Nutrient Transport Modelling in the Daugava River Basin - DiVA Portal

a) Streamflow, calibration periodb) Streamflow, validation periodReportedcm/year40353025201510505000019931994199519961997c) Nitrogen load, calibration period19981999cm/year35302520151050600001980198119821983198419851986198719881989d) Nitrogen load, validation periodModelled4000050000ton/year30000200001000020000199319941995199619971998e) Phosphorus load, calibration period1999ton/year40000300002000010000200001980198119821983198419851986198719881989f) Phosphorus load, validation period15001500ton/year1000500ton/year10005000019931994199519961997199819991980198119821983198419851986198719881989Figure 7. Reported and modelled values of yearly means of streamflow,nitrogen loads and phosphorus loads from the Daugava River for the calibration period(1993­2000) and the validation period (1980­1990).Table 2 shows a statistical summary of the comparison of observed and predictedvalues. Generally, the prediction of yearly values is a lot better than the prediction ofmonthly values. Regressions lines were made between reported and modelled values.The R 2 value of the regression of modelled and reported yearly nitrogen loads is 0.78and the corresponding slope of regression is 1.17. The R 2 value for yearly phosphorusloads is 0.5, but since the regression slope is only 0.14 the ability of the model to predictphosphorus loads must be considered to be very low. The regression slope for monthlymeans is generally much lower than for yearly means. This is due to the fact that themodel underestimates peak flows. For yearly values the impact of peak flows is not sosignificant, which is why the regression slope for yearly means is higher than formonthly means. Plots of the regressions are found in Appendix F.16