Abstract
Assessing agricultural drought is of great importance as it is viewed as the most serious problem in most
countries in terms of food security, economy, and social stability. Various drought indices have been
developed in order to describe the characteristics of drought such as severity, extent, frequency and
duration. These indices can be classified into two categories: ground-based and remotely-sensed indices.
Ground-based drought indices are more accurate but limited in coverage, while remote sensing drought
indices cover large areas but have poor precision. Therefore there is need to apply advanced data fusion
methods based on satellite data and ground-based drought indices to fill this gap. However there is a lag
time between drought events and the impacts they cause.
Due to the semi arid conditions of Botswana, the country is prone to the occurrence of droughts and has
a great influence on agriculture and economy of the country at large. In order to monitor droughts in
Botswana this paper proposes that it is necessary to link the pre meteorological observations and the
consequential vegetation drought. This is neededed for effective monitoring of agricultural drought and
early warning. In this study, MODIS reflectance data and data from recent satellites such as landsat OLI,
Sentinel will be used to discover relationships between vegetative drought and meteorological drought
using vegetation condition index (VCI) derived from NDVI and NDWI, and meteorological drought
derived from SPI and SPEI in Botswana. Dataset derived from Soil Moisture Active Passive (SMAP)
will be used to generate %soil moisture content. The %moisture content will be compared with
experimental results from the field. Pearson correlation analyses were performed between single remote
sensing drought indices and in-situ drought indices, NDVI and SPEI. Preliminary studies show that VCI
derived from NDWI (VCI-2) over Southern District of Botswana can be used as an approach to monitor
and provide early warnings. However, there is weak correlation SPEI and VCI-1 and VCI-2 ranging
from -1 to 0.2.

How to cite: Matsuokwane Manyothwane, T. and Mengistu Tsidu, G.: Dryland land crop yield sensitivity to drought in Botswana: Development ofstatistical tools based on satellite remote sensing, observation and climate models foruse in risk assessment, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-3481, https://doi.org/10.5194/egusphere-egu23-3481, 2023.

There exist well known relations between Precipitable Water Vapor (PWV) and extreme rainfall which are of prominent importance in the context of climate change. These relations, however, are mostly established in mid-latitudes and for flat terrain. Ethiopia, however, is located in the tropics and features a complex orography, both of which may modulate these relations. We investigate PWV and extreme precipitation over Ethiopia by use of Regional Climate Models (RCMs) from the Coordinated Regional Climate Downscaling Experiment (CORDEX). We first evaluate the RCMs by comparing their annual PWV cycles with the ones obtained from Global Positioning System observations and reanalysis in the past. Additionally, we focus on the behaviour of PWV before and after a heavy-rainfall event. It is found that there are two characteristic timescales, both for the build-up and for the decline around the event of the heavy precipitation: a timescale of about 2 days and a longer timescale that extends beyond ten days which seems unreported in the literature. The RCMs are capable of reproducing the PWV annual cycle and the spatial variability. However, there is a predominantly dry bias that strongly increases with elevations. The RCMs reproduce well the spatial differences of the PWV anomaly peak during a heavy-rainfall event but overestimate the timescales of build-up and decline. Future PWV-changes scale linearly with the near-surface temperature changes at a rate of 7.7% per degree warming and locally increase up to 40% for the end-of-the-century RCP8.5 scenario. Changes in rainfall extremes, on the other hand, do not follow this trend especially in north-western Ethiopia, potentially caused by an overall decrease in rainfall in that region.

How to cite: Van Schaeybroeck, B., Kawo, A., Van Malderen, R., and Pottiaux, E.: The use of regional climate models for estimating past and future precipitable water vapor and extreme precipitation over Ethiopia, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-2428, https://doi.org/10.5194/egusphere-egu23-2428, 2023.

The response of the hydrological cycle to global warming is one of the greatest concerns of climate change. Especially, extreme precipitation can lead to severe physical and economic impacts on human and natural systems. Though extreme precipitation is expected to increase over many land areas an important question remains: which factors drive the uncertainty in extreme precipitation? Answering this will help better understand, prepare for, and ultimately, predict future extreme precipitation. 

