Abstract
Although complex hydrological models with detailed physics are becoming more common, lumped and semi-distributed models are still used for many applications and offer some advantages, such as reduced computational cost. Most of these semi-distributed models use the concept of the hydrological response unit or HRU. In the original conception, HRUs are defined as homogeneous structured elements with similar climate, land use, soil and/or pedotransfer properties, and hence a homogeneous hydrological response under equivalent meteorological forcing. This work presents a quantitative methodology, called hereafter the principal component analysis and hierarchical cluster analysis or PCA/HCPC method, to construct HRUs using gridded meteorological data and hydrological parameters. The PCA/HCPC method is tested using the water evaluation and planning system (WEAP) model for the Alicahue River Basin, a small and semi-arid catchment of the Andes, in Central Chile. The results show that with four HRUs, it is possible to reduce the relative within variance of the catchment up to about 10%, an indicator of the homogeneity of the HRUs. The evaluation of the simulations shows a good agreement with streamflow observations in the outlet of the catchment with an Nash–Sutcliffe efficiency (NSE) value of 0.79 and also shows the presence of small hydrological extreme areas that generally are neglected due to their relative size.
Highlights
The concept of Hydrologic Response Units (HRU) has risen as one of the most common approaches for semi-distributed hydrological modelling [1,2]
The principal component analysis (PCA)/HCPC method consists in the creation of a dataset of raster files comprising hydrologic parameters and meteorological variables used by the target hydrological model
We show the main results in each part of the methodology: (i) The results of the principal component analysis and the hierarchical clustering and (ii) the results of the hydrological modeling using the different schemes of the HRU
Summary
The concept of Hydrologic Response Units (HRU) has risen as one of the most common approaches for semi-distributed hydrological modelling [1,2]. Flügel [2] defined an HRU as a homogeneous structured element having similar climate, land-use, soil and/or pedotransfer properties, a homogeneous hydrological response under equivalent meteorological forcing. HRUs are usually defined by the superposition of land use and soil type and after the classification, quantitative or qualitative relations are used to estimate hydrologic parameters on each HRU. One of the most common approaches has been to include the sub-basins in the process, the intersection of the sub-basins, land use categories and soil type polygons in a GIS represents the minor elements for hydrologic modelling [4,8]
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