Techniques for Calibration and Validation of SWAT Model in Data Scarce Arid and Semi-Arid Catchments in South Africa

https://serval.unil.ch/resource/serval:BIB_320A56663B51.P001/REF.pdf

Potential of satellite and reanalysis evaporation datasets for hydrological modelling under various model calibration strategies

Large-scale distributed watershed models are data-intensive, and preparing them consumes most of the research resources. We prepared high-resolution global databases of soil, landuse, actual evapotranspiration (AET), and historical and future weather databases that could serve as standard inputs in Soil and Water Assessment Tool (SWAT) models. The data include two global soil maps and their associated databases calculated with a large number of pedotransfer functions, two landuse maps and their correspondence with SWAT's database, historical and future daily temperature and precipitation data from five IPCC models with four scenarios; and finally, global monthly AET data. Weather data are 0.5° global grids text-formatted for direct use in SWAT models. The AET data is formatted for use in SWAT-CUP (SWAT Calibration Uncertainty Procedures) for calibration of SWAT models. The use of these global databases for SWAT models can speed up the model building by 75-80% and are extremely valuable in areas with limited or no physical data. Furthermore, they can facilitate the comparison of model results in different parts of the world.

/pdf/global-soil-landuse-evapotranspiration-historical-and-future-54yattan9j.pdf

Global soil, landuse, evapotranspiration, historical and future weather databases for SWAT Applications.

Hydrological models are usually calibrated against observed streamflow (Qobs), which is not applicable for ungauged river basins. A few studies have exploited remotely sensed evapotranspiration (ETRS) for model calibration but their effectiveness on streamflow simulation remains uncertain. This paper investigates the use of ETRS in the hydrological calibration of a widely used land surface model coupled with a source–sink routing scheme and global optimization algorithm for 28 natural river basins. A baseline simulation is a setup based on the latest model developments and inputs. Sensitive parameters are determined for Qobs and ETRS-based model calibrations, respectively, through comprehensive sensitivity tests. The ETRS-based model calibration results in a mean Kling–Gupta Efficiency (KGE) value of 0.54 for streamflow simulation; 61% of the river basins have KGE > 0.5 in the validation period, which is consistent with the calibration period and provides a significant improvement over the baseline. Compared to Qobs, the ETRS calibration produces better or similar streamflow simulations in 29% of the basins, while further significant improvements are achieved when either better ET or precipitation observations are used. Furthermore, the model results show better or similar performance in 68% of the basins and outperform the baseline simulations in 90% of the river basins using model parameters from the best ETRS calibration runs. This study confirms that with reasonable precipitation input, the ETRS-based spatially distributed calibration can efficiently tune parameters for better ET and streamflow simulations. The application of ETRS for global scale hydrological model calibration promises even better streamflow accuracy as the satellite-based ETRS observations continue to improve.

Satellite-based Evapotranspiration in Hydrological Model Calibration

Evaluating satellite-based evapotranspiration estimates for hydrological applications in data-scarce regions: A case in Ethiopia.

. The main objective of this study was to calibrate and validate the
eco-hydrological model Soil and Water Assessment Tool (SWAT) with
satellite-based actual evapotranspiration (AET) data from the Global Land
Evaporation Amsterdam Model (GLEAM_v3.0a) and from the Moderate Resolution
Imaging Spectroradiometer Global Evaporation (MOD16) for the Ogun River Basin
(20 292 km 2 ) located in southwestern Nigeria. Three potential
evapotranspiration (PET) equations (Hargreaves, Priestley–Taylor and
Penman–Monteith) were used for the SWAT simulation of AET. The reference
simulations were the three AET variables simulated with SWAT before model
calibration took place. The sequential uncertainty fitting technique (SUFI-2)
was used for the SWAT model sensitivity analysis, calibration, validation and
uncertainty analysis. The GLEAM_v3.0a and MOD16 products were subsequently
used to calibrate the three SWAT-simulated AET variables, thereby obtaining
six calibrations–validations at a monthly timescale. The model performance
for the three SWAT model runs was evaluated for each of the 53 subbasins
against the GLEAM_v3.0a and MOD16 products, which enabled the best model run
with the highest-performing satellite-based AET product to be chosen. A
verification of the simulated AET variable was carried out by (i) comparing
the simulated AET of the calibrated model to GLEAM_v3.0b AET, which is a
product that has different forcing data than the version of GLEAM used for
the calibration, and (ii) assessing the long-term average annual and average
monthly water balances at the outlet of the watershed. Overall, the SWAT
model, composed of the Hargreaves PET equation and calibrated using the
GLEAM_v3.0a data (GS1), performed well for the simulation of AET and
provided a good level of confidence for using the SWAT model as a decision
support tool. The 95 % uncertainty of the SWAT-simulated variable
bracketed most of the satellite-based AET data in each subbasin. A validation
of the simulated soil moisture dynamics for GS1 was carried out using
satellite-retrieved soil moisture data, which revealed good agreement. The
SWAT model (GS1) also captured the seasonal variability of the water balance
components at the outlet of the watershed. This study demonstrated the potential to use remotely sensed
evapotranspiration data for hydrological model calibration and validation in
a sparsely gauged large river basin with reasonable accuracy. The novelty of
the study is the use of these freely available satellite-derived AET
datasets to effectively calibrate and validate an eco-hydrological model for
a data-scarce catchment.

/pdf/multi-site-calibration-and-validation-of-swat-with-satellite-n8poexw6wq.pdf

Joseph O. Adejuwon

Papers

Multi-site calibration and validation of SWAT with satellite-based evapotranspiration in a data-sparse catchment in southwestern Nigeria