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Recently, there has been a growing interest in extreme drought in the hydrological impact assessment due to climate change, but most studies are either drought index based on weather information or development of drought prediction systems to monitor the status. Therefore, it is not enough to evaluate water resource availability that reflect watershed characteristics. In order to evaluate and predict the precise water resource availability during drought, it is necessary to evaluate the characteristics of the hydrological environment considering the artificial water use in the watershed. CAT (Catchment hydrologic cycle Assessment Tool, Kim et. al, 2017) was used to evaluate the characteristics of the hydrological environment. CAT provides tools for analyzing artificial water use such as water supply, water reuse and groundwater intake. In this study, the water resource availability of Boryeong-Dam watershed (163.6 ㎢), which is known to be an extreme drought region, was evaluated considering the complicated agricultural water use in the upstream region. Rainfall and observed inflow data were used from 1999 to 2016, and daily climate data such as mean temperature, relative humidity, wind speed, and duration of sunshine were used. Comparing the simulated runoff with the observed runoff in the upstream area of Boryeong-Dam watershed, the model efficiency was improved by more than 10 % compared with the existing simulated runoff without consideration of the agricultural water use. This is the result before parameter calibration. If the detailed water use such as groundwater intake is taken into consideration, the model efficiency will be improved more.AcknowledgementsThis research is supported by the Research Program (20190101-001) of Korea Institute of Civil Engineering & Building Technology and by the Korea Environmental Industry & Technology Institute (KEITI) grant funded by the Ministry of Environment (Grant 18AWMP-B083066-05). [ABSTRACT FROM AUTHOR]

The complex hydrological network of the Indus River basin has provided water for agricultural purposes since the establishment of the first villages and complex urban societies in the area (the Indus Civilisation, c.4.6-3.9 kyr BP). To understand precipitation patterns and variability during the transient Holocene and to investigate a possible multi-decadal drought toward the end of the Indus Civilisation apogee, we use climate model simulations to study precipitation seasonality and changes in climate dynamics. PMIP3's models simulate a large range of changes across the Holocene, and includes an even larger variability in the representation of the present day climatic mean. Therefore, we have developed metrics characterising present day precipitation variability that can assess climate model abilities and have the potential to statistically correct their results.The northern part of the Indus River basin is a buffer zone between extra-tropical westerly activity and south-easterly monsoon influence that overlaps with major orographic features. We investigated the atmospheric dynamic associated with each component, as well as their coupling, mainly using ERA-Interim reanalysis at daily, monthly and annual timescales. We first show that orographic-led wind convergence alone is sufficient to explain precipitation generation at the basin scale, with little variability between the seasons. Then we characterise the influence of upper-level western disturbances on winter precipitation. We also show that summer synoptic activity is affected by a tropical/extratropical interaction. Finally, we address the question of large-scale teleconnections and inter-annual variability in relation to previous results. [ABSTRACT FROM AUTHOR]

Under present day climate change predictions, with both higher magnitude and altered frequencies of flood events, uncertainties exist in how the behaviour of river systems will change in the future. This uncertainty is greater when considering the impact of vegetation on the dynamics of fluvial systems, which itself may also vary because of climate change. Physical modelling can be a valuable tool to understand the processes on a smaller scale, in particular by simulating the effects of vegetation using surrogates that can grow rapidly, thereby mimicking the forcing induced by vegetation growth. Previous studies using surrogate vegetation in flume experiments on braided rivers (e.g. Tal and Paola, 2007; Bertoldi et al., 2015), have shown the potential for this modelling approach. For this research, we allowed braided river systems to evolve under constant conditions in two 2.5 m wide by 10 m long flume channels, set-up in the Total Environments Simulator at the University of Hull. Once equilibrium conditions were reached under bare sediment conditions, Alfalfa was periodically seeded and allowed to germinate and then grow for different time periods. After each period of growth, we used a sequence of high and low magnitude flood events in order to capture change in morphology arising from the different sequences of events. Morphological changes were captured using a terrestrial laser scanner to collect over 50 DEMs. These DEMs demonstrate the impact surrogate vegetation has on both stabilizing the river system and modifying the patterns of bank erosion and channel migration in a braided system. Furthermore, frequent spatial analysis of erosion and deposition based on the flow direction within the channel network allowed us to determine erosion and deposition width for individual segments of the river system. Collating these segments yields a large dataset that indicates both bank erosion rates and volumetric channel migration rates for different stages of vegetation growth/maturity under different sequences of flood events. [ABSTRACT FROM AUTHOR]

