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Drought is a natural hazard which occurs in all climatic zones and affects different sectors such as irrigation, energy, water supply, and ecology. Monitoring and predicting drought are pressing challenges since drought is becoming more common and severe owing to the impacts of climate change and increased climatic variability. However, in many areas of the globe, the temporal and spatial characterization of droughts and trends in their frequency and severity is hindered by a lack of reliable, long-term locally measured data and unevenly distributed, erratic meteorological stations. In this situation, remote sensing datasets such as Climate Hazards Group InfraRed Precipitation with Station Data (CHIRPS) can offer valuable insights into long-term developments and the spatial characteristics of droughts. Nonetheless, it is often uncertain to which extent data such as CHIRPS succeeds in representing local dynamics and how this varies between geographical regions and climate zones. 

In this analysis, we aim to evaluate spatial drought conditions over the Seyhan River basin in Turkey in the Eastern Mediterranean. Using the Standardized Precipitation Index (SPI) as a drought index, the applicability of CHIRPS as a long-term satellite precipitation product for drought monitoring is investigated. We compare two spatial representations of the SPI: one derived on a per-pixel basis from CHIRPS data since 1981, the other based on data from 19 meteorological stations scattered across the basin which was spatialized using inverse distance weighted interpolation. Our results offer insights into the relative accuracy of CHIRPS data in the Eastern Mediterranean, and avenues towards optimizing the quality of spatial drought characterization approaches. 

How to cite: Orieschnig, C. A. and Cavus, Y.: Spatial characterization of drought through CHIRPS and a station-based dataset in the Eastern Mediterranean, IAHS-AISH Scientific Assembly 2022, Montpellier, France, 29 May–3 Jun 2022, IAHS2022-372, https://doi.org/10.5194/iahs2022-372, 2022.

Seyhan River Basin has great importance for agricultural production, industry, energy and tourism sectors in Turkey. This study investigates temporal characteristics of meteorological droughts in the river basin at station-scale. Six major droughts were identified lasting 2 years at minimum from the average precipitation time series of 19 meteorological stations over the basin. We have adopted a methodology specifically for the river basin where local meteorological data are limited. The river basin was divided into four sub-basins. Each sub-basin was represented by one meteorological station which has a high correlation with the basin-average precipitation and also covers as many of the major droughts as possible. The Standardized Precipitation Index (SPI) was calculated for the meteorological stations at different time scales. The site-specific drought analysis elucidated the probability of mild, moderate, severe, and extreme droughts. The temporal occurrence illustrates that the river basin has experienced severe prolonged droughts every ten years on average. Mild drought dominates at each time scale and their frequencies increase with increasing time scale although severe and extreme events are observed with a higher probability in some major droughts. A significant change of the probabilities of the drought classes was not found in the representative stations, instead, we observed no consistent change. This analysis presented valuable information for the river basin on the temporal variability of the drought, and also shed light on the need for such analyses for regional drought adaptation and mitigation. Given the limitations that emerged on the determination of the representative stations, it would be advisable to consider additional data (such as remote sensing or satellite) in future studies to gain further insights into the temporal characteristics of drought.

How to cite: Cavus, Y., Aksoy, H., and Stahl, K.: Characterizing major droughts in the context of dry period in Seyhan River basin, Turkey, IAHS-AISH Scientific Assembly 2022, Montpellier, France, 29 May–3 Jun 2022, IAHS2022-276, https://doi.org/10.5194/iahs2022-276, 2022.

Drought is an insidious scourge that results from a decline in precipitation from levels considered normal. The data used cover a period of 118 years (1901-2019) which ensures a good coverage of the studied region. Two approaches (SPI and SPEI) were applied to assess drought in the Volta bassin in Togo. The results show that there has been a decrease in rainfall in the Volta bassin in Togo in recent years. In terms of SPI, 36 years have indices lower than -0.5 and 4 years lower than -1 in the Dapaong station. The longest periods of drought are observed between 1958-1990 or 33 years and 2010-2019 or 10 years. The SPEI show 9 years with an index lower than -0.5 and only one year (2001) with an index lower than -1. The longest droughts occurred during the period 2009-2019, or 10 years, as for the IPS. This shows a trend of aridification of the climate in this area.

How to cite: Somiyabalo, P., Ibouraïma, Y., and Ernest, A.: Modelling of meteorological drought using the SPI and SPEI indices in the Volta watershed in Togo, IAHS-AISH Scientific Assembly 2022, Montpellier, France, 29 May–3 Jun 2022, IAHS2022-176, https://doi.org/10.5194/iahs2022-176, 2022.

