Book of Extended Abstracts. International Symposium on Drought and Climate Change, 24–25 November 2022

Abstract:

The International Symposium on Drought and Climate Change was organized within the frame-work of the NCN SHENG project HUMDROUGHT (humdrought.igf.edu.pl), by the Hohai University (China) and the Institute of Geophysics, Polish Academy of Sciences (Poland). The meeting was held online from 24–25 November 2022. 
    During the symposium, 4 Keynote and 19 standard Speeches were presented by representa-tives of 11 countries, namely: China, Columbia, Ethiopia, Germany, India, Iran, Italy, Nether-lands, Poland, Spain, and Tunisia. The number of participants in the Symposium reached al-most 50.
    Drought-related issues have been discussed, focusing on multiple spatiotemporal scales to pin-point global to continental trends, as well as showing how drought affects specific countries and catchments.
    The abstracts collected here touch on multiple topics and techniques, such as: i) drought change assessment, ii) drought propagation, iii) soil moisture and ecological drought, iv) drought monitoring and modelling, including the use of remote sensing, v) human effects on drought development and propagation, vi) drought prediction and uncertainty analysis.

Abstract:

Climate change will increase in frequency and intensity of period with below than normal precipitation. During such periods, known as meteorological droughts, the decline in annual run-off may be proportionally larger than the corresponding decline in precipitation. Reasons behind this exacerbation of runoff deficit during dry periods remain largely unknown, and this challenges the predictability of when this exacerbation will occur in the future and how intense it will be. In this presentation I will discuss the role played by evaporation and subsurface storage in the propagation of the meteorological drought as well as processes related to the amplification and recovery of such phenomena. Understanding this has important implications for defining sustainable water management strategies and understanding potential ecological traits and is becoming more and more urgent due to the increasing frequency and magnitude of drought events like the one that has hit Italy in 2022.

Abstract:

Flash drought is a space-time phenomenon with rapid intensification which poses serious threats to terrestrial ecosystems. However, the understand of flash drought propagation under climate change and regional human activities is still insufficient, and its potential causes remain unresolved. To explore this key issue, an integrated framework is proposed to describe the drought propagation process in the Yangtze River Basin, and trend and attribution analyses are utilized to explore potential influence fac-tors. The framework is conducive to better understanding of flash drought processes and provides scientific guidance for flash drought early warning, prevention and mitigation.

Abstract:

Drought occurs due to the accumulative effect of certain climatological and hydrological variables over a certain period. As droughts are becoming a frequent phenomenon also in regions generally not affected by them, they are becoming a significant research topic, also thanks to the development of advanced monitoring methods and models. Focusing on the Vistula basin in Poland, the present work investigates changes in drought indexes and connected metrics by analysing satellite data. The use of satellite information allows for deriving trends at the watershed scale, therefore providing spatially-distributed medium/long-term changes. The present analysis takes advantage of the potentiality of Google Earth Engine and its freely-available datasets, showing that nowadays drought is a major concern also for a region that used to be wetter in the past.

Abstract:

This study is an attempt to determine the spatial-temporal pattern of meteorological droughts and exploration of the relationship between drought and elevation over Indus River basin. Gridded monthly precipitation and temperature data of 0.12°×0.12° spatial resolution for a time period of 42 years (1979–2020) is utilized. Modified Mann-Kendall test and Sen’s slope method have been used to identify significant trends in the region. Drought events are identified based on Standardized Precipitation Evapotranspiration Index (SPEI) by determining of SPEI-annual and SPEI-seasonal (pre-monsoon, monsoon, post-monsoon, and winter). Results show that the trends in the drought indices have very high heterogeneity across different seasons. Overall, 13% (14%) stations show drying (wetting) trends for annual time series analysis. However, seasonally, it is found that monsoon and post- monsoon seasons have larger area in the basin with wetting trends. Moreover, pre-monsoon season have larger area with drying trends. A correlation between SPEI trends with respect to elevation is observed.

Abstract:

Agricultural drought threatens global water security, food security, and human well-being. Accurate identification of agricultural drought is the premise of all work. However, it is currently challenging to achieve relatively reliable and accurate assessments using remote sensing data products. We selected soil moisture datasets from GLDAS, FLDAS, ERA5-land, and MERRA-2, precipitation from GPCC, and vegetation conditions from NDVI. Drought Severity Index (DSI), Soil Moisture Anomaly index (SMA), Standardized Precipitation Index (SPI), and Vegetation Condition Index (VCI) were calculated separately in regions with different wet and dry conditions. The objective was to find relatively reliable and accurate product and drought index by cross-validation, then apply them to agricultural drought assessment in nine agricultural regions of China. The results showed that: (1) Under different wet and dry conditions, the DSI calculated using GLDAS showed good performance in identifying agricultural drought; (2) The northern arid and semiarid region, the Northeast Plain, the Huang-Huai-Hai Plain, and the Loess Plateau frequently experienced moderate and severe agricultural droughts, especially in the region of the boundaries. Besides, the northern part of Qinghai-Tibet and the northwest region of the Yunnan-Guizhou Plateau, all with a frequency of about 20%; (3) Agricultural droughts in the agricultural regions of northern China have significantly slowed in the last 20 years, both the Yunnan-Guizhou plateau and Southern China have shown a significant increasing trend since 2002. Future agricultural droughts in the humid south need to receive more attention. This paper could help to better understand China’s agricultural drought and could provide a method for agricultural drought assessment in regions without observational data.

