Displays

The turbulent shear stress and momentum regimes dominate and drive the energy exchange mechanisms among the hydrometeorological processes in the atmospheric boundary layer. To seek for stochastic analogies among the latter, Dimitriadis (2017) studied the observed variability of key hydrometeorological processes in local and global scale under the stochastic framework of the Hurst-Kolmogorov dynamics. It is found that several stochastic similarities exist in both the marginal and dependence structures of the examined processes. This conclusion permits the development of an integrated stochastic view of the atmospheric dynamics in the boundary layer as compared to traditional deterministic approaches. Finally, a robust algorithm for the explicit stochastic synthesis of the above processes from fine to large scales is presented and the merits and limitations compared to other existing methods are discussed.

Dimitriadis, P., Hurst-Kolmogorov dynamics in hydrometeorological processes and in the microscale of turbulence, Ph.D. thesis, Department of Water Resources and Environmental Engineering, School of Civil Engineer, National Technical University of Athens, 2017.

How to cite: Dimitriadis, P. and Koutsoyiannis, D.: Analogies in stochastic behaviour from the microscale of turbulence to the large-scale hydrometeorological processes under the Hurst-Kolmogorov dynamics, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-19367, https://doi.org/10.5194/egusphere-egu2020-19367, 2020

For most hydroclimatic applications, precipitation and temperature are of particular interest for modeling purposes and future projections. Both variables strongly affect the water cycle, they can easily be measured and have the benefit of typically being readily available from many meteorological stations worldwide. In order to account for precipitation and temperature variability, their interdependence and their physical correlation, several multivariate analysis methods have been adopted in the hydroclimatic literature in recent years. In fact, the total number of papers published per year has nearly doubled from roughly 300 per year in 2010 to nearly 600 per year in 2018. In line with this increasing use of multivariate methods, the notion of Copula-based probability distribution has also attracted tremendous interest to deal with the complexity of compound events in the multidimensional pool. A Copula is a function that connects a multivariate distribution to its one-dimensional margins. The Copula concept is particularly advantageous, because it allows for a joint distribution of random variables with great flexibility for the marginal distribution and because it takes into account the dependence structure of these variables. However, there seems to be a lack of comprehensive understanding of the fundamental requirements of the Copula concept such as the strength and dependability of correlation between variables, autocorrelation effects and the choice of representative Copula families, which potentially compromises the accuracy of projections of future environmental processes and natural hazards.

Therefore, we bring forward a step-by-step guide on Copula-based modeling for hydroclimatic variables such as temperature and precipitation, which (1) provides end-users with an overview of necessary requirements, statistical assumptions and consequential limitations of Copulas, and (2) offers clear guidelines on how to implement Copulas. Based on a systematic literature, we also discuss common pitfalls and misconceptions using a specific hydroclimatic case study in Sweden and provide a Copula modeling framework to support researchers and decision makers in addressing climatological hazards and sustainable development.

How to cite: Tootoonchi, F., Haerter, J., Raty, O., Grabs, T., Sadegh, M., and Teutschbein, C.: Copula-based multivariate methods in hydroclimatic applications: avoiding common misconceptions and pitfalls., EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-1115, https://doi.org/10.5194/egusphere-egu2020-1115, 2019

      Since the implementation of Green for Grain Project (GFGP) in the 1990s, the precipitation in the Loess Plateau has increased significantly. The warming and wetting trend in this area is becoming statistically significant. However, the correlation between precipitation increase and regional vegetation restoration is still controversial. To explore the main factors influencing the regional precipitation change, this study selected 6 main contributing factors of the precipitation in the Loess Plateau based on the cloud-precipitation physics and used the statistical methods to analyze the long-term change trend and the spatial and temporal distribution of precipitation in the Loess plateau before and after GFGP and to quantify the contribution rate of different factors to precipitation change in this area. The results show that: 1) the precipitation increased significantly (95% confidence level) after Green for Grain Project since 1999, with an increase rate of 4.96 mm/a; 2) From the perspective of spatial and temporal distribution, the precipitation in the southern part of the Loess plateau was significantly increasing with an increase rate of 20-50mm in the period of 2000-2015 compared with the average annual value in the base period (1985-1999). Among them, the summer precipitation increased significantly, while the winter precipitation changed non-significantly; 3) The contribution analysis shows that the summer precipitation in the Loess Plateau is mainly affected by regional actual evapotranspiration (AET) and vegetation coverage (NDVI) after GFGP, with the contribution rates of 27.1% and 40.0%, which respectively indicates that the summer precipitation in the Loess Plateau increased mainly due to the regional vegetation restoration and the associated ET increase. The winter precipitation in the Loess Plateau is mainly affected by the precipitable water (PW) in the air and water vapor flux (VF), with the contribution rates of 33.5% and 31.7%, which indicates that the winter precipitation is mainly affected by atmospheric circulation and transport of external water vapor. Based on this study, we speculate that the warming and wetting trend of Loess Plateau in recent years is not only closely related to global climate change, but also significantly affected by local climate change brought by vegetation restoration. The above conclusions are important for future ecological restoration and water resources management in the water-scarce Loess Plateau.

