Precipitation, evapotranspiration, soil moisture and snow cover climatologies are important for the basin hydrology (e.g. by impacting runoff and streamflow) and for the current and future utilization potential of water resources. Information on these parameters is therefore important for assessing available water supply at basin scale. Such data are also extremely valuable for the calibration and validation of hydrologic simulation models.
Hydrologic-hydrodynamic models can be used to analyze the impact of human activities and effects of climate changes on water resources. Important use cases include design and evaluation of new hydraulic infrastructure (reservoirs, inter-basin transfer schemes etc.), assessment of the effect of water diversions, e.g. for irrigation, and estimation of runoff and river flow under future climate conditions. Hydrologic-hydrodynamic models can also be used in operational forecasting tools that predict river discharge for short to medium time horizons. Forecasting systems benefit from the assimilation of all available in-situ and remote sensing data.
This EO service comprises both a characterization of the hydrological conditions of a catchment or basin through the direct observation of important components of the water cycle (e.g. rainfall, evapotranspiration, soil moisture, terrestrial storage change, river stage and snow cover) as well as hydrological modelling of the water balance inside the water basin as well as the rainfall-runoff modeling of the basin’s sub-catchments and hydrodynamic modeling of river flow.
While hydrological modelling can provide a number of valuable results, it is important to bear in mind the limitations and constraints involved in this process, primarily relating to input data e.g. spatial resolution of rainfall and the quality of DEM (cf. 2.1.11). Simple rainfall-runoff modelling approaches with a one-dimensional river routing model are unsuitable for assessment of land-use / land cover change scenarios and cannot provide predictions of flood extent or two-dimensional distribution of flooded areas. Moreover, water quality simulations are not possible. In addition and because river discharge cannot presently be measured from remote sensing missions, in-situ river discharge data is essential for proper model calibration and validation. It is important that in-situ river discharge data is available for the post-2000 period and overlaps in time with the satellite-based precipitation products used to force the model.
More advanced models can provide support for water allocation decisions. In water scarce basins, water resources have to be fairly shared between different sectors (agriculture, domestic, power, industry, ecosystems), different geographic units (countries, provinces etc.) and between the present and the future. This can be implemented in hydrological models using simple network-flow optimization, stochastic dynamic programming and related techniques for more complex systems (model predictive control). Such decision support systems benefit from updated information on the state of the water resources system provided by in-situ and satellite observations, and they can provide quantitative information on trade-offs between these multiple objectives and provide guidance for operational management of hydraulic infrastructure. Such decision support systems benefit from updated information on the state of the water resources system provided by in-situ and satellite observations.