We evaluated the largest and most diverse set of surface soil moisture products ever evaluated in a single study. We found pronounced differences in performance among individual products and product groups. Our results provide guidance to choose the most suitable product for a particular application.

South and Southeast Asia face significant food insecurity and hydrological hazards. Here we introduce a South and Southeast Asia hydrological monitoring and sub-seasonal to seasonal forecasting system (SAHFS-S2S) to help local governments and decision-makers prepare for extreme hydroclimatic events. The monitoring system captures soil moisture variability well in most regions, and the forecasting system offers skillful prediction of soil moisture variability 2–3 months in advance, on average.

The sigmoid-shaped complementary relationship (CR) for regional evaporation proposed by Han and Tian (2018, 2020) is reconsidered in terms of (1) its ability to give reasonable evaporation results from sites worldwide, (2) evidence for the three-state evaporation process it posits, (3) the validity of the proof provided by Han and Tian (2018), and (4) the relevance of model studies that seem to support it. Arguments for the sigmoid shape deserve to be taken seriously but remain unconvincing.

The assessment of the collected water quality information is for the managers to find a way to improve the water environment to satisfy human uses and environmental needs. We found groundwater containing high concentrations of nutrient mixes with rain water in the ditches. The stable solutes are diluted during rain. The change in nutrients over time is determined by and uptaken by organisms and chemical processes. The water is more enriched with nutrients and looked dirtier during winter.

We evaluate groundwater recharge rates in a semi-arid area that has undergone land-use changes. The widespread presence of old saline groundwater indicates that pre-land-clearing recharge rates were low and present-day recharge rates are still modest. The fluctuations of the water table and tritium activities reflect present-day recharge rates; however, the water table fluctuation estimates are unrealistically high, and this technique may not be suited for estimating recharge in semi-arid areas.

Assessments of current, local, and regional flood hazards and their future changes often involve the use of hydrologic models. A reliable model ideally reproduces both local flood characteristics and regional aspects of flooding. In this paper we investigate how such characteristics are represented by hydrologic models. Our results show that both the modeling of local and regional flood characteristics are challenging, especially under changing climate conditions.

The net exchange of water between the surface and atmosphere is mainly determined by the freshwater flux: the difference between evaporation (E) and precipitation (P), or E−P. Although there is consensus among modelers that with a warming climate E−P will increase, evidence from satellite data is still not conclusive, mainly due to sensor calibration issues. We here investigate the degree of correspondence among six recent satellite-based climate data records and ERA5 reanalysis E−P data.

This study investigates the role and value of distributed rainfall in the runoff generation of a mesoscale catchment. We compare the performance of different hydrological models at different periods and show that a distributed model driven by distributed rainfall yields improved performances only during certain periods. We then step beyond this finding and develop a spatially adaptive model that is capable of dynamically adjusting its spatial model structure in time.

Maximizing economic benefits with higher water productivity or lower water footprint is the core sustainable goal of agricultural water resources management. Here we look at spatial and temporal variations and developments in both production-based (PWF) and economic value-based (EWF) water footprints of crops, by taking a case study for China. A synergy evaluation index is proposed to further quantitatively evaluate the synergies and trade-offs between PWF and EWF.

This study aimed to select and characterise the main sources of input uncertainty in urban sewer systems, while accounting for temporal correlations of uncertain model inputs, by propagating input uncertainty through the model. We discuss the water quality impact of the model outputs to the environment, specifically in combined sewer systems, in relation to the uncertainty analysis, which constitutes valuable information for the environmental authorities and decision-makers.

Gravity and tilt time series acquired at Conrad Observatory (Austria) reflect gravity and deformation associated with short- and long-term environmental processes, revealing a complex water transport process after heavy rain and rapid snowmelt. Gravity residuals are sensitive to the Newtonian effect of water mass transport. Tilt residual anomalies capture strain–tilt coupling effects due to surface or subsurface deformation from precipitation or pressure changes in the adjacent fracture system.

We used unique chemical signatures of precipitation, hillslope soil water, and groundwater sources of streamflow to explore seasonal variation in runoff generation in a snow-dominated mountain watershed underlain by glacial till and permeable bedrock. Reacted hillslope water reached the stream first at the onset of snowmelt, followed by a dilution effect by snowmelt from May to June. Groundwater and riparian water were important sources later in the summer. Till created complex subsurface flow.

