Extreme Runoff Events Research Articles

Uncertainty based modeling of rainfall-runoff: Combined differential evolution adaptive Metropolis (DREAM) and K-means clustering

Simulation of rainfall-runoff process in urban areas is of great importance considering the consequences and damages of extreme runoff events and floods. The first issue in flood hazard analysis is rainfall simulation. Large scale climate signals have been proved to be effective in rainfall simulation and prediction. In this study, an integrated scheme is developed for rainfall-runoff modeling considering different sources of uncertainty. This scheme includes three main steps of rainfall forecasting, rainfall-runoff simulation and future runoff prediction. In the first step, data driven models are developed and used to forecast rainfall using large scale climate signals as rainfall predictors. Due to high effect of different sources of uncertainty on the output of hydrologic models, in the second step uncertainty associated with input data, model parameters and model structure is incorporated in rainfall-runoff modeling and simulation. Three rainfall-runoff simulation models are developed for consideration of model conceptual (structural) uncertainty in real time runoff forecasting. To analyze the uncertainty of the model structure, streamflows generated by alternative rainfall-runoff models are combined, through developing a weighting method based on K-means clustering. Model parameters and input uncertainty are investigated using an adaptive Markov Chain Monte Carlo method. Finally, calibrated rainfall-runoff models are driven using the forecasted rainfall to predict future runoff for the watershed. The proposed scheme is employed in the case study of the Bronx River watershed, New York City. Results of uncertainty analysis of rainfall-runoff modeling reveal that simultaneous estimation of model parameters and input uncertainty significantly changes the probability distribution of the model parameters. It is also observed that by combining the outputs of the hydrological models using the proposed clustering scheme, the accuracy of runoff simulation in the watershed is remarkably improved up to 50% in comparison to the simulations by the individual models. Results indicate that the developed methodology not only provides reliable tools for rainfall and runoff modeling, but also adequate time for incorporating required mitigation measures in dealing with potentially extreme runoff events and flood hazard. Results of this study can be used in identification of the main factors affecting flood hazard analysis.

Rainwater harvesting in Dry Chaco: Regional distribution and local water balance

Rainwater harvesting (RWH) has been essential for the establishment of human settlements in many dry regions of the world that lacked suitable surface or groundwater resources. A vast fraction of the South American Dry Chaco ecoregion still relies on RWH to support, not only livestock production, but domestic and industrial uses as well. As a result, water capture and storage infrastructure is widely disseminated throughout the region. In this paper we characterized the most typical RWH systems in two contrastingly developed sub-regions of Dry Chaco, ranging from extensive ranching to intensive beef and dairy production (central Argentina and western Paraguay, respectively). In each sub-region, we quantified RWH systems density, spatial distribution and associations with landscape features; furthermore, we illustrated how the daily dynamic of water stock in a typical RWH system contributes to assess their capture and storage efficiency. We found that randomly distributed low sophisticated RWH systems prevailed in central Argentina, while clustered distributed high sophisticated ones were more common in western Paraguay. RWH systems density was ten times higher in western Paraguay (0.94 vs. 0.098 units/km2), showing an exponential association with land cleared fraction and proximity to villages. The daily dynamic of water stock of the RWH impoundment showed that water harvest events were exponentially associated with precipitation magnitude events (R2 = 0.86), while annual water losses were explained by infiltration and evaporation fluxes (59 vs. 41%, respectively). Across both sub-regions, RWH accounts for less than 1% of the annual precipitation, playing a minor role on the regional water balance; however at a local level, they can affect several hydrological fluxes including the onset of groundwater recharge and the mitigation of extreme runoff events.

