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Aggregation in environmental systems – Part 2: Catchment mean transit times and young water fractions under hydrologic nonstationarity

Here I show that seasonal tracer cycles yield strongly biased estimates of mean transit times in nonstationary catchments (and, by implication, in real-world catchments). However, they can be used to reliably estimate the fraction of “young” water in streamflow, meaning water that fell as precipitation less than roughly 2–3 months ago. This young water fraction varies systematically between high and low flows and may help in characterizing controls on stream chemistry.

Diagnosing hydrological limitations of a land surface model: application of JULES to a deep-groundwater chalk basin

This paper presents a strategy to diagnose hydrological limitations of a Land Surface Model. It includes the adaptation of the model for hydrological applications and highlights challenges faced while moving towards high resolution modelling.

Regional analysis of groundwater droughts using hydrograph classification

To improve the design of drought monitoring networks and water resource management during episodes of drought, there is a need for a better understanding of spatial variations in the response of aquifers to major meteorological droughts. This paper is the first to describe a suite of methods to quantify such variations. Using an analysis of groundwater level data for a case study from the UK, the influence of catchment characteristics on the varied response of groundwater to droughts is explored.

Towards observation-based gridded runoff estimates for Europe

Water storages and fluxes on land are key variables in the earth system. To provide context for local investigations and to understand phenomena that emerge at large spatial scales, information on continental freshwater dynamics is needed. This paper presents a methodology to estimate continental scale runoff on a 0.5° spatial grid, which combines the advantages of in-situ observations with the power of machine learning regression. The resulting runoff estimates compare well with observations.

Large-basin hydrological response to climate model outputs: uncertainty caused by internal atmospheric variability

Our paper is one of very few studies where the influence of stochastic internal atmospheric variability (IAV) on the hydrological response is analyzed. On the basis of ensemble experiments with GCM and hydrological models, we found, e.g., that averaging over ensemble members filters the stochastic term related to IAV, and that a considerable portion of the simulated trend in annual Lena R. runoff can be explained by the externally forced signal (global SST and SIC changes in our experiments).

Storm type effects on super Clausius–Clapeyron scaling of intense rainstorm properties with air temperature

We present an empirical study of the rates of increase in precipitation intensity with air temperature using high-resolution 10 min precipitation records in Switzerland. We estimated the scaling rates for lightning (convective) and non-lightning event subsets and show that scaling rates are between 7 and 14%/C for convective rain and that mixing of storm types exaggerates the relations to air temperature. Doubled CC rates reported by other studies are an exception in our data set.

Quantitative high-resolution observations of soil water dynamics in a complicated architecture using time-lapse ground-penetrating radar

In this study, we analyze a set of high-resolution, surface-based, 2-D Ground-Penetrating Radar (GPR) observations of artificially induced subsurface water dynamics. In particular, we place close scrutiny on the evolution of the capillary fringe in a highly dynamic regime with surface based time-lapse GPR. We thoroughly explain all observed phenomena based on theoretical soil physical considerations and numerical simulations of both subsurface water flow and the expected GPR response.

Global trends in extreme precipitation: climate models versus observations

We present a systematic comparison of changes in historical extreme precipitation in station observations (HadEX2) and 15 climate models from the CMIP5 (as the largest and most recent sets of available observational and modeled datasets), on global and continental scale for 1901-2010, using both parametric (linear regression) and non-parametric (the Mann-Kendall as well as Sen’s slope estimator) methods, taking care to spatially and temporally sample observations and models in comparable ways.

A high-resolution global-scale groundwater model

In this paper we present a high resolution global-scale groundwater model of an upper aquifer. An equilibrium water table at its natural state is contructed. Aquifer parameterization is based on available global-datasets on lithology and conductivity combined with estimated aquifer thickness. The results showed groundwater levels are well simulated for many regions of the world. Simulated flow paths showed the relevance of including lateral groundwater flows in global scale hydrological models.

ERA-Interim/Land: a global land surface reanalysis data set

ERA-Interim/Land is a global land-surface reanalysis covering the period 1979–2010. It describes the evolution of soil moisture, soil temperature and snowpack. ERA-Interim/Land includes a number of parameterization improvements in the land surface scheme with respect to the original ERA-Interim and a precipitation bias correction based on GPCP. A selection of verification results show the added value in representing the terrestrial water cycle and its main land surface storages and fluxes.

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