Abstract:

CMIP6 and single model initial-condition large ensemble (SMILE) simulations are applied to find possible changes in the ratio of coverage (ROC) of extreme precipitation in China. Related results indicate that trend of ROC in the period 1961–2020 for China is underestimated by CMIP6 multi-model ensembles. Then, further analyses point out that the accuracy of model simulations to reveal a trend in observation has been improved based on the two observation constraint approaches and the SMILE-based approach. In addition, the reliability of spatial distribution has also been enhanced. Projected results indicate that ROC increases with the increment of global warming across different approaches. Among them, results based on observation constraint approaches and SMILE-based approach, which show enhanced accuracy and reliability, present larger ROC than directly using CMIP6 ensembles. Thus, it can be concluded that extreme precipitation will be more widespread in China combined with multiple evidence and methods.

Abstract:

Satellite-based observations of soil moisture, leaf area index, precipitation, and evapotranspiration, facilitate agro-hydrological modeling thanks to the spatially distributed information. In this study, the Climate Change Initiative Soil Moisture dataset (CCI SM, a product of the European Space Agency (ESA)) adjusted based on Soil Water Index (SWI) was used as an additional (in relation to discharge) observed dataset in agro-hydrological modeling over a large-scale transboundary river basin (Odra River Basin) in the Baltic Sea region. This basin is located in Central Europe within Poland, Czech Republic, and Germany and drains water into the Baltic Sea. The Soil and Water Assessment Tool+ (SWAT+) model was selected for agro-hydrological modeling, and 26 discharge stations and soil moisture (for topsoil and entire soil profile) were calibrated for 1476 sub-basins during 1997–2019. Kling–Gupta efficiency (KGE) and SPAtial EFficiency (SPAEF) were chosen as objective functions for runoff and soil moisture calibration, respectively. Two calibration strategies were compared: one involving only discharge data (single-objective), and the second one involving discharge and satellite-based soil moisture (multi-objective). In the single-objective approach, the average KGE for discharge was above 0.60. In the multi-objective approach, the accuracy for the main discharge stations significantly increased (KGE above 0.67) compared to the single-objective approach. The results show that in this transboundary river basin, adding satellite-based soil moisture into the calibration process could improve the accuracy and consistency of agro-hydrological modeling.

Abstract:

Anthropogenic factors contribute to the uneven distribution of hydrological droughts and differences in the duration and magnitude of hydrological drought in upstream and downstream areas. This study assesses how reservoir storage and water demand intensify or mitigate hydrological drought in the Shaying River basin in China. The study uses “downstreamness” as a concept to show the effect of a reservoir network on hydrological drought. For the period 1990–2018 we show that when water storage is unequally distributed between upstream and downstream areas the spatial distribution of hydrological drought also differed across upstream and downstream regions. Moreover, water demand also clearly influenced hydrological drought. Furthermore, we show a significant decreasing trend of water storage and outflow in studied reservoirs while the rates of precipitation and evaporation did not indicate a significant decreasing trend. This finding clearly shows the dominant role of human activities in intensifying hydrological drought and how this is distributed between upstream and downstream parts of a river basin. As such, this study provides useful insights that can support policymakers in formulating and evaluating drought and water policies at the river-basin scale, thus targeting solutions for both upstream and downstream areas.

Abstract:

With the aggravation of climate change, drought has become a more prominent extreme event with significant influences on both natural ecosystems and human society. The IPCC AR6 new results show that the changes in meteorological and agricultural droughts display an increasing trend in some regions. And the increasing trend shows that anthropogenic climate change plays an important role in exacerbating agricultural and ecosystem droughts. The atmospheric evaporation demand (AED) is a key variable in addressing drought change. Changes in AED are not only a direct response to climate warming, but also a driving factor for drought changes, affecting the physiological processes of vegetation.
    In assessment of drought changes and their impacts, the selection of drought indices is crucial. Our study explored changes in drought condition over China and evaluated the effectiveness of four different drought indices (SPEI, SPI, MCI, and PDSI) in reflecting drought change. Four drought indices all displayed “drying trend” in North, Northeast, and Southwest China during 1961–2019. The above four indices consistently show better performance in the Middle and Lower Reaches of the Yangtze River, and in western Northwest, Northeast, and South China.

Abstract:

Satellite products such as normalized difference vegetation index (NDVI), the fraction of vegetation cover (FVC), and evapotranspiration are worth to drought assessment and alert. We consider time series of SPOT vegetation NDVI and FVC, as well as Satellite Application Facility on Land Surface Analysis (LSA SAF), reference evapotranspiration ET₀ to estimate potential evapotranspiration E_p at 3 km resolution and 10-days’ time step in northern Tunisia. In addition, based on satellite LSA SAF observations of actual evapotranspiration E, we produce maps of the ratio E/E_p or relative productivity. To analyze drought conditions, we consider the time horizon from January to May relevant for cereal crops. Resulting relative productivity maps are then compared to field evidence relative to areas damaged by drought. Bias correction method is then used to correct relative productivity cumulative distribution. Results show that two thresholds are required to correct relative productivity maps to assign zero for low levels and one for high levels of relative productivity. In addition, quantile-quantile regression is worth completing relative productivity map correction.