Sediment-assisted nutrient transfer from a small, no-till, tile drained watershed in Southwestern Ontario, Canada

Sediment and nutrient exports were evaluated in a small agriculture-dominated watershed that drains into Rondeau Bay, on the northern shore of Lake Erie in Southwestern Ontario, Canada. The following hypothesis was tested: the quantity and quality of suspended sediment yields in agricultural settings controls nutrient transfer from surface runoff. Stream discharge and water quality were monitored at three locations along a tributary reach within the Rondeau Bay basin during the 2013 growing-harvest season (May–October). Water samples were analyzed in the laboratory for suspended sediment concentration, particle size, and sediment-assisted nitrogen and phosphorus content. Estimated total sediment yield over the 6-month monitoring period was ∼50t (0.13tha−1). A mid-season change in contributing sediment sources was inferred based on the observations of suspended sediment transfer and particle size following a ∼92mm rainfall event. This extreme runoff event marked a change in the discharge-suspended sediment response seen in the catchment, which included a July–September abrupt decrease in suspended sediment concentration and a coincident increase in fine-grained particle abundance. Clockwise event hysteresis suggested adjacent and/or likely channel derived sediment sources. Finally, there was a positive relationship between suspended sediment concentration and phosphorus (R2=0.86, n=63) and orthophosphate (R2=0.75, n=63). Estimated nutrient concentrations exceeded provincial load guidelines, which suggests that present land management efforts to minimize nutrient loading via surface runoff require further evaluation. This research concludes that agricultural-based nutrient loading into Lake Erie is sediment-assisted and that this sediment potentially derives from in-channel and tile drain sources. The findings have important implications for future soil loss and thus nutrient loading from agricultural settings, especially during extreme events.

Rock-magnetic signature of precipitation and extreme runoff events in south-eastern Patagonia since 51,200 cal BP from the sediments of Laguna Potrok Aike

A 106-m long sediment sequence from the maar lake Laguna Potrok Aike in southern Patagonia was recovered in the framework of the International Continental Scientific Drilling Program (ICDP) Potrok Aike maar lake Sediment Archive Drilling prOject (PASADO). About half of the sedimentary sequence is composed of mass movement deposits (MMDs) and the event-corrected record reaches back to 51,200 cal BP. Here we present a high-resolution rock-magnetic study revealing two sedimentary facies associated with MMDs and characterized by two different types of spurious gyroremanent magnetization (GRM) acquired during static alternating field demagnetization. The first rock-magnetic signature is detected in MMDs composed of reworked sand and tephra material. The signature consists of GRM acquired during demagnetization of the natural remanent magnetization (NRM) and other rock-magnetic properties typical of iron sulfides such as greigite. We interpret these intervals as authigenic formation of iron sulfides in suboxic conditions within the MMD. The second rock-magnetic signature consists of a series of 10 short intervals located on the top of MMDs characterized by GRM acquisition during demagnetization of the isothermal remanent magnetization (IRM). Based on geological, limnological, stratigraphic and climatic evidence these layers are interpreted as reflecting pedogenic hematite and/or goethite brought to the lake by runoff events related to precipitation and permafrost melt. The pedogenic iron minerals mobilized from the catchment most likely settled out of suspension on top of MMDs after a rapid remobilization event. The series of runoff events corresponds to periods of increased lacustrine productivity in Laguna Potrok Aike and are coeval within the limit of the chronology to warm periods of the Last Glacial as recorded in Antarctica, the deglaciation in the mid-latitudes of the Southern Hemisphere and enhanced precipitation during the Early Holocene in southeastern Patagonia.

RECONSTRUCCIÓN DEL ESCURRIMIENTO HISTÓRICO EN LA CUENCA ALTA DEL RÍO NAZAS, DURANGO

The drought of the past few years in north-central Mexico underscores the need for extensive hydroclimatic data that can reveal fluctuations and trends over time, in order to establish water resource planning and mitigation measures. Using dendrochronological techniques, an 800-year streamflow reconstruction was developed for the upper Nazas River watershed in Durango. The reconstruction showed high inter-annual and multiannual hydroclimatic variability and decadal droughts were detected in the 1250s, 1320-1340s, 1370-1380s, 1440-1450s, 1460-1470s, 1650-1660s, 1710-1730s, 1790-1810s, 1920-1940s, 1970-1980s, and 1990s. Some of the droughts were longer and of higher intensity than ones observed in climate records. Extreme flow events were detected in the years 1212, 1229, 1242, 1245, 1271, 1313, 1404, 1427, 1451, 1504, 1520, 1563, 1566, 1620,1671, 1681, 1735, 1816, 1833, 1869, 1920, 1956, 1959, and 1992, and they were linked with the El Nino–Southern Oscillation (ENSO) warm phase. Water decision-makers in the Comarca Lagunera region could use this information to establish probabilities of droughts and occurrence of extreme runoff events for management purposes.

