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Five open source free hydrologic models that you can use to model runoff of micro to macro watersheds



The principal objective of hydrologic models is to forecast the runoff of a surface water body, especially dendritic systems like rivers, streams, etc. The inputs to these models are generally Rainfall/Precipitation, Soil Characteristics, and other Climatic parameters like evapotranspiration, humidity, etc. LULC and geo-morphology are also used as the required input parameters of the hydrologic models. Both input and output of these models are temporally as well as spatially variable. Now the resolution varies with different models. Some models consider all the sub-basins to be a single watershed and determine the output based on the characteristics of this single watershed(lumped).In contrast, some other models will consider the {impact|effect} of each of the sub-basins on the central outflow of the watershed(distributed).In a few models, the entire watershed is divided into grids or units of uniform dimension. However, the accuracy is highest for the models, which considers the {impact|effect} of each sub-basins on the overall outflow of the basin. Below are the five selected hydrologic models which are free to use for non-commercial purposes and all of them are available as a free download. Although real-time support is not available there are many tutorials provided by the developers as well as users which make them easy to use and apply. The software in the present list is selected based on its, ease of use, development history, and level of accuracy. Availability of both temporal and spatial scales of prediction is also considered as a criterion of selection. Here is the list :

HYSIM is a rainfall/runoff model which has recently included the climate change scenarios and becomes the first model of its kind in the world. The full form of HYSIM-CC is the Hydrological Simulation model for Climate Change.

The requirement to analyze the impacts of climate change in an array of development projects is becoming more and more a donor-specified necessity. In many instances the projections of temperature and precipitation distributed by the IPCC will in themselves be enough, in other areas, such as water resources and agriculture, additional analysis and modeling is required. This is not just a question of assessing the overall change in water stress. The way in which the temperatures and precipitation are distributed over the year will also be critical. More substantial temperatures in the growing season might not be stabilized by extra precipitation at other times. Changes in the seasonal pattern of snowfall and snowmelt may mean that spring flushes, important for wetlands and fish spawning, no longer occur.

It is an open-source and public domain GIS {integrated|integral} modeling environment (the FREEWAT platform) for the estimation of both water quantity and quality in surface water and also groundwater with a capability to add the water management and planning module. FREEWAT is developed as an amalgamated plugin for the well-known QGIS (http://qgis.org)GIS open source desktop software.

It is a powerful software for simulation of water resource system functions having just a few components as well as large intricate models consisting of many hundreds of components. Both the natural river system and the water supply network can be modeled. Analysis like the {impact|effect} of River regulation, forecasting travel times, the ability to include and calibrate hydrological models and the differentiation of river flow at any point into its 'natural', 'cumulative abstraction' and 'release' components are some of the features available on river networks. 

The inclusion of Microsoft® Visual Basic® for Applications (VBA), the same macro language used in Excel, allows any degree of customization that may be needed. This means that Aquator can model complicated licensing, catchment transfers, and sophisticated reservoir rules more accurately than other packages.

The Soil & Water Assessment Tool is micro to macro watershed management model used to mimic the quality and quantity of surface and groundwater and to {predict|forecast} the environmental {impact|effect} of land use, land management practices, and climate change. SWAT is widely used to analyze the result of soil erosion prevention and controlling procedures, the effect of non-point source pollution control and regional management in watersheds, etc. The objective of the SWAT model is to forecast the impact of management decisions on water, sediment, nutrient, and pesticide yields with realistic accuracy. SWAT model considers the hydrologic response unit (HRU) as the "smallest spatial unit of the model, and the standard HRU definition approach lumps all similar land uses, soils, and slopes within a sub-basin based upon user-defined thresholds".


HEC-HMS has been developed for the U.S. Army Corps of Engineers. However, software developed at the Hydrologic Engineering Center is made available to the public whenever appropriate. Use is not restricted and individuals outside of the Corps of Engineers may use the program without charge.It is the most popular and widely used hydrologic model having the capability to analyze the runoff for different rainfall scenarios. The model is divided into three palettes. One panel is for inputting the loss method where the amount of water lost from the basin can be approximated. The second palette is for the climatic parameters and the last is for the watershed modeling parameters or to incorporate the characteristics of the hydrograph. The software has the capacity to model runoff based on different empirical models commonly used in hydrology. This model can predict daily runoff, the volume of runoff, peak runoff, etc.

Among these five models, the best model can be decided based on the Ease of Use, Number of Inputs, Parameter Estimation, and Calibration Requirement, Accuracy and Number of additional features like the ability to predict quality parameters, the inclusion of the capability to analyze the effect of climate change or impact of water resource managerial decision, approximation of runoff with the help of different methods, etc.

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