To promote the advancement of novel observation techniques that may lead to new sources of information to help better understand the hydrological cycle, the International Association of Hydrological Sciences (IAHS) established the Measurements and Observations in the XXI century (MOXXI) Working Group in July 2013. The group comprises a growing community of techenthusiastic hydrologists that design and develop their own sensing systems, adopt a multidisciplinary perspective in tackling complex observations, often use low-cost equipment intended for other applications to build innovative sensors, or perform opportunistic measurements. This paper states the objectives of the group and reviews major advances carried out by MOXXI members toward the advancement of hydrological sciences. Challenges and opportunities are outlined to provide strategic guidance for advancement of measurement, and thus discovery.

Abstract. In recent years, the interest in the prediction and prevention of natural hazards related to hydrometeorological events has grown due to the increased frequency of extreme rainstorms. Several research projects have been developed to test hydrometeorological models for real-time flood forecasting. However, flood forecasting systems are still not widespread in operational context. Real-world examples are mainly dedicated to the use of flood routing model, best suited for large river basins. For small basins, it is necessary to take advantage of the lag time between the onset of a rainstorm and the beginning of the hydrograph rise, with the use of rainfall-runoff transformation models. Nevertheless, when the lag time is very short, a rainfall predictor is required, as a result, meteorological models are often coupled with hydrological simulation. While this chaining allows floods to be forecasted on small catchments with response times ranging from 6 to 12 h it, however, causes new problems for the reliability of Quantitative Precipitation Forecasts (QPF) and also creates additional accuracy problems for space and time scales.The aim of this work is to evaluate the degree to which uncertain QPF affects the reliability of the whole hydrometeorological alert system for small catchments. For this purpose, a distributed hydrological model (FEST-WB) was developed and analysed in operational setting experiments, i.e. the hydrological model was forced with rain observation until the time of forecast and with the QPF for the successive period, as is usual in real-time procedures. Analysis focuses on the AMPHORE case studies in Piemonte in November 2002.

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This article presents the development of distributed thermodynamic model for energy and mass balance computation between soil surface and shallow atmospheric layers and its inclusion into the hydrological model FEST-EWB (Flash-flood Event-based Spatially distributed rainfall-runoff Transformation-Energy Water Balance). This model is also thought for a synergic use of hydrological model with remote sensing data. In particular, the energy budget is solved looking for the representative thermodynamic equilibrium temperature (RET) defined as the land surface temperature (LST) that closes the energy balance equation for any pixel of basin surface. So using this approach, through the system between the mass and energy equations, soil moisture (SM) is linked to the latent heat flux (LE) and then to LST. The RET thermodynamic approach solves most of the problems of the actual evapotranspiration (ET) and SM computation. In fact, it permits to avoid computing the effective ET as an empirical fraction of the potential one. This approach, based on the RET, has been tested at field scale (10 ha) with energy fluxes and LST measured with an eddy covariance station in Landriano (Italy

Deriving accurate estimates of reference evapotranspiration is required for water resource management, irrigation water requirement computations, and successful hydrological modeling. The Food and Agricultural Organization of the United Nations (FAO) recommended the Penman-Monteith equation as the standard for estimating reference evapotranspiration. An alternative method for application at sites where only air temperature measurements are available is the Hargreaves-Samani equation. The primary objective of this study is to investigate the possibility for application of the Hargreaves-Samani equation in alpine areas for computing daily reference evapotranspiration. An evaluation of the Hargreaves-Samani equation and its modifications proposed in literature is made by comparing daily estimates with Penman-Monteith results at 51 meteorological stations in the Upper Po River Basin (Italy) and the Rhone River Basin (Switzerland). Significant error was encountered in all methods using the Hargreaves-Samani equation. A relationship for adjusting the Hargreaves-Samani coefficient on the basis of local elevation is proposed, calibrated, and validated. The resulting modified Hargreaves-Samani equation showed a significant reduction of error for estimating daily reference evapotranspiration. The proposed equation is not intended for replacement of the Penman-Monteith method but for application in alpine rivers when only air temperature data are available.

Abstract. The most widely used method for snow dynamic simulation relies on temperature index approach, that makes snow melt and accumulation processes depend on air temperature related parameters. A recently used approach to calibrate these parameters is to compare model results with snow coverage retrieved from satellite images. In area with complex topography and heterogeneous land cover, snow coverage may be affected by the presence of shaded area or dense forest that make pixels to be falsely classified as uncovered. These circumstances may have, in turn, an influence on calibration of model parameters.In this paper we propose a simple procedure to correct snow coverage retrieved from satellite images. We show that using raw snow coverage to calibrate snow model may lead to parameter values out of the range accepted by literature, so that the timing of snow dynamics measured at two ground stations is not correctly simulated. Moreover, when the snow model is implemented into a continuous distributed hydrological model, we show that calibration against corrected snow coverage reduces the error in the simulation of river flow in an Alpine catchment.

Abstract:With the objective of improving flood predictions, in recent years sophisticated continuous hydrologic models that include complex land-surface sub-models have been developed. This has produced a significant increase in parameterization; consequently, applications of distributed models to ungauged basins lacking specific data from field campaigns may become redundant.The objective of this paper is to produce a parsimonious and robust distributed hydrologic model for flood predictions in Italian alpine basins. Application is made to the Toce basin (area 1534 km 2 ). The Toce basin was a case study of the RAPHAEL European Union research project, during which a comprehensive set of hydrologic, meteorological and physiographic data were collected, including the hydrologic analysis of the 1996-1997 period. Two major floods occurred during this period. We compare the FEST04 event model (which computes rainfall abstraction and antecedent soil moisture conditions through the simple Soil Conservation Service curve number method) and two continuous hydrologic models, SDM and TDM (which differ in soil water balance scheme, and base flow and runoff generation computations).The simple FEST04 event model demonstrated good performance in the prediction of the 1997 flood, but shows limits in the prediction of the long and moderate 1996 flood. More robust predictions are obtained with the parsimonious SDM continuous hydrologic model, which uses a simple one-layer soil water balance model and an infiltration excess mechanism for runoff generation, and demonstrates good performance in both long-term runoff modelling and flood predictions. Instead, the use of a more sophisticated continuous hydrologic model, the TDM, that simulates soil moisture dynamics in two layers of soil, and computes runoff and base flow using some TOPMODEL concepts, does not seem to be advantageous for this alpine basin.

Climate change can have profound impacts on water availability. In order to assess the impacts on water resources in complex Alpine river basins, an integrated model that can simulate mutual interactions between natural hydrological processes and anthropogenic disturbances is required. The objective of this study is to show the potential of such an integrated approach in quantifying the impacts of climate change on water resources availability in the Upper Po river basin in Italy. Results show that in the time slice 2041-2050 summer river discharge is expected to decrease with respect to 2001-2010, due to a substantial decrease of seasonal precipitation and an accelerated snow melt that causes an earlier snow depletion. Glaciers volume is expected to decrease to half the current value in 2025, while the minimum elevation of the lowest point of the glaciers is expected to increase from 1890 m asl to about 2850 m asl. It is shown that this change can affect regulation of large artificial reservoirs at higher elevation that are mainly dependent on glacier melt for their supply. Increase of annual precipitation is expected to increase groundwater detention that can be used as supplement to diminished river discharge during summer.