AFDM to national systems across southern Africa and the process of co-design of these systems with national agencies and end-users. The system has been evaluated on several time scales, historically and for short-term (flood) and seasonal (drought) forecasts. Predictability is discussed with respect to end-users needs, especially at the community scale, and how more recent approaches to predict at the community scale are being incorporated into these monitoring systems, using high-performance computing, machine learning and data assimilation.

How to cite: Sheffield, J., Kimball, J., Du, J., and Verbist, K.: Approaches to community–scale drought and flood early warning, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-16309, https://doi.org/10.5194/egusphere-egu23-16309, 2023.

The study investigates the sensitivity of water resources, droughts and hydropower generation to climate change in the Lake Malawi and Shire River basins, covering three different aspects:

• Analysis of the variability and trends of meteorological and hydrological droughts based on observational data from 1970 to 2013;
• Drought analysis for future conditions and investigation of potential changes in water balance and various drought indicators;
• Hydrological simulation and sensitivity analysis of the Lake Malawi water balance and water level, as well as its discharge and associated hydropower generation in the Shire River.

The key findings of these analyses are:

• Between 1970 and 2013, meteorological droughts have increased in intensity and duration. This can be attributed to a decrease in precipitation and an increase in temperatures and evaporation.
• The hydrological system of Lake Malawi reacts to meteorological droughts with a time lag (up to 24 months), so that hydrological droughts can be predicted up to 10 months in advance by meteorological drought parameters. Hydrological droughts are characterized by water levels below 474.1 m asl in Lake Malawi.
• Despite all the differences and uncertainties in climate projections, they agree that meteorological droughts will continue to increase in the future, in the form of increasing drought intensities DI (+25% to +50% for 2021-2050 and +131% to +388% for 2071-2100) and increasing drought months DM (3-5 and 7-8 more drought months per year, respectively).
• The water level in Lake Malawi, as a residual of the catchment water balance, is very sensitive to changes in precipitation and evaporation. Outflow from the lake is a direct function of lake water level, and the combination of projected precipitation decline and temperature increase ultimately leads to significantly reduced flow in the Shire River and a decline in annual hydropower production of between 1% and 2.5% (2021-2050) and 5% and 24% (2071-2100). Sometimes, individual projections even suggest that the outflow from Lake Malawi would temporarily dry up and the power supply in the country would be interrupted.

It is shown that failure to meet the 1.5°C global temperature increase target will have a severe impact on droughts and water resources in Malawi. This in turn has implications for hydropower production, as a result of which the achievement of most of the Sustainable Development Goals (SDGs) will be at risk.

How to cite: Bronstert, A., Mtilatila, L., and Vormoor, K.: Impacts of climate change on hydrological extremes and hydropower production in tropical Africa: catchments of Lake Malawi and the Shire River in Malawi, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-12047, https://doi.org/10.5194/egusphere-egu23-12047, 2023.

African Easterly Waves (AEWs) are the most important precipitation-producing dynamic systems in tropical Africa and Atlantic, where dust in the atmosphere is abundant. But the past studies lack consensus on the sign and magnitude of the dust radiative forcing impact on AEWs primarily because of the disagreement in calculating dust solar radiation absorption. The incapability of coarse-resolution models to represent various dust-AEW interactions is another source of uncertainty. The present study uses a high-resolution atmospheric general circulation model, HiRAM, to investigate the sensitivity of AEWs to the dust direct radiative forcing when dust shortwave absorption varies within the observed limits. Global simulations are conducted with the 25 km grid spacing to adequately simulate AEWs and associated circulation features. Four 10-year experiments are conducted: One control experiment without dust and three others with dust assuming dust is an inefficient, standard, and very efficient shortwave absorber. The results show that AEWs are highly sensitive to dust shortwave absorption. As dust shortwave absorption increases, AEW activity intensifies and broadens the wave track shifting it southward. The 6-9 day waves are more sensitive to dust shortwave absorption than the 3-5 day waves, where the response in the former has a stark land-sea contrast. The sensitivity of AEW to dust solar radiation absorption arises from a combination of energy conversion mechanisms. Although baroclinic energy conversion dominates the energy cycle, the responses to dust shortwave heating in barotropic and generation terms are comparable to that in baroclinic conversion.

How to cite: Bangalath, H. K., Raj, J., and Stenchikov, G.: Sensitivity of African Easterly Waves to Dust Direct Radiative Forcing, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4000, https://doi.org/10.5194/egusphere-egu23-4000, 2023.