The 8th Global FRIEND conference highlighted the advance in hydrological science and innovation in water management. 52 accepted papers cover study areas in precipitation and climate impact; observation, analysis and simulations of hydrologic processes; floods in the changing environments; drought monitoring and analysis; water resources and environmental impacts. The outcome of the conference presented in the proceedings will be shared and discussed widely among UNESCO IHP networks.

This is our latest research on hydrological regime change, possible reasons for Taihu water stage increase and flood risks in Taihu Basin. Quantitative evaluation of hydrological response to climate change and human activities affecting Taihu water stage. The findings are useful for improved understanding of changing hydrological processes in the Taihu Basin under rapid development of urbanization.

The 2017 Hanjiang autumn flood appeared to have higher surface water levels at the same discharge rate than previously at the Huangzhuang gauging station. It is seriously impacted the flood control. This paper analyses the 2000–2017 data from the Huangzhuang reach in the Hanjiang River, including surface water levels, the surface water fall, erosion-deposition variation and the engineering activities.

In connection with global climate change is the reduction of the area of glaciation in the basins of mountainous rivers. This often leads to the occurrence of extreme natural phenomena such as flooding and others.

The role of recharge and catchment storage is crucial to understand streamflow drought sensitivity. Here we introduce a model experiment with recharge stress tests as complement to climate scenarios to quantify the streamflow drought sensitivities of catchments in Switzerland. We identified a pre-drought period of 12 months as maximum storage-memory for the study catchments. From stress testing, we found up to 200 days longer summer streamflow droughts and minimum flow reductions of 50 %–80 %.

Balancing water allocations between upstream irrigated agriculture and downstream users and environments is a major challenge in China's Yellow River. Increasing temperatures in the Hetao Irrigation District indicate that solar radiation has decreased over the past 50 years but surprisingly actual evaporation has not changed. Expansion of the length of the irrigation growing season due to increasing temperatures could lead to higher demands for irrigation.

The downward of rainfall trend occurred in the study area in 1972, affecting a few coastal stations. In 1976, this decline extended to the South West and throughout the coastal region. In 1980, the drop covered the entire basin. This decline has resulted in an estimated deficit of 30 % on average in the eastern region, the coastal region and the Mina. However, the central part of the basin experienced a 20 % decrease compared to the period before the break (1968–1980).

The first reason which led to study this area is that Mono basin shows a sharp increase in population and local economic growth generally projected to accelerate. Another reason is that the Mono basin is already facing the consequences of climate change, with recurrent and localized droughts and flash floods years. These conditions would expected to be exacerbated in the future. Such results could help to anticipate the future impacts of climate changes on agriculture, water resources.

The research of ruptures on rainfall and discharge long serial data from 1950 to 1995 on 3 close basins (of 2000 to 6000 km²) in Central African Republic has shown a high variability. The continental rupture of 1970 marking the drought on large West and Central African river basins is not clearly observed. However, all the studied basins have shown a degradation of their hydrological regimes since the end of the 1980s due to the drought severity.

To improve the hydrometric methods in the high-altitude area, and learn more about the hydrological mechanism in the Qinghai-Tibet Plateau, a series of observation research were carried out in the Niyang River watershed, a tributary of the Yarlung Zangbo River. The applicability of the hydrometric methods and instruments were discussed according to the monitoring situation. Based on the δD, δ18O, and the geochemical observed dataset, the runoff composition characteristics were analyzed.

Using 1956～2012 years of river runoff series data of 27 rivers in hilly gully area of Loess Plateau in Shaanxi province 39 hydrological station data, reduction of social and economic water consumption, plotting the annual precipitation and annual runoff double cumulative curve of annual runoff flow series consistency test, the consistency processing of annual runoff data and the quantitative analysis of its influence were also made.

In the middle and lower reaches of the Hanjiang River in February 2018, another serious diatom bloom occurred. This paper analyzes the key hydrological factors that occur in this diatom bloom and proposes a water dispatching optimization plan and specific countermeasures. The suggestion is that Comprehensive protection of the Hanjiang River water ecological environment, completely solve the watershed problem of non-point source pollution.

