China's Northwest Arid Region (NAR), with dry and cold climate conditions and glaciers widely developed in the high mountains, provides vital water resources for Asia. The consecutive cold, warm, dry and wet days have much higher impacts on the water cycle process in this region than extreme temperature and precipitation events with short durations but high intensities. Parametric and nonparametric trend analysis methods widely used in climatology and hydrology are employed to identify the temporal and spatial features of the changes in the consecutive cold, warm, dry and wet days in the NAR based on China's 0.5 degrees x 0.5 degrees meteorological grid datasets of daily temperature and precipitation from 1961 to 2018. This study found that (1) the consecutive cold days (Cold Spell Duration Indicator, CSDI), and the consecutive dry days (CDD) decreased, while the consecutive warm days (Warm Spell Duration Indicator, WSDI), and the consecutive wet days (CWD) increased from 1961 to 2018, (2) and the eastern Kunlun Mountains were the hot spots where all of these consecutive climate indices changed significantly, (3) and the changes in these consecutive climate indices were highly correlated with the rise in the Global Mean Land/Ocean Temperature Index. The results indicated that winters tended to warmer and dryer and summer became hotter and wetter during 1961-2018 in the NAR under the global warming, which can lead to the sustained glacier retreat and the increase in summer runoff in this region, and the eastern Kunlun Mountains are the area where could face high risks of water scarcity and floods if the changes in these climate indices continue in the future. Given the vulnerability of the socio-economic systems in the NAR to a water shortage and floods, it is most crucial to improve the strategies of water resources management, disaster prevention and risk management for this region under climate change.

The extreme floods of recent years underline the urgency of studying long-term changes of floods and their driving processes. This paper reports results on this issue obtained within the framework of subproject 6 of the DFG research group SPATE (Space-Time Dynamics of Extreme Floods). The analyses use an extensive dataset of flood observations at rivers and complementary information to determine and explain significant changes in flood probabilities. The data show that the flood-rich periods of the last 500 years in Europe have been significantly colder than usual. Over the last 60 years, the number of flood-rich periods in north-western Europe has increased. This increase is due to more intense precipitation. In medium-sized and large catchments of southern and eastern Europe, on the other hand, lower soil moisture and less snow cover have led to decreasing flood probabilities. These results are intended as a basis for more reliable design flood estimates in a changing world.

This paper addresses the nexus of climate change and variability, soil moisture and surface runoff over the Lake Baikal catchment. Water level and distribution of dissolved and suspended matter over Lake Baikal are strongly affected by river inflow during rain-driven floods. In this study, we evaluate river flow changes at 44 streamflow gauges as well as related precipitation, evaporation, potential evaporation and soil moisture obtained from the ERA5-Land dataset. Based on Sen's slope trend estimator, Mann-Kendall non-parametric test, and using dominance analysis, we estimated the influence of meteorological parameters on river flow during 1979-2019. We found a significant correlation between the precipitation elasticity of river flow and catchment characteristics. Half of the gauges in the eastern part of the Selenga River basin showed a significant decreasing trend of average and maximum river flow (up to -2.9%/year). No changes in the central volume date of flood flow have been found. The reduction in rainfall amount explains more than 60% of runoff decrease. A decrease in evaporation is observed in areas where precipitation decrease is higher than 0.8%/year. Catchments, where the precipitation trends are not as substantial, are associated with increasing evaporation as a result of the increasing potential evaporation. Negative precipitation trends are accompanied by negative trends of soil moisture. Finally, the study reveals the sensitivity of catchments with steep slopes located in humid areas to precipitation change.