How to cite: Gao, X., Wang, J., Wang, Y., Zhao, X., Zhao, Y., and Sun, M.: The spatial and temporal characteristics of precipitation and the key contributing factors in the Loess Plateau since the implementation of Green for Grain Project, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-12005, https://doi.org/10.5194/egusphere-egu2020-12005, 2020

In the context of global climate change and intensive human activities, the runoff process in the Lancang River Basin has been greatly changed. This study proposed a lumped watershed hydrological model considering land use/cover change (LWHM-LUCC) for the frequency calculation and attribution analysis of annual runoff of Lancang River Basin from physical causes aspect. We first detected the variability of precipitation, evaporation, and runoff time series at annual time scale of the Lancang River Basin during 1961–2014 through the hydrological variation diagnosis system. Then, the inconsistent runoff frequency calculation method based on LWHM-LUCC model were applied to analyze the annual runoff frequency distribution in past, current and future period, respectively. Besides, the contribution rates of climate change and human activities on runoff variation were quantatively determined based on LWHM-LUCC model and scenarios simulation. The result showed that there was an abrupt increase of evaporation in 2002, and an abrupt decrease of runoff in 2004. From the distant past period, near past period, to the current period, the design runoff in the Lancang River Basin showed a declined trend, whereas the runoff in the current and future periods remained basically unchanged, and the difference between current and distant past period was much larger than that between current and near past period. The contribution rates of precipitation, evaporation, land use and other human activities to runoff variation were around 38%, 31%, 0% and 31%, respectively. This indicated climate change has greater impact on runoff variation than human activity in the Lancang River Basin.

How to cite: Xie, P., Yu, T., Wu, L., and Wu, Z.: Inconsistent hydrological frequency calculation and attribution analysis of annual runoff of Lancang river basin based on LWHM-LUCC model, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-16857, https://doi.org/10.5194/egusphere-egu2020-16857, 2020

Central Asia, which is one of the most complex regions in the world, is crisscrossed with transboundary rivers shared by several countries. This work analyzes the effects of climate change and human activities on hydrological processes and water resources in these transboundary rivers over the past half century. The results show that the average temperature in the Tienshan Mountains experienced “sharp” increases in 1998, with the average temperature after 1998 being 1.0°C higher than that during 1960–1998. This rapid warming has accelerated glacier shrinkage and decreases in snow cover. These changes influenced the hydrological processes, causing an earlier runoff peak and aggravated extreme hydrological events. Changes in mountainous hydrological processes affected regional water availability and intensified future water crisis in Central Asia. The mismatched spatial distributions of water and land resources, along with the intense human activities (e.g., overexploitation of water resources), have ultimately led to the present water crisis in Central Asia's river basins. This is the main reason for ongoing water conflicts in the region's transboundary rivers. In addition, with the ongoing high temperature prevailing over the central Asia region, the normalized difference vegetation index (NDVI) of natural vegetation in Central Asia during 1982–2013 exhibited an increasing trend at a rate of 0.004 per decade prior to 1998, after which the trends reversed, and the NDVI decreased at a rate of 0.003 per decade. Shrub cover and patch size exhibited a significant increase in 2000–2013 compared to the 1980s–1990s, including shrub encroachment on grasslands. The ecological crisis has not been alleviated due to the increased precipitation.

How to cite: Chen, Y., Li, Z., Fang, G., and Li, W.: Hydrological Processes Changes in the Transboundary Rivers of Central Asia, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-12555, https://doi.org/10.5194/egusphere-egu2020-12555, 2020

The simultaneous growth in climate-driven fluctuations of river flow regimes and global freshwater demand threatens the security of anthropogenic and ecologic uses of streamflows. Dams have long been designed to reconcile the conflict between patterns of human water uses and the temporal variability of flows, and are operated worldwide. In this context, there is a need to understand the combined influence of reservoir operations and climate variability on regulated streamflow regimes, and disclose whether observed hydroclimatic fluctuations can be accommodated by existing reservoirs. Here, these issues are addressed through a quantitative analysis of flow regime alterations by dams as driven by heterogeneous uses and variable regulation capacities (i.e., storage capacity scaled to the average inflow). In particular, the concept of streamflow stability is used to compare inter-annual changes in the occurrence probability of synchronous flows observed upstream and downstream of dams. The selection of structures considered in this study is distributed throughout the entire Central-Eastern United States, so as to span heterogeneous hydroclimatic settings and reservoir functions (i.e., flood control, water supply, hydropower production and multi-purpose). Our results reveal that reservoirs devoted to flood control and those operating for water supply produce distinctive impacts on flow regimes. Flood control does not alter the mean discharge downstream, but decreases long-term discharge variability and, thus, homogenize regional flow dynamics. However, regulation for flood control is unable to mitigate the impact of variable climate drivers on the stability of streamflows and hydroclimatic fluctuations typical of unregulated regimes are transferred unaltered in downstream reaches, or even amplified. Water supply, instead, reduces the mean flow of regulated reaches but increases the long-term streamflow variability, thereby enhancing the regional heterogeneity of flows. In this case, regulation smooths inter-annual changes of flow regimes, though at the cost of systematically filtering out medium-to-high discharges, with negative consequences on stream ecosystems. The observed connection between reservoir functions and the features of downstream flow regime alterations by dams represents a critical step forward for a sustainable management of water resources.