In this study, we use a scaling approach for extreme precipitation events developed by O’Gorman and Schneider (2009) to disentangle the thermodynamic and dynamic contributions to these events. Extreme precipitation is scaled by the vertical integral over the product of the vertical velocity (ω; dynamic contribution) and the derivation of the saturation specific humidity (; thermodynamic contribution): . 

We apply this scaling approach to a subset of the CORDEX-FPS ensemble and focus on change signals of seasonal extremes of daily precipitation for two 10-year periods (2090-2099 vs 1996-2005). By keeping either the first term or the second term in the formula constant over the entire time period we obtain the thermodynamic and dynamic signal, respectively. The thermodynamic signal is quite homogeneous over the domain, approximately in the order of Clausius-Clapeyron scaling (~ 7%/K), while the dynamic signal modifies the thermodynamic signal. Thus, the dynamic contribution, which is represented by vertical wind, is key in understanding differences between models and uncertainty in precipitation changes. The vertical wind profiles show, especially for summer, that the vertical winds during extreme events weaken in the future period compared to the historical period. This seemingly counterintuitive result could be due to more downdrafts leading to extreme precipitation in the future period instead of updrafts. However, a comprehensive interpretation is the subject of ongoing research.

How to cite: Ritzhaupt, N., Sobolowski, S. P., and Maraun, D. and the the CORDEX Flagship Pilot Study on Convection over Europe and the Mediterranean – ensemble: Applying a scaling approach for extreme precipitation to disentangle thermodynamic and dynamic contributions to CORDEX-FPS simulations​, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-12221, https://doi.org/10.5194/egusphere-egu23-12221, 2023.

Extreme precipitation events are responsible for severe damage to various aspects of human society and ecosystems. Short-term extremes especially affect people in urban areas through flash floods. Extremely heavy precipitation is increasing in frequency and intensity due to global warming and Regional Climate Models (RCMs) of high-resolution are needed to estimate associated increased risks. However, even the RCMs that explicitly resolve deep convection are known to significantly underestimate subdaily precipitation extremes. Impact modellers and other users of climate projections therefore often use some form of bias correction. 

In this study, we propose bias adjustment methods especially designed for the estimation of future subdaily extreme precipitation return levels. These methods take into account the scaling intensity-duration-frequency (IDF) relationship between different levels of accumulation, and jointly estimate extreme rainfall over multiple rainfall durations (i.e. from hourly to multi-day extreme precipitation events). After comparison with established methods, we identify only one method that preserves the scaling IDF relationship, which is a necessary condition to have bias-adjusted return levels consistent among the different durations. A comparative analysis in a multi-model pseudo-reality setting shows that this method is superior to existing bias adjustment methods.

Finally, future projections of bias-adjusted subdaily precipitation return levels for Belgium are obtained in the form of an ensemble of 28 EURO-CORDEX simulations at 0.11° spatial resolution, under the RCM8.5 emission scenario.

How to cite: Van de Vyver, H., Van Schaeybroeck, B., De Cruz, L., Hamdi, R., and Termonia, P.: Improved bias-adjustment methods for subdaily precipitation extremes, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-3516, https://doi.org/10.5194/egusphere-egu23-3516, 2023.

Understanding the impact of orography on the probability distribution of extreme precipitation at short (i.e., sub-daily) temporal scales, as well as on extreme-rainfall causative processes, is critical for managing risk from rainfall-triggered natural hazards in mountainous regions. High-resolution convection-permitting models (CPMs) are crucial for this type of analysis since they better represent convective processes key to short-duration extremes.