Mid- to late Holocene flood frequency changes in the northeastern Alps as recorded in varved sediments of Lake Mondsee (Upper Austria)

Annually laminated (varved) lake sediments with intercalated detrital layers resulting from sedimentary input by runoff events are ideal archives to establish precisely dated records of past extreme runoff events. In this study, the mid- to late Holocene varved sediments of Lake Mondsee (Upper Austria) were analysed by combining sedimentological, geophysical and geochemical methods. This approach allows to distinguish two types of detrital layers related to different types of extreme runoff events (floods and debris flows) and to detect changes in flood activity during the last 7100 years. In total, 271 flood and 47 debris flow layers, deposited during spring and summer, were identified, which cluster in 18 main flood episodes (FE 1–18) with durations of 30–50 years each. These main flood periods occurred during the Neolithic (7100–7050 vyr BP and 6470–4450 vyr BP), the late Bronze Age and the early Iron Age (3300–3250 and 2800–2750 vyr BP), the late Iron Age (2050–2000 vyr BP), throughout the Dark Ages Cold Period (1500–1200 vyr BP), and at the end of the Medieval Warm Period and the Little Ice Age (810–430 vyr BP).Summer flood episodes in Lake Mondsee are generally more abundant during the last 1500 years, often coinciding with major advances of Alpine glaciers. Prior to 1500 vyr BP, spring/summer floods and debris flows are generally less frequent, indicating a lower number of intense rainfall events that triggered erosion. In comparison with the increase of late Holocene flood activity in western and northwestern (NW) Europe, commencing already as early as 2800 yr BP, the hydro-meteorological shift in the Lake Mondsee region occurred much later. These time lags in the onset of increased hydrological activity might be either due to regional differences in atmospheric circulation pattern or to the sensitivity of the individual flood archives. The Lake Mondsee sediments represent the first precisely dated and several millennia long summer flood record for the northeastern (NE) Alps, a key region at the climatic boundary of Atlantic, Mediterranean and East European air masses, aiding a better understanding of regional and seasonal peculiarities of flood occurrence under changing climate conditions.

Ascospores of the parasitic fungus Kretzschmaria deusta as rainstorm indicators during a late Holocene beech-forest phase around lake Meerfelder Maar, Germany

Discrete reddish-brown, predominantly minerogenic detrital layers along the Holocene, annually laminated sediment sequence of Lake Meerfelder Maar represent extreme runoff events. We conducted detailed microfacies analyses and a high-resolution palynological investigation, focusing on ten detrital layers throughout the Holocene. We studied triad samples taken directly under, in and above the detrital layer. Fagus sylvatica (beech) was a dominant species in the regional forest around Lake Meerfelder Maar after ca. 3,800 years ago. Three detrital layers occurring during the Fagus phase exhibit short-term maxima of ascospores of the parasitic fungus Kretzschmariadeusta. In contrast, the ascospore contents are low in the event layers deposited during the early and middle Holocene. Fagus is a vulnerable host species for Kretzschmaria deusta and the fungus is common on Fagus. Ascospores are formed on the trunk base, and under normal weather conditions, few spores appear outside the forest. We interpret the short peaks in abundance of K.deusta in the event layers as indicators for rainstorms during which material was transported from the forest floor into the lake by strong winds and stormwater runoff. The open beech forest facilitated wind transport of the ascospores. We recommend analysis of fungal spores in lake sediments because fungal records may help to identify extreme weather events, even when such events are not macroscopically visible in the sediment sequence.