How to cite: Ferrazzi, M., Vivian, R., and Botter, G.: Impact of reservoir operations and climate variability on regulated flow regimes, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-9353, https://doi.org/10.5194/egusphere-egu2020-9353, 2020

At present, the seasonally flooded wetland of the Kilombero River is mainly used by small-scale farmers who predominantly produce rice and maize during the wet season. Some community-based irrigation systems do exist, which reduce the consequences and risks of climate variabilities regarding e.g. the onset of the rainy season and which allow year-round farming. Like other sub-Saharan wetlands, the Kilombero Valley floodplain is a highly dynamic environment, which is amplified due to increasing variability in the onset and intensity of the wet season.

In this study, we identify drivers of change and farmers’ decision-making strategies using focus group discussions with different types of farmers. In particular, we examine the differences between farmers from rain-fed and irrigated agriculture in terms of their agricultural practices and decision-making strategies for dealing with hydro-climatic risks. The results map the perceptions and visions of the people whose actions shape this highly dynamic environment and identify a range of options for action that go beyond the optimality paradigm.

Understanding how aspirations and visions about the future shape agricultural practices and hence human-water interaction is crucial to understand possible changes and dynamics of coupled socio-ecological systems. Therefore, this study is embedded into a wider multi-method approach integrating qualitative and quantitative data to inform and modify hydrological modelling. Here, the qualitatively collected data and findings of this research provide ground for developing additional scenarios for hydrological models and allow for contextualizing model results. Thus, human-water interactions can be better represented and the local populations’ perception and reactions to hydro-climatic risks can be assessed.

This research is part of the Collaborative Research Centre 228 “Rural Future Africa” funded by the German Research Foundation (DFG).

How to cite: Höllermann, B., Näschen, K., Tibanyendela, N., Kwesiga, J., and Evers, M.: Farmers’ decision-making strategies for dealing with hydro-climatic risks in the Kilombero Valley, Tanzania , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-9053, https://doi.org/10.5194/egusphere-egu2020-9053, 2020

The Transboundary Santa Cruz Aquifer (TSCA) is located in Northwestern Mexico and Southwestern United States (U.S.). Groundwater from the transboundary aquifer is being shared by the states of Arizona in the U.S. and Sonora in Mexico; particularly by the cities of Nogales, Arizona and Nogales, Sonora. The Arizona-Sonora border region is subject to climate uncertainties, limited water availability, and water quality issues. The objective of this study is to assess the impacts of changes in groundwater demand, effluent discharge, and climate uncertainties within the TSCA. Groundwater recharge in the TSCA is highly sensitive to climate uncertainties and physical water and wastewater transfers from both the U.S. and Mexico. Perennial flows in the area depend on the effluent discharges from both the U.S. and Mexico. Population growth and residential construction have increased groundwater demand in the area, in addition to wastewater treatment and sanitation demands. These human activities, coupled with climate uncertainties and possible reductions to effluent discharge, influence the hydrology of the area. We use a conceptual water budget model to analyze the long-term impact of the different components of potential recharge and water losses within the aquifer, including changes in projected climate that are based on three downscaled CMIP5 RCP8.5 Global Climate Models. Water budget model simulations for most effluent discharge and groundwater pumping scenarios reflected groundwater deficit. Additionally, climate projections showed variations that range from severe long-term drying to positive wetting. This research improves the understanding of the impact of climate uncertainties and water management decisions on water sustainability, with an accessible methodology that can be globally applied.

How to cite: Tapia, E., Shamir, E., and Megdal, S.: Impacts of Variable Climate and Effluent Flows on the United States-Mexico Transboundary Santa Cruz Aquifer, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-1199, https://doi.org/10.5194/egusphere-egu2020-1199, 2019

Understanding the impacts of human activity on the environment is critical to water resources planning and ecosystem services sustainability.  The goal of this work is to develop decision making and support tools for natural resources conservation and assessment at the Lower Mekong River basin by leveraging satellite observations of Earth, physical hydrological modeling (doi:10.3390/rs10060885), and freshwater health index framework (doi: 10.1016/j.scitotenv.2018.01.040).  The approach adopted in this work relied on a comprehensive suite of hydrological data products and a regional hydrological decision support system application for the Lower Mekong River basin compiled and developed to improve water accounting and floodplain management.  The social-ecological framework named the freshwater health index (FHI) takes account of the interplay between governance, stakeholders, freshwater ecosystems and the ecosystems services they provide.  Various dam reservoir scenarios have been examined based on stakeholder engagement to enhance the results of the integrative social and ecological nature of fresh waters at the Srepok, Sesan, and Sekong (3S) River basins of the Lower Mekong.  Preliminary results represented by ecosystem vitality indicator has corroborated seasonal flow patterns change in response to water storage capacity increase.  For instance, current modeled reservoirs at the 3S River basin exhibit a deviation from natural flow decrease of 10% when compared with baseline reservoirs.  Governance and Stakeholders role has been found critical to the health of the 3S freshwater ecosystem.  The approach methodology utilized in this work employing the integration of satellite earth observation data and hydrological modeling to investigate ecosystem freshwater health is applicable on a global scale.  This work is part of an ongoing research partnership work between the National Aeronautical and Space Agency (NASA) and the Conservation International (CI) dedicated to improving natural resources assessment for conservation and sustainable management.