Here, we assess the ability of multi-model CPM ensemble CORDEX-FPS to represent the upper tail of sub-daily precipitation in a complex-orography region in the Eastern Italian Alps. In this area, different orographic impacts on sub-daily precipitation upper tail were reported at different event durations, and significant temporal trends in precipitation intensity were reported during the last few decades, making it a challenging and interesting test case for CPM simulations. An ensemble of six CPMs with a horizontal grid spacing of ∼2.2 km, driven by ERA-Interim reanalysis, are analysed and evaluated against ∼180 rain gauges. Since CPM simulations are too short (10 years) for analysing extremes using conventional methods, we use a non-asymptotic statistical approach (Simplified Metastatistical Extreme Value, SMEV), which was proven to provide reliable results even using short time records. We explore how the model spread vary with elevation and the ability of the multi-model mean to reproduce the distribution parameters and the extreme quantiles up to 100-year return period at different elevations.

How to cite: Correa Sánchez, N., Dallan, E., Marra, F., Fosser, G., and Borga, M.: Impact of orography on sub-daily precipitation upper tail from convection-permitting climate model simulations: a multi-model ensemble perspective, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-14134, https://doi.org/10.5194/egusphere-egu23-14134, 2023.

The intensity of precipitation extremes across Europe is expected to increase through the 21^st century under a warming climate . Current coarse-resolution global climate models broadly project increased variability of both wet and dry extremes; however, they rely on parametrizations schemes of crucial processes controlling extreme precipitation such as convection. These methods often introduce errors and thereby induced uncertainties in projections of extremes in the water cycle that are relevant for policy makers and infrastructure planning. The need for accurate extreme event information on such extremes became further evident after the July 2021 floods (Ibebuchi, 2022) and summer 2022 record-breaking heatwaves/drought across Western Europe.

The ongoing H2020 Next Generation Earth Modelling Systems (NextGEMS) project aims to address these issues with the development of fully-coupled storm-resolving Earth-System Models. Using some of the first runs of the Integrated Forecast System (IFS) from ECMWF and ICON from MPI-M at 4 km and 5 km horizontal resolution respectively, we examine individual extreme precipitation events across Europe and evaluate their representation against similar analogues in the Copernicus European Regional Reanalysis (CERRA) and observational datasets. The unprecedented high resolution of the fully-coupled Storm-Resolving Models and CERRA allows for an evaluation of precipitation characteristics in complex terrain like the Alps (Hughes et al., 2009) or complex coastlines. We first evaluate the spatial and temporal structure of the events, compare their representation to coarse-resolution GCMs and then examine the potential drivers such as atmospheric river using integrated moisture transport and vertical structure of the low-level jet (Swain et al., 2015).

Hughes, M., Hall, A., & Fovell, R. G. (2009). Blocking in Areas of Complex Topography, and Its Influence on Rainfall Distribution. Journal of the Atmospheric Sciences, 66(2), 508–518. https://doi.org/10.1175/2008JAS2689.1

Ibebuchi, C. C. (2022). Patterns of atmospheric circulation in Western Europe linked to heavy rainfall in Germany: preliminary analysis into the 2021 heavy rainfall episode. Theoretical and Applied Climatology, 148(1), 269–283. https://doi.org/10.1007/s00704-022-03945-5

Seneviratne, S.I., X. Zhang, M. Adnan, W. Badi, C. Dereczynski, A. Di Luca, S. Ghosh, I.

Iskandar, J. Kossin, S. Lewis, F. Otto, I. Pinto, M. Satoh, S.M. Vicente-Serrano, M. Wehner, and B. Zhou, 2021: Weather and Climate Extreme Events in a Changing Climate. In Climate Change 2021: The Physical Science Basis. Contribution of Working Group I to the Sixth Assessment Report of the Intergovernmental Panel on Climate Change [Masson-Delmotte, V., P. Zhai, A. Pirani, S.L. Connors, C. Péan, S. Berger, N. Caud, Y. Chen, L. Goldfarb, M.I. Gomis, M. Huang, K. Leitzell, E. Lonnoy, J.B.R. Matthews, T.K. Maycock, T. Waterfield, O. Yelekçi, R. Yu, and B. Zhou (eds.)]. Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA, pp. 1513–1766, doi:10.1017/9781009157896.013.