Characterizations and modeling of turbidity in a water supply reservoir following an extreme runoff event

The findings from an integrated program of short- and long-term monitoring, individual particle analyses (IPA), and mechanistic modeling to characterize and simulate the turbidity (Tn) effects of an extreme runoff event (2011) on a water supply reservoir were documented. A robotic profiling platform and rapid profiling instrumentation resolved turbidity and temperature (T) patterns in time and space in the reservoir. Metalimnetic enrichment in Tn following the event was reported and attributed to the entry of turbid stream water as density currents, or plunging inflows. The diminishment of high Tn levels following the event was well represented by a first-order loss rate of about 0.023 d−1. The highest Tn levels were avoided in water withdrawn for the water supply following the event by selection of vertical intake alternatives, although Tn values in the withdrawal remained distinctly above typical baseline conditions for nearly 2 months. Based on IPA, the Tn-causing particles were mostly clay minerals in the 1–20 μm size range. The operation of sorting processes determining settling losses from the minerogenic particle population, according to their size and shape, following the runoff event was resolved. The set-up and testing of a mechanistic Tn model, composed of 2 submodels, a 2-dimensional hydrothermal/transport submodel, and a Tn kinetics submodel, is described. The hydrothermal/transport submodel was tested separately and performed well in simulating the dynamics of the reservoir’s stratification regime and the entry of the dense streams as plunging inflows during the extreme runoff event. The overall Tn model needed to represent the loss processes of both settling and coagulation to perform well in simulating the in-reservoir and withdrawal Tn patterns following the runoff event.

Trend analysis of extreme runoff events in major river basins of Peninsular Malaysia

This study performed trend analysis of extreme runoff events (high flow and seven-day low flow) of four major river basins located in Peninsular Malaysia in Southeast Asia. Trend analysis using Spearman’s rank test and standard normal homogeneity test using 25 years (1982–2006) of runoff data found no statistically significant trend in extreme events of Kelantan and Pahang basins. Muda was found to have a decreasing trend in high flow which was changed to an increasing trend after a significant ‘change point’ in year 1992, while there was a continuous increasing trend in the low flow. Similarly, Perak was found to have decreasing trend in high flow but increasing trend in low flow. Hydrological trends detected in this study vary widely among watersheds despite the fact that they are located in the similar climatic zones. We argue that the changes in flow regime are evident even at a smaller spatial scale, and the presence of trends has significant implications on how water resources be managed.

Temporal and spatial variations and statistical models of extreme runoff in Huaihe River Basin during 1956–2010

Based on the daily runoff data from 20 hydrological stations above the Bengbu Sluice in the Huaihe River Basin during 1956–2010, run test, trend test and Mann-Kendall test are used to analyze the variation trend of annual maximum runoff series. The annual maximum series (AM) and peaks over threshold series (POT) are selected to describe the extreme distributions of generalized extreme value distribution (GEV) and generalized Pareto distribution (GPD). Temporal and spatial variations of extreme runoff in the Huaihe River Basin are analyzed. The results show that during the period 1956–2010 in the Huaihe River Basin, annual maximum runoff at 10 stations have a decreasing trend, while the other 10 stations have an unobvious increasing trend. The maximum runoff events almost occurred in the flood period during the 1960s and 1970s. The extreme runoff events in the Huaihe River Basin mainly occurred in the mainstream of the Huaihe River, Huainan mountainous areas, and Funiu mountainous areas. Through Kolmogorov-Smirnov test, GEV and GPD distributions can be well fitted with AM and POT series respectively. Percentile value method, mean excess plot method and certain numbers of peaks over threshold method are used to select threshold, and it is found that percentile value method is the best of all for extreme runoff in the Huaihe River Basin.

Life changes as polar regions thaw

Summary Spiders and shrubs grow bigger, while ice shields are shrinking. Climate change is already affecting biotopes in both polar regions, while scientists are trying to establish what is happening and why. Michael Gross reports.