The sensitivity of a geomorphology-based hydrological modelling is evaluated according to four DEMs from 5 m to 50 m resolution in Brittany, France. A set of 8 basins (5–565.7 km²) is used in a pseudo-ungauged context to explore the potential of Prediction in Ungauged Basin (PUB). The results show that a coarse-worldwide DEM such as SRTM (25 m) supported similar performances than the finer one available from the French mapping institute.

Various estimators of the Hurst exponent characterizing long-term persistence exist, while the values estimated by them may differ. The contribution reviews the possible reasons causing the presence of long-term persistence in time series. Based on the six, relatively long discharge time series from mountainous catchments located in the Elbe River basin close to the borders between Czechia and Germany and two selected estimators, it is shown that the length of time series plays a crucial role.

This paper presents recent thoughts by members of EURO-FRIEND Water project 3 “Large-scale-variations in hydrological characteristics” about research needed to characterize and understand large-scale hydrology under global changes. Emphasis is put on the necessary efforts to better understand 1 – the impact of low-frequency climate variability on hydrological trends and extremes, 2 – the role of basin properties on modulating the climate signal producing hydrological responses on the basin scale.

In order to understand water management issues in the future, it is fundamental to analyze the different elements of hydrologic processes occurring in the watershed under future climate scenarios. In this study, a set of data and modelling algorithms were used to simulate water situation in Rdom watershed (Morocco) in the future. Dramatic decrease of water resources has been predicted with uneven distribution across the study watershed.

The rainfall timeseries of the Koliba/Corubal River watershed were homogenized and the gaps filled. The rainfall variability is similar to that observed in West Africa, with a recovery towards the end of the 1980s and early 2000s. The mean monthly rainfall, the Potential Evapotranspiration, and the flow rates were used to calibrate and validate the model. The values of the Nash criteria close to 100 have made it possible to extend the monthly flow data from Koliba/Corubal until 2015.

A 2D hydrodynamic model was established based on MIKE Flood, which could simulate the flooding submergence from a burst levee. The flood risks in the urban area were quantitatively evaluated for several scenarios including burst levee, proactive flood diversion and their combinations. The results could provide scientific supports for urban flood risk analysis, flood dispatching and management. The methodology has been applied in Qiqihar, which is one of the main cities in northeast China.

With the rapid development of cities in China, urban flooding becomes a growing problem, which not only affect the living quality of the public, but also threatens urban safety. Recently, urban flooding is attached more attention. By analyzing and summarizing urban flooding data from recent decades, which includes frequency, scope of influence, and losses, the causes and status quo of urban flooding problems in China is generalized.

Flooding has been the most severe hazard in China from time immemorial, due to its special geographical, climatic and socio-economic conditions. In recent years, against the background of global climate change and rapid urbanization, extreme hydro-meteorological events have obviously increased in China, in turn affecting the sustainable social and economic development.

Nowadays, during the period of the global climate change, scientists around the world have noticed an increased incidence of extreme natural disasters. The authors of the study suggested methods of using climate change as a part of a genetic model of maximal floods runoff. This model makes possible the introducing of climate changes directly through the maximal stocks of snow and precipitation during the spring flood and runoff coefficients.

Urban floods due to intense precipitation is a major problem in many developing countries, especially in Africa. Rainfall measurement using cellular communication networks is a cost effective method to monitor the heavy rainfall that cause these floods. The method is based on analyzing signal fluctuations due to rain between telecommunication antennas. Here we present simulation studies to test how rainfall measured by this method can help predicting floods in urban areas.

This paper analyses a 42 year time series of daily precipitation in Ichkeul Lake Basin (Tunisia) in order to predict extreme dry-spell risk. A comparison of observed and estimated maximum dry events (42 year return period) showed that Gumbel distribution fitted to annual maximum series gives better results than the exponential (E) distribution combined with partial duration series (PDS). Indeed, the classical Gumbel approach slightly underestimated the empirical duration of dry events.

Globally, flooding is the most common of all environmental hazards with vast devastating socio-economic effect leading to enormous losses to lives and properties. This study focuses on flood risk assessment based on urban and coastal flood estimation due to the physical peculiarity of the Lagos region and urbanization characteristics. Based on flood change detection at twenty minutes intervals for the different flow regimes display that the time of concentration is attained at 1 hour 20 min.