Swain, D. L., Lebassi-Habtezion, B., & Diffenbaugh, N. S. (2015). Evaluation of Nonhydrostatic Simulations of Northeast Pacific Atmospheric Rivers and Comparison to in Situ Observations. Monthly Weather Review, 143(9), 3556–3569. https://doi.org/10.1175/MWR-D-15-0079.1

How to cite: Wille, J. and Fischer, E.: Dynamical representation of extreme precipitation events in storm resolving global climate models within the NextGEMS project, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-8455, https://doi.org/10.5194/egusphere-egu23-8455, 2023.

This contribution discusses future changes in Gulf Stream temperatures, winter precipitation over northwestern Europe, and their connection. We compare HighResMIP historical and ssp5-8.5 scenario simulations generated with five different configurations of the global coupled model HadGEM3-GC3.1, including one at a pioneering 50-km-atmosphere–1/12°-ocean global resolution. The highest resolution model projects an increase in winter rainfall over Europe outside or to the extremes of multimodel ensembles, such as CMIP6 and HighResMIP, for which both the highest ocean and atmosphere resolutions are essential: on the one hand, only the eddy-rich ocean (1/12°) projects a progressive northward shift of the Gulf Stream and substantial surface warming of the region; on the other, only the 50-km atmosphere translates such warming into strengthened extratropical cyclone activity over the North Atlantic and, hence, increased rainfall over Europe. The results suggest that climate projections relying on traditional ~100-km-resolution models might underestimate climate changes in the North Atlantic and Europe, demonstrating the importance of improved Gulf Stream representation for robust uncertainty estimates of climate risk.

We also present the first results of the STREAM project, which aims to study the role of the ocean mesoscale in driving North Atlantic and European climate variability and predictability. We describe the results of the HighResMIP simulations generated with the EC-Earth global climate model at the T1270-ORCA12 resolution (about 15 km in both the atmosphere and the ocean) and explore the main model biases and response to climate change, as well as the variability in the North Atlantic circulation associated with subpolar oceanic deep mixing. 

How to cite: Moreno-Chamarro, E., Caron, L.-P., Ortega, P., Loosveldt Tomas, S., Roberts, M. J., Carreric, A., Frigola, A., and Martín Martínez, E.: Linking future Gulf Stream warming and increased European winter precipitation in an eddy-rich model, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5185, https://doi.org/10.5194/egusphere-egu23-5185, 2023.

Precipitation is commonly analysed from an Eulerian perspective, in which rainfall is considered at a fixed location. Lagrangian analysis of precipitation represents an alternative approach. Here, precipitation objects – for example, convective cells – are identified in a precipitation field and are then tracked through space and time, allowing object properties over the whole life of a convective cell to be collected. This approach offers additional insights into the mechanisms by which convective cells develop and behave across their lifecycle, which would not be evident from standard analysis methods.

In this study, we perform Lagrangian analysis of convective cells under different large-scale circulation regimes. Tracking is based on convection-permitting simulations with the COSMO-CLM at 0.025° resolution over central Europe. All identified precipitation objects are tracked through space and time, collecting cell characteristics for each object, e.g. cell area, intensity, distance travelled, etc. Here we associate precipitation objects with categorical synoptic-scale circulation patterns and compare the cell properties between the different categories.

How to cite: Meredith, E. P., Ulbrich, U., and Rust, H. W.: Lagrangian analysis of convective rainfall under different synoptic forcing, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4462, https://doi.org/10.5194/egusphere-egu23-4462, 2023.

Rainwater drainage systems and other hydraulic infrastructure are scaled considering the intensity of precipitation and its probability of occurrence. The estimation of precipitation intensity through the analysis of the frequency of occurrence of extreme precipitation events is a key instrument for the dimensioning of hydraulic infrastructures and the associated risk of collapse. Sub- or over-estimated rainfall intensities can cause significant problems in various types of hydraulic infrastructures, including flood mitigation and support works due to flooding.