The West African Sahel experienced a long drought from the 1970s to the 1990s during which runoff has paradoxically increased, as a response to human and climate-induced changes in surface conditions. Despite the vegetation recovery (re-greening) observed at regional scale over the past 30 years, surface runoff is still increasing, suggesting that the Sahelian eco-hydrological system passed a tipping point and is now trapped in a « high runoff » state. To study this hypothesis, we developed a system dynamics model incorporating vegetation-hydrology interactions at annual time scale. The model successfully reproduced the vegetation collapse and the increase of runoff-prone bare soil areas monitored over 65 years on a pilot site in Northern Mali. Our results confirmed the existence of a tipping point between alternative high/low runoff states at the small catchment scale. According to the model, a reverse shift to the pre-drought low runoff state is possible, but the conditions in which this shift would occur remain uncertain. The system trajectory presents a strong sensitivity to annual rainfall variability (amplitude and temporal structure). This study suggests that the increasing runoff in a re-greening environment is caused by the tipping of some areas to a high runoff/low vegetation state, illustrating how a regime shift in sub-systems can result in eco-hydrological changes at larger scale. The associated large-scale changes of the rainfall partitioning may alter evapo-transpiration and thus the surface-atmosphere feed-back. Those changes also bear strong environmental and socio-economic consequences, either adverse (increase of degraded areas to the detriment of agriculture, and increased flood risk) or beneficial (increased water resource in ponds and water tables). [ABSTRACT FROM AUTHOR]

Sediment dynamics in river catchments are governed by tectonics, climate and biota. They act directly on the transport process by controlling topography and sediment transport capacity (runoff) and indirectly by controlling the flux and grain size distribution (GSD) of sediments supplied from hillslopes to the fluvial system. Since climate is the main driver for biotic activity, both effects are strongly coupled, and often difficult to disentangle. However, while climate forcing shows a clear trajectory towards increased erosion with increasing humidity, the effect of vegetation is more ambiguous. On short timescales vegetation reduces hillslope erosion and sediment supply from hillslopes by stabilizing soils and trapping sediments. On longer timescales an increased sediment residence time and enhanced biochemical weathering of material in the soils enhances the production fine grained material and hence strongly alters the GSD of material delivered to the fluvial transport system. We state that the influence of vegetation on the grain size distribution of sediments supplied to the river system is a key factor in the biotic control on sediment dynamics, since it exerts a strong control on the transport mechanics and morphodynamics in the river system which in turn control incision and deposition and hence landscape evolution. To investigate vegetation induced shifts in GSD, we collected grain size samples of hillslope and channel sediments in four granitic mountainous river catchments located along the strong bioclimatic gradient of the Chilean Coastal Cordillera, ranging from the arid, non-vegetated Atacama desert in the north (26°S) to the humid and densely vegetated Cordillera Nahuelbuta in the south (38°S). 78 volumetric bulk samples were taken with grain sizes ranging from clay (d = 0.3μm) to boulders (d >300mm). By sampling hillslope and fluvial sediments from the hilltop to the channel outlet we track the effect of vegetation on the spatial variability of GSDs along the sediment transport path.Results show that hillslope sediments in humid areas contain higher fraction of fines compared to the arid areas, while channel sediments in contrast are much coarser. Uniform GSDs in the arid catchments reflect nonselective and thus transport-limited conditions in the river channels. In contrast, in humid catchments GSDs show strong differences between fine hillslope sediment and coarse channel deposits, indicating size selective and supply-limited transport conditions in catchment with higher vegetation coverage. [ABSTRACT FROM AUTHOR]