The link between land-use management and fluvial flood risk

There is much policy interest in the possible linkages that might exist between land use and downstream fluvial flood risk. On the one hand, this position is sustained by observations from plot- and field-scale studies that suggest land management does affect runoff. On the other, upscaling these effects to show that land-management activities impact upon flood risk at larger catchment scales has proved to be elusive. This review considers the reasons for why this upscaling is problematic. We argue that, rather than it reflecting methodological challenges associated with the difficulties of modelling hydrological processes over very large areas and during extreme runoff events, it reflects the fact that any linkage between land management and flood risk cannot be generalized and taken out of its specific spatial (catchment) and temporal (flood event) context. We use Sayer’s (1992) notion of a ‘chaotic conception’ to describe the belief that there is a simple and general association between land management and downstream flood risk rather than the impacts of land management being spatially and temporally contingent in relation to the particular geographical location, time period and scale being considered. Our argument has important practical consequences because it implies that land-management activities to reduce downstream flood risk will be different to traditional flood-reduction interventions such as levees. The purpose of demonstration projects then needs careful consideration such that conclusions made for one project are not transferred uncritically to other scales of analysis or geographical locations.

Soil Carbon and Nitrogen Storage in Upper Montane Riparian Meadows

Though typically limited in aerial extent, soils of high-elevation riparian wetlands have among the highest density of soil carbon (C) and nitrogen (N) of terrestrial ecosystems and therefore contribute disproportionally to ecosystem services such as water retention, forage production, wildlife habitat, and reactive N removal. Because much soil C and N is stored in labile forms in anaerobic conditions, management activities or environmental changes that lead to drying cause mineralization of labile soil organic matter, and loss of C and N. Meadows are focal points of human activities in mountain regions, often with incised stream channels from historically heavy grazing exacerbated by extreme runoff events. To quantify soil C and N stores in montane riparian meadows across hydrologic conditions, 17 meadows between 1950- and 2675-m elevation were selected in the central Sierra Nevada Range, California, that were classified using the proper functioning condition (PFC) system. Results indicate that C and N density in whole-solum soil cores were equivalent at forest edge positions of properly functioning, functioning at-risk, and nonfunctioning condition. Soils under more moist meadow positions in properly functioning meadows have at least twice the C, N, dissolved organic C, and dissolved organic N (DON) than those under nonfunctioning meadows. Densities of total N and DON, but not C, of functioning at-risk meadows are significantly lower (P < 0.05) than those of properly functioning meadows at mid-slope and stream-bank positions, suggesting accelerated loss of N early in degradation processes. Though variable, the soil attributes measured correspond well to the PFC riparian wetland classification system.

Modeling Turbidity and the Effects of Alum Application for a Water Supply Reservoir

High loads of inorganic particles received following runoff events from terrigenous sources can cause elevated turbidity (Tn) levels in water supply lakes and reservoirs. The development, successful testing, and application of a mechanistic Tn model is documented for Kensico Reservoir, New York, the terminal reservoir of New York City’s multireservoir unfiltered water supply, where a standard of Tn<5 nephelometric turbidity units (NTU) must be met in the withdrawals. The model includes three submodels: (1) hydrothermal/transport; (2) turbidity; and (3) alum floc deposition. The alum floc deposition submodel supports simulation of the extent of local deposits formed from alum additions made to reduce high Tn delivered from extreme runoff events. The modeling is supported by long-term monitoring of the inflows, reservoir, and withdrawals, characterization of the turbidity-causing particles (mostly clay minerals, 1–10 μm in diameter), resolution of specific conductance (tracer) patterns with rapid profiling instrumentation, and characterizations of the alum floc deposits. The two-dimensional hydrothermal/transport and Tn submodels are demonstrated to perform well in both long- and short-term simulations. Predictions of extent and magnitude of the alum floc deposits are shown to be consistent with the available information. Application of the tested model establishes violations of the Tn standard that would have occurred for extended intervals without the alum additions. The volume of the in-reservoir floc deposit formed from this practice is estimated.