The aim of this study is to determine how climate change will influence extreme rainfall and, consequently, the future sizing of hydraulic systems, including rainwater drainage and hydraulic passages. Towards this aim, the Intensity-Duration-Frequency (IDF) curves were computed (durations between 24 and 72 hours), considering the historical period between 1950 and 2001, and for future precipitation projections (ensemble of biased-corrected Regional Climate Models, RCMs). The period 2041‒2070 under the RCP8.5 (Representative Concentration Pathways) and 2071‒2100 under the RCP4.5 and RCP8.5 emission scenarios were analyzed for 25 udometric stations studied in Brandão et al. (2001 and 2004) located in mainland Portugal.

Results show an increase in precipitation intensity, however, the differences between the projected IDF and those obtained with observed data (ERA5 dataset) for the 2, 5, 10, 20, 50, and 100 years return periods are not spatially uniform. The outcomes reveal North/South contrasts between the station’s IDFs, being also quite apparent in the influence of the orography.

Overall, this study is the first approach to the problem of extreme rainfall in a changing climate, due to the severe consequences of sudden floods and the resilience of territories and their hydraulic infrastructures to these extreme events. Therefore, planning of new policies and the dimensioning of new and existing infrastructures in the medium and long term is thus highly relevant.

Acknowledgment: This work was supported by National Funds by FCT - Portuguese Foundation for Science and Technology, under the project UIDB/04033/2020.

Keywords: Climate change, IDF curves, Hydraulic passages, Extreme precipitation, Drainage systems, Portugal.

How to cite: Andrade, C., Mourato, S., Guimarães, R., and Brandão, C.: Climate change scenarios for IDF curves for mainland Portugal, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-13995, https://doi.org/10.5194/egusphere-egu23-13995, 2023.

Recent extreme heat events, especially those that have occurred in the Western United States (WUS), are fueling wildfires and funneling smoke at an unprecedented level, impacting air/water quality and leading to an increase in respiratory hospitalizations. Under greenhouse warming, extreme weather conditions that favor wildfire ignition are expected to occur more frequently over the contiguous United States (CONUS). Therefore, predicting wildfire danger under a changing climate is essential in managing future wildfires and protecting the welfare of people and the environment. In response to mitigating wildfire risks, the Canadian Fire Weather Index (FWI) was developed to provide a numeric rating representing the intensity of a spreading fire. In this work, we utilized fine-scale (0.25° x 0.25°) daily meteorological inputs from thirty-five general circulation models in NASA Earth Exchange Global Daily Downscaled Projections Coupled Model Intercomparison Project Phase 6 (NEX-GDDP-CMIP6) data to calculate the FWI. Using the daily maximum temperature, relative humidity, wind speed, and precipitation from NEX-GDDP-CMIP6, we calculated the FWI of historical and future simulations from the periods of 1950 to 2100 under different emission scenarios (Shared Socioeconomic Pathways 2-4.5 and 5-8.5). We have analyzed the FWI for the GISS-E2-1-G model, which indicates a 2-3% increase per decade in future fire danger under both emission-pathway-driven climate scenarios during the dry season in the Southwestern US. We have found that the FWI climatology in the Southwestern US during the Summer presents high to extreme fire danger (> 50) and higher FWI values in the future compared to historical observations. Moreover, we have explored the uncertainties across multiple models using NEX-GDDP-CMIP6 statistically downscaled data and found a significant spread of the FWI across the models for historical observations and future simulations. To correlate the link between the FWI and actual fire occurrence, we will calculate the FWI using reanalysis data (MERRA-2) and validate the FWI with actual fire occurrence data from Global Fire Emissions Database (GFED) with a special emphasis on the WUS. While supporting the US NCA and NASA’s Climate Adaptation Service Investigator (CASI), we will also try to contribute FWI to NASA’s FireSense, an initiative to bring an Earth systems approach to improving wildfire and wildland fire management.

How to cite: Madrazo, M. K., Lee, H., Khodayari, A., Wang, W., Park, T., and Raymond, C.: The impact of climate change on fire danger over the contiguous United States, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-16986, https://doi.org/10.5194/egusphere-egu23-16986, 2023.