Rising availability of remote sensing imagery provide novel opportunities to improve the understanding of the hydrology of multiple water bodies. The analysis of 443 Landsat images between 1984–2017 and 48 Sentinel-2 images between 2015–2017 confirms the possibility of monitoring floods within individual depressions of the Senegal River floodplain. First results based on in situ data also reveal the potential to refine hydrological relationships between the water height and the flooded area.

Drought monitoring and early warning are critical aspects of drought preparedness and can help mitigate impacts on society and the environment. We reviewed academic literature in England and Chinese on the topic of drought monitoring and early warning in China. The number of papers on this topic has increased substantially but the most recent advances have not been operationalised. We identify the methods that can be translated from the experimental to national, operational systems.

This paper aims to analyze hydrological drought characteristics in the pan-European region based on past drought events from 1990 to 2017. Our study shows that the most severe droughts during our study period were observed from 1992 to 1997, where on average Europe experienced drought events, which lasted up to 4 months. Slow responding variables, such as groundwater, are better in showing extreme drought compared to fast responding variables such as runoff.

Numerous indices exist for the description of hydrological drought, some are based on absolute thresholds of overall streamflows or water levels and some are based on relative anomalies with respect to the season. This article discusses paradigms and experiences with such index uses in drought monitoring and drought analysis to raise awareness of the different interpretations of drought severity.

In Europe, ca. 65% of drinking water is groundwater. Its replenishment depends on rainfall, but droughts may cause groundwater levels to fall below normal. These groundwater droughts can limit supply, making it crucial to understand their regional connection. The Groundwater Drought Initiative (GDI) assesses spatial patterns in historic—recent groundwater droughts across Europe for the first time. Using an example dataset, we describe the background to the GDI and its methodological approach.

New Zealand droughts are investigated using two commonly used measures: one based on precipitation alone, and one on precipitation minus evaporation. Comparison of these two measures shows that as evaporation increases as a result of anthropogenic climate change, drought events are getting bigger. This trend is particularly apparent in the driest and hottest parts of New Zealand.

The temporal evolution of drought events characteristics is discussed. Data from observations and simulations of the regional climate model RCA4 MPI-ESM-LR under two Representative Concentration Pathways (RCPs) scenarios for the period (1941–2100) are used. An amplification of drought frequencies is projected in the future under the RCP8.5 scenario. The maximum duration is expected to hardly change under the RCP8.5 scenario or even to decline.

The Minjiang River is the largest river in Fujian Province. In 1993, the Shuikou Reservoir, which has an effective storage capacity of 700 million m³, was built at about 161 km above the estuary. The completion of the Shuikou Dam trapped most of the upstream sediment in the reservoir area, resulting in a drastic decrease in sediment in the lower reaches of the Minjiang River.

This study focused on a climate change impact assessment on water resources in the Klong Yai River basin in Thailand using multiple Global Climate Models (GCMs). According to the projections, maximum surface air temperature is projected to increase around 0.3–1.4°. Precipitation in the near future (2017–2026 and 2027–2036) shows an increasing trend. The SWAT model was used in Klong Yai River basin in order to assess the amount of inflow into reservoirs under the climate change conditions.

This paper analyses the change of total suspended sediment (TSS) and total organic nitrogen (TON) loads of the Red River from 1960–2015 in which numerous dams in both China and Vietnam have been constructed. Strong decrease of TSS and TON loads allocated to the dam impoundments in spite of population and deforestation increase. The TSS flux decrease has driven a clear reduction of associated elements (nitrogen), which let to hypothesis a change in biogeochemical processes in the coastal zone.

An integrated monitoring approach has developed for the Ob river. The novelty is in transition to high-performance computing under processing of remote sensing data for the Gulf of the Kara Sea the Ob Bay and modeling of aquatic ecosystem degradation. The long-term trend in the development for the ecosystem of the Novosibirsk reservoir in the Ob river basin are explained by the structural-dynamic modeling.

People from the Senegalese Peanut Basin deal with a dramatic increase of water scarcity due both to a rain deficit and a surface water salinization. We carried out the analysis of daily rain from 1950 to 2015 and water salinity of 78 wells on 300 km². We confirm a climatic break in 1970 leaded a long dry period until 2009, with a decreased of the rainy day number per year, probably driving a large extension of well salinization and salt soil crusting accelerated by a large tidal event in 1984.