Question

Describe briefly a conceptual model of the hydrological cycle. Include in your discussion reasons for conceptualisation of the hydrological cycle in the manner required for development of your model. (typing answer please)

Answer 1

CONCEPTUAL MODEL OF HYDROLOGICAL CYCLE:

The hydrological cycle is a conceptual model that describe the model and movement of water between biosphere,atmosphere,and hydrosphere. water on this planet can be stored in any of the following forms: atmosphere, lakes ,river,soil, glaciers.

The term hydrology can be treated as an important subject for the people and their environment. It treats water of the earth, their occurrence, circulation and distribution, their chemical and physical properties and their reaction with the environment including their relation to living things . It also deals with the relationship of water with the environment within each phase of hydrological cycle. Due to rapid urbanisation and industrialisation including deforestation, land cover change, irrigation, various changes have been occurred in hydrological systems.

. Hydrological modeling i is a simplified representation of real world system. The best model is the one which give results close to reality with the use of least parameters and model complexity. Models are mainly used for predicting system behaviour and understanding various hydrological processes. A model consists of various parameters that define the characteristics of the model. A runoff model can be defined as a set of equations that helps in the estimation of runoff as a function of various parameters used for describing watershed characteristics. The two important inputs required for all models are rainfall data and drainage area. Along with these, water shed characteristics like soil properties, vegetation cover, watershed topography, soil moisture content, characteristics of ground water aquifer are also considered. Hydrological models are now a day considered as an important and necessary tool for water and environment resource management.

This model describes all of the component hydrological processes. It consists of a number of interconnected reservoirs which represents the physical elements in a catchment in which they are recharged by rainfall, infiltration and percolation and are emptied by evaporation, runoff, drainage etc. Semi empirical equations are used in this method and the model parameters are assessed not only from field data but also through calibration. Large number of meteorological and hydrological records is required for calibration. The calibration involves curve fitting which makes the interpretation difficult and hence the effect of land use change cannot be predicted with much confidence. Many conceptual models have been developed with varying degree of complexity. Stanford Watershed Model IV (SWM) is the first major conceptual model developed by Crawford and Linsley in 1966 with 16 to 20 parameter.

DISCUSSION:

VIC model with simple grid based network and found that it perform well in moist areas. this model for irrigation planning in a small watershed and conclude that it can be efficiently used for the management of water for agricultural purposes. Yang et al (2000) compared 3 models and suggests that MIKE SHE model can be used in smaller catchments. HBV model can be used flood forecasting and many other purposes. Borah and Bera (2003) have made a comparison between SWAT, HSPF and DWSM model and found 17 applications of SWAT and conclude that it can be applied for continuous simulations of flow, soil erosion, nutrient and sediment transport etc. MIKE SHE model requires extensive model data and physical parameter which may not be available all the time and make it difficult to set up the model. Also users are unable to modify the code but it had high processing ability compared to other models. It has extensive graphical capabilities for pre and post processing and thus makes the modelling easier.

REASONS:

In general, rainfall-runoff models are the standard tools used for investigating hydrological processes. A large number of models with different applications ranges from small catchments to global models has been developed. Each model has got its own unique characteristics and respective applications. Some of them are comprehensive and uses the physics of underlying hydrological processes and are distributed in space and time. The models are used for the modelling of both gauged and ungauged catchments, helps in flood forecasting, proper water resource management and evaluation of water quality, erosion and sedimentation, nutrient and pesticide circulation, land use and climate change etc. Each model has various drawbacks like lack of user friendliness, large data requirements, absence of clear statements of their limitations etc. In order to overcome these defects, it is necessary for the models to include rapid advances in remote sensing technologies, risk analysis, etc. By the application of new technologies, new distributed models can be developed for modelling gauged and ungauged basins.