This study aims to investigate drought and flooding area in West Africa during the pre-industrial and projected future periods. The datasets used consist of CHIRPS-2 and CRU for observed reanalysis and CORDEX/CMIP6 for climate model scenarios. The CORDEX/ CMIP6’s potential evapotranspiration (PET) and precipitation correlate well with observation dataset over the study area with respective KGE up to 0.75 and 0.9. The pre-industrial period used in this research covers 1971-2000, while the projection period is defined according to the global warming level and the RCPs. Results showed that, the spatial and temporal repartition of SPEIs was elucidated by applying the Empirical Orthogonal Function (EOF) analysis, which showed that during the pre-industrial period, the wettest areas were located at the eastern and southern part of West Africa. The analyses on projected scenarios reveals that most of the coastal countries in Gulf of Guinea will be globally wetter under all the GWLs studied, with some interleaving as coastal countries (Senegal, Ivory-Coast, Benin, Togo and Nigeria). Some years will experiment extreme drought, whilst Savanna will get positive changes, which will lead them to become less dry compare to period 1971-2000. An investigation on the spatial concentration of precipitation using precipitation concentration index (PCI), have involved this study to highline an uniform spatial distribution of annual and wet season precipitations over gulf of Guinea and Savanna, follow by an increasing of uniform and moderate spatial distribution of precipitation under RCP4.5, and negative changes over eastern and western part of the study area for projection RCP8.5, explaining the high variability of concentration of precipitation over these regions.

Keywords: Drought and flood area, climate model, West Africa, global warming

How to cite: Kodja, D. J., Koubodana, H. D., Quenum, G. M. L. D., Amoussou, E., Akognongbé, A. S. J., Mahé, G., Paturel, J.-E., Vissin, E. W., and Houndénou, C.: Investigation of drought and flooding areas in coastal countries of West Africa in the context of global warming, IAHS-AISH Scientific Assembly 2022, Montpellier, France, 29 May–3 Jun 2022, IAHS2022-192, https://doi.org/10.5194/iahs2022-192, 2022.

The 2018 summer drought in Europe was particularly extreme in terms of intensity and impact due to the combination of low rainfall and high temperatures. However, it remains unclear how this drought developed in time and space in such an extreme way. In this study we aimed to get a better understanding of the role of land-atmosphere interactions. More specifically, we investigated whether there was a change in water vapor originating from land, if that caused a reduction in rainfall, and by this mechanism possibly the propagation and intensification of the drought in Europe. We used a global gridded dataset of the fate of land evaporation (i.e., where it ends up as precipitation) to investigate whether the drought intensification and propagation was impacted by the reduction in water vapor transported from the regions that first experienced the drought. It was found that during the onset phase of the 2018 drought in Europe that the water vapor originating from land played an important role in mitigating the precipitation anomalies as, for example, the share of land evaporation contributing to precipitation increased from 27% (normal years) to 38% (2018) during July in West of Europe. Land evaporation played a minor role in amplifying it during the intensification phase of the drought as the share of land evaporation contribution to precipitation decreased from 23% (normal years) to 21% (2018) during August in West of Europe. These findings are somewhat in contrast to similar studies in other continents that found the land surface to play a strong amplifying role for drought development. These results were recently published here: https://doi.org/10.3390/w13202856. Speculating what this case study means for future extreme droughts in Europe, we can at least conclude that for West of Europe the positive feedback loop between drought, soil moisture, vegetation, evaporation and precipitation is still weak even under extreme circumstances, and that probably quite a severe climate changes scenario would be needed to change this.

How to cite: Al Hasan, F., van der Ent, R., and Link, A.: The Effect of Water Vapor Originating from Land on the 2018 Drought Development in Europe, IAHS-AISH Scientific Assembly 2022, Montpellier, France, 29 May–3 Jun 2022, IAHS2022-67, https://doi.org/10.5194/iahs2022-67, 2022.

Climate change will influence the severity and intensity of floods and droughts throughout Europe. Ensemble projections of future changes in discharge show large variation. Several methods for performance-based weighting exist that have the potential to increase the robustness of the change signal. Here we use future projections of an ensemble of three hydrological models forced with climate datasets from the Coordinated Downscaling Experiment - European Domain (EURO-CORDEX). The experiment is set-up for nine river basins spread over Europe that hold different climate and catchment characteristics. We evaluate the ensemble consistency and apply two weighting approaches; (1) the Climate model Weighting by Independence and Performance (ClimWIP) that focuses on meteorological variables and (2) the Reliability Ensemble Averaging (REA) that is in our study applied to discharge statistics per basin. For droughts we focus on the change in discharge during low flow periods of 7-days.