How to cite: Mohammed, I., Bolten, J., Souter, N., Shaad, K., and Vollmer, D.: Sustainability of the Lower Mekong River under human impact: A freshwater ecosystem health investigation, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5675, https://doi.org/10.5194/egusphere-egu2020-5675, 2020

A major part of Pakistan’s economy is dependent upon agriculture which is irrigated from the water resources of the Upper Indus Basin (UIB). Therefore the human impact of hydroclimatic variability in this area is of paramount importance. The Upper Indus Basin is characterized by uncertain hydro-climatic behaviour with changing patterns in different sub-basins. Many studies have worked on hydro-climatic trends at basin scale but only few studies focused on the hydroclimate, precipitation dynamics and their magnitude at sub-basin level. Based upon this scenario, high resolution seasonal and annual climatology of UIB was developed. It is based on precipitation normals 1995-2017 obtained from four different gridded satellite datasets (Aphrodite, Chirps, PERSIANN-CDR and GPCC) as well as quality- controlled high and mid elevation ground observations (1250–4500 m a.s.l.). The quality-control of the gridded dataset is computed by the anomaly method. In order to, evaluate the data quality of the gridded rainfall, four statistics i.e., BIAS, Mean Absolute Error (MAE), Mean Absolute Percentage Error (MAPE) and Root Mean Square Error (RMSE) are used in this study. Using running trends and spectral analysis with multi-gauge based anomaly, the study analyses the precipitation and runoff   seasonal and annual temporal variability at sub-basin scale. For this, Mann–Kendall test was employed to detect the presence of any trend while their slope is calculated by Theil Sen’s slope method. The nonparametric Pettitt Test was also used in this study to eventually identify the change point in hydro-climatic time series. The results indicated that bias corrected CHIRPS precipitation datasets performed better in simulating precipitation with RMSE, MAE, MAPE [%] and BIAS followed by APHRODITE. The annual and seasonal precipitation climatology exhibited higher precipitation in the lower side of the basin. The comparison between short and long duration climatologies is being investigated as well. The annual running trend analysis of precipitation exhibited a very slight change whereas a more significant increase was found in the winter season (DJF) and most of sub-basins feature a significant decreasing rate in precipitation and constant change point within the monsoon period (JJA). Similarly, trend analysis for runoff in main rivers of Upper Indus Basin at Gilgat, Indus (Besham Qila, Bunji) exhibit nonsignificant increase except Hunza and Indus at Kharmong which are showed decrease annual trends and will be further investigated for seasonal patterns. Overall, these findings would assist to better understand precipitation, snow- and ice-melt runoff dynamics, addressing the hydroclimatic behaviour of the Karakoram region.

How to cite: Liaqat, M. U., Ranzi, R., Grossi, G., and Mahmood, T.: Characterization of Interannual and Seasonal Variability of Hydro-Climatic Trends in the Upper Indus Basin , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5867, https://doi.org/10.5194/egusphere-egu2020-5867, 2020

Located over eastern Tibetan Plateau, the upper Yellow River basin (UYRB) provides about half of the total annual discharge of the entire Yellow River basin in northern China, and influences more than one hundred million people over downstream regions. In the Anthropocene, human activities such as greenhouse gases emission, human-induced land cover change and water management are changing the terrestrial hydrological process and streamflow extremes over UYRB. However, quantifying their separate influence is a great challenge due to limited observations and difficulty in modeling hydro-thermal processes over alpine regions.

Here we find significant fingerprints of anthropogenic climate change and land cover change in decreasing total water storage and increasing extremely low streamflow over UYRB headwater. While anthropogenic climate change, reservoir operation and land cover change significantly decreasing the probability of extreme flooding event over the UYRB by 31%, 45% and 10% respectively. The newly-developed Conjunctive Surface-Subsurface Process version 2 (CSSPv2) land surface model was first implemented at a high resolution (3km) over the UYRB. Comprehensive evaluations show the model well captures the variation and variability of hydrological variables. Simulations with and without land cover change were then compared to assess the impact of land cover change, while reservoir influence was calculated by comparing the modeled naturalized streamflow with observed streamflow. CSSPv2 was also driven by CMIP5 outputs with natural or anthropogenic forcings to assess influence of anthropogenic climate change. An integrated hydro-climate attribution framework was finally used to unify the contributions of different factors. Our results highlight the local-scale human influences (including land cover change and water management) on the streamflow extremes, which are still not well incorporated in current global climate models for detection and attribution studies.

How to cite: Ji, P. and Yuan, X.: Synergistic impacts of climate and land cover change, and water management on terrestrial hydrology over headwaters with an integrated attribution framework, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-6278, https://doi.org/10.5194/egusphere-egu2020-6278, 2020

Seawater intrusion in coastal areas is now rising as a serious problem for river deltas in the world, especially when high tidal levels occur. Red River Delta plays a paramount role in the economy and society of Vietnam and has already been experiencing the increase in salinity concentrations. The combination of high tidal levels and multi-purposes reservoirs operations in the upstream watershed could exacerbate saltwater intrusion. This research, therefore, analyses the impacts of different water management plans, according to reservoirs operations coupled with sea level rise scenarios, on salinity dynamics in the Red River Delta. Two sea level rise projections referred to RCP4.5 and RCP8.5 emission scenarios have been selected for the simulations of future salinity intrusions in 2050 and 2100. In consideration of the important junction of the 3 main upstream rivers (Lo, Thao and Da River), discharge at Son Tay gauge station is selected as the upstream boundary condition for riverflow. Different discharge scenarios in Son Tay station are, hence, adopted based on statistical analysis of runoff data after the construction of the major reservoirs, started in 1973. Taking into account the 25%, 50%, 75%, 95% exceedance quantiles of the minimum monthly riverflow in Son Tay station combined with 4 downstream sea level rise scenarios, 16 salinity profiles along the Red River Delta reaches were obtained by 1D-hydrodynamic simulations. The results are useful as a guidance to plan multi-purposes reservoirs operations, considering environmental, agricultural, industrial and flood-protection targets.