Alluvial fans are important paleoclimatic archives, thatmay record high-frequency climatic oscillations. However, climate signals may be overprinted or even be destroyed by autogenic processes caused by channel avulsion and lobe switching. Here we present new data from two different Late Pleistocene (MIS 3-2) alluvial fan systems in northern Germany and compare these systems to experimental alluvial fans and other field examples. The selected fan systems formed under similar climatic and tectonic conditions, but differ in size, type, and drainage area allowing to estimate the role of climate and autogenic controls on flow processes, facies architecture, and fan-stacking patterns. Luminescence dating is used to determine the timing of fan onset and aggradation. Fan onset occurred in response to climate change at the end of MIS 3 when temperatures decreased and periglacial climate conditions were established in northern central Europe. A related increase in sediment supply and strongly variable precipitation patterns probably promoted fan formation. The major period of fan aggradationwas approximately between 33 and 18 ka, followed by fan inactivity, abandonment, and incision during the Lateglacial. The highest aggradation rates occurred during the early stage of fan building, when up to 35 m thick sediment accumulated within a few thousand years. Sand-rich, sheetflood-dominated fans are related to larger, low-gradient fan catchments. Steep depositional fan slopes (5 degrees 17 degrees) and short-lived high-energy floods promoted supercritical flowconditions. Well sorted, sediment-laden, rapidly waning flows favored the deposition and preservation of supercritical bedforms and allowed for the aggradation of stable antidunes. Steep, dip-slope catchments enhanced stream gradients and promoted the transport of coarser sediments. These fans have lower gradient slopes (2-6 degrees) and are dominated by channelized flows, alternating with periods of unconfined sheetfloods. Meter-scale coarsening upward successions, characterized by sandy sheetflood deposits at the base, overlain by multilateral or smaller single-story gravelly channel fills may be related to highfrequency climatic fluctuations or seasonal fluctuations in water and sediment supply. These coarsening-upward successions are commonly bounded by a paleo-active layer, from which ice-wedge casts penetrate downwards. The comparison to experimental fans and other field examples implies that the recurrent pattern ofmultistory, multilateral and single-story channel bodieswith a lateral offset to vertical stacking patternmost probablywas controlled by autogenic switch in an avulsion-dominated system. The change in deposition from alluvial-dominated processes to aeolian sedimentation with minor alluvial influences during the Lateglacial records alternation of dry and ephemeral wetter phases that are related to rapid climatic variations. The main phase of aeolian sand-sheet deposition probably correlates with Heinrich event H1 between approximately 18-16 ka and reflects sedimentation in response to aridification and highmeanwind speeds.

Floods are a widespread natural disaster with substantial economic implications and far-reaching consequences. In Northern Pakistan, the Hunza-Nagar valley faces vulnerability to floods, posing significant challenges to its sustainable development. This study aimed to evaluate flood risk in the region by employing a GIS-based Multi-Criteria Decision Analysis (MCDA) approach and big climate data records. By using a comprehensive flood risk assessment model, a flood hazard map was developed by considering nine influential factors: rainfall, regional temperature variation, distance to the river, elevation, slope, Normalized difference vegetation index (NDVI), Topographic wetness index (TWI), land use/land cover (LULC), curvature, and soil type. The analytical hierarchy process (AHP) analysis assigned weights to each factor and integrated with geospatial data using a GIS to generate flood risk maps, classifying hazard levels into five categories. The study assigned higher importance to rainfall, distance to the river, elevation, and slope compared to NDVI, TWI, LULC, curvature, and soil type. The weighted overlay flood risk map obtained from the reclassified maps of nine influencing factors identified 6% of the total area as very high, 36% as high, 41% as moderate, 16% as low, and 1% as very low flood risk. The accuracy of the flood risk model was demonstrated through the Receiver Operating Characteristics-Area Under the Curve (ROC-AUC) analysis, yielding a commendable prediction accuracy of 0.773. This MCDA approach offers an efficient and direct means of flood risk modeling, utilizing fundamental GIS data. The model serves as a valuable tool for decision-makers, enhancing flood risk awareness and providing vital insights for disaster management authorities in the Hunza-Nagar Valley. As future developments unfold, this study remains an indispensable resource for disaster preparedness and management in the Hunza-Nagar Valley region.

Daily floods including event, characteristic, extreme and inundation in the Lancang-Mekong River Basin (LMRB), crucial for flood projection and forecasting, have not been adequately modeled. An improved hydrological-hydrodynamic model (VIC and CaMa-Flood) considering regional parameterization was developed to simulate the flood dynamics over the basin from 1967 to 2015. The flood elements were extracted from daily time series and evaluated at both local and regional scales using the data collected from in-situ observations and remote sensing. The results show that the daily discharge and water level are both well simulated at selected stations with relative error (RE) less than 10% and Nash-Sutcliffe efficiency coefficient (NSE) over 0.90. Half of the flood events have NSE exceeding 0.76. The peak time and flood volume are well reproduced while both peak discharge and water level are slightly underestimated. The results tend to worsen when the characteristics of flood events are extended to annual extremes. These extremes are generally underestimated with NSE less than 0.5 but RE is within 20%. The simulated rainy season inundation area generally agrees with observations from remote sensing, with about 86.8% inundation occurrence frequency captured within the model capacity. Ignoring the regional parameterization and reservoir regulation can both deteriorate flood simulation performance at the local scale, resulting in lower NSE. Specifically, systematically higher water levels and up to 27% overestimation of peak discharge are found when ignoring regional parameterization, while ignoring reservoir regulation would cause up to 23% overestimation for flood extremes. It is expected that these findings would contribute to the regional flood forecasting and flood management.