For basins with a strong climate signal, in Southern and Northern Europe, the consistency in the set of projections is large. For rivers in Central Europe the differences between models become more pronounced. Both weighting methods favor projections from similar GCMs and assign high weights to a single or few best performing GCMs. The ClimWIP method results in ensemble mean weighted changes that differ only slightly from the non-weighted mean. The REA method influences the weighted mean more. The weights assigned to the CORDEX model simulations based on basin specific discharges highly vary from basin to basin.

How to cite: Sperna Weiland, F., Visser, R., Greve, P., Bisselink, B., Brunner, L., and Weerts, A.: Performance-based weighting of CORDEX projections of hydrological climate change impacts over Europe, IAHS-AISH Scientific Assembly 2022, Montpellier, France, 29 May–3 Jun 2022, IAHS2022-352, https://doi.org/10.5194/iahs2022-352, 2022.

Droughts are known to be one of the most damaging and costly natural hazards as a result of their large spatial scale, creeping nature and long duration. They have widespread primary and secondary impacts, and as such, proactive drought management is crucial to mitigate those impacts. In order to do so, it is crucial to understand the drought risk – i.e. the characteristics of the drought hazard, who or what is exposed to the drought hazard, and who (or what) is vulnerable to the effects of drought. Drought mitigation is one of five strategic objectives under the United Nations Convention to Combat Desertification (UNCCD) 2018-2030 Strategic Framework, under which a monitoring framework and a range of indicators was agreed by country Parties to the UNCCD.

Here we present new guidance created to help Parties to the UNCCD report on their progress towards Strategic Objective 3 ‘To mitigate, adapt to, and manage the effects of drought in order to enhance resilience of vulnerable populations and ecosystems’. Progress is monitored using three indicators, capturing the three fundamental components of risk: drought hazard, exposure to drought and vulnerability to drought. The three indicators, as agreed by Parties to the UNCCD, are:

• Trends in the proportion of land under drought over the total land area,
• Trends in the proportion of the total population exposed to drought, and
• Trends in the degree of drought vulnerability.

Acknowledging the need for global applicability, the methods recommended to calculate these three indicators balance state-of-the-art science with relative simplicity, whilst also meeting the requirements set out in official UNCCD Decisions, guidelines of the World Meteorological Organization, and where possible utilising datasets used for other reporting activities (e.g. the Sustainable Development Goals). The methods for each indicator are illustrated using contrasting case studies, highlighting the flexibility of the approaches recommended, as well as opportunities for the future of national reporting on drought risk.

How to cite: Barker, L., Rickards, N., Sarkar, S., Hannaford, J., Magee, E., and Rees, G.: Assessing drought risk to track progress in drought adaptation, mitigation and management at the global scale, IAHS-AISH Scientific Assembly 2022, Montpellier, France, 29 May–3 Jun 2022, IAHS2022-674, https://doi.org/10.5194/iahs2022-674, 2022.

The city of Grahamstown in the Eastern Cape Province of South Africa has been experiencing an extended period of below average rainfall for more than 7 years. The public perception of this drought is that it could be a consequence of climate change and represents the new ‘normal’ for this area. This study looks at this drought in the context of daily rainfall records extending back to the start of the 20^th century. The rainfall data are analysed in several ways to determine if this drought is really exceptional and to try and identify any unique characteristics of the recent drought period. The analyses are all relatively simple non-statistical methods, largely because statistical trend tests are considered by the author to frequently suggest results that are more artifacts of the data analysis methods than real, particularly in data sets that show cyclical trends (frequently shown to be one of the key characteristics of South African rainfall data).  

A relatively simple analysis using the cumulative departure of monthly rainfall totals from the calendar month means shows a systematic downward slope since 2014 (Figure 1). However, there was a similar general downward trend between 1940 and 1960, as well as between 1980 and 1990, suggesting that, from this perspective, the current period is not exceptional. A comparative analysis using a similarly long rainfall record for a farm located in a drier area, but only 20 km from the city, shows a relatively different pattern of historical rainfall variations.

Other types of analysis using different rainfall characteristics show different things. The rainfall data for over 120 years are also used to force a hydrological model to generate simulated streamflow, groundwater recharge and soil moisture storage to further investigate the drought characteristics from a broader perspective than simply the rainfall data themselves. The rainfall data are also used to simulate the performance of a domestic rainwater storage tank to investigate the feasibility of using household level interventions to mitigate against deficiencies in the municipal water supply.    

How to cite: Hughes, D.: Anatomy of an extended drought in part of the Eastern Cape Province, South Africa, IAHS-AISH Scientific Assembly 2022, Montpellier, France, 29 May–3 Jun 2022, IAHS2022-147, https://doi.org/10.5194/iahs2022-147, 2022.