How to cite: Nguyen, H. T., Nguyen, H. Y., Balistrocchi, M., and Ranzi, R.: Water management plans and sea level rise impacts on seawater intrusion in the Red River Delta, Vietnam, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-6684, https://doi.org/10.5194/egusphere-egu2020-6684, 2020

Urmia Lake watershed, which is located at the northwest of Iran has gone through crucial hydroclimatological changes that resulted in Urmia Lake Desiccation. Long term average temperature and precipitation trends, precipitation pattern transition and changes in precipitation-snow timing are some of the hydroclimatological changes that have occurred in this watershed. Aforementioned changes are provoked by anthropogenic activities such as land cover changes, booming urbanization, unauthorized exploitations of Urmia Lake and inefficient crop management, followed by natural factors that could be caused by climate change.

In this study we aim to address contributing hydroclimatological factors and vegetation changes that resulted in Urmia Lake desiccation. In order to examine the vegetation changes in this watershed, we analyzed remote sensing data. In this regard, normalized difference vegetation index (NDVI)-based models for two sub-basins in East Azerbaijan province and West Azerbaijan -located at two sides of Urmia Lake watershed- are developed by an ensemble of satellite data from 1990 to 2019. Data of Landsat 5 TM satellite from 1990 to 2013 and Landsat 8 OLI/TIRS satellite from 2013 to 2019, are collected and analyzed to consider vegetation changes. Hydrological data for precipitation, temperature and Urmia Lake water level elevation are also considered for analyzing hydroclimatic impacts. The adequacy of NDVI-based models and long term hydrological time series are checked by Mann-Kendall trend test.

The evaluation of NDVI-based models shows an increasing trend in vegetation. In comparison, the studied sub-basin in West Azerbaijan province has a higher level of increasing trend than the sub-basin in East Azerbaijan province. The evaluation of precipitation time series shows a decreasing trend and temperature data exhibit an increasing trend. The trend pattern changes validates the hypothesis that increasing trend of vegetation in Urmia Lake watershed is in proportion to the escalating agricultural activities. Furthermore, the escalation of land use is higher in West Azerbaijan province where there exists more agricultural activities.

How to cite: Tootoonchi, R., Nourani, V., Andaryani, S., and Tootoonchi, F.: Application of Mann-Kendall trend test and Normalized Difference Vegetation Index (NDVI) in hydroclimatological change detection – A Case Study of Urmia Lake watershed, Iran, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-6904, https://doi.org/10.5194/egusphere-egu2020-6904, 2020

Stochastic comparison of climate model outputs to observed relative humidity fields

We compare the stochastic behaviour of relative humidity outputs of climate models for the 20^th century to the historical data (stations and reanalysis fields) at several temporal and spatial scales. In particular we examine the marginal distributions and the dependence structure with emphasis on the Hurst-Kolmogorov behaviour. The comparison aims to contribute to the quantification of reliability and predictive uncertainty of relative humidity climate model outputs over different scales in a framework of assessing their relevance for engineering planning and design.

(Acknowledgement: This research is conducted within the frame of the course "Stochastic Methods" of the National Technical University of Athens (NTUA). The School of Civil Engineering of NTUA provided moral support for the participation of the students in the Assembly.)

How to cite: Koumakis, A., Dimitriadis, P., Iliopoulou, T., and Koutsoyiannis, D.: Stochastic comparison of climate model outputs to observed relative humidity fields, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8112, https://doi.org/10.5194/egusphere-egu2020-8112, 2020

Over the past few decades, clear evidence has underlined that global climate has changed and this trend is projected to continue in the future. As a consequence, climate change concerns an increase in temperature and variations in rainfall patterns, which may be responsible for changes in landslide occurrences. In principle, landslide is supposed to respond to climate change correspondingly. However, the influence of climate change on landslide occurrences has not been defined quantitatively yet and whether the effect could exacerbate or reduce landslides impact on a regional scale is still unclear. Thus, this study aims to employ several meteorological factors to serve as a bridge to explore the intrinsic correlation between climate change and landslide occurrences.

To demonstrate the methodology, this paper illustrates the Emilia-Romagna region (Italy, historic data from 1979 to 2019) as a case study due to its high quality observation over past decades Firstly, we carry out an explorative temporal and spatial distribution characteristic analysis of meteorological factors including temperature, precipitation, evaporation and soil moisture to explore its change rule. In addition, data derived from the ERA5 dataset is calibrated with the observed data in the targeted zones in order to yield thresholds to estimate landslide risk. By using two types of thresholds, relationships between climate parameters and consequences such as landslide triggering, landslide event frequency, and landslide event magnitude are established. Furthermore, we calculate the exceedance probabilities and forecast the overall trend of occurrence of landslide influenced by climate change in the future.