Abstract:

The recent drought events highlighted the impacts caused by hydrological drought and low-flow events to society and ecosystems. In Germany, some rivers even dried out during the drought events of 2018, 2019, and 2022 causing massively damages to the ecosystem. Also, the impact on the economy due to restrictions on water use is immense. In this work we present a conceptual approach for a holistic low-flow risk analysis as base for an effective risk management including risk acceptance, transparent evaluation of mitigation measures and communication. The low-flow risk combines probabilities and consequences of low-flow events on a (sub-)catchment scale. However, the risk analysis is based on synthetic long-term time series (continuous risk modelling), as these appear to be more suitable for low-flows than scenario-based simulations, which are well known from flood risk analysis. The holistic approach requires a representation of all relevant processes, starting from weather generation, the hydrological and hydrodynamic response, and the consequences to society and ecosystems. 

Abstract:

The process of propagation of low flows is studied in the River Vistula in Poland. A history of low flow events in the basin is derived on the basis of statistical analysis of flow measured at 15 gauging stations located along the river and in 12 stations on its main tributaries in the 1951–2018 period. The main characteristics of low flows: minimum flow, duration and deficit of flow are calculated and analysed (at-side trend analysis, variability with the course of the river). On this base the most severe low flows are listed at each gauging stations and on the Little, Upper, Middle, and Lower Vistula reaches. The method of QdF (flow-duration-probability) was used to estimate the flow non-exceeded in d-days with the probability 50% and the index of low flow dynamics D. The results are compared in time and along the river. The exposure to drought are examined in terms of temporal and spatial aspects. 

Abstract:

Time series clustering is an important field of data mining and can be used to identify interesting patterns. This study introduces a new way to obtain clusters of time series by representing them with feature vectors that define the trend, seasonality and noise components of each series, in order to identify areas of the Iberian Peninsula that follow the same pattern of change in their maximum temperature during 1931–2009. Singular spectrum analysis decomposition in a sequential manner is used for dimensionality reduction, which allows the extraction of the trend, seasonality and residual components of each time series corresponding to an area of the Iberian region; then, the feature vectors of the time series are obtained by modelling the extracted components and estimating the parameters. Finally, the series are clustered using a clustering algorithm, and the clusters are defined according to the centroids. The results identified three differentiated zones, allowing to describe how the maximum temperature varied: in the north and central zones, an increase in temperature was noted over time, and in the south, a slight decrease, moreover different seasonal variations were noted according to zones.

Abstract:

In the Anthropocene, droughts cannot be considered as natural phenomena/ hazards. Therefore, it became crucial to assume human impacts and their interactions with the water system in drought vulnerability assessment through the concept of the socio-hydrology. We applied the socio-hydrological approach for identifying drought-vulnerable areas in the Vistula River basin. The Soil and Water Assessment Tool (SWAT) model was used to derive missing hydro-climatic variables, such as soil moisture at sub-basins and hydrological response unit level. The vulnerability indicator was selected based on the statistical significance of the factors affecting the water resources and socio-economics of the drought-prone. The preliminary results showed that the middle part of the Vistula catchment is more exposed to drought than the upper and lower parts of the main river course.

Abstract:

In the last decade, uncertainty in drought assessment studies has received increasing attention in the hydrometeorological research community. Spatio-temporal characteristics of drought are affected by uncertainties resulting from the calculation of standardized drought indices. To the best of our knowledge, no studies have been conducted so far on the impact of these uncertainties on the assessment of the spatial extent of droughts. In the present study, the uncertainty of determining the spatial extent of meteorological drought in individual classes is investigated for various probability distributions and the accumulation time scale used for determination of the Standardized Precipitation Index (SPI). In the studies, the E-OBS daily gridded precipitation data for the Vistula catchment in Poland were used along with four parametric distribution functions (Birnbaum-Saunders – BS, Weibull – WEI, Generalized Extreme Value – GEV, and Gamma – GAM) and nonparametric approach. Preliminary results indicate significant discrepancies in the spatial extent of individual drought category indicating higher uncertainty in determining the areas affected by severe and extreme droughts.

Abstract:

Groundwater resources in many regions are not immune to climate change. More attention is being paid to the role of groundwater in maintaining ecological flows in rivers during a drought due to decreased precipitation and snowmelt under climate change. Karst aquifers are vulnerable to the increasing occurrence of climate extremes events. This abstract will give an overview of some modern approaches which are used in the assessment of the climate change impact on the karst groundwater. Methods include GIS implementation and remote sensing tools which can contribute to local, regional, and global scale research. Combining the modern research tools with traditional, in-situ obtained data, can lead to more reliable results and more sustainable water management in the future.