Comparing CFSR and conventional weather data for discharge and soil loss modelling with SWAT in small catchments in the Ethiopian Highlands

Vincent Roth,Tatenda Lemann

doi:10.5194/hess-20-921-2016

Abstract

Abstract. Accurate rainfall data are the key input parameter for modelling river discharge and soil loss. Remote areas of Ethiopia often lack adequate precipitation data and where these data are available, there might be substantial temporal or spatial gaps. To counter this challenge, the Climate Forecast System Reanalysis (CFSR) of the National Centers for Environmental Prediction (NCEP) readily provides weather data for any geographic location on earth between 1979 and 2014. This study assesses the applicability of CFSR weather data to three watersheds in the Blue Nile Basin in Ethiopia. To this end, the Soil and Water Assessment Tool (SWAT) was set up to simulate discharge and soil loss, using CFSR and conventional weather data, in three small-scale watersheds ranging from 112 to 477 ha. Calibrated simulation results were compared to observed river discharge and observed soil loss over a period of 32 years. The conventional weather data resulted in very good discharge outputs for all three watersheds, while the CFSR weather data resulted in unsatisfactory discharge outputs for all of the three gauging stations. Soil loss simulation with conventional weather inputs yielded satisfactory outputs for two of three watersheds, while the CFSR weather input resulted in three unsatisfactory results. Overall, the simulations with the conventional data resulted in far better results for discharge and soil loss than simulations with CFSR data. The simulations with CFSR data were unable to adequately represent the specific regional climate for the three watersheds, performing even worse in climatic areas with two rainy seasons. Hence, CFSR data should not be used lightly in remote areas with no conventional weather data where no prior analysis is possible.

Highlights

Represented, spatially distributed hydrometeorological and hydro-climatic data are the most important input parameters for hydrological modelling with the Soil and Water Assessment Tool, called SWAT hereafter (Arnold et al, 1998, 2012; Douglas-Mankin et al, 2010)
For Andit Tid, situated on the eastern escarpment of the Blue Nile Basin, the belg and kremt rainfall seasons were temporally adequately represented; i.e. the timely occurrences of the rainy seasons were correctly represented through the Climate Forecast System Reanalysis (CFSR) data
In this paper we studied the applicability of CFSR weather data to three small-scale watersheds in the Ethiopian Highlands with the goal of assessing the usability for future modelling in data-scarce regions

Summary

Introduction

Represented, spatially distributed hydrometeorological and hydro-climatic data are the most important input parameters for hydrological modelling with the Soil and Water Assessment Tool, called SWAT hereafter (Arnold et al, 1998, 2012; Douglas-Mankin et al, 2010). A great deal of effort is being invested into rainfall and climatic data collection, many areas of Ethiopia have no adequate precipitation data, and where such data are available, the monitoring network contains substantial temporal and spatial gaps. This makes it necessary to use other sources of modelled rainfall data for SWAT modelling. The Climate Forecast System Reanalysis (CFSR, 2016) readily provides, for any coordinated on the globe, a climate data set adapted to SWAT This data set is the result of the close cooperation between two US organizations, the National Centers for Environmental Prediction (NCEP) and the National Center for Atmospheric Research (NCAR), which have completed a global climate data reanalysis over 36 years from 1979 through to 2014. The CFSR data are based on a spectral model which includes the parametrization of all major physical processes as described in detail in Kalnay et al (1996), Kistler et al (2001), and Saha et al (2010)

Objectives

Methods

Results

Conclusion