The results show that there is an overall upward trend in the annual average temperature and soil moisture is found to decrease throughout these years; Hilly areas are more sensitive to changes in both temperature and precipitation compared with the coastal areas which is consistent with the variation of landslides occurence . The results provide useful foundation for further hydrological landslide risk management in the region.

How to cite: Liu, Y., Han, D., and Pregnolato, M.: Assessing climate change effects on the occurrence of hydrological landslides in Emilia Romagana ( Italy) region, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8402, https://doi.org/10.5194/egusphere-egu2020-8402, 2020

Trends are customarily identified in rainfall data in the framework of explanatory modelling. Little insight however has been gained by this type of analysis with respect to their performance in foresight. In this work, we examine the out-of-sample predictive performance of linear trends through extensive investigation of 60 of the longest daily rainfall records available worldwide. We devise a systematic methodological framework in which linear trends are compared to simpler mean models, based on their performance in predicting climatic-scale (30-year) annual rainfall indices, i.e. maxima, totals, wet-day average and probability dry, from long-term daily records. Parallel experiments from synthetic timeseries are performed in order to provide theoretical insights to the results and the role of parsimony in predictive modelling is discussed. In line with the empirical findings, it is shown that, prediction-wise, simple is preferable to trendy.

How to cite: Iliopoulou, T. and Koutsoyiannis, D.: Rainfall trends in hindsight and in foresight, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8753, https://doi.org/10.5194/egusphere-egu2020-8753, 2020

Population growth, economic development and risk-blind urbanization often increase exposure to risk, including that due to floods. While rural flooding may affect much larger areas of land, urban floods are more challenging to manage, since the higher population and asset density in the urban environment increase the environmental and social impacts of floods and make the potential flood damages more costly. Therefore, the need for integrated flood insurance policy and products on extended parts of the world is pronounced in order to reduce the financial consequences of extreme flood events, which endanger in many cases the environmental, social and economic stability. As the assessment of the so-called collective risk is a typical issue faced in insurance and reinsurance practices, in this study we investigate the stochastic dynamics of daily stream flow series with particular interest to the existence of clustering mechanisms in floods, which is known to increase the potential risk. We analyse collective risk on the US-CAMELS dataset, treating the streamflow exceedances over given thresholds as proxies for insurance claim amounts. Moreover, we develop modelling and simulation approaches of extreme flows as a step towards the deeper understanding of the relationship between the stochastic patterns of flood occurrence and proxies of insurance claims, paving the way for a more efficient use of the available streamflow records.

Acknowledgement: This research is conducted within the frame of the course "Stochastic Methods" of the National Technical University of Athens (NTUA). The School of Civil Engineering of NTUA provided moral support for the participation of the students in the Assembly.

How to cite: Manolis, G. T., Papoulakos, K., Iliopoulou, T., Dimitriadis, P., Tsaknias, D., and Koutsoyiannis, D.: Clustering mechanisms of flood occurrence; modelling and relevance to insurance practices, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-9357, https://doi.org/10.5194/egusphere-egu2020-9357, 2020

Long term time series of daily rainfall and daily river flows are analysed in order to detect the occurrence of drought rich periods through the application of the theory of runs. In detail, we consider the time series of the daily rainfall in Bologna (1813-2019) and daily river flows of the Po River at the closure section (1920-2017). These data sets are a valuable opportunity to assess long term changes of precipitation and water resources availability and the effect of recent climate change. The occurrence of multiyear droughts is a major concern in the context of Italy for the potential impact on irrigation as well as water supply for civil and industrial use. The design suitable adaptation techniques needs to be based on a careful assessment of the probability of multiyear droughts and their intensity. Our results point out the occurrence of critical events along the whole span of the considered observation period, as well as the contingency of a number of recent droughts that point out a condition of potential vulnerability.

How to cite: De Paolis, M. C. and Lisi, M.: Multiyear drought assessment for long term rainfall and river flows in Italy, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-9505, https://doi.org/10.5194/egusphere-egu2020-9505, 2020

A comprehensive study of humic substances (HS) in the surface water of Ukraine have been carried out. It reveals the nature of the basic laws of humic substances intake, the spatial-temporal distribution, and the physicochemical processes of the intra-water transformation. The spatial differentiation of the studied parameters largely depends on the zonal-genetic conditions of humus formation. The HS content in the azonal system of cascade of the Dnipro reservoirs, decreases from the upper - the Kyiv - to the lower - the Kakhovka - reservoirs. Based on the coefficient of the HS water migration, which is characterizes their ratio in the water and catchment soils, the zoning of the Ukrainian territory is carried out.

The basic properties of the surface water HS - polydispersity, solubility, and the effect on the water blooming formation - are studied. It is shown that humic acids (HA) dissolved in water are more highly-molecular and polydisperse in comparison with fulvic acids (FA). Their most fine particle fractions, which content is 50–65% for HA and about 50% for FA, dominate in the surface water HS. The quantitative characteristics and features of the interphase distribution of HA and FA and the change in their molecular weight in the system “soil catchment complex - river water – suspended matter - bottom sediments” are established.

It is shown that sorption by suspended substances play a major role in the processes of self-purification of water from humus, while the oxides and hydroxides of Fe, Al, and Mn have the maximum sorption capacity for the HS. Conducting the laboratory experiments, sorption isotherms of the HS are obtained by Fe hydroxides and clay minerals of suspended substances of the Dnipro reservoirs. Also, the study states that among the various natural water factors, the conformational changes of HS are predominantly due to a change in pH.