Association between anomalies of moisture flux and extreme runoff events in the south-eastern Alps

Abstract. The aims of the paper are (i) to describe the annual distribution of extreme runoff events on the Mura, Drava and Sava Rivers, (ii) to demonstrate their association with moisture fluxes, and (iii) to explain their annual distribution by moisture flux climatology. Extreme runoff events were defined as rapid increases in daily mean discharge. Moisture flux anomalies were studied within six pixels of the ERA-40 database around the studied region. In general, extreme runoff events were concentrated in the summer and autumn and were usually associated with anomalies in moisture flux, mainly from the south. Nevertheless, while southern and western moisture fluxes were typical of Sava River events that occurred mainly in autumn, summer events prevailed on the Mura River and were frequently associated with moisture fluxes from the east or the north. It is remarkable that moisture fluxes from the west and south have their maxima in the autumn, whereas those from the east and north have their maxima in the summer. Therefore, the climatology of moisture flux seems to be one of the major reasons for the annual distribution of extreme runoff events in the study region. This result should be confirmed in other regions in the future.

Mid-Holocene gullying indicating extreme hydroclimatic events in the centre of the Russian Plain

At the Satino site in the center of the Russian Plain, major events of the Holocene erosion history are concentrated on sides of river valleys incised into smooth moraine landscape. Valley sides are dissected by Pleistocene gullies. Extraordinary for the Holocene was formation of four new permanent gullies. Three of them had appeared in the Late Atlantic – Early Subboreal time. One gully permitted direct dating of the fan base, which gave estimation of its appearance between 4.3-4.6 ka BP (cal). Two other gullies were constrained within the two intervals 5.2-5.5 and 5.9-6.2 ka BP (cal), based on assumed correlation with extreme runoff events dated over the area. After a long break of erosion, two of the gullies had exhibited the second phase of activity between 3.0-3.7 ka BP (cal). As in the Bronze Age no settlements are known in the study area and surroundings; human reinforcement of erosion was minor if any. The four intervals of extraordinary linear erosion on valley sides coincided with extremely high runoff events in streams of various sizes, which left prominent geomorphic and sedimentological features: meander arcs, coarse-grained alluvium, buried floodplain soils, etc. Altogether, this is considered to indicate a highly irregular climatic pattern in the area in the interval of 3.0-6.2 ka BP (cal) with several phases containing a series of extreme downpours, which had no analogs throughout the Holocene.

Contrasting extreme runoff events in areas of continuous permafrost, Arctic Alaska

Spring snowmelt floods in the Arctic are common and can be expected every year, mainly because of the extensive snow cover that ablates relatively quickly. However, documentation of extreme flows (both low and high) in the Arctic is lacking in part because extreme flows are relatively rare and gauging sites are very sparse, with most of short duration. In the nested Kuparuk River research watersheds on the North Slope of Alaska, two large summer floods have been observed (July 1999 and August 2002) in the headwaters; these high flows are contrasted to the low flows (drought conditions) observed in the summers of 2005 and 2007. It is clear that the continuous permafrost and the limited near-surface storage in the shallow active layer are responsible for both the high and low flow responses. Or, stated another way, the active layer is a poor buffer to both floods and droughts. When contrasting summer floods with snowmelt floods, it is clear from flood frequency analyses that the smaller, high-gradient headwater basins will be dominated by summer floods while those watersheds draining the low gradient coastal plain will be dominated by snowmelt floods. The two summer floods in the headwaters had flows that were three to four times greater than the largest measured snowmelt flood, while on the coastal plain the 2002 summer storm for the whole of the Kuparuk River only produced the maximum summer runoff of record that was about 1/4 of the maximum snowmelt flood. So, on the coastal plain and even for the Greater Kuparuk River that drains across the coastal plain, snowmelt floods dominate. Drought conditions prevail in summers when the limited surface water storage in the active layer and surface water bodies is depleted because evapotranspiration exceeds precipitation.