Using a large ensemble of simulated flows throughout the northwestern USA, we compare daily flood statistics in the past (1950–1999) and future (2050–1999) periods and find that nearly all locations will experience an increase in flood magnitudes. The flood season expands significantly in many currently snow-dominant rivers, moving from only spring to both winter and spring. These results, properly extended, may help inform flood risk management and negotiations of the Columbia River Treaty.

European extreme precipitation is expected to change in the future; this is based on climate model projections. But, since climate models have errors, projections are uncertain. We study this uncertainty in the projections by comparing results from an ensemble of 19 climate models. Results can be used to give improved estimates of future extreme precipitation for Europe.

Peat-forming wetlands (mires) provide multiple ecosystem services, which depend on peat remaining waterlogged. Using hydrological modelling, we show that, contrary to a common assumption, groundwater inflow can be a quantitatively important and functionally critical element of the water balance of mires in hard-rock upland and mountain areas. This influence is such that patterns of groundwater upwelling and seepage explain the spatial distribution of mires in the landscape.

Partial wavelet coherency method is improved to explore the bivariate relationships at different scales and locations after excluding the effects of other variables. The method was tested with artificial datasets and applied to a measured dataset. Compared with others, this method has the advantages of capturing phase information, dealing with multiple excluding variables, and producing more accurate results. This method can be used in different areas with spatial or temporal datasets.

In poorly instrumented catchments, satellite altimetry offers a unique possibility to obtain water level observations. Improvements in instrument design have increased the capabilities of altimeters to observe inland water bodies, including rivers. In this study, we demonstrate how a dense Sentinel-3 water surface elevation monitoring network can be established at catchment scale using publicly accessible processing platforms. The network can serve as a useful supplement to ground observations.

A two-stage blending approach is proposed for the data fusion of multiple satellite precipitation estimates (SPEs), which firstly reduces the systematic errors of original SPEs based on a Bayesian correction model and then merges the bias-corrected SPEs with a Bayesian weighting model. The model is evaluated in the warm season of 2010–2014 in the northeastern Tibetan Plateau. Results show that the blended SPE is greatly improved compared with the original SPEs, even in heavy rainfall events.

It remains unclear at which timescale the complementary principle performs best in estimating evaporation. In this study, evaporation estimation was assessed over 88 eddy covariance monitoring sites at multiple timescales. The results indicate that the generalized complementary functions perform best in estimating evaporation at the monthly scale. This study provides a reference for choosing a suitable time step for evaporation estimations in relevant studies.

We implemented both urban water use schemes in a model (Weather Research and Forecasting model) and assessed their cooling effects with different amounts of water in different parts of the city (center, suburbs, and rural areas) for both road sprinkling and urban irrigation by model simulation. Then, we developed an optimization scheme to find out the optimal water use strategies for mitigating high urban temperatures.

Different parts of water have often been used as tracers to determine the age of water in streams. The stable tracers, such as deuterium, are thought to be unable to reveal old water compared to the radioactive tracer called tritium. We used both tracers, measured in precipitation and in a stream in Luxembourg, to show that this is not necessarily true. It is, in fact, advantageous to use the two tracers together, and we recommend systematically using tritium in future studies.

The megadrought experienced in Chile (2010–2020) has led to larger than expected water deficits. By analysing 106 basins with snow-/rainfall regimes, we relate such intensification with the hydrological memory of the basins, explained by snow and groundwater. Snow-dominated basins have larger memory and thus accumulate the effect of persistent precipitation deficits more strongly than pluvial basins. This notably affects central Chile, a water-limited region where most of the population lives.

Land surface model (LSM) is a critical tool to study land responses to droughts and heatwaves, but lacking comprehensive observations limited past model evaluations. Here we use a novel dataset at a water-limited site, evaluate a typical LSM with a range of competing model hypotheses widely used in LSMs and identify marked uncertainty due to the differing process assumptions. We show the extensive observations constrain model processes and allow better simulated land responses to these extremes.

NASA’s SMAP satellite provides estimates of the amount of water in the soil. With measurements from a network of 20 monitoring stations, the accuracy of these estimates has been studied for a 4-year period. We found an agreement between satellite and in situ estimates in line with the mission requirements once the large mismatches associated with rapidly changing water contents, e.g. soil freezing and rainfall, are excluded.