Moreover, the quantitative indicators of the HS wash-off from the Prypiat catchment surface, the marshiest river basin in Ukraine, are calculated. The role of different pathways of water flow in the formation of the HS runoff is shown. Based on the data gathered, the material balance of HS within the cascade of the Dnipro reservoirs is calculated, and the role of the Prypiat river as the main source of HS is explained.

The results of the study indicate that the cascade of the Dnipro reservoirs is a powerful biogeochemical barrier that facilitates the transition of HS and associated with them pollutants from solution phase into bottom sediments, and in the reservoirs with delayed water exchange, FA are characterized not only by the transporting but also accumulating function.

Finally, the thermodynamic calculations of coexisting forms of HS in water were conducted. It is concluded that in the physicochemical conditions typical for the surface water of Ukraine, water contains 13–15% of free fulvate ions capable of binding heavy metals, which is an important characteristic for assessing the buffer capacity of water.

How to cite: Osadcha, N., Osadchyi, V., Nabyvanets, Y., Ukhan, O., Osypov, V., and Luzovitska, Y.: Humic substances migration in the surface water of Ukraine, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-9764, https://doi.org/10.5194/egusphere-egu2020-9764, 2020

We compare the stochastic behaviour of temperature outputs of climate models for the 20th century
to the historical data (stations and reanalysis fields) at several temporal and spatial scales. In
particular we examine the marginal distributions and the dependence structure with emphasis on
the Hurst-Kolmogorov behaviour. The comparison aims to contribute to the quantification of
reliability and predictive uncertainty of temperature climate model outputs over different scales in a
framework of assessing their relevance for engineering planning and design.

(Acknowledgement: This research is conducted within the frame of the course "Stochastic Methods"
of the National Technical University of Athens (NTUA). The School of Civil Engineering of NTUA
provided moral support for the participation of the students in the Assembly.)

How to cite: Angelopoulos, G., Dimitriadis, P., Iliopoulou, T., and Koutsoyiannis, D.: Stochastic comparison of climate model outputs to observed temperature fields, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10425, https://doi.org/10.5194/egusphere-egu2020-10425, 2020

We compare the stochastic behaviour of precipitation outputs of climate models for the 20^th century to the historical data (stations and reanalysis fields) at several temporal and spatial scales. In particular we examine the marginal distributions and the dependence structure with emphasis on the Hurst-Kolmogorov behaviour. The comparison aims to contribute to the quantification of reliability and predictive uncertainty of precipitation climate model outputs over different scales in a framework of assessing their relevance for engineering planning and design.

(Acknowledgement: This research is conducted within the frame of the course "Stochastic Methods" of the National Technical University of Athens (NTUA). The School of Civil Engineering of NTUA provided moral support for the participation of the students in the Assembly.)

How to cite: Gerotoliou, S., Iliopoulou, T., Dimitriadis, P., and Koutsoyiannis, D.: Stochastic comparison of climate model outputs to observed precipitation fields, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10842, https://doi.org/10.5194/egusphere-egu2020-10842, 2020

This study characterizes gridded precipitation data over India in terms of presence of potential temporal trends and their upper tail properties. Daily gridded precipitation data having resolution of 0.25° prepared by Indian Meteorological Data (IMD) for a record period of 110 years (1901–2010) over entire India is used for the analysis. The objectives of this study are (i) to assess presence of potential trends in annual maximum daily precipitation series by using a variety of non-parametric methods and (ii) to investigate the upper tail behavior of daily precipitation series. Detailed trend detection analysis is carried out to find abrupt change/step or monotonic trend using a variety of non-parametric and graphical methods. Detection of abrupt change/step in the data is accomplished through Modified Pettitt’s test whereas the monotonic trends are examined by applying different tests, such as original and modified Mann Kendall (MK) tests, Spearman rank correlation (SRC), Block bootstrap (BBS) with MK and SRC and innovative trend analysis (ITA). Quantitative assessment of monotonic trend is performed based on Sen’s slope method. The implication of change magnitude is studied in terms of percentage change over mean.  Further, the upper tail behaviour of annual maximum daily precipitation series is tested based on the framework of generalized extreme value (GEV) theory. Subsequently, the behaviour of extremes in the precipitation data is diagnosed in terms of their frequency of occurrence by using a state-of-the-art algorithmic procedure which is a graphical method, famously known as Mean Excess Function (MEF). Finally, Multi-criteria decision – making (MCDM) techniques are used for identification of critical regions in terms of behaviour of extremes (i.e., increasing or decreasing trend, change magnitude, upper tail properties) over India.