Drop-box weir for measuring flow rates under extreme flow conditions

M easuring discharge rates in stream flows laden with sediment using precalibrated flow structures, such as flumes and weirs, is difficult and flow measurements can quickly become inaccurate. This is because large particles ranging from sand-sized particles to rocks easily clog the structures, changing the approach velocities and flow directions during a runoff event. These conditions often occur during extreme runoff events when there is sufficient transport capacity in the flows, causing deposition. Furthermore, assumptions are often made for individual structures regarding the approach conditions in a stream channel, such as a minimum channel slope and direction of flow. The drop-box weir is one of two flow-measuring devices (the other is the critical-depth flume) that can be used to monitor under these conditions and give accurate flow measurements. The operating principle of the drop-box weir is to maximize the turbulence in stream flows to suspend large sediment particles. This is accomplished by forcing two water streams to flow into each other from opposite sides of a box, after falling into the box. The box is located upstream from a V-measuring section. At low flow rates, the water streams enter the box toward the front near the V section. At increasingly larger …

Drop-box weir for measuring flow rates under extreme flow conditions

Measuring discharge rates in stream flows laden with sediment using precalibrated flow structures, such as flumes and weirs, is difficult and flow measurements can quickly become inaccurate. This is because large particles ranging from sand-sized particles to rocks easily clog the structures, changing the approach velocities and flow directions during a runoff event. These conditions often occur during extreme runoff events when there is sufficient transport capacity in the flows, causing deposition. Furthermore, assumptions are often made for individual structures regarding the approach conditions in a stream channel, such as a minimum channel slope and direction of flow. The drop-box weir is one of two flow-measuring devices (the other is the critical-depth flume) that can be used to monitor under these conditions and give accurate flow measurements.

Hydrological changes and Holocene climate variations in NW China, inferred from lake sediments of Juyanze palaeolake by factor analyses

The eastern Juyanze palaeolake in hyperarid north-western China (41.75–42°N, 101.5–102°E) provides evidence of a complex hydrological pattern during the Holocene. Multivariate statistics based on lithological, geochemical and mineral data from the reference site G36 in the centre of the lake were performed to reconstruct the interrelation between lake hydrology and climate variability of the last 11,000 yr. Principal component analyses (PCA) analyses enabled us to extract the three system variables runoff, lake level/water budget and salinity as the major factors which have influenced the lake history during a highly variable Holocene climate. We can also demonstrate that the independent variable total organic carbon (TOC) is not only a function of bio-productivity in lakes under warm-wet climate conditions but more frequently related to surface runoff processes, which can result in over-estimation of pollen types used for climate reconstructions. A combined consideration of all system variables with lithological parameters, catchment characteristics and the local groundwater situation show that lake formation and its persistence strongly depended on local rainfall/runoff and the status of the underlying aquifer. Our results indicate remarkable differences between the early Holocene and mid to late Holocene lake formation, owing to changes in the aquifer system beneath the lake. At about 10,700 cal BP freshwater lake formation starts with extreme runoff events under a wet climate. Repeated dry climate spells of reduced runoff. The overall climate during the early Holocene points to wet conditions with frequent phases of very high runoff and highest lake levels until about 8900 cal BP. Extremely low runoff occurred between 8900 and 8100 cal BP, indicating already dry climate conditions some hundred years prior to the worldwide recorded responses of the 8.2 ka cold-dry event. A second period of major dry climate conditions with generally low but fluctuating runoff, unstable water budget and deposition of aeolian sand lasted for about 2100 yr between 7500 and 5400 cal BP. These climate conditions corroborate previous assumptions of a mid Holocene dry period in arid north-western China. Increased runoff after 5400 cal BP under wet climate conditions led to a complete refill of the aquifer at about 5000 cal BP and favoured the development of a saline lake for about 3500 yr. In terms of hydrology the time between 5400 and 4000 cal BP appears to be the climate optimum. Compared with the early Holocene wet climate, the mid to late Holocene local rainfall was less pronounced and displays a general decreasing trend towards complete desiccation of the lake. Our results indicate an extremely variable moisture availability in arid regions of north-western China during the entire Holocene. Owing to the interplay of the East Asian Summer Monsoon with the westerly waves at the boundary of the summer monsoon limit, variations from dry to wet climate conditions seem to have been more pronounced than in other monsoon regions of China.