Cold region hydrology is conditioned by distinct cryospheric and hydrological processes. While snowmelt is the main contributor to both surface and subsurface flows, seasonally frozen soil also influences the partition of meltwater and rain between these flows. Cold regions of the Northern Hemisphere midlatitudes have been shown to be sensitive to climate change. Assessing the impacts of climate change on the hydrology of this region is therefore crucial, as it supports a significant amount of population relying on hydrological services and subjected to changing hydrological risks. We present an exhaustive review of the literature on historical and projected future changes on cold region hydrology in response to climate change. Changes in snow, soil, and streamflow key metrics were investigated and summarized at the hemispheric scale, down to the basin scale. We found substantial evidence of both historical and projected changes in the reviewed hydrological metrics. These metrics were shown to display different sensitivities to climate change, depending on the cold season temperature regime of a given region. Given the historical and projected future warming during the 21st century, the most drastic changes were found to be occurring over regions with near-freezing air temperatures. Colder regions, on the other hand, were found to be comparatively less sensitive to climate change. The complex interactions between the snow and soil metrics resulted in either colder or warmer soils, which led to increasing or decreasing frost depths, influencing the partitioning rates between the surface and subsurface flows. The most consistent and salient hydrological responses to both historical and projected climate change were an earlier occurrence of snowmelt floods, an overall increase in water availability and streamflow during winter, and a decrease in water availability and streamflow during the warm season, which calls for renewed assessments of existing water supply and flood risk management strategies.

Glacial lake outburst flood (GLOF) is one of the major natural disasters in the Qinghai-Tibetan Plateau (QTP). On 25 June 2020, the outburst of the Jiwenco Glacial Lake (JGL) in the upper reaches of Nidu river in Jiari County of the QTP reached the downstream Niwu Township on 26 June, causing damage to many bridges, roads, houses, and other infrastructure, and disrupting telecommunications for several days. Based on radar and optical image data, the evolution of the JGL before and after the outburst was analyzed. The results showed that the area and storage capacity of the JGL were 0.58 square kilometers and 0.071 cubic kilometers, respectively, before the outburst (29 May), and only 0.26 square kilometers and 0.017 cubic kilometers remained after the outburst (27 July). The outburst reservoir capacity was as high as 5.4 million cubic meters. The main cause of the JGL outburst was the heavy precipitation process before outburst and the ice/snow/landslides entering the lake was the direct inducement. The outburst flood/debris flow disaster also led to many sections of the river and buildings in Niwu Township at high risk. Therefore, it is urgent to pay more attention to glacial lake outburst floods and other low-probability disasters, and early real-time engineering measures should be taken to minimize their potential impacts.

Climate change is occurring globally, with wide ranging impacts on organisms and ecosystems alike. While most studies focus on increases in mean temperatures and changes in precipitation, there is growing evidence that an increase in extreme events may be particularly important to altering ecosystem structure and function. During extreme events organisms encounter environmental conditions well beyond the range normally experienced. Such conditions may cause rapid changes in community composition and ecosystem states. We present the impact of an extreme pulse event ( a flood) on soil communities in an Antarctic polar desert. Taylor Valley, McMurdo Dry Valleys, is dominated by large expanses of dry, saline soils. During the austral summer, melting of glaciers, snow patches and subsurface ice supplies water to ephemeral streams and wetlands. We show how the activation of a non-annual ephemeral stream, Wormherder Creek, and the associated wetland during an exceptional high-flow event alters soil properties and communities. The flow of water increased soil water availability and decreased salinity within the wetted zone compared with the surrounding dry soils. We propose that periodic leaching of salts from flooding reduces soil osmotic stress to levels that are more favorable for soil organisms, improving the habitat suitability, which has a strong positive effect on soil animal abundance and diversity. Moreover, we found that communities differentiated along a soil moisture gradient and that overland water flow created greater connectivity within the landscape, and is expected to promote soil faunal dispersal. Thus, floods can 'precondition' soils to support belowground communities by creating conditions below or above key environmental thresholds. We conclude that pulse events can have significant long-term impacts on soil habitat suitability, and knowledge of pulse events is essential for understanding the present distribution and functioning of communities in soil ecosystems.