How to cite: Gupta, N. and Chavan, S.: Characterization of Extreme precipitation over India, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-12883, https://doi.org/10.5194/egusphere-egu2020-12883, 2020

The adequate supply of the ever-increasing demand of fresh water continues to be a challenge in parts of the globe. This challenge has been aggravated due to increasing population and climate change. The anticipation for better lifestyles and improved water supply has resulted in an increase in migration from rural settlements leading to an increase in the populations of many cities globally. This study therefore investigates the variability and trends in the surface water demand and supply of the city of Gaborone and surrounding areas in response to population growth and climate change using the Water Evaluation and Planning (WEAP) model for future scenarios. The study includes analysis of population trends, water production and consumption rates, hydrological aspects of the study area as well as projected climate data at a high spatial resolution of 1 km². The current General Circulation (GCM) or Regional Climate (RCM) models are not able provide such data. Therefore, the climate data for existing GCMs is statistically downscaled using the high resolution Worldclim data to spatial resolution of 1 km² and bias corrected against Global Climatology Precipitation Center (GPCC) precipitation. The GCM data for the mid-range Concentration Representative Pathways (RCP4.5) and high emission RCP 8.5 future scenarios of Coupled Model Inter-comparison Project Phase 5 (CMIP5) are employed in the study. Under both RCP4.5 and RCP8.5 scenarios, the reservoir inflow indicates that the level of reservoirs at Foresthill, Diremogolo, Gabane hill, Oodi hill and Mabutswe will be reduced during 2081-2097 period. The unmet water demand of the whole study area will be 52.5 million m³ in 2050 as compared to 1490 million m³ in 2100 under RCP 8.5 climate and high population growth scenarios. However, the unmet demand under RCP4.5 climate and high population growth scenarios will be 51.14 million m³ in 2050 as compared to 1450 million m³ in 2100. On the other hand, the unmet water demand will be reduced by as much as 50% under both scenarios if low population growth rate of 2.2% is assumed. As an option of water management, increasing water loss reduction by 3% every year could drastically reduce the unmet water demand.

How to cite: Mosekiemang, B. and Mengistu Tsidu, G.: Surface water demand and supply of Gaborone city and surrounding areas: Response to climate change and population increase, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18392, https://doi.org/10.5194/egusphere-egu2020-18392, 2020

The rivers around the world have been transformed due to various anthropogenic activities and have led to the altered natural flow regime, which is crucial for controlling the essential environmental conditions within the river which in turn forms the biotic diversity. This study quantifies the adverse impacts due to the construction of dams on the hydrology of the Godavari and Krishna River Basins over the last half a century. The quantification of hydrologic alteration at five representative gauging stations of both the rivers has undertaken using Indicator of Hydrological Alteration (IHA) and the Flow Health (FH) methods based on the Range of Variability approach. To evaluate the alterations of flow regime due to the impact of dams (anthropogenic) only, the data for wet and dry years were excluded from the analysis as these represent the impact of climate variability. The IHA results reveal that the average monthly flow (especially from June to September), annual extreme streamflow indices (1-, 3-, and 7-day maxima flow), and rise and fall rates were among the most affected ones when compared to the pre-impacted period. The improved overall hydrologic alteration values for the Dhalegaon, Nowrangpur, K. Agraharam, and Vijayawada stations were found approximately 75.5%, 73.2%, 76.9 %, and 67.9 % respectively, suggesting a significant impact on the overall riverine ecosystem. The flow health (FH) analysis scores for high flow (HF) (K.Agraharam and Yadgir) highest monthly (HM) (Dhalegaon, K.Agraharam, and Yadgir), Low Flow (LF) (Dhalegaon) and flood flow intervals (FFI) (Dhalegaon and Vijayawada) during the test period were in the very high alteration range and these all hydrological indicator represents important ecological functions in both the rivers. The results showed in this study may guide in strategizing the multi-step process needed to improve the riverine ecosystems of Godavari and Krishna Basins and their ecological functioning.

Keywords: Hydrological alteration; Krishna River; Godavari River; Ecosystem

How to cite: Singh, R. K. and Jain, Dr. M. K.: Impact assessment of anthropogenic interpositions on hydrological regimes of Godavari and Krishna River Basins, India, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-21131, https://doi.org/10.5194/egusphere-egu2020-21131, 2020

The statistical characteristics of precipitation and temperature in the Daqing River Basin from 1980 to 2015 are analyzed, including the analysis of the homogeneity, trend, mutation and periodicity. Among them, the analysis of homogeneity is based on the method of cumulative value. The trend analysis adopts the methods of moving average, M-K test and R/S. M-K test is also used for the mutation analysis. The wavelet transform is used in the periodic analysis to draw the contour of real part and modulus of precipitation and temperature, as well as the map of the wavelet variance and the main period trend. The results show that the precipitation in the Daqing River Basin from 1980 to 2015 is uniform and has a significant upward trend, and has a sudden change in 2008. As for the periodicity, there are three kinds of periodic changes in 22-32 years, 8-16 years and 3-7 years. In the 22-32 year scale, there are two quasi oscillations of the dry and wet alternation, and four quasi oscillations in the 8-16 year scale. In the graph of the wavelet variance, the peak corresponds to the time scale of 28 years, which indicates that the oscillation of 28 years is the strongest, which is the first main period of precipitation change. From 1980 to 2015, the temperature in the Daqing River Basin is also uniform, and has an obvious upward trend, and has a sudden change in 1992. As for the periodicity, there are three kinds of periodic change, 5-10 years, 14-20 years and 25-32 years, respectively. In the 25-32 year scale, there are two quasi oscillations of dry and wet alternation, and three quasi oscillations in the 14-20 year scale. There are three obvious peaks in the map of wavelet variance, which correspond to the time scales of 28 years, 18 years and 8 years in turn.

How to cite: Jiao, Y., Liu, J., Li, C., Qiu, Q., and Wang, W.: Characteristics of precipitation and temperature in the Daqing River Basin, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-22066, https://doi.org/10.5194/egusphere-egu2020-22066, 2020